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Unmanned Spaceflight.com _ Rosetta _ 3D shape, cartography, and geoid of Comet 67P C-G

Posted by: Phil Stooke Aug 6 2014, 02:11 PM

Explorer 1 said:

"A 2D map of C-G seems like a tough order; the projection math alone..."


Don't worry! If you can put a grid on the surface (as we have seen already), you can warp that grid into any map projection you like. Mapping will be no huge problem - in fact I expect they have a rough one already (I've been playing with one myself).

Phil

Posted by: acastillo Aug 6 2014, 02:44 PM

It would appear that the neck is an "erosional" feature (not sure if erosion is the right word), and maybe not the contact boundary between 2 separate bodies. At some point in the future, the neck will sublime away and the comet will split in two.

Posted by: AndyG Aug 6 2014, 03:47 PM

QUOTE (acastillo @ Aug 6 2014, 03:44 PM) *
It would appear that the neck is an "erosional" feature...


Gravity must be very low there, caught as it is between two lumps o' rock. A higher chance for material to be lost, maybe?

Andy

Posted by: scalbers Aug 6 2014, 04:06 PM

QUOTE (Explorer1 @ Aug 6 2014, 11:43 AM) *
A 2D map of C-G seems like a tough order; the projection math alone... wink.gif


Interesting though that a unique coordinate system (projection) is possible as seen in the rotating map. None of the overhangs appear to wrap back on themselves as seen from the central projection point. Thus a 2D map should be possible with access to the shape model (as Phil alluded to earlier).

Posted by: TheAnt Aug 6 2014, 04:46 PM

QUOTE (acastillo @ Aug 6 2014, 04:44 PM) *
It would appear that the neck is an "erosional" feature (not sure if erosion is the right word), and maybe not the contact boundary between 2 separate bodies. At some point in the future, the neck will sublime away and the comet will split in two.


I concur, not that we have a final word yet but I do tend to think the shape is from melting and erosion, rather than 2 objects that have merged since that is a less likely scenario.

@AndyG: Gravity is nearly negligible, gas pressure define this environment with sublimation and active geysers, though I wonder if the latter could create a static charge.

Posted by: Gerald Aug 6 2014, 04:52 PM

QUOTE (scalbers @ Aug 6 2014, 06:06 PM) *
Interesting though that a unique coordinate system (projection) is possible as seen in the rotating map. ...

That's possible with any http://en.wikipedia.org/wiki/Simply_connected_space object (no "handle-shaped holes") in 3d via a http://en.wikipedia.org/wiki/Homeomorphism (continuous map).
For objects with holes, like doughnuts different coordinate systems are needed. The shape of the nucleus is strange, but fortunately not that strange.

Posted by: scalbers Aug 6 2014, 05:02 PM

QUOTE (Gerald @ Aug 6 2014, 04:52 PM) *
That's possible with any http://en.wikipedia.org/wiki/Simply_connected_space object (no "handle-shaped holes") in 3d via a http://en.wikipedia.org/wiki/Homeomorphism (continuous map). ...

Sounds good, though it seems to me that C-G would be more straightforward than some other simply connected objects. A latitude/longitude with respect to C-Gs center of gravity appears to be possible as a "planetocentric" or "cometocentric" coordinate. It would be a simple tracing of rays emanating from the central point and then intersecting the surface. Each ray has just a single intersection with the surface.

Posted by: Gerald Aug 6 2014, 05:23 PM

QUOTE (scalbers @ Aug 6 2014, 07:02 PM) *
...Each ray has just a single intersection with the surface.

As long as there are no relevant overhangs (in the sense of the rays). I'm not quite sure whether this holds for the comet.
It could become a little more tricky.

Posted by: scalbers Aug 6 2014, 05:38 PM

QUOTE (Gerald @ Aug 6 2014, 05:23 PM) *
As long as there are no relevant overhangs (in the sense of the rays). I'm not quite sure whether this holds for the comet.
It could become a little more tricky.

Good point. A closer look at the recent animation shows a few localized breaks in the grid lines. This correlates with some local topography that has addtional intersection points with the rays pointing at the center of gravity. Perhaps one would have to filter out these bumps in a shape model to come up with a reference shape that could be specified using a cometocentric coordinate. Then the actual surface can be compared with normals to this reference shape.

Posted by: mcgyver Aug 8 2014, 07:47 PM

QUOTE (acastillo @ Aug 6 2014, 03:44 PM) *
It would appear that the neck is an "erosional" feature (not sure if erosion is the right word), and maybe not the contact boundary between 2 separate bodies. At some point in the future, the neck will sublime away and the comet will split in two.

Eyewitnessing it will be simply amazing.
On the opposite side, mapping an evolving body will be a pain!

Posted by: Phil Stooke Aug 8 2014, 08:04 PM

Not a pain, it just means the cartographers have long-term employment!

Phil

Posted by: Explorer1 Aug 8 2014, 08:06 PM

Wouldn't the two lobes just gradually come back together together as the neck erodes, if their mass remains the same? Unless a decrease in radius forces C-G to rotate faster and faster (I guess we'll find out soon!)

Posted by: Phil Stooke Aug 8 2014, 10:00 PM

I think you're right, the lobes would collapse together as the neck was eroded.

Phil


Posted by: Mercure Aug 8 2014, 10:05 PM

I believe the centrifugal forces at the rotational rate of ~ 1 revolution per day are stronger than the combined gravitational attraction of the two lobes. If the neck breaks they would come apart, as I see it. Would be interesting to see calculations of the eventuality.

Posted by: djellison Aug 8 2014, 10:17 PM

Rotation rate is 12.7 hours. The circumference drawn by the 4km length of the comet ( a 2km radius ) is 12.6 km

So very roughly - it's doing 1km/hr or 0.28m/sec. V^2/r is thus 0.000039 m/sec^2

Surface gravity is approximated as 10^-3 m/sec^2 3 orders of magnitude higher than the centripetal acceleration due to rotation.

Thus no - they would not fly apart. They would collapse together.


Posted by: nprev Aug 8 2014, 10:20 PM

The key variable between these scenarios is mass, which will presumably be known in time to a high degree of precision. (Probably not nearly as soon as it would be for a symmetrical body; Rosetta's navigators are probably gonna have an interesting time for quite a few orbits until they get a handle on the mass distribution of C-G).

EDIT: Whups, cancel that. What Doug said. Obviously the system's mass is constrained well within an order of magnitude already.

Posted by: ngunn Aug 8 2014, 10:22 PM

Every irregular object eroded from the outside must eventually form a neck which breaks and the two parts will settle together, tumbled or not. How would they get the energy to fly apart again?

Posted by: nprev Aug 8 2014, 10:28 PM

Could acquire more angular momentum from impacts over time; then the variable would become the shear strength of the 'neck'. But as Doug observed, it's not spinning fast enough.

Posted by: djellison Aug 8 2014, 10:37 PM

If it were rotating fast enough to displace the two halves if the 'neck' were to disappear....then it would also be rotating fast enough to rip itself to shreds.

What I have in essence done is prove that the comet can exist (which is somewhat self evident)

Posted by: SteveM Aug 8 2014, 10:42 PM

I'm not convinced by the emerging consensus that the neck is an erosional feature. It seems to me that the neck is near a gravitational low (i.e., "downhill" from the rest of the comet) and any loose material near the comet would be likely to settle there.

In previous passes by the Sun the comet would eject both volatile gases and particles of solids; some of them might not achieve escape velocity. The volatiles would be reheated on the surface and escape again but we would expect the solids to settle back in the lowest point, the comet's neck. This model predicts a dustier area near the neck with a comparatively lower concentration of volatiles.

We'll see what turns up but I'm not a geologist so what do I know.

Steve M

Posted by: djellison Aug 8 2014, 11:10 PM

QUOTE (SteveM @ Aug 8 2014, 03:42 PM) *
I'm not convinced by the emerging consensus that the neck is an erosional feature


It's where the bulk of activity appears to be
http://sci.esa.int/rosetta/54471-comet-activity-on-2-august-2014/


Posted by: djellison Aug 9 2014, 12:08 AM

QUOTE (Gerald @ Aug 8 2014, 03:36 PM) *
Hmm, according to the http://en.wikipedia.org/wiki/67P/Churyumov%E2%80%93Gerasimenko, the escape velocity is estimated to 0.46 m/s, corresponding to about 0.33 m/s for a circular orbit.
So I'd say within the current uncertainty, respecting the rotation, the resulting surface gravity at the parts most distant to the center of mass is about zero.


No - the centripetal acceleration is 4 orders of magnitude less than the escape velocity.


Posted by: JCG Aug 9 2014, 01:11 AM

QUOTE (Gerald @ Aug 8 2014, 01:36 PM) *
Hmm, according to the http://en.wikipedia.org/wiki/67P/Churyumov%E2%80%93Gerasimenko, the escape velocity is estimated to 0.46 m/s, corresponding to about 0.33 m/s for a circular orbit.
So I'd say within the current uncertainty, respecting the rotation, the resulting surface gravity at the parts most distant to the center of mass is about zero.
A significantly more compact body with the same angular momentum would be torn apart.

This opens a scenario almost opposing the contact binary approach, meaning head and body could have been broken apart already by centrifugal pseudo-force, and kept together by the stretched "neck", which would give the "rubber" duck metaphor more sense than originally anticipated.
This way the inner of the comet would be exposed at the neck.
Additional momentum could have been provided by impacts or by http://en.wikipedia.org/wiki/Yarkovsky%E2%80%93O%27Keefe%E2%80%93Radzievskii%E2%80%93Paddack_effect.


Back of the envelope:
Gravity /centripetal ~ GM/r^2//V^2/r ~ GpP^2 where G = grav constant of 6.67x 10^-11 (mks), p = density ~ 10^3 (mks) and P = period ~4.6x10^4 sec.
Ratio ~ 10^2
Gravity wins hands down. Tidal forces are insufficient.
Adjustments to Fg due to odd shape may cause ratio be somewhat less, but increasing density will go the other way.

Posted by: JohnVV Aug 9 2014, 01:28 AM

QUOTE (jgoldader @ Aug 7 2014, 09:24 AM) *
Any chance of Gaspra? I did some work on that back before the Galileo flyby; it would be great to print it out.

Thanks!
Jeff

there is a 3d mesh ( low-res) for gaspra
http://forum.celestialmatters.org/viewtopic.php?f=4&t=636
http://imgbox.com/EDBV1esK
my g-drive link to the mesh
https://drive.google.com/file/d/0B6ZYAd08tZL-MEN2VzY0VEVEdUE/edit?usp=sharing

QUOTE
Not a pain, it just means the cartographers have long-term employment!

Phil

well for 67P a Simplecylindrical map is " out the window"
the vid on youtube looks to be using a Simplecylindrical map
https://www.youtube.com/watch?v=CNGu7KbXzOs
you can tell by the STRETCHED green dots that look like lines

But a "cubemap " would work fairly well

Posted by: Greenish Aug 9 2014, 01:42 AM

I had been curious about the gravity field so was googling about... this poster shows some of the weirdness of "which way is up" in a simplified contact binary scenario. It makes perfect sense, but I never considered that there could be the equivalent of Lagrange points near these bodies. Close-in "orbits" would certainly not be circular, even halos are possible. And the details near the neck... hard to know.

http://www.lr.tudelft.nl/fileadmin/Faculteit/LR/Nieuws_en_Agenda/Artikelen/Posters/Docs/Jinglang_Feng.pdf
snip:




Posted by: machi Aug 9 2014, 01:53 AM

According to my calculations gravity/centripetal ratio for r=2000 m and vrot=0.28 m/s is G/a=0.0143*Ro (density)
Comets could be very fluffy so density can be between 100 to 1400 kg/m3.
Ratio is then 1.5 to 20× (not ~100 or ~1000).

Posted by: Gerald Aug 9 2014, 02:10 AM

QUOTE (JCG @ Aug 9 2014, 03:11 AM) *
Back of the envelope:
Gravity /centripetal ~ GM/r^2//V^2/r ~ GpP^2 where G = grav constant of 6.67x 10^-11 (mks), p = density ~ 10^3 (mks) and P = period ~4.6x10^4 sec.
Ratio ~ 10^2
Gravity wins hands down. Tidal forces are insufficient.

This would be bad for Philae, so I've looked, where the discrepancy may come from.
One reason is -- if I calculated correctly -- a factor of 1 / 3π for the density calculation in the spherical case.
The other one is the estimated density, which has been estimated as 10^2 kg/m³.
Together we get a discrepancy factor of 30π, about 94.
Now add the non-spherical shape, and things are open again.

-- This shows, how important the ongoing gravimetric measurements are.

Posted by: Adam Hurcewicz Aug 10 2014, 05:16 PM

OK, here is visualization from Celestia. I made model in Blender, texture is from Itokawa, orbital data from SPK/BSP od NAIF NASA/JPL

http://www.youtube.com/watch?v=kETzagV37ig

Posted by: Gerald Aug 10 2014, 06:03 PM

For 67P/C-G, and similarly asymmetric bodies, I'd suggest a projection on an appropriate gravitationally equipotential surface, either respecting the centrifugal forces, or using the body at rest.
"Appropriate" means, the average height of the topography over the equipotential surface should be zero, if possible. As a constraint a surface should be taken, which consists of one component without singularities (and without overlapping itself, which is probably a corollary).
Projections go along the field lines of gravity.
The result is still a non-planar map.
This could be projected in a second step to planar tiles/stripes (mercator-like in a very general sense) by constraining the http://mathworld.wolfram.com/IntrinsicCurvature.html http://en.wikipedia.org/wiki/Curvature.
The width of the stripes would vary because of the varying intrinsic curvature.

... just to close this gap preliminarily, until an official decision is made.

Posted by: Harder Aug 10 2014, 06:36 PM

thanks, Gerald, for your insights. I noticed you follow the Rosetta blog, too. Unless another Gerald is at work there! My own name (Peter Groeneweg) is a bit too difficult so on the ESA blogs I'm PeterG.

In my previous entry my use of the English language is perhaps "difficult" too, so let me say here what I really wanted to say: I feel privileged to be a member, a junior member to be more precise, of a forum that has experts like Phil in its ranks. No unmanned spaceflight subject seems too arcane for the forum!

A further thought: is a cartography system the province of ESA, or does it need endorsement by the international organization(s)? One thing seems sure: after the initial spectacular success at 67P/C-G I expect more missions to follow and a sound cartography system seems most useful to have by then.

Posted by: fredk Aug 10 2014, 06:38 PM

QUOTE (Gerald @ Aug 10 2014, 06:03 PM) *
Projections go along the field lines of gravity.

Why along the field lines (and with respect to an equipotential surface)? That would rely to some extent on knowledge of the internal mass distribution, which may be significantly nonuniform, and at the very least would require nontrivial numerical modelling to determine. It would strike me as a good property of a projection to depend only on the geometry of the body's surface.

But all of this is probably moot since such bodies have been mapped in the past. In practice, I'd guess the projection would be tailored to the body, since some projections may not work for bodies when the surface "folds back on itself".

Posted by: Gerald Aug 10 2014, 07:11 PM

QUOTE (Harder @ Aug 10 2014, 08:38 PM) *
... I noticed you follow the Rosetta blog, too. Unless another Gerald is at work there! ...

I admit, I couldn't help to extend the funny metaphorical thought experiment about the Philae descent and landing (with limited type setting options).
But names don't need to be unique, necessarily.

QUOTE (fredk @ Aug 10 2014, 08:38 PM) *
Why along the field lines..?

Because it corresponds to the intuitive and physical concept of "up" and "down".
Notions like slope / steepness, depression, hill, etc. make a sense. It's kind of generalization we are used to from Earth on a physical basis, not merely geometric.

Technical difficulties to find the field of gravity are going to be reduced by the orbital measurements. These measurements allow even to determine the interior mass distribution to some degree. But an estimation would do the job, too.

The surface shouldn't fold back to itself (conjectural to some degree at this point), since the gravitational potential should be defined uniquely, at least for the non-rotating body.
The body itself may be layered or contain overhangs, of course.

Posted by: Phil Stooke Aug 10 2014, 09:43 PM

The up and down can be incorporated into topography by mapping height (and slope etc.) relative to the equipotential surface (with or without rotational accelerations included - with them, it corresponds to what Peter Thomas has called Dynamic Topography) - there's a literature on this especially by Peter Thomas and colleagues.

There is no one best way to map a non-spherical object, just as there is not for a sphere. In fact, we need lots of maps in different projections, and using different versions of the shape, to explore the range of possibilities, most of which few people have ever thought about in detail. For instance, the shape model used to establish locations and drive the projection might be any of these:

True topographic shape
Equipotential surface
Convex hull
Triaxial Ellipsoid (best fit)
Sphere
- also other possible shapes such as a cylinder could be considered, especially for more elongated objects.

For anything but the first, the actual surface would be projected onto the shape model along radii or surface normals (body or model), then that shape drives the map projection.

Although simple cylindrical maps contain severe distortions they are very useful as intermediate steps in mapping and they are easy to import into many mapping and visualization systems. My Itokawa mosaic, for instance, includes many distortions and one small area where the mosaic is not unique (radii exit the surface and reconnect with it, as we may see at 67P as well. But there are ways to cope with these issues and you have to start somewhere.

"A further thought: is a cartography system the province of ESA, or does it need endorsement by the international organization(s)? One thing seems sure: after the initial spectacular success at 67P/C-G I expect more missions to follow and a sound cartography system seems most useful to have by then."

ESA can choose its own method of mapping, no international agency has any role in it except the IAU Working Group for cartographic coordinates and rotational elements - the coordinate system should conform to their guidelines. But mapping - no. The field is still very immature and no standards exist, nor should they until we have much more experience with different methods.

Phil

Posted by: JohnVV Aug 10 2014, 11:38 PM

the problem at this time is we do not have a mesh to work with
-- yes one could use "Blender" and hand carve a cube into something that looks like it

now a cube map has advantages ( sometimes) for some shapes

a hi-passed map for a mesh of Vesta ( old map 2006 data) in a uv mapped cubemap
( from a normal by Chris Laurel)
north,90 to180,0 to 90,
-90 to 0,-180to -90, south
http://imgbox.com/SWtfSXBO

the new DEM hi passed for comparison
-- in Simple Cylindrical projection
http://imgbox.com/yeEoGXR1

now vesta is a bad example it is rather spherical ( i just happen to be working on this asteroid right now)

so for 67p a SimpleCyl. map will not work well . BUT it is a good intermediate format and so is sinusoidal


Posted by: Y Bar Ranch Aug 11 2014, 02:16 PM

QUOTE (SteveM @ Aug 8 2014, 05:42 PM) *
I'm not convinced by the emerging consensus that the neck is an erosional feature. It seems to me that the neck is near a gravitational low (i.e., "downhill" from the rest of the comet) and any loose material near the comet would be likely to settle there.

Actually, the neck is not near a gravitational low. If you could hollow out a little sphere at where the center of mass is for the comet, at that point there'd be no gravity since the mass would be pulling from all directions equally. That's somewhere near the neck. Taking off and flying away from the neck perpendicular to the main axis is probably the lowest energy trajectory for departing (now I'm guessing).

Posted by: djellison Aug 11 2014, 02:47 PM

QUOTE (Y Bar Ranch @ Aug 11 2014, 07:16 AM) *
Actually, the neck is not near a gravitational low.


QUOTE
If you could hollow out a little sphere at where the center of mass is for the comet, at that point there'd be no gravity since the mass would be pulling from all directions equally. That's somewhere near the neck.


Are these not contradictory statements?

Posted by: ngunn Aug 11 2014, 02:48 PM

QUOTE (Y Bar Ranch @ Aug 11 2014, 03:16 PM) *
Actually, the neck is not near a gravitational low.


I think there is confusion here between the scalar quantity gravitational potential and its gradient, gravitational field strength. The centre of the Earth, for example, is a low point in the gravitational potential. If you could dig a tunnel all the way there objects would certainly fall down it, even though on arrival they would have zero weight.

Posted by: Gerald Aug 11 2014, 03:37 PM

If you take a binary of two spherical bodies, the center of mass is in the middle of the line between those two bodies, but that's no gravitational low; it's more like a saddle; and it's a http://en.wikipedia.org/wiki/Lagrangian_point (L1) at the same time, although the center of mass of two bodies doesn't need to be a Lagrangian point, in general. There are two lows at the respective centers of the two bodies.

For 67P/C-G there may also be two (or more) local gravitational lows, the deeper one near the center of the larger component.
The center of mass should be between the gravitational low of the larger component and the neck.
The neck should be near a Lagrangian point (a saddle in the field of gravity), which is between the local gravitational low of the smaller component and the center of mass.
At the center of mass there should be a net gravitational pull towards the local gravitational low of the larger component.

The center of mass is a point on the rotation axis.

Start with the Earth-Moon system as an easier-to-understand example, when reading the second paragraph a second time.

Posted by: Y Bar Ranch Aug 11 2014, 04:02 PM

QUOTE (djellison @ Aug 11 2014, 09:47 AM) *
Are these not contradictory statements?

Not contradictory, more like a non sequitur. huh.gif

Posted by: Y Bar Ranch Aug 11 2014, 04:08 PM

QUOTE (Gerald @ Aug 11 2014, 10:37 AM) *
If you take a binary of two spherical bodies, the center of mass is in the middle of the line between those two bodies, but that's no gravitational low; it's more like a saddle;

That's what I meant to express. A small perturbation from the saddle point not exactly on the upward isoline and its downhill to one of the two lobes.

So escape velocity from the saddle point is likely lowest for the comet and it would dissipate at a higher rate, and any spray that doesn't make it off the comet from the neck is likely pulled to one of the lobes, adding to the saddle-ness of the saddle point. So for an asymetrical body, it seems that process is unstable and the asymmetry would grow, i.e., more necking.

There's probably an unstable process between the two lobes too, with one having a higher rate of dissipation and the heavier one stealing some of the lighter one's mass. But this is more guessing on my part.

Posted by: Gerald Aug 11 2014, 04:36 PM

QUOTE (Y Bar Ranch @ Aug 11 2014, 06:08 PM) *
That's what I meant to express. A small perturbation from the saddle point not exactly on the upward isoline and its downhill to one of the two lobes.
...

That's really hard to tell at the moment, since the local gravitational lows are probably within the nucleus. Since the surface of the larger component is farther away from its local gravitational low than the surface of the neck is away from the line between the two(?) gravitational lows, we've two opposite effects which may or may not cancel out.

But I share the impression, that the surface of the nucleus isn't in perfect equilibrium between the several forces (gravity, inertial pseudo-forces, friction).
If there is some mass waste from the neck or from the smaller component towards the larger one, the field of gravity, and the rotation also change. Asymmetric loss of volatiles may change the angular velocity too.
This might eventually lead to ejection or collapse of some parts. As the comet gets closer to the Sun, I'd guess, we may see some dynamics.

Posted by: ngunn Aug 11 2014, 04:42 PM

QUOTE (Y Bar Ranch @ Aug 11 2014, 05:08 PM) *
So escape velocity from the saddle point is likely lowest for the comet and it would dissipate at a higher rate, and any spray that doesn't make it off the comet from the neck is likely pulled to one of the lobes, adding to the saddle-ness of the saddle point. So for an asymetrical body, it seems that process is unstable and the asymmetry would grow, i.e., more necking.


I really don't think that's true. Consider a body consisting of two perfect touching spheres. Place a small test sphere on the surface of one of them and where would it roll to? Towards the contact point for sure as that is the point of lowest potential on the surface of the body. Thus the neck would tend to grow thicker.

Posted by: Y Bar Ranch Aug 11 2014, 04:50 PM

QUOTE (ngunn @ Aug 11 2014, 12:42 PM) *
I really don't think that's true. Consider a body consisting of two perfect touching spheres. Place a small test sphere on the surface of one of them and where would it roll to? Towards the contact point for sure as that is the point of lowest potential on the surface of the body. Thus the neck would tend to grow thicker.


It would do that only because it is constrained to roll on the surface of the two spheres.

Posted by: Phil Stooke Aug 15 2014, 06:18 PM

Ok... I have been taking some time out from what I should really be doing - finishing a book (Emily will understand this) - to play around with some ideas about what a map of 'the nucleus that dare not speak its name' should look like.

Let me preface this by saying - this is a horrible map, very distorted and inaccurate, and the Rosetta team will do much better soon and completely discredit me. This is only intended to illustrate roughly what a proper map might look like. It's cylindrical, so the projection is very distorted to begin with.

We had a video of a shape with a lat-long grid, so that forms the basis of my coordinate system. I took images from orientations which roughly matched frames from the video and overlaid them. Two sources of error immediately - the shape was based on low res images and will not fit high res images very well to begin with, and the overlay is only approximate due to different view directions, so it's hard to match positions properly. Then I copied areas grid cell by grid cell and pasted them and distorted them to fit the grid. Lots of problems and bad fits especially in the neck area, obviously.

The grid is spaced at 15 degrees like the shape model video grid. Longitude 180 is in the middle. A separate version is annotated to show where the main features are.

Phil




Posted by: Explorer1 Aug 15 2014, 07:13 PM

Very impressive! The axis must be tilted quite a lot; given the length of the seasons it might be a very long time until much of the 'southern hemisphere' is in sunlight to fill in the black spaces.

Posted by: wildespace Aug 16 2014, 07:54 AM

I have seen members here mention generating synthetic "in-between" frames from two images, so this is a callout for someone to hopefully generate a bunch of frames between the two fantastic OSIRIS images that made up that 3D view: http://blogs.esa.int/rosetta/2014/08/14/comet-67pc-g-in-3d/

The generated frames could be used to create a more "comfortable" anaglyph, or even an animation of the comet's rotation.

Posted by: MoreInput Aug 16 2014, 08:46 PM

Thanks for the map, Phil.

What about the idea to split the map into two part: one map for the potatoe shaped head, and one map for the body of the comet? On both maps there would be a circular black shape where the both are connected (the Neck).


Posted by: ngunn Aug 16 2014, 09:42 PM

That same idea occurred to me: map them separately as if they were Pluto and Charon, only in contact. Each part approximates a spheroid well enough. Making the common rotation axis the lynch-pin of the coordinate system forces horrendous distortions on the map. Furthermore any advantage in doing so will most likely prove ephemeral when the rotation axis shifts due to mass wasting at perihelion.

In fact the two parts may roll a bit and settle together differently at that time. How fares the coordinate system then?

Posted by: JohnVV Aug 17 2014, 04:55 AM


this gif animation ( pre orbit data )
http://scitechdaily.com/images/New-3D-View-of-the-Rosetta-Comet.gif

I have been able to get a ??? fair pointcloud out of the gif
-- view in meshlab
http://imgbox.com/V48RLBAA

that is then meshed - in meshlab and cleaned up in blender
http://imgbox.com/El8ZEJ3X http://imgbox.com/06iTfz4T

a link to a zip on my g-drive
67p.8-21-2014Mesh.zip - 1.8 meg with a 4k texture
https://googledrive.com/host/0B6ZYAd08tZL-V1UtRDM5cmFOT0U/67p.8-21-2014Mesh.zip

Posted by: Phil Stooke Aug 17 2014, 05:33 AM

Re - mapping the lobes separately - it's an interesting idea and I would welcome any efforts along those lines. As I said in an earlier post, there's no one best way to do it, and we need many efforts to tackle this problem in different ways. But right now I think we should wait for a more detailed shape model and more images.

Phil

Posted by: JohnVV Aug 20 2014, 10:26 PM

still working on this , just an early preview

http://imgbox.com/V48RLBAA

I was able to extract a pointcloud from the gif animation
http://blogs.esa.int/rosetta/2014/07/28/updated-comet-shape-model/

needs cleaning and meshing and is only a rough draft ....

Phils map from post 188
http://www.unmannedspaceflight.com/index.php?showtopic=7872&view=findpost&p=212119

as expected there is a LOT of distortion

Posted by: Phil Stooke Aug 22 2014, 03:39 AM

JohnVV wrote:

I was able to extract a pointcloud from the gif animation
-------

needs cleaning and meshing and is only a rough draft ....

Phils map from post 188
--------

as expected there is a LOT of distortion


Wow! Considering how I put that thing together, I'm amazed how well the rendering worked out. Well done!

Phil

Posted by: JohnVV Aug 22 2014, 03:50 AM

phil
there is a zip with a obj mesh in it here
https://googledrive.com/host/0B6ZYAd08tZL-V1UtRDM5cmFOT0U/67p.8-21-2014Mesh.zip

i have 0 long on the flat "base" and 180 on the top of the "head"

it would be nice if the ESA would release there mesh ...

Posted by: mcgyver Aug 22 2014, 02:13 PM

QUOTE (JohnVV @ Aug 17 2014, 04:55 AM) *
this gif animation ( pre orbit data )
http://scitechdaily.com/images/New-3D-View-of-the-Rosetta-Comet.gif

I have been able to get a ??? fair pointcloud out of the gif
-- view in meshlab
http://imgbox.com/V48RLBAA

that is then meshed - in meshlab and cleaned up in blender

Do you explain somewhere the method you used to get the meshed version from pointcloud version? I'd like to print a 3d-model of Pathfinder landing site (remember it?), but there are so many holes in the 3d data I found (a 20 years old VRML model...) that it's impossible to fill them up by hand.


Posted by: Malmer Aug 22 2014, 04:07 PM

I'm playing around making a highresolution 3D representation of Comet 67P/Churyumov-Gerasimenko using a hybrid stereo correlation/shape from shading approach...

Take a look:
http://mattias.malmer.nu/wp-content/uploads/2014/08/trim.21B8694C-303A-490B-BA7D-B683D8388A36.mov

Posted by: JohnVV Aug 22 2014, 05:50 PM

QUOTE
Do you explain somewhere the method you used to get the meshed version from pointcloud version? I'd like to print a 3d-model of Pathfinder landing site (remember it?), but there are so many holes in the 3d data I found (a 20 years old VRML model...) that it's impossible to fill them up by hand.

this thread is not the place for that

i will post an explanation in the imaging processing
but very basically
1) used "bundler-sfm"
2) used meshlab
3) then minor correcting in Blender

Posted by: JohnVV Aug 23 2014, 01:35 AM

QUOTE (Malmer @ Aug 22 2014, 12:07 PM) *
I'm playing around making a highresolution 3D representation of Comet 67P/Churyumov-Gerasimenko using a hybrid stereo correlation/shape from shading approach...

Take a look:
http://mattias.malmer.nu/wp-content/uploads/2014/08/trim.21B8694C-303A-490B-BA7D-B683D8388A36.mov


nice vid
i take it that is from the red/blue image release
as Phil has posted mapping is going to be a pain
do to the second sphere on top that makes a HIDDEN area from using a simple-cylindrical map

http://imgbox.com/TOi0XjP0

Posted by: Malmer Aug 23 2014, 06:42 AM

QUOTE (JohnVV @ Aug 23 2014, 03:35 AM) *
nice vid
i take it that is from the red/blue image release
as Phil has posted mapping is going to be a pain
do to the second sphere on top that makes a HIDDEN area from using a simple-cylindrical map

http://imgbox.com/TOi0XjP0


Yes. I used the a and b images from that release. Well spotted! I can get very high resolution depth data from that pair. I used that pair as a quick test because it was easy to get it to work.



I think limiting one self to using a simple cylindrical map for a concave object is inheritly wrong. What to do if you come across something with a higher genus topology. (Like a toroid or double toroid) then you would always have multiple overlaps. I like the idea of using multiple local cylindrical maps like mentioned earlier.


Posted by: Phil Stooke Aug 23 2014, 02:37 PM

Hi Malmer - cartographers have already discussed these issues, so nobody is limiting anything to cylindrical maps. But the standard cylindrical maps are useful in many cases despite bad distortions because they are easily imported into common visualization software.

As an example, a toroidal world - like a comet nucleus with a vent burned right through it - could be mapped onto a plane using two dimensions, the azimuth around the ring itself and the azimuth around the cross-section (if you see what I mean) - two perpendicular azimuth dimensions mapped into a rectangle. It could also be mapped in azimuthal projections as the top and bottom faces, each one a circle with a hole in the middle. A Pretzel world - multiple piercings, a sort of hipster comet - could be done in more complex variations of the same ideas.

Even cylindrical mapping can be done differently - especially as a transverse cylindrical projection where, for instance, an extremely elongated object like Eros can be surrounded by a cylinder whose long axis coincides with the object's long axis (instead of the rotation axis). Only the outer ends don't get mapped well like that, and they are done on small separate maps, as we often do polar maps in addition to a cylindrical Mercator projection.

Separate maps of different areas are fine - we do it all the time on Earth after all - but they don't solve the issue of making one global map.

Phil

Posted by: Malmer Aug 23 2014, 05:36 PM

For my own selfish purposes I will probably use some kind of LSCM unwrap to have resonably distortionfree and areapreserving representation.

Posted by: mcgyver Aug 23 2014, 10:06 PM

QUOTE (Malmer @ Aug 22 2014, 04:07 PM) *
I'm playing around making a highresolution 3D representation of Comet 67P/Churyumov-Gerasimenko using a hybrid stereo correlation/shape from shading approach...

Take a look:
http://mattias.malmer.nu/wp-content/uploads/2014/08/trim.21B8694C-303A-490B-BA7D-B683D8388A36.mov


Simply amazing!
Are you also able to obtain a 3d STL model from those data?

Posted by: Malmer Aug 23 2014, 10:42 PM

QUOTE (mcgyver @ Aug 24 2014, 12:06 AM) *
Simply amazing!
Are you also able to obtain a 3d STL model from those data?


As it is now it is just a heightfield. It is just a quick proof of concept. I am going to use it to build a full shapemodel.

Posted by: Toma B Aug 24 2014, 10:07 AM

QUOTE (Malmer @ Aug 24 2014, 12:42 AM) *
I am going to use it to build a full shapemodel.


WOW!!!! That's amazing!!! Awesome!!!! blink.gif
While you build full model can you upload some more of the so far finished stuff....perhaps youtube???

Posted by: machi Aug 25 2014, 10:42 AM

QUOTE (wildespace @ Aug 16 2014, 09:54 AM) *
I have seen members here mention generating synthetic "in-between" frames from two images, so this is a callout for someone to hopefully generate a bunch of frames between the two fantastic OSIRIS images that made up that 3D view: http://blogs.esa.int/rosetta/2014/08/14/comet-67pc-g-in-3d/

The generated frames could be used to create a more "comfortable" anaglyph, or even an animation of the comet's rotation.


It's possible (and Gerald already did this) but it's complicated by the shape of 67P and it's very time consuming job especially in case of rotation animation (which is possible thanks to the http://www.planetary.org/multimedia/space-images/small-bodies/comet-cg-20140806-navcam-montage.html).
My guess is at least one hundred control points for every pair of images. For whole animation (one revolution) it's 1300-1500 control points.

QUOTE (Malmer @ Aug 22 2014, 06:07 PM) *
I'm playing around making a highresolution 3D representation of Comet 67P/Churyumov-Gerasimenko using a hybrid stereo correlation/shape from shading approach...

Take a look:
http://mattias.malmer.nu/wp-content/uploads/2014/08/trim.21B8694C-303A-490B-BA7D-B683D8388A36.mov


It looks very impressive! It reminds me some works from the former(?) UMSF member who did 3D images from HiRISE cameras by shape-from-shading method.


Posted by: Gerald Aug 25 2014, 12:08 PM

QUOTE (machi @ Aug 25 2014, 12:42 PM) *
... it's very time consuming job ...
My guess is at least one hundred control points for every pair of images...

By automated matching of 256x256 = 65536 (overlapping) small tiles, and storing the respective displacements, I've tried to get this somehow managed.
But areas with few features, e.g. large shadows or very smooth patches, are hard to match, and result in very noisy parts, despite noise filtering. Some features aren't visible in both images, so again hard to match.
Here a visualization of such a displacement map:
http://imgur.com/dbAY4Ny
The displacement map can then be used to generate a radius map (kind of a depth map), provided some telemetry data are known or estimated:
http://imgur.com/ZEsFRMr
From this, a 3d-mesh could be generated. (But the quality of the above map isn't too convincing.)
I've used the displacement map to generate the interpolated frames.
(Credit for the underlying images, used to generate the above maps: ESA / Rosetta / MPS for OSIRIS Team MPS / UPD / LAM / IAA / SSO / INTA / UPM / DASP / IDA)

Posted by: JohnVV Sep 2 2014, 11:41 PM

QUOTE
t would be interesting to see a map of where "down" is in the different surface areas of the comet.


down in the -- north up and south down ---
a repost from a different forum
the bottom two images in the bottom right image


been working on mapping the esa jpg images to a updated mesh
-- not looking good YET
a 10 deg grid test map
then warped to the mesh -- this is SCARY
( as in Oct. 31 scary )
then just the updated mesh and esa images from aug. 7 and 15
http://imgbox.com/aBdHGJod http://imgbox.com/nMJoBp6E

http://imgbox.com/OQ2VnB6S http://imgbox.com/MFW6ZaVx

Posted by: charborob Sep 3 2014, 12:42 AM

What I would like to see is an image of the comet surrounded with short arrows pointing in the "down" direction.

Posted by: JohnVV Sep 3 2014, 01:08 AM

with "Down as the direction of the SouthPole
a few images

http://imgbox.com/K6Z2abSo http://imgbox.com/7H7tvBy2 http://imgbox.com/RJdYyo42
http://imgbox.com/D8GFZ3bv http://imgbox.com/NHfLNSc0


Navcam from the 14,15,20 and two images of my mesh in blender
Copyright: ESA/Rosetta/NAVCAM
and me - John vanvliet

a DEM from the mesh i am using
the center is 0 long / 0 lat -180 to 180
http://imgbox.com/GGJOv942

Posted by: SteveM Sep 3 2014, 01:20 AM

QUOTE (charborob @ Sep 2 2014, 07:42 PM) *
What I would like to see is an image of the comet surrounded with short arrows pointing in the "down" direction.
A similar result would be obtained by color coding a map of the comet to show height in reference to the "geoid”. The colors would quickly show which regions of the comet were uphill or downhill from each other.

Of course, the shape of 67P C-G's geoid will be interesting in itself – and something of a chore to compute.

Posted by: Y Bar Ranch Sep 3 2014, 11:14 AM

QUOTE (ngunn @ Sep 2 2014, 01:16 PM) *
You made that statement before, but the opposite is in fact the case. The midpoint is the place on the comet's surface where gravitational potential is lowest...

If you were to take two spherical objects and connect them with a stick (or have them orbit each other) then the low potential point would not be at the midpoint between them, I.e., at the center of mass of the two body system. There would be two low points, at the center of mass of each of the two spheres. The midpoint of the system is a saddle point, with a higher potential than either of the two centers.

Posted by: Malmer Sep 3 2014, 11:49 AM

QUOTE (JohnVV @ Sep 3 2014, 01:41 AM) *
down in the -- north up and south down ---
a repost from a different forum
the bottom two images in the bottom right image


been working on mapping the esa jpg images to a updated mesh
-- not looking good YET
a 10 deg grid test map
then warped to the mesh -- this is SCARY
( as in Oct. 31 scary )
then just the updated mesh and esa images from aug. 7 and 15
http://imgbox.com/aBdHGJod http://imgbox.com/nMJoBp6E

http://imgbox.com/OQ2VnB6S http://imgbox.com/MFW6ZaVx



Is that your own shapemodel or is it something ESA have made that is in the public domain?

Im working on building my own. but I would like to have another stereo pair from osiris before i continue in ernest. (i want to make an ultra high density model)

I have reverseengineered all the spacecraft positions relative to the comet for all pictures up until now but i have no real coordinate system yet. Is there a consensus northpole and a southpole and a prime meridian that i can use to build that?

Just points on the surface would help smile.gif


edit:
oh.. you just posted those pictures... where did you get that information?

Posted by: ngunn Sep 3 2014, 12:07 PM

QUOTE (Y Bar Ranch @ Sep 3 2014, 12:14 PM) *
If you were to take two spherical objects and connect them with a stick (or have them orbit each other) then the low potential point would not be at the midpoint between them, I.e., at the center of mass of the two body system. There would be two low points, at the center of mass of each of the two spheres. The midpoint of the system is a saddle point, with a higher potential than either of the two centers.


That's absolutely correct, but materials on the comet surface cannot fall towards either of the two centres. They are constrained to move on or above the surface. That being so, the neck is the lowest potential location they can migrate to.

Posted by: JohnVV Sep 3 2014, 05:14 PM

QUOTE
Is that your own shapemodel or is it something ESA have made that is in the public domain?

no it is all mine
i used motion to make a "point cloud" from two videos
then meshed it and just finished a rough edit

i am about to add details from the images using "shape from shade"
an old bit of code from a siggraph paper "mini_sfs"
and a newer phd paper and code
http://code.google.com/p/hyperion-cv/

i have NOT uploaded version TWO yet
version 1 is here
https://googledrive.com/host/0B6ZYAd08tZL-V1UtRDM5cmFOT0U/67p.8-21-2014Mesh.zip

--- VERSION 2 is here "67P.09.03.2014.zip"
https://googledrive.com/host/0B6ZYAd08tZL-V1UtRDM5cmFOT0U/67P.09.03.2014.zip

Posted by: Phil Stooke Sep 3 2014, 06:05 PM

I am very impressed by this, John! Looking forward to seeing it evolve.

Phil


Posted by: Y Bar Ranch Sep 3 2014, 06:33 PM

QUOTE (ngunn @ Sep 3 2014, 08:07 AM) *
That's absolutely correct, but materials on the comet surface cannot fall towards either of the two centres. They are constrained to move on or above the surface. That being so, the neck is the lowest potential location they can migrate to.

OK, here's my super simple comet model. Two spheres, radius 2 and radius 1, connected by a cylinder neck of length = 1 and radius = 1/2. Streamlines are down the gradient of the potential. Contours are the potential. YMMV on accuracy. I can improve it and generate the 3D field with some more accurate estimations of the lobes and neck. Fun to fiddle with.



Posted by: ngunn Sep 3 2014, 07:19 PM

QUOTE (Y Bar Ranch @ Sep 3 2014, 07:33 PM) *
super simple comet model


Excellent! Now focus on the force vectors just at the points where they intersect the surface of the 'comet' and imagine them resolved into normal and tangential components. Chuck out the normal components and map the tangential ones as arrows drawn on the 'cometary' surface. You would then have a first approximation local slope direction map as requested by Mercure and charborob a few posts up. EDIT: now at post 227 in the other Rosetta thread, Early Orbital Operations.

EDIT: Interestingly, your diagram already shows that the steepest gradient (angle between force vector and the normal) is to be found on the inner side of the smaller lobe, exactly the place on the actual comet where there are features tentatively attributed to a landslip.

Posted by: Malmer Sep 3 2014, 08:54 PM

QUOTE (JohnVV @ Sep 3 2014, 07:14 PM) *
no it is all mine
i used motion to make a "point cloud" from two videos


Ah, you used ESAs videos of their shapemodel and reverseengineered it. Clever.

I'm just using the "raw" images to build my own. (I want to make it from scratch just as an exercise in image processing)

I'm using a very simple shape from shading algorithm that i made myself to add the details. (Would make your skin crawl)

The race is on smile.gif




Posted by: Y Bar Ranch Sep 3 2014, 09:09 PM


I'd be interested in grabbing whatever you guys come up with. Point cloud is OK. Then I can play with gravity modeling.

Posted by: Malmer Sep 3 2014, 09:48 PM

Will post as soon as it is resonably correct.

Posted by: JohnVV Sep 3 2014, 09:50 PM

QUOTE
I'd be interested in grabbing whatever you guys come up with. Point cloud is OK. Then I can play with gravity modeling.

i just zipped up a the mash as of today
-- a low res 1.3 meg .obj file
the zip contains a map-grid uv mapped
https://googledrive.com/host/0B6ZYAd08tZL-V1UtRDM5cmFOT0U/67P.09.03.2014.zip

Posted by: Malmer Sep 3 2014, 10:32 PM

QUOTE (JohnVV @ Sep 3 2014, 11:50 PM) *
i just zipped up a the mash as of today
-- a low res 1.3 meg .obj file
the zip contains a map-grid uv mapped
https://googledrive.com/host/0B6ZYAd08tZL-V1UtRDM5cmFOT0U/67P.09.03.2014.zip


I will use it to line up mine so that we work in the same coordinate system.

(Just noticed that I made my 100th post and became a "Member" today after nine years. I guess I read a lot and post very little...)

Posted by: Gerald Sep 3 2014, 10:50 PM

QUOTE (Y Bar Ranch @ Sep 3 2014, 08:33 PM) *
OK, here's my super simple comet model...

Does the model already contain the shift due to rotation?

Posted by: Mercure Sep 3 2014, 10:52 PM

QUOTE (ngunn @ Sep 3 2014, 08:19 PM) *
map the tangential ones as arrows drawn on the 'cometary' surface.


Yes, I also think that would be the best visualisation, with arrow length indicating gravitational pull. Or perhaps visualize it as 'stubs' or 'sticks' on the surface of the model, with tilt and length of the stubs indicating gravitational direction and pull.

Such a visualization would also be interesting seen in conjunction with outgassing, to see if hotspots correlate with areas of relatively weak gravity or not.

Y Bar Ranch, very interesting first stab at a visualisation, thank you for doing it.

Posted by: MarsInMyLifetime Sep 4 2014, 02:59 AM

Another way that readers might better associate with the upcoming Philae landing process would be to have a set of points positioned above each candidate landing site about 10km off the surface with a downward pointing arrow representing the direction and relative strength of attraction on each such 100kilogram point. Then we could appreciate the unique issues with being positioned correctly at release for a descent into the intended spot. Ignoring the orbital velocity, just the "down" vector at those locations would be interesting to see. Is this possible, and even useful for others?

Posted by: Y Bar Ranch Sep 4 2014, 12:12 PM

QUOTE (Gerald @ Sep 3 2014, 05:50 PM) *
Does the model already contain the shift due to rotation?

No...just a simple malformed dumbbell right now

Posted by: CAP-Team Sep 4 2014, 06:50 PM

QUOTE (JohnVV @ Sep 3 2014, 11:50 PM) *
i just zipped up a the mash as of today
-- a low res 1.3 meg .obj file
the zip contains a map-grid uv mapped
https://googledrive.com/host/0B6ZYAd08tZL-V1UtRDM5cmFOT0U/67P.09.03.2014.zip


Thanks! Let's see if I can convert it to 3ds and then to CMOD smile.gif

Posted by: mcgyver Sep 4 2014, 07:08 PM

QUOTE (CAP-Team @ Sep 4 2014, 06:50 PM) *
Thanks! Let's see if I can convert it to 3ds and then to CMOD smile.gif

What about STL? Is it possible?

Posted by: JohnVV Sep 4 2014, 08:11 PM

3ds to cmod is rather easy
now the plugin is for the OLD!!! blender python API
so you need to use Blender 2.49b

and building the tool " cmodview" from the celestia SVN source will save a ASCII mesh to a binary mesh

also my mesh IS NOT a "3ds "
it is a Alias Wavefront format
that is almost identical to the PDS vertex shape file

Posted by: Malmer Sep 4 2014, 08:33 PM

QUOTE (JohnVV @ Sep 4 2014, 10:11 PM) *
3ds to cmod is rather easy
now the plugin is for the OLD!!! blender python API
so you need to use Blender 2.49b

and building the tool " cmodview" from the celestia SVN source will save a ASCII mesh to a binary mesh

also my mesh IS NOT a "3ds "
it is a Alias Wavefront format
that is almost identical to the PDS vertex shape file


The 3ds format is really not much fun. The 3DS format does not support more than one UV coordinate per vertex. You will get problems along UV seams

Posted by: djellison Sep 4 2014, 09:09 PM

QUOTE (mcgyver @ Sep 4 2014, 12:08 PM) *
What about STL? Is it possible?


Download and install Blender ( http://www.blender.org/ )

Import OBJ

Export STL.

Done.

(Caution - you will not want to try and print an object like this on a 3D printer as-is. You will need to bifurcate it into hemispheres - such as I've done for other small bodies like Eros, Itokawa and Vesta http://nasa3d.arc.nasa.gov/search/ellison/model )

Posted by: Gerald Sep 4 2014, 10:07 PM

Some qualitative sensitivity analysis of trajectories to a rotating contact binary starting from an equatorial position about 10km from the center.
This gif shows a 10 and a 100 trajectories version to a binary consisting of two spheres, radii 1250 and 750m, density 1000 kg/m³ (to get about 1e13kg with this geometry), rotation period 12.4 hours; initial tangential velocity of the lander is zero (relative to the inertial frame at rest relative to the center), initial radial velocity 0.5 m/s:
http://imgur.com/s9i00oH
The trajectories are shown in a reference frame, rotating with the binary.
Only the region on one side of the neck isn't accessible, even in theory.

High sensitivity to initial radial velocity of the lander, in 0.1 m/s steps from 0.0 to 0.5 m/s:
http://imgur.com/x0EKsIy
and to initial tangential velocity (0.0 and 0.1 m/s):
http://imgur.com/K3bsGuI

Sensitivity to the comet's mass is higher for low initial radial velocity (0.1 m/s) of the lander
http://imgur.com/k1SUg8A
than for higher initial radial velocity (0.4 m/s); this may have been expected:
http://imgur.com/tb9usav
(assuming no relevant programming flaws)

Posted by: fredk Sep 4 2014, 10:23 PM

Nice. So did you chose the rotation axis to be perpendicular to the line joining the two centres? I guess that crudely corresponds to C-G.

Posted by: Gerald Sep 4 2014, 10:30 PM

Yes.

Posted by: Malmer Sep 4 2014, 11:05 PM

QUOTE (JohnVV @ Sep 3 2014, 11:50 PM) *
i just zipped up a the mash as of today
-- a low res 1.3 meg .obj file
the zip contains a map-grid uv mapped
https://googledrive.com/host/0B6ZYAd08tZL-V1UtRDM5cmFOT0U/67P.09.03.2014.zip



I cant really get the scale right. Is it an arbitrary scale on your model?

Posted by: JohnVV Sep 5 2014, 06:47 PM

Blender is not a "cad/cam" set-up
so the dimensions are NOT in Meters or KM

also depending on what software you are using to import the mesh , it might be big or small

but the proportions will not change



Posted by: Malmer Sep 5 2014, 07:04 PM

QUOTE (JohnVV @ Sep 5 2014, 08:47 PM) *
Blender is not a "cad/cam" set-up
so the dimensions are NOT in Meters or KM

also depending on what software you are using to import the mesh , it might be big or small

but the proportions will not change


I'm using imagemodeler to generate a relatively sparse pointcloud. I'm manually placing all the markers on each image to make sure that there is maximum precision in the camera solve. I'm calibrating the scale to match the spacecraft distances that ESA give for the images.

I will drop that data into Nuke to generate a dense cloud by stereo correlation. Then I will add the last bit of detail using SFS.

There will probably be a bit of 3dsmax aswell.


Posted by: JohnVV Sep 16 2014, 05:44 AM

well the landing site is near 190 long and just a bit north about 15 north

some pics in 3D of the area and a DEM ( using SFS)
http://imgbox.com/3c8Z0BLz http://imgbox.com/K72JO0oK

http://imgbox.com/WpxwnXNb

there is a zip of the mesh ( not 100% accurate to the comet ,just an approximation )
https://googledrive.com/host/0B6ZYAd08tZL-V1UtRDM5cmFOT0U/PhilaeLandingSite.zip
PhilaeLandingSite.zip
│   ├── PhilaeLandingSite.mtl
│   ├── PhilaeLandingSite.obj
│   ├── Philae_s_primary_landing_site1.png
│   ├── sfs_DEM.32bitFloat.tiff
│   └── sfs_DEM.8bit.png

the heightmap is from this image
http://www.esa.int/spaceinimages/Images/2014/09/Philae_s_primary_landing_site
using Shape From Shade

Posted by: JohnVV Sep 24 2014, 12:43 AM

with the few images and the video
"Possible landing sites on _ Mögliche Landestellen auf Churyumov-Gerasimenko - YouTube [720p].mp4 "
can anyone add a bit more pinpoint area for a few locations
0 long
180 long
90 North
prime meridian
as far as i can tell they are someplace in the red circles below
http://imgbox.com/lfw7IBDQ http://imgbox.com/l6EcpvTn http://imgbox.com/5sKg8Gc4

http://imgbox.com/3IMQvTaN

Posted by: Malmer Sep 24 2014, 01:17 AM

QUOTE (JohnVV @ Sep 24 2014, 02:43 AM) *
with the few images and the video
"Possible landing sites on _ Mögliche Landestellen auf Churyumov-Gerasimenko - YouTube [720p].mp4 "
can anyone add a bit more pinpoint area for a few locations
0 long
180 long
90 North
prime meridian
as far as i can tell they are someplace in the red circles below



I really want that data aswell... (and an exact distance between north south wouldn't hurt either)

Posted by: JohnVV Sep 24 2014, 02:25 AM

from the image
"Comet_on_16_August_c.jpg" has 180 x 0 and 90N in it
and a few other images

it looks like one can make a line from some boulders in the crater to the N pole
http://imgbox.com/Wd6QYzyj


Posted by: Malmer Sep 26 2014, 04:18 AM

Shapemodel update.

I used a combination of stereo correlation, shape from shading and some space carving to build this mesh.

It is fairly untreated at this point and will evolve as we get access to more pictures...





Posted by: JohnVV Sep 26 2014, 06:59 AM

using a multi resolution approach
http://imgbox.com/zKjq7oVU
this is the 1 pixel per degree resolution , using a 360x180 displacement map

now i can align the displacement maps better for a 2ppd mesh
then maybe a 4 ppd , but until there is some KNOWN lat/long for some features ........

Posted by: Y Bar Ranch Sep 26 2014, 12:12 PM

QUOTE (Malmer @ Sep 26 2014, 12:18 AM) *
Shapemodel update.
I used a combination of stereo correlation, shape from shading and some space carving to build this mesh.
It is fairly untreated at this point and will evolve as we get access to more pictures...


Is your model available on-line? Would like to suck it into my Simple Gravity Sim and play with it.

Posted by: Phil Stooke Sep 26 2014, 01:04 PM

JohnVV - that imgbox link seems to be infected with something nasty - is there some other way you can distribute your images?

Phil


Posted by: Malmer Sep 26 2014, 01:07 PM

QUOTE (Y Bar Ranch @ Sep 26 2014, 02:12 PM) *
Is your model available on-line? Would like to suck it into my Simple Gravity Sim and play with it.


I will post a link here later today. The perpetually dark side of my model looks very bad at this point so I need to clean that up so that I do not get laughed at...



EDIT:
The link:
http://mattias.malmer.nu/2014/09/early-shapemodel-comet-67pchuryumov-gerasimenko/

Posted by: fredk Sep 26 2014, 02:53 PM

QUOTE (Phil Stooke @ Sep 26 2014, 02:04 PM) *
JohnVV - that imgbox link seems to be infected with something nasty - is there some other way you can distribute your images?

That image is well within the UMSF posted image size limit...

Posted by: djellison Sep 26 2014, 03:04 PM

I know many corporate firewalls block imgbox content. That's certainly the case here at JPL.

Posted by: JohnVV Sep 26 2014, 06:57 PM

reupladed to use UMSF thumbnail

Posted by: Malmer Oct 2 2014, 02:14 AM

I reprojected the VIRTIS heatmap to a more usable Lat Long format.

I hope it might help trying to determine where to put north and stuff in my model to be in the same coordinate space as ESA.



Posted by: JohnVV Oct 2 2014, 02:37 AM

i had to redefine the "NorthPole" ( rotated x + 90 degrees )
[attachment=33886:1.jpg]
normally the NP and SP would be at the top and bottom
BUT do to mapping issues with the two lobes that will not map well into a SimpleCylindrical map
redefining 180long/0lat as the northpole and the NorthPole as 0long /0lat
[attachment=33887:1440x721BASE.jpg] [attachment=33888:2.jpg]

the real northpole is at the center of the above DEM ( 8 bit copy of the 32 bit image)

and remapped with 90 north at the top and 0 longitude / 0 latitude in the center
[attachment=33889:90n1.png]
( the duck's body is in the center and the "head" is on the left and right )

Posted by: Malmer Oct 2 2014, 03:34 AM

QUOTE (Malmer @ Oct 2 2014, 04:14 AM) *
I reprojected the VIRTIS heatmap to a more usable Lat Long format.

I hope it might help trying to determine where to put north and stuff in my model to be in the same coordinate space as ESA.






The projection choosen has considerable overlaps where the neck and the head share the same map coordinates. That is a bit easier to see when draped over the shape model.

So I rendered a little movie:

http://mattias.malmer.nu/2014/10/virtis-heatmap/



Posted by: 4th rock from the sun Oct 14 2014, 11:21 AM

Ok, posting on this thread the shadow map from Malmer's version.
http://www.imagebam.com/image/3fadfd357512573

The coordinates are not compatible with the Virtis release, so I'll try to revise that.


(Noticed that I'm using two accounts to post on the forum, will try so solve that, but don't be scared, there's only one 4throck ;-) )

Posted by: JohnVV Oct 14 2014, 06:30 PM

i have stated MANY times
x is rotated x+90

that i had to rotate my mesh x+90
the real Northpole is in the center
the northpole of the Simplecylindrical map above is really 180 long and 0 lat
the southpole of the Simplecylindrical map above is really 0 long and 0 lat


SEE: post #110 above

Posted by: 4th rock from the sun Oct 14 2014, 10:40 PM

OK, I got that laugh.gif

Working from the mesh provided by ESA and deriving a normal + shadow map you get this:



It overlays nicely with the VIRTIS global map :-)
And it's might be good enough to register images...

Posted by: JohnVV Oct 15 2014, 01:54 AM

here is Malmer's mesh converted to a 32 bit DEM then to a 8 bit jpg
Zero longitude and Zero latitude is in the center of the image
--- 90 north ---
-180 to 0 to 180
--- 90 south --
[attachment=33957:Malmer.jpg]

---- added too -----
comparison between the two
i DO KNOW my mesh has a bit of a issue on the "body " it is to thick and needs to be a bit longer on one side
[attachment=33961:sidebyside.jpg] [attachment=33962:sidebyside1.jpg]

Posted by: 4th rock from the sun Oct 15 2014, 02:26 AM

Here's what I get from the ESA mesh, now using normal simple cylindrical projection.

Ambient occlusion (kind of like shaded relief + altimetry )



Normalmap (basically slope orientation)


Very interesting surface!

Posted by: JohnVV Oct 15 2014, 02:48 AM

4Th if you are using blender
i posted a short 7 point quick guide for converting a mesh to a simple cylindrical mesh on the ISIS3 support forum
https://isis.astrogeology.usgs.gov/IsisSupport/index.php/topic,3881.0.html

Posted by: 4th rock from the sun Oct 15 2014, 07:42 AM

Thanks for the tip. Here's what I get for a "DEM":




For reference, I'm using the model released here: http://blogs.esa.int/rosetta/2014/10/03/measuring-comet-67pc-g/

Posted by: Malmer Oct 19 2014, 06:29 PM

My shapemodel with my new global map applied.

http://youtu.be/d5PeN_8PRg8

Posted by: vikingmars Oct 19 2014, 07:38 PM

QUOTE (Malmer @ Oct 19 2014, 08:29 PM) *
My shapemodel with my new global map applied.

INCREDIBLE !!!! I could not believe my eyes ! Thanks so much Mattias smile.gif
Now, just imagine that we are going to LAND on such a celestial body...

Posted by: CAP-Team Oct 19 2014, 09:15 PM

I succeeded in transforming the shape file into CMOD for use in Celestia (anyone still using this?)
But I got the rotation axis wrong. Anyone care to share their .ssc?

Posted by: JohnVV Oct 20 2014, 01:11 AM

mine, but you will have to edit it
i am not yet using the esa rotation bc rotation nor the esa location bsp

you are likely looking for this option
"Orientation [ 90 1 0 0 ]"
and are in "Quaternions"
that 90 i add is do to the fact that blender rotates the X axis 90 degrees
a quick approximation for the esa mesh

CODE
"67p : 67P/Churyumov_Gerasimenko" "Sol"

{
  Class "comet"
  #Mesh    "67p.bin.cmod"
  Mesh "ESA_Rosetta67P.bin.cmod"
# Texture ""       # coded into the cmod
  Radius               2.455
  Albedo               0.2

  Orientation [ 90 1 0 0 ]

  OrbitFrame { EclipticJ2000 { Center "Sol" }}

  Beginning  "1900 01 01 00:00:00.000"
  Ending     "2101 01 01 00:00:00.000"

  SpiceOrbit
  {
    Kernel "Churyumov_Gerasimenko.bsp"
    Target "1000012"
    Origin "10"
    Period  9
    BoundingRadius 1e10
  }
UniformRotation
{
   Period 0.5
   Inclination 275
   #AscendingNode <degrees>
   #MeridianAngle <degrees>
   #Epoch <date>

}

}

Posted by: Adam Hurcewicz Oct 20 2014, 08:04 AM

QUOTE (CAP-Team @ Oct 19 2014, 11:15 PM) *
I succeeded in transforming the shape file into CMOD for use in Celestia (anyone still using this?)
But I got the rotation axis wrong. Anyone care to share their .ssc?



I love Celestia software smile.gif so please add here cmod model.

Here is my ssc file to comet and Rosseta in one file:

CODE
"67P:Churyumov-Gerasimenko" "Sol"
{
    Class "comet"
    Mesh "aaa4.cmod"
    Radius 2.1
    Albedo 0.2
    
    Timeline
[
    {
    Beginning "2010 06 03 00:00:00.000"
    Ending    "2016 01 01 00:00:00.000"
    
    OrbitFrame { EclipticJ2000 { Center "Sol" } }
    
    SpiceOrbit {
        Kernel [
        "CORL_DL_002_01____C__00045.BSP" # 2010 JUN 03 00:00:00.000 - 2016 JAN 01 00:00:00.000
        "CORB_DV_040_01_______00074.BSP" # 2014 JAN 01 00:00:00.000 - 2016 JAN 01 00:00:00.000
        ]
        Target          "1000012"
        Origin          "10"
        
        BoundingRadius  1e7
        }
        
SpiceRotation {
    Kernel [
        "PCK00010.TPC"
        "ROS_V23.TF"
        "ROS_CHURYUMOV_V01.TF"
        "ROS_CGS_RSOC_V03.TPC"
        "ROS_140919_STEP.TSC"      
        "NAIF0010.TLS"
        "CATT_DV_001_01_______00001.BC" # 2013 DEC 31 20:55:00.000 - 2016 JAN 01 03:04:10.000
        "CATT_DV_040_01_______00074>BC" # 2014 JAN 01 00:00:00.000 - 2016-JAN 01 00:09:59.999
    ]
    Frame "67P/C-G_CK"
    BaseFrame "eclipj2000"
}
    }
]
}



"Rosetta" "Sol"
{
    Class "spacecraft"
    Mesh "rosetta.3ds"
    Radius 0.016
    Albedo 0.5
    
    Timeline
[
    {
    
    Beginning "2004 03 02 09:26:21.583"
    Ending    "2014 10 22 08:56:09.740"

    OrbitFrame { EclipticJ2000 { Center "Sol" } }
    
    SpiceOrbit {
        Kernel [
        "ORHR_______________00122.BSP" # 2004 MAR 02 09:26:21.583 - 2014 AUG 04 01:16:37.085
        "RORB_DV_040_01_______00074.BSP" # 2014 JAN 01 00:00:00.000 - 2014 OCT 22 08:56:09.740
        ]
        Target          "-226"
        Origin          "10"
        BoundingRadius  1e7
      }
      
    SpiceRotation {
        Kernel [
        "PCK00010.TPC"
        "ROS_V23.TF"
        "ROS_CHURYUMOV_V01.TF"
        "ROS_CGS_RSOC_V03.TPC"
        "ROS_140919_STEP.TSC"      
        "NAIF0010.TLS"
        "ATNR_P040302093352_00127.BC" # 2004-MAR-02 09:33:52.767 2014-MAR-03 06:31:19.141
        "RATT_DV_040_01_01____00074.BC" # DEC 31,2013  23:59:59.0000 (TDB)    OCT 14,2014  10:01:07.1823
        "RATM_DM_008_01____C__00062.BC" # SEP 23,2014  10:01:07.1823 (TDB)    OCT 24,2014  10:01:07.1824
        "RATM_DM_009_01____A__00072.BC" # OCT 24,2014  10:01:07.1824 (TDB)    NOV 21,2014  23:26:07.1828
    ]
    Frame "ROS_SPACECRAFT"
    BaseFrame "eclipj2000"
}
    }
]
}

Posted by: Malmer Oct 20 2014, 08:19 AM

QUOTE (vikingmars @ Oct 19 2014, 09:38 PM) *
INCREDIBLE !!!! I could not believe my eyes ! Thanks so much Mattias smile.gif
Now, just imagine that we are going to LAND on such a celestial body...


It is just such an incredibly hostile landscape. I could not recover the finer details so my model is rather smooth compared to the real thing. I would really like to see the models that the OSIRIS team have at their disposal by now.

At least the J site seems to be a little less scary. I wonder how well resolved it is by OSIRIS now. Must be down to the individual pebble... Frustrating thing to be able to see all the dangers but being unable to do anything much else than holding thumbs and hoping for the best...


Posted by: mcgyver Oct 20 2014, 03:29 PM

QUOTE (Malmer @ Oct 19 2014, 06:29 PM) *
My shapemodel with my new global map applied.

http://youtu.be/d5PeN_8PRg8

Any idea about where to get a printed copy of this model at reasonable prices?!? I tried with 3dhubs, which promises very low prices... but even an hollow version would cost 60,00$ w.r.t. 5$ of raw material! :-(

If anybody is interested I also prepared an hollow file ready for printing 10cm wide or 15cm.


Posted by: mcgyver Oct 20 2014, 03:32 PM

QUOTE (Malmer @ Oct 19 2014, 06:29 PM) *
My shapemodel with my new global map applied.

http://youtu.be/d5PeN_8PRg8


Amazing.
Any chance the model is downloadable in DAE or 3DS format with textures?

Posted by: djellison Oct 20 2014, 03:33 PM

A model of that size is going to be about that much. And you don't need to 'hollow' the model - the middleware between an STL file and the printer will do that for you autonomously to suit the requirements of the printer whilst using no more material than necessary.

Posted by: Malmer Oct 20 2014, 11:03 PM

QUOTE (mcgyver @ Oct 20 2014, 05:32 PM) *
Amazing.
Any chance the model is downloadable in DAE or 3DS format with textures?



Soon. I want to fill in a few gaps and create a high definition NormalMap for the whole thing. Then it will look pretty cool in planetarium software and so on...

A 3d print would be nice aswell... a black one.


Posted by: Bjorn Jonsson Oct 21 2014, 12:08 AM

These 3D models/animations are simply incredible. My only 'complaint' is that this makes me rather unhappy with most of my own shape models/DEMs I've been experimenting with - many of them suddenly look awful ;-) (my global DEM of Enceladus is an exception though but I haven't completed it yet).

Posted by: Malmer Oct 23 2014, 07:17 PM

QUOTE (Bjorn Jonsson @ Oct 21 2014, 02:08 AM) *
These 3D models/animations are simply incredible. My only 'complaint' is that this makes me rather unhappy with most of my own shape models/DEMs I've been experimenting with - many of them suddenly look awful ;-) (my global DEM of Enceladus is an exception though but I haven't completed it yet).


Thank you for the very nice comment. I guess all those years making effects for commercials have payed off smile.gif

And you are selling yourself short Björn. Your stuff is hardly awful. You have done some of the more iconic images on this forum.

Posted by: CAP-Team Oct 24 2014, 08:25 PM

The model in CMOD format can be downloaded http://members.home.nl/astronomievandaag/celestia/67p4.zip.
I used Adam Hurcewicz's .ssc (with some slight modifications and updated kernels) but the rotation axis is still not right.

Posted by: JohnVV Oct 24 2014, 09:13 PM

not right ? as in what ?

see this post for the aprox locations of the north pole
http://www.unmannedspaceflight.com/index.php?s=&showtopic=7883&view=findpost&p=213312

the axis of rotating is through the north / south pole

Posted by: chuckclark Dec 1 2014, 08:07 PM

Phil -- are we ready for me to give a shot at making a constant-scale natural boundary (foldable) map of this thing?

I've located a source here in Atlanta who can turn a 3d file into a plastic model, from which I can work.

Someone will need a shape-model file with graticles incised. Tayfun? I don't suppose you are following along with?



Posted by: Phil Stooke Dec 5 2014, 02:43 PM

Hi Chuck - I think it's premature. Despite the wonderful images we have of the northern hemisphere, we have practically nothing in the south (it was literally nothing until we began to get a few dark limbs silhouetted against the background coma). This time next year we'll have global imaging and a full shape model.

Phil


Posted by: JohnVV Dec 5 2014, 04:59 PM

QUOTE
shape-model file with graticles incised.

i can add Longitude lines but LATITUDE will be a issue on this odd shaped hunk of ice

just look back on some posts where i wrapped a lat/long texture around it

Posted by: flug Dec 6 2014, 10:12 AM

QUOTE (CAP-Team @ Oct 24 2014, 02:25 PM) *
The model in CMOD format can be downloaded http://members.home.nl/astronomievandaag/celestia/67p4.zip.
I used Adam Hurcewicz's .ssc (with some slight modifications and updated kernels) but the rotation axis is still not right.

FYI I got working on this today and ended up putting together a Celestia package to model the launch and landing (well, at least the first landing!) of Philae using Celestia and SPICE data.

It's an 80 meg download but that's because it includes all the necessary SPICE files--some of those files are quite large.

http://brenthugh.com/celestia/Celestia_Rosetta_Philae_Landing_SPICE.zip

To use it, first install Celestia, then install the BrianJ/Chris Laurel Rosetta package http://www.celestiamotherlode.net/catalog/spacecraft.php. Then install this new package right over the BrianJ Rosetta package in the Celestia folder 'extras/rosetta_brianj". Then look in the directory for the file "readme-philaelanding.txt" for further instructions and tips.

I made a https://www.youtube.com/watch?v=WmkVt5chXWs.

Even though this uses all the ESA SPICE data (actual data for the comet & Rosetta, planned data for Philae--though by all indications the Philae flight plan was followed closely to the point of first bounce), as you note there are still plenty ways to put it together wrong--by having the model mounted backwards or rotated 90 degrees, or scaled too large or too small, or by picking up the wrong SPICE kernel, or whatever.

So this very well might have mistakes! In particular, like you I am worried about the direction of rotation of the comet. I was under the impression that the comet rotated in the opposite direction as shown in this Celestia model. I was under the impression that when Philae bounced up, it didn't have much horizontal velocity of its own but that the comet was very quickly rotating under it, and that rotation was responsible for most of Philae's horizontal travle over the surace. But that would imply rotation in the opposite direction of that shown here, wouldnt it?

So it's possible that the 3d mesh I'm using needs one more rotation about the long axis. But on the flip side: The axis and direction of rotation in Celestia seems to match well with https://www.youtube.com/watch?v=w0s0-x3NEPw and https://www.youtube.com/watch?v=CNGu7KbXzOs. So perhaps I was mistaken about the direction of rotation myself, and this is correct . . .

Regardless, it is interesting and fun to play around. Anyone is welcome to take the parts I've added or put together and improve or use them any way you'd like.

Posted by: scalbers Dec 6 2014, 02:12 PM

Great to see you on the forum flug as I had earlier mentioned one of your simulations. The rotation indeed should be counterclockwise when looking down from over the north pole.

Posted by: chuckclark Dec 6 2014, 03:40 PM

QUOTE (Phil Stooke @ Dec 5 2014, 09:43 AM) *
Hi Chuck - I think it's premature. Despite the wonderful images we have of the northern hemisphere, we have practically nothing in the south. This time next year we'll have global imaging and a full shape model.

Phil


Well, granted, but even if we have no global imaging, a constant-scale natural boundary map, made from the tentative shape model, would display graticles and topological districts in reasonably accurate proportions.

After the shape model is refined, I could adjust the map accordingly.

And as the images arrive, we'd have the mapping blank (so to speak) ready to go.

Note that the empty grid of a constant-scale natural boundary map, unlike an empty grid in a conventional projection, captures district proportions, so topological content (or at least prototopological, i.e. folding, content) is transformed to the plane.

The downside would be we'd need to make two models with incised graticles, and I'd have to do the handwork twice, but that's not such a big investment of time, is it?, in order to have an accurate mapping blank ready to accept images as they arrive. The investment of dollars to make the model twice is a consideration, too, but these days that's not much dough, either. Less than the cost of driving Atlanta to Houston.

Otherwise, in the interim, we have to endure viewing the available images in grossly distorting formats.




Posted by: Brian Lynch Dec 7 2014, 05:42 PM

QUOTE (flug @ Dec 6 2014, 05:12 AM) *
...I am worried about the direction of rotation of the comet. ... I was under the impression that when Philae bounced up, it didn't have much horizontal velocity of its own but that the comet was very quickly rotating under it, and that rotation was responsible for most of Philae's horizontal travle over the surace...


Looks awesome! The rotation looks about right, it should have an axis pointed at the right ascension and declination http://blogs.esa.int/rosetta/2014/10/03/measuring-comet-67pc-g/ (this also matches with the SPICE attitude data that may be integrable in Celestia).

Also, Check out the topic http://www.unmannedspaceflight.com/index.php?showtopic=7896&st=945 for some previous discussions about simulation and visualization.

Posted by: Malmer Dec 7 2014, 06:57 PM

I'm proud to announce the release my latest Shape Model!

Download on my blog:

http://mattias.malmer.nu/2014/12/new-shapemodel/




Posted by: Jam Butty Dec 7 2014, 09:08 PM

Malmer, your shape models are quite frankly astounding !!
and an incredibly useful navigational tool.

Thanks very much for sharing.

Posted by: vikingmars Dec 8 2014, 08:28 AM

WOW ! WOW ! WOW ! Thank you so much Mattias (and wish that Francois Hollande was here again at Cite des Sciences to see it smile.gif ) wheel.gif wheel.gif wheel.gif wheel.gif wheel.gif wheel.gif

Posted by: flug Dec 9 2014, 12:18 AM

QUOTE (Malmer @ Dec 7 2014, 12:57 PM) *
I'm proud to announce the release my latest Shape Model!

Download on my blog:

http://mattias.malmer.nu/2014/12/new-shapemodel/


I am literally fainting with amazement. That model is really, really beautiful. Gorgeous, and incredibly detailed.

Posted by: Brian Lynch Dec 9 2014, 08:07 AM

QUOTE (Malmer @ Dec 7 2014, 01:57 PM) *
...my latest Shape Model!


Many thanks, this is great! I've now been able to align the sight lines from Rosetta to Philae with those from Philae to approximated locations on your model (after registering http://www.esa.int/spaceinimages/Images/2014/10/Philae_s_primary_landing_site_from_30_km_b using MeshLab).

The resulting solution (basically bundle adjustment) rotated your model about 10 deg in roll and pitch and about 165 deg in yaw (lining it up closer to the ESA .obj file), and nicely only applied a 3.8% increase in scale. The centroid also shifted about 0.5 km, mostly in the z-axis.

Attached are some plots of the results. The first figure shows Philae's trajectory in blue, with sight lines coming from Rosetta in pink for each time the lander was spotted in http://blogs.esa.int/rosetta/2014/11/17/osiris-spots-philae-drifting-across-the-comet/ (blue circles marking the locations in Philae's trajectory, red X's marking the approximated locations in the registered image). The green lines are sight lines to the post-touchdown positions (one from the OSIRIS image series, the other from http://blogs.esa.int/rosetta/2014/11/14/philaes-first-touchdown-seen-by-rosetta/) and the yellow line is the sun vector emanating from the location of the shadow in the NAVCAM image.

The second figure is an overall view with Rosetta and Philae trajectories (red and blue, respectively) included. You can also see Rosetta's position and orientation at the time the registered image was taken (Sep. 14, 17:48) and the camera location used for image registration (a separate process but could be linked to aid in the solution).

The third plot shows a "top-down" view to make comparison with the OSIRIS touchdown images easier.

 

Posted by: mcgyver Dec 9 2014, 11:51 AM

QUOTE (Malmer @ Dec 7 2014, 07:57 PM) *
I'm proud to announce the release my latest Shape Model!

Download on my blog:

http://mattias.malmer.nu/2014/12/new-shapemodel/


I can't access your blog as my company firewall sees it as a "games" site and blocks it. Have you got any weird meta-keyowrds in your page?

Posted by: mcgyver Dec 9 2014, 03:29 PM

QUOTE (Malmer @ Dec 7 2014, 07:57 PM) *
I'm proud to announce the release my latest Shape Model!

Download on my blog:

http://mattias.malmer.nu/2014/12/new-shapemodel/


I had to download the object to my smartphone and then upload it to my PC but I eventually got it! rolleyes.gif

Is there any "known processing artifact" in your model? The neck of the comet looks relly weird.

edit:
I mean, in the visible side.

Posted by: fredk Dec 9 2014, 04:01 PM

QUOTE (Brian Lynch @ Dec 9 2014, 08:07 AM) *
Attached are some plots of the results.

Can you predict the positions of the lander shadow on the ground, for the three pre- and one post-first-bounce OSIRIS images? I'm curious if they're outside the released frames, since there's no sign of shadows in those images. Of course the released OSIRIS is a composite and it may not be clear exactly how far each individual frame extends. But based on the lander's height, I might have guessed the shadow would be visible in the post-bounce part of the image (or maybe just off it to the right).

Posted by: Brian Lynch Dec 9 2014, 07:35 PM

QUOTE (fredk @ Dec 9 2014, 11:01 AM) *
...the positions of the lander shadow on the ground, for the three pre- and one post-first-bounce OSIRIS images? ...I might have guessed the shadow would be visible in the post-bounce part of the image...

Sun vectors from Philae at each pre-touchdown position are added but they don't seem to hit the surface. The post-bounce shadow at 15:43 is a bit difficult since I don't have a position for Philae at that time worked out yet. Based on a preliminary analysis of the intersection between the sight line for Philae and the sun vector at the first post-bounce (15:35:32), the trajectory is approximately at 6.3 deg above the horizon. I'll take a look at what altitude Philae would have along the sight-line in order to maintain the same angle (ie. assume it is following a straight trajectory) and get back to you with an answer.


 

Posted by: fredk Dec 9 2014, 08:13 PM

Thanks, Brian.

I guess you could place an upper bound on the height of the lander above the surface (to the extent that's well defined) that would result in a shadow visible on the OSIRIS frame.

But in the released image the shadow would fall close to the right edge of the image and might be over the edge depending on the precise direction of sunlight and lander height.

Posted by: Brian Lynch Dec 9 2014, 10:00 PM

Here is a look at the estimated shadow location from the second post-touchdown position at 15:43. You can see the small yellow line extending into the surface (ie. where we should see the shadow based on the approximated location of Philae). It does appear to be within the bounds of the OSIRIS image and just below the inset for that post-touchdown point. My intuition says that the shadow would not be sharp enough from that distance to become a significant feature in the image, but maybe the vacuum of space and direct sunlight means that shadows are always sharp in these cases... (imaging experts?).

Does anyone know if they have released each of the original OSIRIS images for the touchdown mosaic? We could try looking for the shadow by comparing it to a "before" image, but there could be endless debate over whether said shadow is actually a rock, image artifact, etc. The NAVCAM image seems to show the shadow at 15:35:32 quite nicely but the surrounding terrain is relatively featureless compared to the ground where we expect to see the second shadow.

 

Posted by: fredk Dec 10 2014, 12:00 AM

QUOTE (Brian Lynch @ Dec 9 2014, 11:00 PM) *
My intuition says that the shadow would not be sharp enough from that distance to become a significant feature in the image, but maybe the vacuum of space and direct sunlight means that shadows are always sharp in these cases... (imaging experts?).

The comet was at about 3 AU from the sun during the landing, so the sun subtended about 1/6 degree. That's pretty small. But it all depends on how far the shadow was from the lander, what I'll call the distance d. The total shadow width will be the width of the lander plus the spread due to the non-zero angular size of the sun. This spread is approximately 0.003d. What is your estimate of d? For d = 100 m, this gives a shadow spread of only 30 cm, and the shadow would likely still be visible.

But I agree that on a rough surface like this the only way to be sure that some dark smudge is the lander's shadow is to compare before and after OSIRIS frames.

Posted by: Brian Lynch Dec 10 2014, 12:32 AM

QUOTE (fredk @ Dec 9 2014, 07:00 PM) *
What is your estimate of d?

d = 139 m (ie. 0.003d = 41.7 cm)

I'm guessing the 41.7 cm width is the total added width from the penumbra? So if we assume a lander size of 1 m, then the shadow should be 1.417 m or about 5x5 pixels.

Posted by: Malmer Dec 10 2014, 01:25 AM

Thank you all for all the kind comments! I hope you have fun with it. It will be obsolete as soon as we get better data so it is not cleaned to perfection or anything.

If you find artifacts and errors please mark on an image so i can fix or explain if not.

Posted by: fredk Dec 10 2014, 01:45 AM

The total width of umbra + penumbra will be ~1.4 m. The penumbra annulus will have a width of 40 cm, leaving 60 cm for the width of the umbra. This is all dependent on the real distance and exact size of the lander, but it looks very likely that the shadow should be visible, at least by blink comparison.

Posted by: djellison Dec 10 2014, 05:24 AM

QUOTE (Brian Lynch @ Dec 9 2014, 02:00 PM) *
Does anyone know if they have released each of the original OSIRIS images for the touchdown mosaic?


They have not. Honestly - I'm not expecting anything from OSIRIS apart from perhaps one Philae-on-the-ground image between now and the first PSA release in >6 months time.

Posted by: Malmer Dec 11 2014, 11:41 AM



Is there a date for the first release of OSIRIS data?
And the Navcam dataset, will that be released at the same time?

Posted by: djellison Dec 11 2014, 03:30 PM

Even if there were one scheduled on the PSA - I'm afraid I wouldn't trust it. It'll show up when it shows up. If I saw anything on the PSA before the middle of next year - I would be pleasantly surprised.

Posted by: JTN Jan 24 2015, 09:55 PM

The recent ESA release included some sketch maps (http://www.esa.int/spaceinimages/Images/2015/01/Comet_regional_maps, http://www.esa.int/spaceinimages/Images/2015/01/Getting_to_know_Rosetta_s_comet_region_maps) naming regions on 67P.

To help find my way around the comet, I (very roughly) annotated Mattias' 7 Dec shape model with this information by hand. Doubtless a better job could be done with more care (I've never done anything like this before), but the released maps seem pretty approximate and don't always agree with each other.

The annotated .obj can be downloaded http://www.chiark.greenend.org.uk/~jacobn/2015/01/67p_model/.
[Edit: apparently the colour information -- which is the whole point -- is a non-standard extension to the .obj format, so I don't know what tools other than http://www.meshlab.org/ will display it.]


Posted by: Malmer Feb 3 2015, 02:46 PM

SHAPEMODEL UPDATE:

Has better coverage on the "blackside".

http://mattias.malmer.nu/2015/02/shapemodel-update-2/

Can't wait to see what you do with it!

Posted by: Malmer Feb 11 2015, 10:56 PM

Comet 67P. Fully computer generated image using my latest 3d model and 8K by 4K pixel normal and albedomaps.






Posted by: nprev Feb 12 2015, 06:17 AM

ohmy.gif ...stunning!!!

Posted by: flug Feb 12 2015, 06:56 AM

W!O!W!

<Jaw drops to floor . . . >

Posted by: vikingmars Feb 12 2015, 08:51 AM

QUOTE (Malmer @ Feb 11 2015, 11:56 PM) *
Comet 67P. Fully computer generated image using my latest 3d model and 8K by 4K pixel normal and albedomaps.

INCREDIBLE !!!!!
Thanks a lot Mattias : you are the best
wheel.gif wheel.gif wheel.gif wheel.gif wheel.gif wheel.gif

Posted by: Bjorn Jonsson Feb 12 2015, 11:33 PM

WOW!!! Your renders from the 3D model are so realistic that it's almost possible to confuse them with real photos. Great job.

Posted by: Malmer Feb 13 2015, 12:20 AM

A little more work on the normalmap should help. I have got the pipeline working but there is more work to be done...


Posted by: mcgyver Feb 18 2015, 10:59 AM

I collected these data from various sources:

CODE
Data,Earth,67p
Semimajor axis (10^6 km),           149.6,    518,    a
Sidereal orbit period (days),      365.3,    6.4400, years    period
Perihelion  (10^6 km),      147.1,    186,    q
Aphelion (10^6 km),      152.1,    850,    Q
Orbit inclination (deg),           0,    7.0402009,    i
Orbit eccentricity,                0.0167,    0.64097393,    e
Sidereal rotation period (hrs),    23.9,    12.4043,
Date of perihelion transit,    -,    2015-Aug-13 01:43:31,    Tp
Argument of perihelion,    -,    12.78560607,    peri
Longitude of the ascending node,    -11.26064,    50.14210951,    node
Mean anomaly,    355.53,    319.3033468,    M
Mean motion,    -,    0.15295360°/day,    n
North pole RA,    -,    69.3,
North Pole Dec,    90,    64.1,
Obliquity to orbit (deg),          23.4,    52,



This should make easier to calculate comet season, for better predicting when Philae will get more sun.

Posted by: Astro0 Feb 19 2015, 10:31 PM

Last night I attended a fantastic talk on Rosetta operations and science results in Canberra.

The presenters were Dr Paolo Ferri, ESA's Head of Mission Operations and Professor Mark McCaughrean, Senior Science Advisor in the Directorate of Science & Robotic Exploration at ESA.


My work colleague Dr Korinne McDonnell, ESA's Prof Mark McCaughrean and Dr Paolo Ferri and me.


During the talk they showed a bunch of great images and used Mattias' wonderful shapemodel animation of 67P during the presentation, noting the great work being done in the amateur community. Well done!

Another highlight was a sneak preview of the next instalment in the 'Adventures of Rosetta and Philae' animated films. We weren't allowed to record it but they said it would be released in a few days. smile.gif


Posted by: Malmer Mar 8 2015, 11:21 AM

Made some 360 animations of my 67p shapemodel.

http://youtu.be/yBltmJ2qzdM

http://youtu.be/zdLp3g27Ha8

and without the dust

http://youtu.be/RXun2zjriB0

http://youtu.be/0mUSipvi-d4

Textures and stuff will be released as soon as they are a little more polished.

Posted by: Gerald Mar 8 2015, 01:42 PM

Proper inference of the 3d volume structure of the jets is really non-trivial. The best approach I'm knowing of is called computer tomography, in a broader sense, with lot of number crunching, see e.g. https://wwwmath.uni-muenster.de/num/Preprints/1998/natterer_1/paper.pdf.
Great achievement!

Posted by: Mercure Mar 11 2015, 07:47 AM

Truly astounding model, Malmer. I have a first generation Oculus Rift and I can only imagine how cool it will be to manipulate and navigate around your model with the soon-to-be-released hi-res consumer version. We're on the brink of a new era in scientific visualisation, and I think a model such as yours will be a prime example of what can be done.

Posted by: Malmer Apr 20 2015, 01:20 PM

I built a little webpage that displays Rosettas view of 67P. Updated every 10 minutes...

http://mattias.malmer.nu/rosetta-now/

Posted by: elakdawalla Apr 20 2015, 04:44 PM

That is so cool, thank you! Would it be possible to make a version that allows a user to simulate the view in the past at a specific time?

Posted by: Malmer Apr 20 2015, 05:46 PM

Thanks!

Well... As it is now I'm rendering the images offline a couple of days in advance. So there is currently no way of it to display images outside the range of already rendered views. (First image being 2015 apr 18 00:00)

But I will continue rendering and I was thinking about adding some kind of time request or animation feature.

It has been a lot to learn in one go. First time writing c code. First time using spice, first time using php and first time in prolly 16 years writing html. So much fun.

First up is adding some dust (it is a comet afterall)

Posted by: Malmer Apr 24 2015, 08:41 AM

Added a two hour animation loop centered on the current time. Makes it easier to get a feel for the motion.

Posted by: DoF Apr 26 2015, 02:01 PM

Great work Malmer, the loop is a good addition. A further improvement that could be done is to add the timestamps for the loop images in a list somewhere, which would show that timestamps render when you mouse over it. That way you could also go through the loop sequence at your own pace if you wanted to by simply slowly (or quickly) moving the mouse over the list of timestamps.

Posted by: Phil Stooke May 8 2015, 01:27 PM

Aha! I've discovered an amazing map projection which will work brilliantly with our (current) favourite comet nucleus. And it's not brand new, it's hundreds of years old. Admittedly it needs a bit of tweaking. Unfortunately I can't tell you any more right now - but fear not, a solution to the mapping problem is at hand. I won't be doing anything with this until we have seen the southern hemisphere properly.

Phil

Posted by: Malmer May 12 2015, 09:50 AM

So you have found a marvelous projection but the margin is too narrow to contain it? wink.gif

Posted by: Malmer May 13 2015, 11:37 PM

My new shapemodel:

http://mattias.malmer.nu/2015/05/new-shapemodel-based-on-the-esa-navcam-bonanza/

It has a new global map aswell.


Posted by: charborob Aug 13 2015, 11:58 AM

A new interactive viewer for comet 67P/C-G has been produced by ESA. It also gives easy access to Navcam images. Worth a try.
http://blogs.esa.int/rosetta/2015/08/13/new-interactive-viewer-for-comet-67pc-g/
http://sci.esa.int/comet-viewer/?model=esa

Posted by: elakdawalla Aug 13 2015, 04:06 PM

OMG


Posted by: stevesliva Aug 13 2015, 06:13 PM

http://sci.esa.int/comet-viewer/?model=esa
http://sci.esa.int/comet-viewer/?model=malmer

Neat!

Posted by: Explorer1 Aug 13 2015, 06:57 PM

I second that; wow! Especially the observations viewing.

Imhotep is misspelled though...

Posted by: Habukaz Aug 13 2015, 07:24 PM

Cool that malmer's work was used. I haven't had time to properly check out the feature yet.

Posted by: Bill Harris Aug 14 2015, 12:05 AM

So the Philae touch-down point which was initially named Abydos is now named Wosret?

--Bill

Posted by: Malmer Sep 26 2015, 03:19 PM

While playing around with map projections for my 67P shapemodel I started playing with different tools for making areapreserving "maplets". When seeing the various pieces they sortof resembled a sewing pattern. So I went ahead and looked for a set of good seam lines that would make as few pieces as possible.

Here is the result:



 

Posted by: PDP8E Oct 14 2015, 12:24 AM

I didn't really know where to put this... but it is very cool... it is Comet 67PC-G compared to Los Angeles!

I ran across it on one of my peregrinations about the internet
It is by an obviously talented image-artist named Matt Wang.




I find that images like this bring the sizes of objects into a sharp focus - a deeper understanding of what we are seeing

found it here:
http://mentalfloss.com/article/60082/rosettas-comet-compared-los-angeles

Thank you Matt Wang


Posted by: chuckclark Oct 14 2015, 10:50 AM






Now THAT's nice!


Posted by: SteveM Aug 27 2016, 12:54 PM

A question for the shape modelers: Are their detailed enough observations to detect possible changes in the comet's shape / topography between the period of approach to the Sun and the period of departure? The comet is big and the changes would be small, but are they detectable?

Since things were changing rapidly around perihelion (and Rosetta had to back off for navigation / safety reasons) it seems reasonable to ignore data near perihelion.

Steve M

Posted by: Gerald Aug 27 2016, 01:07 PM

By shading and shadows, http://blogs.esa.int/rosetta/2015/09/18/comet-surface-changes-before-rosettas-eyes/.
But I'm unaware of a synopsis of all significant changes between pre and post perihelion.

Posted by: SteveM Aug 30 2016, 02:12 PM

Thanks for the link; changes with "the rims of the features expanding by a few tens of centimetres per hour" should add up to something detectable after a year (even though the changes mentioned were only in daylight).

Maybe one of our experts (Malmer?) could develop a before and after model. Some of the http://www.esa.int/Our_Activities/Observing_the_Earth/Copernicus/Sentinel-1/Sentinel-1_provides_new_insight_into_Italy_s_earthquake show what might be done to make such small changes visible over a large area.

Steve M

Posted by: JohnVV Aug 30 2016, 08:53 PM

QUOTE
A question for the shape modelers: Are their detailed enough observations to detect possible changes in the comet's shape / topography between the period of approach to the Sun and the period of departure? The comet is big and the changes would be small, but are they detectable?

should be doable BUT i would guess that the changes might be close to the " error bars " and might have to be puled out of the "noise"

i have not tried using stereo pipeline on the released pds data , nor used bundler on the released data for "shape from motion"

so it is only a guess

Posted by: SteveM Sep 3 2016, 01:47 PM

This https://www.youtube.com/watch?v=UobzGZH2VnE from ESA indicates (starting about one minute into the report) that isolated changes on Comet 67P C-G have been measured on the order of several meters and that ESA plans to develop a revised shape model to detect further changes in the comet. It seems they think the project will reveal more widespread changes.

Steve M

Posted by: chuckclark Mar 12 2018, 08:24 PM

e-poster now up for mapping 67P in my peculiar method:

http://www.hou.usra.edu/meetings/lpsc2018/eposter/2879.pdf

Posted by: chuckclark Mar 18 2020, 02:24 AM

2020 e-poster now up, constant-scale natural boundary maps with photomosaics:

https://www.hou.usra.edu/meetings/lpsc2020/eposter/2126.pdf

Posted by: Bill Harris Jun 24 2023, 06:12 PM

I have friends with 3D printers and I'm wanting to have a model of Comet 67P printed. However, 3D printing is one technology I've not explored yet and I'm needing help setting me the right direction. Or is "3D shapemodel" even the correct term for 3D printing?
I recall that Malmer's model was the best 8 years ago, and I see that ESA has one on their website.
Suggestions on what I should have my friend use, or where to start looking for a 3D print file...

--Bill

Posted by: mcaplinger Jun 24 2023, 09:48 PM

QUOTE (Bill Harris @ Jun 24 2023, 11:12 AM) *
Suggestions on what I should have my friend use, or where to start looking for a 3D print file...

You need an STL file. A google search of "comet 67p stl file" turned up several options. There may be one on the ESA website somewhere but I got lost in a maze of links leading from https://open.esa.int/rosetta-3d-model/

Posted by: Phil Stooke Jun 24 2023, 10:01 PM

https://pdssbn.astro.umd.edu/holdings/ro-c-multi-5-67p-shape-v2.0/extras/

This PDS page has an STL file.

Phil

Posted by: Bill Harris Jun 25 2023, 08:22 AM

Mike, Phil--
Thanks, that's a great start on this 3D Maze!

--Bill

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