3D shape, cartography, and geoid of Comet 67P C-G Options

[fredk]

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.

[Brian Lynch]

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.

[Malmer]

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.

[fredk]

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.

[djellison]

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.

[Malmer]

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

[djellison]

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.

[JTN]

The recent ESA release included some sketch maps (one, two) 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 here.
[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 MeshLab will display it.]

[Malmer]

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!

[Malmer]

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

[nprev]

...stunning!!!

[flug]

W!O!W!

<Jaw drops to floor . . . >

[vikingmars]

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

[Bjorn Jonsson]

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

[Malmer]

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