Rev 126 - Feb 4-22, 2010 - Mimas (main target), Tethys, Iapetus, Calypso and mutual events too Options

[scalbers]

CAP-Team - my first step in updating the map is using a more full disk low-phase image as can be seen here:



VP - I'm using these three triaxial dimensions: 414.8 394.4 381.4. Good question about the fit as Mimas is a great test of our handling of triaxial ellipsoids. Here is a look at the degree of fit (and size relative to the limb) with the image I'm using:



How nice to have Saturn backlighting & highlighting the dark limb, right where this is needed

Steve

[volcanopele]

Well, the issue that I have is that my Herschel comes out looking oblong in the north-south direction, which I think it should..., but it pushes some of the craters north and south of Herschel closer to the poles than what is shown in the map on your website.

[Phil Stooke]

Sounds like the dreaded Peters Projection! Seriously, is it a map projection mismatch?

Phil

[scalbers]

Perhaps VP is working with a planetographic map as I think that corresponds with an oblong appearance for Herschel. The official maps on the CICLOPS site also appear to be planetographic. Conversely I am working with planetocentric coordinates (still on the triaxial ellipsoid), where Hershel should probably look more round.

It appears possible to convert between planetocentric and planetographic. One way (at least for the latitude part) might be the reverse of what is discussed below:

https://isis.astrogeology.usgs.gov/IsisSupp...hp?topic=1550.0

Here BTW is a map using three images from the new flyby.



Steve

P.S. I recall running into the Peters projection on another project, thankfully not this one!

[Bjorn Jonsson]

Looks great even though the contrast stretch is a bit extreme for my taste (completely black shadows in craters etc.). Is the automatic contrast stretch applied to the source images one of the reasons for this?

[scalbers]

Bjorn - yes it's true this looks quite a bit more contrasty and darker compared with say my Enceladus map. For Mimas many of the first images on the map were at higher phase angles. That coupled with such a battered surface tended to give a preponderance of shadowed craters. This kind of became the norm for contrast when newer images are added. New images at low phase thus have to be contrast stretched quite a bit to look consistent. Nonetheless it appears to be a good suggestion and I will try to soften the shadows (and avoid losing details) with some of the imagery.

Here's a slightly less contrasty 4K version:



Steve

[Adam Hurcewicz]

Steve, what software you use to making maps? I searched Google and nothing..

[scalbers]

Adam - I'm using IDL. Using this software I wrote various procedures that help me navigate images, handle the map projections, and do the mapping.

Steve

[Adam Hurcewicz]

Iapetus color image (19 Feb. 2010)

N00151720.jpg ®
N00151716.jpg (G)
N00151719.jpg (

Attached thumbnail(s)

 

[elakdawalla]

Nice! Here's my version Used all the images, stacked to attempt to reduce JPEG artifacts, enlarged 200%.

Attached thumbnail(s)

 

[Adam Hurcewicz]

Here is Iapetus animation from 4 images:

http://saturn.jpl.nasa.gov/photos/raw/rawi...?imageID=213904
http://saturn.jpl.nasa.gov/multimedia/imag...7/N00151741.jpg

http://saturn.jpl.nasa.gov/photos/raw/rawi...?imageID=213887
http://saturn.jpl.nasa.gov/multimedia/imag...7/N00151724.jpg

http://saturn.jpl.nasa.gov/photos/raw/rawi...?imageID=213862
http://saturn.jpl.nasa.gov/multimedia/imag...7/N00151699.jpg

http://saturn.jpl.nasa.gov/photos/raw/rawi...?imageID=213833
http://saturn.jpl.nasa.gov/multimedia/imag...7/N00151670.jpg

[Bjorn Jonsson]

Using Steve's updated map of Mimas I made a quick and dirty shape from shading (SFS) DEM and combined it with my earlier DEM of Mimas created using stereo imagery (see this thread for more information on these 'combined DEMs'). The stereo DEM itself hasn't been updated with the new data (I don't expect to update it until this data hits the PDS) so the resulting stereo+SFS DEM is not accurate - this is a test render:



This image has a field of view of 45° and the altitude above the surface is ~125 km. There is some longitudinal striping that I managed to partially hide by carefully selecting the light source location. I'm using a uniform white map for a texture map so all of the details come from the DEM.

[elakdawalla]

Bjorn, it's very hard to mosaic the Mimas images because Cassini was moving so fast that the perspective shifted markedly from frame to frame. But "official" mosaics are also lacking because when they reproject the images they do so onto an ellipsoid, which destroys limb topography in the resulting mosaic. Will your DEM of Mimas eventually enable you to reproject Cassini images onto an appropriately lumpy body, producing Mimas "mosaics" (maybe should call them "rendered mosaics") that have proper limb topography?

[Bjorn Jonsson]

Yes, the DEM enables this and the accuracy of the resulting images/"mosaics" depends solely on the accuracy of the DEM. An annoying problem/artifact is the east-west striping and in this case the stereo DEM also is very crude as previously noted. Here is a test render where Steve's map has been draped over the DEM without applying any shading:



The viewing geometry is the same as previously. This reveals that some of the DEM's topography may be due to albedo variations in the source map and not due to topographic shading. 'Blinking' these two images is rather interesting.

[Exploitcorporati...]

Always so much to catch up on...fantastic DEM perspectives, Bjorn. That's a scene I've had in my imagination for ages, finally made real. Your map is beautiful as always, Steve. I'd like to suggest possibly using images from the 28 June 2007 pass for detail west of Herschel and the transition to the coverage from August 2005. The fine fractures and/or crater chains show up much better, and it seems to beat the resolution of the partial Voyager coverage. I'm reposting Gordan's excellent color version for reference. You're all awesome. Belated welcome to Adam too!

ugordan's Mimas 28/06/07: