Textures Project suggestion: Comet 67P texture

[martins]

This post: http://orbiter-forum.com/showthread.php?p=496952&postcount=6437 gave me an idea:

There are shape models for 67P/Churyumov–Gerasimenko, but apparently no global texture maps to go with them (please correct me if I'm wrong). Would it be an interesting project for the orbiter community to try and generate such a texture map, to create a cool 67P addon for Orbiter?

There are plenty of high-quality images from the Rosetta orbiter from all directions, so the raw data should be available. It's just a matter of processing those data.

I guess the work flow would look something like this:

• Take a shape model and extract vertex coordinates
• Parameterize the vertex coordinates in a way that allows mapping to texture coordinates
• Take a Rosetta image, and figure out the camera position in terms of the shape model
• project the image onto the mesh surface
• map the image into parameter space
• repeat for the next image, and so on
• merge the projected images in parameter space (seam removal, lighting adjustment, etc.)
• assign texture coordinates to the vertices according to the parameterization, and wrap the finished global map around it.
• Marvel at cool orbiter object

One of the tricky bits is to find a suitable parameterization. Because of the complicated shape, a direct mapping into longitude/latitude pairs may not be possible, as discussed in the other thread. Another way could be this: approximate the shape model with a spherical harmonics expansion (probably wouldn't require a large number of terms). Then define a mapping from the spherical harmonics surface to a sphere. Use the sphere coordinates of a mapped vertex as the parameterisation.

Of course there is plenty of other challenging stuff as well (registration of individual images after mapping, lighting correction/shadow removal, etc.) but if it works, we'd have something that doesn't exist anywhere else. Maybe you could even sell it back to ESA :thumbup:

Any interest? Suggestions?

 

[Urwumpe]

One problem will sure be, that during the next months, the comet will change its appearance a lot, during the perihelion passage. 3 meters of radius less might not be that much in terms of size, but the texture will likely change a lot.

 

[martins]

True, so this may require a cutoff date for the source images. Or, even more ambitious, one could try to create a dynamic texture model, where multiple textures are created from images sorted into temporal slots, and the textures applied to the model are blended according to simulation date.

 

[Urwumpe]

True, so this may require a cutoff date for the source images. Or, even more ambitious, one could try to create a dynamic texture model, where multiple textures are created from images sorted into temporal slots, and the textures applied to the model are blended according to simulation date.

I think that only the first is really achievable. Such global coverage at fairly low resolution exists at least for the landing site survey, which could be good enough for government work.

For the latter, we would need to not just change the texture "tiles" of the regions that Rosetta observed at that MJD, but in reality merge older tiles with the new data, so that there are no sudden transitions in the model.

That is something that gives me quite a few head-aches (How to handle photography strips created at different inclinations? Reducing data size?), so I would leave that to somebody smarter.

 

[kuddel]

After a quick net-survey some 3D-model sources came up:
http://sci.esa.int/rosetta/54728-shape-model-of-comet-67p/ (.obj & .wrl)
http://www.livecometdata.com/Comet67P_3D/ (data looks like from above)
https://www.youmagine.com/designs/shape-model-of-comet-67p-c-g#!design-documents (.stl)
These might give us a start...

--- edit ---
uh, somebody already did a (better) job :blush:

[ame="http://orbithangar.com/searchid.php?ID=6671"]Rosetta - Comet 67/P Landing Mission, ver. 3D[/ame]