Vesta Albedo Texture

Tips for creating and manipulating planet textures for Celestia.
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FarGetaNik M
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Vesta Albedo Texture

Post #1by FarGetaNik » 26.10.2016, 21:09

I created a high-resolution albedo texture for Vesta. Here a 8k jpg preview (orginal file is 26702x13351 pixels):

vesta-abedo.jpg


The data is from here: http://sbn.psi.edu/archive/dawn/fc/DWNVFC2_2/EXTRAS/HAMO_COLOR/
Unfortunately for an amateur image processing enthusiast the textures are 32bit HDR 1 GB tiff monsters, which I can't handle. So I had to convert them to ordinary 8bit png images for further use. Because of the low contrast, I might have lost some details there, but I have a different problem... anyways an red green violet filter composite (violet mixed with 20% green to simulate "blue") resulted in basically grey map. So this is a near-IR green violet composite, with saturation exagerated by a factor of 2. See how "colorful" it is... :eh: after a bit of google search I found Vesta's bond albedo to be 0.20, wich is consistend assuming the trextures to be gamma-corrected.

I'm very confused by the coordinate system of Vesta. There is one IAU system centered around Olbers Regio, and a Dawn one defined by the Claudia crater. Reading along the documentation of the textures, it says westermost longitude is -210° so I assumed I had to shift the texture by 30° to the left to have 0° centered for use in Celestia. But I don't even know which coordinate system is used there, presumably the Dawn system. The texture doesn't fit the 3D models I use. Which brings up another question: Is the coordinate system based on Vesta's shape? It's approximately an oblate spheroid, but is usually modelled as a triaxial ellipsoid. So if it has a longest axis, does it coincide with the prime meridian or is was chosen randomly?

I guess my offset was simply wrong and I might need an offset of 180° instead if I interprete Vesta maps correctly.

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John Van Vliet
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Post #2by John Van Vliet » 27.10.2016, 07:24

nice

this screenshot is a early map -- same data
http://dawndata.igpp.ucla.edu/tw.jsp?section=geometry/DTMs/DLR_HAMO_DTM

0 long is on the left 180 in the center and 360 on the right
Image

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FarGetaNik M
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Post #3by FarGetaNik » 28.10.2016, 08:37

John Van Vliet wrote:0 long is on the left 180 in the center and 360 on the right

I assume this is in the Dawn/Claudia coordinate system. Ok so for Celestia this needs to be shifted by 180°. May I ask which color filters you used?

I've got another idea how to process these textures properly. I'll come back with my results :wink:

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FarGetaNik M
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Post #4by FarGetaNik » 28.10.2016, 21:22

I'm done, here's my final Vesta albedo texture:

vesta.jpg


This version should contain less artifacts, also it's correctly aligned, at least it fits my mesh of Vesta (as good as it can get, because the texture is in a slightly different projection than the mesh, some areas are shifted to the east, some to the west). Unfortunately, it looks much more dull than anticipated, but I guess this is as realistic as it can get:

Vesta-Albedo.jpg


Let me know if someone wants the 26k version, it's a 141MB png. Because I removed some noise, the effective resolution is somewhat smaller, maybe 16k is appropriate. Also I wonder if Celestia supports Virtual Textures on a mesh... I might try this eventually.


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