I have much better results, but I can't show them yet, because I have no public web space to park the snapshots I made. I have 7 little jpeg 'thumnails' (320?230) to illustrate my results and this point...
Coming from the 'What Celestia should be' debate (
http://www.shatters.net/forum/viewtopic.php?t=163), I'm restricted in input on matters of accuracy ('realism') until I sort out image submission. I left this issue of shadowing out of 'realism' though because it is an easy one to fix given Celestia's great flexibility in data files.
The problem arises because the texture map is an air-brushed 'topographic' map for lunar cartographers. It is designed to show all features illuminated at a constant angle by light from the east - a standard convention - so shadows are fixed. Currently, most other moons in Celestia suffer this problem, esp. Phobos and Saturnian moons.
My solution is to use an albedo map in place of a topographic map, but keeping the bump map. An albedo map is a map that shows suface colour and brightness without shadowing. They are built up as photomosaics from images where the Sun is high up in the sky over a planet or moon. Texture maps for Earth, Mars, all Gas Giants and the Galilean moons delivered with Celestia are already albedo maps. Only planets and moons that have been imaged with enough coverage to gain the data can have complete albedo maps.
I found an almost perfect albedo map for the moon at the USGS Clementine web site:
http://wwwflag.wr.usgs.gov/USGSFlag/Space/clementine/images/albedo.simp750.jpeg
The size is 1080?720, so watch out if you can't deal with non-power-of-two sizes…
The north and south poles still have fixed shadows, but that's because the Moon's axial tilt is only about 1° w.r.t. the ecliptic, and we'll never see the Moon's poles illuminated from on high. The problem cannot be cured, unless nuclear explosions are used in large-scale flash photography.
You can see the fixed shadows give an odd effect over the poles if you speed up time and watch the Moon rotate around it's poles. The shadows always face in to the poles, rather than just away from the Sun… Fortunately, the area concerned is small and often out of the way, so we can live with it.
I also have an excellent result using this technique with Rhea, moon of Saturn, but only from a certain angle. It has bearings on the Voyager tour proposals... More later with images, I hope…
I think albedo maps tend to be presented with a high colour saturation, which I think is not realistic. I have seen the planets through telescopes and they actually have much paler looks to them, but it's a problem easily cured with Paint Shop Pro, e.g. I put a gamma correction of 2.24 on my Moon albedo map for extra brightness.
I think the Bump Map operates on the Texture Map, so if you removed it, the Bump Map has nothing to modify. Likely not a graphics card problem, then. However, I did notice that all a Bump Map does is adjust the colour/brightness of the Texture Map on the object. It does not change the shape of the object from a smooth sphere (as I found when trying to see if the crater Herschel on Mimas became indented). Bump Maps don't cause craters to become pits in a moon's limb. Nor do they make mountains cast long shadows…
Please do not expect full albedo maps for Uranian satellites until at least 2040 (think about it…:wink:).
Spiff.
