Celestia Forums

....I'm seeing pancakes

I have read of this effect some time ago, but can't find it, even when using the search engine.

I'm wondering what is the cause for craters to suddenly invert into pancake-like features, Olympus Mons deflating into a hollow, Valles Marinaris turning into a mountain range....Quiet fascinating....at first
Is there a way to minimise this effect?

Thanks
Chris

Chris,

Most often this is an optical illusion, when an object is illuminated by light coming from one direction but you are viewing it as if the light were coming from the opposite direction.

Some surface texture maps have shadows drawn on them, which can cause a similar effect. As Celestia rotates the object, the shadows don't move. As a result, shadows near the "wrong" terminator will point toward the sun instead of away from it. This would cause the effect you see, I think.

Does this clarify things a little?

Mars especially is terrible for this (even Mars geologists have trouble with some of the craters). It took me AGES to figure out what I was looking at in the Viking images...

The best trick is to find something you can clearly identify, and then use the shadows from that to set the lighting for the rest of the scene. So if the sun is coming from the right, then shadows will be cast to the left - if you find a crater, then the right-hand rim will be casting the shadow to the left. Once you figure that out, you can force the rest of the scene to conform.

It also helps sometimes if you orient the image so the illumination is coming from the same direction as the light in your room is coming from.

So it's best to avoid 'shadowed' texture maps....unless they're pretty special.
Thanks for the clarification and tips. It's nice to understand how these things work in the hope of better control.

Much appreciated
Chris

"Valles Marinaris"?...um...anyone for pizza