Well you about covered them all I think.  Nothing good enough huh?  Could be
said of lots of things I suppose  :-)
I've done the CSG bit too and didn't like it at all.  I've always wanted some of
the shadow side to show up some, as if lit by reflected planet-light or
secondary star or something.  Either that or as though seen at twilight or
through a thin atmosphere.  Then those fog and ambient methods usually do okay.
What's needed for unseen shadows of beyond-atmosphere objects in the daylight
sky would be a new type of thing where a light source would only make the shone
upon parts of objects visible and yet not allow for tracing of any unlit parts
(now I'm wondering if there already is).
Anyway, a work-around would be to use huge specular highlighting (roughness 1)
on a fully clear object.  That way only the lit side shows.  Just a problem of
the possibility of seeing the inside of such a object if the camera were placed
wrong.  In fact the highlighting might show through from behind as well.
A lot of people have done this sort of thing so maybe there are answers, but I'm
think mostly the answer is to tweak the fog, ambient, and background.

Bob

"John Bindas" <big### [at] ixnetcomcom> wrote in message
news:38b969d5@news.povray.org...
| The last few weeks, on my way to work, I noticed the Moon in the morning sky
| and it reminded me of a problem I had months ago doing a sci-fi scene. When
| you look up at the crescent Moon in daylight, you don't see the unlit part
| of the Moon. You just see the lit crescent in a blue sky. This effect is a
| common sci-fi art theme, an alien landscape with two moons and a Saturn-like
| planet in the sky.
|
| What works great for a night-time or a space scene, an ambient of 0 does not
| work for a daylight scene. When I try to duplicate the real world effect in
| POV, I get both the lit and unlit portions of the Moon visible against the
| sky. If I drop the ambient down to 0, the unlit portion is black. If I match
| the ambient to the color of the sky sphere (or some fraction of it like <.2,
| .6, .8>*.10), the unlit portion is visible. I have tried things like
| "negative" spotlights aimed at the unlit portion. Something like:
|
| light_source {
|  <0, 10, 0>
|  color rgb <-.8, -.4, -.2>
|  spotlight
|  radius 15
|  falloff 20
|  tightness 10
|  point_at <0, 0, 0>
| }
|
| With simple white test spheres, this works. However, I spent a lot of time
| tinkering with the "negative" light color and the ambient statement. And
| then I found with any complex texture, it doesn't work. My best success has
| been with a constant fog with a distance set far enough away not to
| interfere the majority of the scene. The unlit portion of the Moon is
| obscured, but not completely invisible. To make the unlit portion invisible
| or mostly invisible, the lit portion becomes too "washed out". I haven't
| tried CSG, and I have a feeling this may the best solution. Anyway, this
| hasn't bothered me enough to make me to break out my old math book and
| calculate the correct angle of the CSG difference to the light source(s). It
| bugs me just enough to ask this group if anyone out there has any hints or
| tricks for a raytracing a moon or planet in daylight?
|
| ---
| jb
|
|

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