Nexus nous apporta ses lumieres en ce 2005-12-31 00:31:
> I've just created my first non-tutorial-related scene and I think it's OK
> for a first attempt but there's a few things I'd like help on.
> 
> 
> The scene is the view from the surface of a small, gray, rocky planet
> (modelled with a height field I generated with Fractint). There's also a
> yellowish star and a big blue gas planet with a dust ring.
> 
> Here's my problems:
> 
> 1) There's black triangular shadowy bits on the height field that just don't
> look right. How do I get rid of them?

Normal with a hight field. You can use the soloution given by thers. Another, but
slower, way would 
be to replace the height field by an equivalent isosurface.

> 2) The star is right in the top right hand corner of the picture and it
> looks squashed. I think that's got something to do with the camera but I
> have no idea how to fix it.

Normal distortion. Using a smaler camera angle and tightening the objects placement
can be done.

> 3) The blue planet has a thin "atmosphere" that I made with a thin spherical
> shell containing blue-colored scattering media. The trouble is that the
> atmosphere cuts off abruptly and looks awful. How do I get spherical
> density_maps to work with scattering media so that the atmosphere drops off
> gradually? I can't get them to work at all; POVRay keeps complaining at me
> if I try.

As an alternative to the other suggestions, you can use an onion pattern for your
density.
Note that you don't need to bring the density to zero inside the planet, you don't see
that part and 
unless you specificaly make the planet hollow, the media won't exist inside the
planet.

> 4) This one's kind of subtle. The dust ring is also made of scattering media
> and circles the entire planet. There is a small region near the night side
> of the planet where light scatters from the ring and passes through the
> atmosphere but it ends up brown instead of blue. It's as if the atmosphere
> is absorbing the blue light from the scattered rays instead of scattering
> them again. Is that supposed to happen? and how do I fix it?
> 

You scather off the blue part, so the light that get true is tinted the complementary
colour. It's 
physicaly acurate, even if you find the result surprising.

> 
> 
> Thanks a lot for your time.
> 
> Nexus
> 
> 
> 


Alain

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