Vahur Krouverk wrote:
> 
> It seems to be bug in version 0.5, not self shadowing. Changes list
> indicates, that "double illumination bug is fixed", perhaps this is the
> reason. If I have time, then I try to verify it (hopefully Nathan will
> take a look at it, as he probably knows better this matter).

I've made some renderings and it seems, that it is bug in POV-Ray. By
default smooth height-fields were double illuminated, but from version
0.5 it is changed to not double illuminate. Seems like smoothing is
changing some surface normals such way, that in intersection point it
appears to be faced backward (inward, into the mountain) and when double
illuminance is turned off, then it is drawn unlit.

In order to test my theory, I've added light source under the
height-field:
light_source {   
  <0.0, 0.0, 0.0>
  color rgb <1.000, 1.000, 1.000>*1.4000
  translate  <-2.0, -2.0, -50.0>
}

after this most of the blackness is gone, i.e. those backward surfaces
are lit by this additional light.

Also, when camera is moved upward, then those backward surfaces are gone
too, so seems like there is error in heightfield intersection (normal)
calculation. I don't know, whether it is due to some coding error or is
it some insolvable or hard-to-solve problem.

In order to make this scene work, there are following possibilities:
1. Create height-field image, which is smoother than current. I imported
it to leveller and smoothed it, after this most of wrong illuminated
surfaces were gone.
2. Double illuminate it by adding double_illuminate keyword.
3. If this can't be done (double illumination is unacceptable from
artistic point of view), then use "rough" height fields or move camera
upward.
4. If this is unacceptable, correct error in POV-Ray source code ;-)


HTH

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