I'm using a height field in one of my scenes to simulate sand dunes--a
nice enough effect, except for a problem I'm having with the diffuse
reflection off the surface. Some of the triangles face the light source
a little too directly, no matter where I put it, so that I get marching
diagonal rows of light spots, shaped like checkerboard squares.
The "smooth" keyword is present. The image does indeed look worse
without it.
Using multiple light sources and area lights does not improve the shiny
checkerboard effect; if anything, it sometimes makes it worse by
creating even more rows of light spots, though usually not as noticeable
as the first row.
I should mention that because the height field is simulating sand dunes
from close up, it's scaled to <100,8,100> (as I recall).

I've played around a lot with the bit depth and size of the height field
file I'm using. Increasing the resolution just makes the checkerboard
areas smaller, but they do not go away. Currently I'm using the maximum
bit depth of 16, with a 1200x1200 height field. The height field is a
1.9 MB PNG file, and anything 2400x2400 or larget is not only unwieldly,
but still produces the same patterns (just a bit smaller).

With the smooth keyword on, there should be no noticeable light spots
such as I'm getting, but they're there. I had an idea for preventing
that.
Since the smooth keyword seems only semi-effective, why not make it
possible to use a numeric operator? Equate "true" to 1.0, the default
value if "smooth" is used, and "false" to 0. Thus, something "smooth
5.0" would do even more smoothing, causing much more of a rounded
appearance, while "smooth "0.5" would produce something more like the
typical unsmoothed flat look, but with a bit of smoothing near the
edges.

Lummox JR

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This really belongs in povray.general or perhaps even the programming
group. Please see my reply at p.g.


Lummox JR wrote:
> 
> I'm using a height field in one of my scenes to simulate sand dunes--a
> nice enough effect, except for a problem I'm having with the diffuse
> reflection off the surface. Some of the triangles face the light source
> a little too directly, no matter where I put it, so that I get marching
> diagonal rows of light spots, shaped like checkerboard squares.
> The "smooth" keyword is present. The image does indeed look worse
> without it.
> Using multiple light sources and area lights does not improve the shiny
> checkerboard effect; if anything, it sometimes makes it worse by
> creating even more rows of light spots, though usually not as noticeable
> as the first row.
> I should mention that because the height field is simulating sand dunes
> from close up, it's scaled to <100,8,100> (as I recall).
> 
> I've played around a lot with the bit depth and size of the height field
> file I'm using. Increasing the resolution just makes the checkerboard
> areas smaller, but they do not go away. Currently I'm using the maximum
> bit depth of 16, with a 1200x1200 height field. The height field is a
> 1.9 MB PNG file, and anything 2400x2400 or larget is not only unwieldly,
> but still produces the same patterns (just a bit smaller).
> 
> With the smooth keyword on, there should be no noticeable light spots
> such as I'm getting, but they're there. I had an idea for preventing
> that.
> Since the smooth keyword seems only semi-effective, why not make it
> possible to use a numeric operator? Equate "true" to 1.0, the default
> value if "smooth" is used, and "false" to 0. Thus, something "smooth
> 5.0" would do even more smoothing, causing much more of a rounded
> appearance, while "smooth "0.5" would produce something more like the
> typical unsmoothed flat look, but with a bit of smoothing near the
> edges.
> 
> Lummox JR

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