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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