Thomas Willhalm wrote:
> 
> Hello,
> 
> if I remember correctly, I came across some code in povray or one of its
> patches that calculates the gradient of a pattern or function. By this
> I mean a function that numerically finds the direction of a real valued
> function f at some point p in space in which f increases most. This was
> done by evaluating the function slightly off p. To improve numerical
> stability, the code in question used the four vertices of a tetrahedron
> and evaluated the function f there. So, if v1,...,v4 denote the vertices
> of a tetrahedron centered at the origin, the function f was evaluated at
> p+v1, p+v2, p+v3 and p+v4.
> 
> Unfortunately I cannot find this code anymore. Does somebody know what
> I'm writing about and the file to look at?

You have some POV-SDL based macros for gradient calculation in
'math.inc'.  Apart from that the isosurface normal calculation code does
something similar too, function 'IsoSurface_Normal()' in 'isosurf.cpp'.

Christoph

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