In article <3875FB3E.46031B75@iastate.edu>, maw### [at] isunetnet wrote:

> I may be compeletely wrong, because I don't have a lot of experience
> with isosurfaces, but I did run into something similar.  It seems to me
> that the isosurface code works "backwards" from normal POV-Ray
> nomenclature. i.e. something like isosurface{y-noise3d(x,y,z)} actually
> adds the height of the noise to the plane whereas
> isosurface{y+noise3d(x,y,z)} subtracts the noise from the surface. 

That isn't backwards at all. The isosurface of the function y-1 will 
consist of all points where y-1 is the threshold value. Increasing the 
amount subtracted from the y coordinate means y has to be higher to 
result in the same value. When noise3d equals 1, y has to equal 1. When 
it is added instead, y has to equal -1 to get the same result.


> Likewise it seems that increasing the x,y,and z values makes for smaller
> noise features. e.g. noise3d(x*20,y*20,z*20) makes finer detail than
> noise3d(x*3,y*3,z*3).

Again, this is not backwards. If you multiply x by 2, than the result of 
that expression(2*x) will be a certain value at half the distance it 
would be without the multiplication. The result is compressing the 
coordinates into a smaller space, scaling down.
If x is 3, 2*x will be 6, and the features that would have been at x=6 
will be at x=3 when 2*x is used.

-- 
Chris Huff
e-mail: chr### [at] yahoocom
Web page: http://chrishuff.dhs.org/

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