In article <web.3d44a3c1a584b11ed02c7b870@news.povray.org>,
 "Rohan Bernett" <rox### [at] yahoocom> wrote:

> I made a planet using an isosurface using f_sphere and f_noise3d, and the
> resulting ball was smaller than the radius of the sphere specified in the
> function. As more levels of noise were added, the ball became smaller
> still.
> 
> The function I used was something like this:
> function{
> f_sphere(x,y,z,6400000)+100000*f_noise3d(x/100000,y/100000,z/100000)}
> 
> Any ideas on why this happens, or how to get around it?

The surface is displaced, so the sphere has to either get bigger or 
smaller anywhere the noise function is not equal to 0. As you use more 
levels of noise, the number of areas that equal 0 get fewer and fewer.
By adding to the sphere function, the points where the threshold value 
is reached get pushed further toward the center of the sphere. 
Subtracting would pull them outward. Just compensate by adjusting the 
sphere radius or by subtracting half the peak noise level from the 
function (this will makes some areas depressions and other areas 
mountains).

BTW, an isosurface doesn't seem like a good idea for a planet...for most 
planets, the largest features are tiny bumps on the surface.

-- 
Christopher James Huff <chr### [at] maccom>
POV-Ray TAG e-mail: chr### [at] tagpovrayorg
TAG web site: http://tag.povray.org/

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