Hey man, why don't you just try:

#declare f=.040;
#declare R=399;
isosurface {
         function
          {noise3d(x*f,y*f,z*f)+((x^2+y^2+z^2)/R^2)
           }
         accuracy 0.01
               threshold 1
                bounded_by {
                sphere{0,500}
                    }
        pigment{Green}
        finish{ambient 0.1}
        normal {crackle}

        }


And then sleep on the results??

"Greg M. Johnson" wrote:

> SPHERE!
>
> "Jerome M. BERGER" wrote:
>
> > "Greg M. Johnson" wrote:
> > >
> > > noise3d (x*f, y*f, z*f)*(R-sqrt(x^2+y^2+z^2))
> > >
> > > Nope.  This is a solid sphere.
> > > I've used R=500 and a dozen orders of magnitude for f.
> > >
> > > I've had a little luck with adding an "*f" term to the right side.  But this
> > > is not the concept, although intuitively the math must be VERY CLOSE....
> > >
> >         What about noise3d(...)-sqrt(...)/R ?
> >
> >                 Jerome
> >
> > --
> > *******************************

> > * they'll tell you what can't * mailto:ber### [at] inamecom
> > * be done and why...          * http://www.enst.fr/~jberger
> > * Then do it.                 *
> > *******************************

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On Tue, 05 Oct 1999 19:13:26 -0400, "Greg M. Johnson"
<gre### [at] my-dejanewscom> wrote:

>Yes, you are linearly scaling the structure. Your density will not change as a
>function of position if you make scalar operations like those.  I want to make
>a sphere that is "100% dense" at r=0, but gradually tapers off to zero or a
>minimum density at r=some R.   This is easy to do with media.

noise3d + min(0,1-sqrt(x*x+y*y+z*z)) 

and play with the threshold. I have only used the superpatch once but
I can guess that this formula will be 100% dense below a certain
radius (probably sqrt(threshold) ) and fade to noise3d at a distance 1
from the origin. Try it out.


Peter Popov
ICQ: 15002700

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I posted a message regarding your questions at the images section of this
newsgroup.

"Greg M. Johnson" wrote:

> I'm having fun making flythroughs of the 3dnoise function in the
> superpatch for povray.
>
> I am trying to understand this mathematically.   If I use:
> 3dnoise(x,y,z)
> I get something with a uniform distribution of porosity.  As the
> threshold approaches 1.0, the percent porosity approaches 0 (% density
> approaches 1.0).  However, if the threshold is 0.0, there is not 100%
> porosity.
>
> I want to understand how to change the radial density of the noise
> function.  Suppose I want to make a sphere where the density approaches
> 0 at r=R.  How would I do this?  Intuitively, I might try:
> 3dnoise(x^0.5,y^0.5,z^0.5)
> . So far, nothing is yielding precisely the results I'm looking for.

--
Samuel Benge

E-Mail: STB### [at] aolcom
Website: http://members.aol.com/stbenge

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