clipka <ano### [at] anonymousorg> wrote:
> Am 23.07.2012 21:58, schrieb Chaanakya:
> > "Chaanakya" <nomail@nomail> wrote:
> >> Hey guys!  I just had a quick question...
> >>
> >> I was trying to generate the graph of this function (in Cartesian coordinates):
> >>
> >> -z + 1.00003 = (3x^2 + 3y^2)/(200000)
> >>
> >> However, when I render the following code, nothing shows up except for the
> >> plane:
> ...
> >> isosurface {
> >>    function {
> >>      -y - ((3*pow(x,2) + 3*pow(z,2))/(200000)) + 1.00003
> >>    }
> >>    // contained_by { box { -2,2 } }
> >>    pigment {
> >>      color Red
> >>    }
> >> }
> ...
> > Even more strangely, when I use the equally valid function
> >
> > function {
> >    y + 3*pow(x,2)/200000 + 3*pow(z,2)/200000 - 1.00003
> > }
> >
> > I get a cube.  I think there's something fundamental about isosurfaces that I'm
> > not understanding?  That is, how should I convert the function z = -3x^2/200000
> > - 3y^2/200000 + 1.00003 into an isosurface?
>
> Do un-comment the "contained_by" line!
>
> At x=0,z=0 you have y = 1.00003, which is outside the default
> contained_by object (box{1,1}), and even at the maximum x and z
> (x=1,z=1) you have y = 1.00000, which just barely touches the box.
>
> I.e. the surface you defined is (for practical purposes) all outside
> default container; so the inside of the default container is either
> completely outside the isosurface (first version) so that you don't see
> anything, or completely inside (second version) so that you simply see
> the container's shape.

I'm trying to figure out exactly what container I should use - if I use box {
<-1,1,-1>,<1,1.00003,1> } I get nothing (I understand why).  If I use box {
<-1,0.9,-1>,<1,1.00003,1> } I get a box.  How do I get the elliptic paraboloid
to show up?

Thanks!

- Chaanakya

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