davidafisher wrote:

> I'm trying to emulate the earth which is an oblate spheriod - flattened
> sphere. The correct result does not occur by scaling the y axis of a sphere

The formula (http://mathworld.wolfram.com/OblateSpheroid.html)
certainly looks just like a sphere with a different scaling for
one axis. Of course, you can also use an isosurface, which has
the advantage that you can add terrain elevation later.

#declare RADIUS_EQUATORIAL = 6.378137;
#declare RADIUS_POLAR      = 6.356752;

isosurface
{
   #local ALPHA_INV = 1/RADIUS_EQUATORIAL;
   #local C_INV     = 1/RADIUS_POLAR;
   function  {ALPHA_INV * (pow(x,2) + pow(z,2)) + C_INV * pow(y,2) - 1}
   max_gradient 2
   contained_by { sphere {0,6.5} }
   pigment {color White}
}

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