Point taken. But is there someone out there that can point out the
places in the code to put the values a and b in something like
this?
// Torus having major radius sqrt(40), minor radius sqrt(12)
#declare Torus=
quartic {
 <
    1,   0,   0,   0,   2,   0,   0,
    2,   0,-104,   0,   0,   0,   0,
    0,   0,   0,   0,   0,   0,   1,
    0,   0,   2,   0,  56,   0,   0,
    0,   0,   1,   0, -104,  0, 784
 >
 sturm
 pigment{White}
 }
This is almost stright form the docs.

Mark Wagner wrote:

> Mr. Art wrote in message <37CD54FE.76230D45@gci.net>...
> >Isn't the equation for a 2D oval/ellips something like
> >(x^2)/a + (y^2)/b = 0? A circle is x^2+y^2=0.
> >Couldn't we find the part of the torus discription
> >that deals with the major radius and add the division
> >parts?
>
> An oval is not an ellipse, they just look similar.  An oval is easier to
> draw freehand, but an ellipse is easier to create mathematically.
>
> Mark

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