I just cheat and do it with polar coordinates: set the radius to a fixed number and rotate around the x and y axis. Then I convert the whole array of polar coordinates to an array of cartesian coordinates. But then again, I''m a newbie...

If I know what you mean:
Sphere: r*r = (x*x) + (y*y) + (z*z)
Ellipsoid: 1 = (x/rx)2 + (y/ry)2 + (z/rz)2
Torus: 1 = (r - sqrt((x/rx)2 + (y/ry)2))2 + (z/rz)2

Those are all I have on hand, I can probably dig up some more from a book I have. Say if that''s what you were looking for.

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For the sphere you can use the cartesian equation as given by 'Null and Void':

r2 = x2 + y2 + z2

or the parametric equations

x = r*cos(theta)*sin(phi)
y = r*sin(theta)*sin(phi)
z = r*cos(phi)

where theta is the angle in the x-y plane measured from the positive x axis and phi is the declination (angle down) from the z axis to the point on the surface of the sphere.

A cone is given by:

z2 = c2(x2/a2 + y2/b2)

A Cylinder by the parametric equations

x = r*cos(theta)
y = r*sin(theta)
z = a

where theta is again the angle in the x-y plane and a is the distance of the point (on the surface of the cylinder) from the x-y plane.

A parabolic bowl can be given by

z = c2(x2/a2 + y2/b2)

Have fun!

Timkin


Edited by - Timkin on October 18, 2001 12:42:32 AM