Re: [Closed REQ 5461]: ellipsoids

["Stuart Levy" <slevy>]

> 1) Can I easily construct an ellipsoid with a major, intermediate, and minor
> axis?  This is for illustrating 3 dimensional, 2nd order tensor quantities.

Yes.  Probably the easiest way to do this is to apply a (non-uniform scaling)
transformation to a sphere.  You can express transformations as 4x4 matrices:

INST transform {
	.5 0 0 0
	0 .8 0 0
	0 0 1.3 0
	0 0 0 1
} geom { < sphere.mesh }
 
Matrices are the transpose of what you'd probably expect, so a translation
component (the sphere's center) appears in the bottom row, rather than
the rightmost column.

For spheres which are smoother though slower to draw you could replace the
{ < sphere.mesh } 
with
{ SPHERE 1 0 0 0 }   # A unit sphere centered on the origin