>   what's the best way to get a stereographic projection in megaPov?
> I mean, projecting the scene to a sphere from its center, then
> projecting the sphere to a plane stereographically. I don't feel like
> defining a camera type but I can do if needed.

The general idea is, that you want to emit camera rays from the pole of
the sphere and double their angle to the camera direction when they hit
the sphere.

1. You can do this with reflection, if you specify a rather fake normal
   for the sphere. PovRay does not seem to allow arbitrary normal
   functions but I don't know about MegaPov.
2. You can do this with refraction, by giving the interior of the
   sphere an ior of 0. If 0 is not allowed or leads to division by 0
   (I would bet it does), you can approximate the intended result by
   specifying an ior close to 0. This could be done in PovRay alone.
3. The size of the sphere does not matter at all. (But note, that the
   sphere's center has to be fixed, not its pole.) For an
   infinitesimally small sphere, its sphereness becomes unimportant
   and non-sphereness will lead only to infinitesimal displacements of
   the camera rays. So you might replace the sphere by some other shape
   which allows for relection with unfaked normals or refraction with
   non-zero ior. This would be possible in PovRay alone. (But again, it
   is only an approximation to what you really want.)

In all these cases, you should be sure, that the camera is not visible
in your scene.

  Mark Weyer

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