[Proj] Perspective view to a sphere (or similar)

[support.mn at elisanet.fi]

Hello,

there are situations when one would like to use a very basic
projection: perspective view to a sphere. To use directly
some photos from the space or airplanes. Or maybe a
screen shot from Google Maps. The most obvious way
would be to use them directly as they are. There are
some spherical projections
in proj-4. But is there exactly a direct view from a view point with
forward and inverse algorithms?

Here is more about that subject and how it should be calculated.

http://en.wikipedia.org/wiki/Perspective_view

http://en.wikipedia.org/wiki/Image:Perspectiva-1.svg

http://en.wikipedia.org/wiki/Image:Perspectiva-2.svg

What is needed:
1) view point coordinates
2) view direction (defaulting to the center of the earth maybe?)
3) distance to the earth surface and to the projection plane
4) rotation angles and zoom factors
5) more? maybe some most common distortion factors for cameras etc??

What is best approximation projection in proj-4
to get some results?

Regards: Janne.