[ptx] Alternative fisheye projections

[Bruno Postle]

Hugin can now create fisheye images which is great, here is one I 
prepared earlier:

http://bugbear.blackfish.org.uk/~bruno/fishfix/074-098-fisheye.jpg

...but true fisheye images have a problem that the edges appear very 
"squashed".  I occasionally see fisheye-like images that don't have 
this distortion, there are a whole load on this site:

http://digitalurban.blogspot.com/2005/11/navy-pier-chicago-panorama.html
http://digitalurban.blogspot.com/2006/02/hidden-london-series-london-roof-tops.html

I think the cartographic name for this is "conformal" meaning that 
any small part of the image shows hardly any shape distortion.

I've tried scripting this conversion with mixed results, here's an 
example:

http://bugbear.blackfish.org.uk/~bruno/fishfix/074-098-fisheye-fixed.jpg
http://bugbear.blackfish.org.uk/~bruno/fishfix/

This looks much better to me, but I know that the math is wrong (the 
picture gets "pinched" in the middle).  Does anyone have any idea 
how to do this properly?

-- 
Bruno