[Radiance-general] Mapping from hemisphere projection to latitude-longitude format

[Claus B. Madsen]

Dear list members,

I use HDRShop to convert between mappings for environment maps, e.g., 
from mirror ball to lat-long, etc.

I now have two other mappings that I wish to convert to lat-long (though 
I realize that both mappings will only give me half a sphere, e.g., top 
half of lat-long map).

1) An image taken with a Sigma 8mm 180 degree field-of-view fish eye 
lens to take a high-res image of the sky (same hemispherical mapping as 
RADIANCE renders into when using the -vth option for rview/rpict)

2) An image of a diffuse hemi-sphere (diameter of 0.3 meters, turned out 
on a lathe) spray painted with a diffuse grey


I am convinced that both mappings are identical (i.e. identical to the 
hemi-spherical projection model in RADIANCE). So far I have used the 
'mirrorball closeup' format in HDRShop but found this to be the wrong 
mapping yielding incorrect lat-long mappings. I have now understood the 
entire geometrical issue and just need a piece of software to warp 
hemisphere images to lat-longs ... perhaps a plugin for HDRShop?

A couple of years ago I raised this issue with the people who wrote 
HDRShop but they claimed the Sigma lens should be treated as mirror ball 
closeup when re-mapping in HDRShop. I am now convinced this is not true 
after having tested it  extensively.

Sincerely,
Claus

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