Hi all

I've just finished what I hope will be the final revision of the Wiki page http://wiki.panotools.org/Lens_Correction_in_PanoTools

It is now, I hope, a clear statement of how PT computes correction parameters, why those are not portable between image formats, and what needs to be done to make them portable.

Bottom line, I think: 
add the physical pixel width as a new 'i/o' parameter.