I wanted to "straighten out" (remove all perspective effects) the facade of a building foubnd in google street view, so that I could take measurements from it (photogrammetry).
Normally hugin can do this easily, at least on images I've photographed myself.
Set a vertical CP-pair left and right, set a horizontal pair top and bottom, optimise all of YPR. Done.
But this screen shot would simply not behave. CP errors were large.
Eventually a memory scratched at me, and I added HFOV to the values to be optimised, but still no success.
Oddly, HFOV was not changed at all, even to a "bad" value.
I tried searching though HFOV values manually, and as I increased it (10 degrees at a time), it suddenly not only changed, but it optimised, as did YPR, and the result was a nigh perfectly rectilinear building (well, facade anyway).
It appears that my fairly random initial HFOV value put the numbers in a bad solution the optimiser couldn't escape from.
