Why do I have to optimise g and t (sheer)?

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Why do I have to optimise g and t (sheer)?

PanoTools NG mailing list
Hello,

I'm using autooptimiser to map pixel positions to azimuth and altitude.
That is, I'm only using a single image plus a dummy 360x180 degree
equirectangular image (which has a direct mapping between az, alt and x,
y).  I do this by tracking stars, plate solving (star identification)
and use the results as control points.

The result is a .pto file like this: http://voksenlia.net/test/lens.pto

Running autooptimiser like this:

 autooptimiser -n lens.pto -o lens2.pto

gives me a reasonable result, which I've visualised here:

 http://voksenlia.net/test/grid.jpg

However, if I in the lens.pto file above comment out "v g0" and "v t0",
the result is always very bad:

 http://voksenlia.net/test/grid2.jpg

The lens is a (full frame) fisheye lens.  Do the g t parameters have a
special meaning in this case, and must be included in the optimisation?

--
Steinar Midtskogen
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Re: Why do I have to optimise g and t (sheer)?

PanoTools NG mailing list
Am 16.05.2015 um 18:51 schrieb Steinar Midtskogen:
> I'm using autooptimiser to map pixel positions to azimuth and altitude.

[...]

> However, if I in the lens.pto file above comment out "v g0" and "v t0",
> the result is always very bad:
>
>   http://voksenlia.net/test/grid2.jpg

Well, the result is visually appealing but obviously not what you
expected. :-)

The shear parameters are very specialized ones and should only be used
if there is actual shear to correct, like it is introduced by scanners
or scanning back cameras: http://tinyurl.com/pt2lzlq

Since this seems to be a hugin problem, perhaps you'd better ask in the
hugin support list: http://tinyurl.com/nseq36a


--
Erik Krause
http://www.erik-krause.de


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