PanoTools NG:
Re: Sigma 8 F3.5 and its sharpness
John Houghton 2007-May-16 17:18:32
--- In #removed#, "ptgroup" <ptgroup@...> wrote:
>
> John:
> as you said before an Hans also:
> if your lens is calibrated 2/3 Point are sufficient.
> But this you have to proof otherwise you need the mentioned amount
of
> points.
I don't know about "proof", but I think it's common sense. If you
fix one of the remapped images on the stitching surface, the
neighbouring overlapping image can be shifted into a position such
that all of the matching features in the overlap area will align,
assuming the lens is accurately calibrated. There is only one
position (y,p,r) of the second image that achieves this alignment.
The optimizer sees only control points, of course. Assigning one
point would not be enough for the optimizer to align the second image
completely. The single point would be aligned, but the second image
could take up any position rotated about that point. As Hans said,
if you assign a second point, there is only one position of the
second image for which both marked features will be aligned. In
effect, the second point prevents rotation of the image into an
arbitrary position.
The same reasoning applies to all the other images, with the result
that the fixed anchor image uniquely determines the positions of all
the other images. They don't individually have the freedom to take
up any other position. All can be exactly aligned by adjustment of
their y,p,r values alone.
In real life, the lens calibration and control point placement are
not going to be 100% accurate. More points will give an averaging
effect in the optimization to help counter minor inaccuracies.
John
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