[ptx] fine tuning 2

[Ph. Gac]

hi Pablo,

thanks for your answer and thanks a lot for your software which I am now using instead of PTOpenGUI since it is quite
stable.

I confirm, with your last release, that when you change X in the text box, and then select Y with the mouse or with TAB,
all the textboxes get cleared and the CP pair is deselected; it cannot be selected again by clicking or double-clicking
in its row, so you have to select another pair and then select it again to change Y!

I'm working on Windows 2000 SP4 with GTK 2.2.4 and also GTK 1.3 which I need for GIMP 1.25 (GIMP 2.0 is really too buggy
for now). It's running on an Athlon XP 1500 with 512 MB DDRam and a 1600x1200x65k screen ("high color", large fonts, but
no display problem so far). It's fine for Hugin but for the one pixel wide features which are sometimes hardly
noticeable.

I began with PTOpenGUI which has a 16x detailed view and allows to set fractional coordinates. These views are generated
by interpolation and it seems they are also warped to help the feature identification. Then I could achieve, in some
specific cases, a 0.5 or even (?!) 0.2 pointing precision. This happened to be useful and I was quite surprised.

Thinking about it, 3 ideas emerged...
1- To infer the perspective parameters, one can in theory use any couples of overlapping points but the ones with the
biggest homographic warping give more significant results. The trouble is that these points also get the biggest optic
distortion, some of which is not taken into account by the a-e parameters (maybe, especially with aspherical lens).
Using CPs nearer the image center, the distortion is negligeable but the warping is also smaller, which can be
compensated for with more precise coordinates.
2- a small error in the first image of the series may induce larger and larger errors to adapt consecutives views which
results in big discrepancies when you want to make the ends meet. Then, global optimization sometimes gets crazy,
especially if you are tempted to let the FOV vary...
3- top-border points are often in the sky... bottom-border points are often on the foreground, and I seldom take my
1.5kg 30cm pod with my 200g 8cm camera... so there are sometimes few usable points. This low number of CPs doesn't allow
the compensation of errors so the coordinates should be as precise as possible.

(But PTOpenGUI detailed view is buggy: when you click in it, it gives strange results: it seems to infer the coordinates
from a displacement and somewhere somehow take the double displacement so you have to click halfway between the point
where you are and the one you want to get some better approximation and repeat this step until the cross is displayed
when you want to go!)

I dont use autopano because it is unusable with modern buildings I'm working on now, which have lots of repeated
features... I used it with a mountain panorama and it gave also poor results, choosing points in distorted areas, or on
the foreground. Hand tuning with PTOpenGUI was very slow but gave a very good compromise. Second best choice was Hugin
autofinetuning.


hum... what about a circle? I don't know if this is easy to do with GTK...
or a circle plus cross lines?
sometimes (esp. when zooming), I wish I had a only a cross instead...

regards,


PS: my on-line collection: http://pho.ediphi.org/Stitch/index.htm

Philippe Gac
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