PanoTools NG:
Re: FW: calibrating a lens/teleconverter combo using PTGui
Jim Watters 2007-Dec-31 20:23:16
Yoram Bernet wrote:
> OK -I think I got it. It seems that the mistake I made was by accepting the
> suggestions offered by PTGui for the 2nd CP of each pair. This time, I
> placed the second CP of each pair somewhere far away on what is supposed to
> be the same line - so - if the line I am trying to straighten is vertical -
> I'd place the first CP at say the top of the line (in the right pane) and
> the second of the pair at the bottom of the line (in the left pane).
>
Yes that would do it. The matching point algorithm does not take into
account that is is a line you are trying to match but finds the exact
same spot in the second image.
> This leads me to the question - are straight line CPs processed in pairs
> (per the CP numbers that show up in the images)? Or - are they processed in
> sets (with all CPs that have the same line number/name in the 'Type' field
> on the table below the images members of a single set)? Is there a rule of
> thumb regarding where to designate the 2nd CP of each pair (clearly, very
> close causes problems - that's what caused the optimizer to say 'too good to
> be true').
>
I not sure how much this matters but....
Going by memory after looking at the code many months ago I believe it
is something like this.
lines are evaluated in groups of 4 points. The first 2 points make a
line, the other points are evaluated as to their distance from that
line. All errors are added up and if it is better than the previous
error then the optimizer stores these settings as the current best, but
continues on evaluating many more variations.
Although the algorithm could be changed to evaluate all the points of a
line at once the overall difference of arriving at the best optimization
probably will not change.
The UI and script are created to add points in pairs. So this is how
straight lines have been adapted to work within those constraints.
As far as best practices for placing line controls points.
See: http://www.panotools.org/mailarchive/msg/32789#msg32789
and http://epaperpress.com/ptlens/index.html Calibration | Target
- The first two points of a line should be at the ends of the line.
- Add another 4 to 6 points ( 2 or 3 pairs)
- One line should be at the edge of the image.
- One line should be about 1/6 to 1/4 from the edge.
--
Jim Watters
Yahoo ID: j1vvy ymsgr:sendIM?j1vvy
jwatters @ photocreations . ca
http://photocreations.ca
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