[ros-users] camera_calibration

[Patrick Beeson]

Yes, I am using the correct checkerboard.  I am doing everything 
correctly.  I am knee deep in the calibrator.py source, and everything 
looks good after the StereoCalibrate() command -- the rotation and 
translation between the two cameras seems reasonable (rotation close to 
I, translation on the right scale).  It seems to be after the 
set_alpha() call where the final projection matrices end up with HUGE 
numbers for focal length (tens of thousands), and the rotation matrices 
have unexpected off diagonal components.

Vijay Pradeep wrote:
> Hi Patrick,
> 
> Is the checkerboard 8x6 corners?  If so, make sure that you always keep 
> the target in a 'landscape' orientation.  If the checkerboard gets close 
> to a 'portrait' orientation, the OpenCV detector may mess up the 
> correspondence between both cameras (thus, making the calibration 
> routine want to rotate one of the cameras 180 degrees).
> 
> This rotational ambiguity can also be solved by using a checkerboard 
> with [odd]x[even] corners.
> 
> Vijay
> 
> On Tue, Apr 6, 2010 at 2:01 PM, Patrick Beeson <beeson.p at gmail.com 
> <mailto:beeson.p at gmail.com>> wrote:
> 
>     Sorry, I just checked and I am actually using the trunk, not latest.
>     The problem is that I'm getting large rotational values, and I'm only
>     ever seeing a horizontal offset in T (top right value in projection
>     matrix) as non-zero, even though the cameras are at slightly different
>     heights.  I can send the saved tar.gz file that contains the images used
>     and the ost.txt created if it helps.
> 
>     Patrick Beeson wrote:
>      > I checked out latest and had to do a small bit of changes to sync the
>      > timestamps of the two cameras whenever frames have very close
>      > timestamps.  So they aren't EXACTLY synced, but VERY closely
>     synced.  I
>      > can try to send you a screen shot of the output.  Note, I am testing
>      > this with a quite small checkerboard (your checkerboard, but with
>     26mm
>      > squares).  Maybe that's the problem?  Maybe I'm sampling a space too
>      > close to the cameras?
>      >
>      > Eric Perko wrote:
>      >> Patrick,
>      >>
>      >> What version of camera_calibration are you using? Boxturtle?
>      >>
>      >> - Eric
>      >>
>      >> On Tue, Apr 6, 2010 at 4:31 PM, Patrick Beeson
>     <beeson.p at gmail.com <mailto:beeson.p at gmail.com>>
>      >> wrote:
>      >>> I'm trying to calibrate two identical 1394 cameras that are
>     sitting next
>      >>> to each other.  The stereo calibration from camera_calibration
>     converges
>      >>> to VERY bad R and T matrices, rotating the frames and
>      >>> the warping the images drastically.  I've tried several times, with
>      >>> no luck.
>      >>>
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