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Help with calibration setting

The place for questions, problems, comments and tips regarding the camera calibration.

Postby Sven » Sun Oct 14, 2007 10:28 am

If DAVID finds the same camera again, it assumes that the camera has not been moved and uses the calibration parameters from config.xml.
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Tobias, I'm a little confused about your rotations...
Let me make some points clear, just to make sure:

If you rotate BOTH camera AND background by 180°, so that the double point stays in the bottom-right corner in the camera image, everything should be fine and you need not change the calibpoints.dat file.

If you rotate only camera OR background, you must change the calibpoints.dat file. It is important for scanning with DAVID that the YZ-plane is visible in the left part of the camera image, and the XY-plane in the right part of the image. If you do that, it is OK that the double point may be in any corner of the image; but it is necessary that the order in calibpoints.dat remains the same (first point is the double point and so on).

(If you do "minuscorner scanning" like discussed in http://www.david-laserscanner.com/forum ... .php?t=133, things may be different.)
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Postby MagWeb » Tue Oct 16, 2007 11:20 am

Ok

now I have this problem too:

Its a problem reloading calibration done in scale of 30

I´m calibrating using to seperate planes 16mm thick, 30% pattern fixed on it. (the two rows towards the corner are quite near to each other).
So, for scale is half of 60 (calibpoints.dat normal scale) I added 32 to the X and Z values where they are equal Zero, for the points are not on the zero planes any longer. (this should be right)

So if I calibrate with the 30mm scaled pattern, telling DAVID that scale is 60mm - everything works fine (calibration and reloading).
But if I calibrate with the 30mm scaled pattern, telling DAVID that scale is 30mm - calibration works, config.xml is changed (also the scalevalue in it)
but the reloaded result is like the cam zoomed in the points (see attachment). The scale value appears right (30).

The same happens using normal calibpoints.dat with pattern fixed on normal planes

Gunter
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Scaleproblem.jpg
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Postby Sven » Tue Oct 16, 2007 5:10 pm

Hello Gunter,

Congratulations, you have found a bug. ;-)
Thanks for reporting!

The bug appears when the scale value is not 60 and DAVID is restarted after calibration. In that case DAVID "forgets" to scale the 3d points before showing them as red crosses. The bug affects only the red crosses on screen, not the calibration - it is correct anyway.

I have fixed the bug, so it will be repaired in the next version.
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Postby chris8677 » Tue Oct 16, 2007 9:58 pm

Sven wrote:Hello Gunter,

Congratulations, you have found a bug. ;-)
Thanks for reporting!

The bug appears when the scale value is not 60 and DAVID is restarted after calibration. In that case DAVID "forgets" to scale the 3d points before showing them as red crosses. The bug affects only the red crosses on screen, not the calibration - it is correct anyway.

I have fixed the bug, so it will be repaired in the next version.


Hello Sven,

So, how can i keep my calibration? I am using 22.5 scale. So should I calibrate using scale 45? will that not change the scanning?

Thanks.
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Postby chris8677 » Tue Oct 16, 2007 10:06 pm

I think I got it. The calibration remains same. Only the red cross on the screen does not stay on the calibration patterns. I scanned with the same setting and it worked. Thank you Gunter and Sven.

this will save a lot of time... :D

Just one more question, since the calibration doesnot change after restart, if I do not change the position of camera, can I remove the calibration corners for next scans? And recalibrate every once in a while.

Thanks.
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Postby Sven » Tue Oct 16, 2007 11:51 pm

You can remove the calibration pattern (black points) on the background, but of course you may neither move nor remove the background planes because they are required for scanning!
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