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David 2.3.4 Green lines on calibration

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

David 2.3.4 Green lines on calibration

Postby Eric Lagman » Thu Apr 23, 2009 4:39 pm

With 2.3.4 there are some changes to the calibration feedback in relation to green lines. "If it succeeds, it shows the calibration error (difference between model and reality) as short green lines. For each marker, there is a small difference between its real pixel coordinates (found in the camera image) and its model position (3d coordinates projected into the camera image according to camera model parameters). These lines are stretched by factor 10! So if you have a 10 pixel long line, this means the calibration marker is 1 pixel away from where the camera model thinks it should be." It would be nice to know if this means I will have problems further along when I try to align my scans. A screen shot of what a good green line calibration should look like would be helpful. Should there be no green lines on a good calibration? Can someone please explain this aspect in more detail. I have attached what the green lines look like on a calibration I did yesterday. Would the attached image shown with green lines visible be acceptable to get an accurate scan from?

Also the announcement for the release was in the general discussion area. It might make more sense to have an announcements category in the forum with a sticky for releases so that people can discuss the changes in each update.
Attachments
Calibration-Green-Lines.jpg
Eric Lagman
 
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Re: David 2.3.4 Green lines on calibration

Postby Simon » Thu Apr 23, 2009 6:50 pm

Hi Eric,
shorter green lines are better. I guess that there is something wrong with position of the double marker (rotated eight) in the lower right.

BTW: It is better to use smaller black rings around the white markers. These black rings doesn't reflect the laser light very well, which might influence the laser plane estimation. You can use smaller black rings, you just have to connect both rings in the lower right with a black line (like a glasses frame instead of a roteaded eight). (Hope it becomes clear what I mean :) )
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Re: David 2.3.4 Green lines on calibration

Postby Eric Lagman » Thu Apr 23, 2009 7:23 pm

Simon wrote:Hi Eric,
shorter green lines are better. I guess that there is something wrong with position of the double marker (rotated eight) in the lower right.

BTW: It is better to use smaller black rings around the white markers. These black rings doesn't reflect the laser light very well, which might influence the laser plane estimation. You can use smaller black rings, you just have to connect both rings in the lower right with a black line (like a glasses frame instead of a roteaded eight). (Hope it becomes clear what I mean :) )


I see what you mean about the rings. I will try to make them smaller and have a black bar go across between them, and see what that does. Could this be causing the black dots at position 11 and 16 to be so far off? It is the 4:3 calibration panel from this thread that is scaled up x2 viewtopic.php?f=1&t=242

I guess it would be good to know what else I can do to make the green lines smaller. Is it that my corner is not precise or level enough, or simply to do with the issue with the black circles being too large? What other factors can contribute to the green lines being long?
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