Checking your calibration

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avogra
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Checking your calibration

Post by avogra »

I was asked a question about lenses via PM and I don't know if I ever posted my way to check for proper calibration here. Maybe some part of it is usefull for others too?

Two things:

Debug-Console: I find this very usefull, because after calibration, David writes the results of all of its measurements into the console. Most important: The angle between the calibration patterns. This helps a lot to quickliy check for a correct calibration or to verify the effect of changes to your setup or preferences. If you know exactly the angle between your panels, you can check that David has got the same understanding of the angle ;)
This revealed, that the setting "CompensateAngleBetweenPattern" is highly unreliable. Without modifying anything, the calculated angle jumped by more than 0,3° if doing multiple calibration runs.
You can enable the console in advanced setings -> Service -> ShowDebugConsole

Verifying Calibration: I think I wrote about this in the official HP forum already. Maybe it is helpful anyway. What I do to verify a correct calibration: I have a reference angle like this https://www.amazon.de/dp/B00VATEQMS/ref ... 1zbGD5CH64. I whitened the inside to have a nice surface for David. Then after calibration, I scan the angle, clean it a bit and export as stl-file. This I load in geomagic verify viewer, where you can measure the exact angle. Only when I measure better than 90° +- 0,1°, I have a good calibration. The measuring in verify viewer is a bit awkward unfortunately.
In David I adjust the following settings:
Advanced Settings -> Calibration -> AutoDetectCalibCornerSetup: uncheck
Advanced Settings -> Calibration -> MultipleCameraOptimization -> CompensateAngleBetweenPatterns: uncheck
Advanced Settings -> Calibration -> CalibrationPanels -> RightCalibrationPattern -> rot_y: adjust here until angle is correct
With rot_y, you can manually compensate for calibration panels that are not exactly square. I have to enter 0.3° to get perfect 90° measurements in verify viewer, so panels seem to be off whopping 0,3°. Still scans align nicely usually.

I think the main flaw of my current setup is, that is not rigid enough. So if I move it around, it bends a bit and results are distorted. Maybe you want to check that too?
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