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General / Re: Placing markers increase camera erros after calibration
« Last post by Paulo on July 23, 2021, 06:44:01 PM »hi aag_frei,
it seems the drone flew always facing in same direction (yaw = 20 deg) i.e. not turning when changing flight line (going forward on 1st line, backward on 2nd line, etc..) and this causes heavy correlation between internal parameters (f,cx,cy) and external orientation....see https://www.agisoft.com/forum/index.php?topic=9820.msg58262#msg58262.
From https://agisoft.freshdesk.com/support/solutions/articles/31000158119-what-does-camera-calibration-results-mean-in-metashape- tutorial:
You may have to fix f,cx,cy in initial alignment to get a result.... and then in final adjustment you may unfix....
Also in final optimizaton, I would deselect all cameras as their accuracy (consumer grade airborne GPS) is not great compared to markers and DJI drones have a history of storing wrong altitude (from your info, the drone flew around 25 m AGL which is very unlikely as it corresponds to 0.6 cm GSD).... But if markers were correctly determined using Leica dGNSS via SAPOS RS or VRS, you should get final errors on markers at the cm level not the dm or m level from your current results...
Hope maybe this gets you further along...
PS. you can look at camera.photo.meta["DJI/RelativeAltitude"] to see at what Altitude AGL the project was flown... In example attached the drone was flying at 120 m AGL with an altitude ASL of 138 m....
it seems the drone flew always facing in same direction (yaw = 20 deg) i.e. not turning when changing flight line (going forward on 1st line, backward on 2nd line, etc..) and this causes heavy correlation between internal parameters (f,cx,cy) and external orientation....see https://www.agisoft.com/forum/index.php?topic=9820.msg58262#msg58262.
From https://agisoft.freshdesk.com/support/solutions/articles/31000158119-what-does-camera-calibration-results-mean-in-metashape- tutorial:
Quote
We recommend to review the adjusted values for the cx, cy, b1 and b2 parameters in the Camera Calibration dialog. If the values for the parameters are too large (hundreds or more for cx, cy and tens or more for b1, b2), then it may be reasonable to re-align the data set having these parameters fixed.If you could show the adjusted camera parameters in Camera Calibration window to see if you have some unrealistic values for cx, cy....
Usually the values for cx and cy are around a couple dozens of pixels (or less), as the values are measured from the center of the image. And the values for b1 and b2 are usually not more than a few units.
If the values are hundreds or even thousands - it indicates that the estimation of the calibration parameters is probably incorrect. Sometimes it may be related to the flight mission specifics, for example, if the camera is not rotated by 180 degrees on the neighboring flight lines. You can try to fix the mentioned parameters and re-align the data set having "adaptive camera model fitting" option disabled.
You may have to fix f,cx,cy in initial alignment to get a result.... and then in final adjustment you may unfix....
Also in final optimizaton, I would deselect all cameras as their accuracy (consumer grade airborne GPS) is not great compared to markers and DJI drones have a history of storing wrong altitude (from your info, the drone flew around 25 m AGL which is very unlikely as it corresponds to 0.6 cm GSD).... But if markers were correctly determined using Leica dGNSS via SAPOS RS or VRS, you should get final errors on markers at the cm level not the dm or m level from your current results...
Hope maybe this gets you further along...
PS. you can look at camera.photo.meta["DJI/RelativeAltitude"] to see at what Altitude AGL the project was flown... In example attached the drone was flying at 120 m AGL with an altitude ASL of 138 m....
