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Feature Requests / Re: Calibration and camera orientation only with (coded) circular targets
« on: January 25, 2018, 08:48:30 PM »Hello !
You should be able to calibrate your camera at first, by define a high marker accuracy (0.01pix) and a super low tie point accuracy (1 000pix).
And then, re-inject that calibration (and fix it) in a normal optimize project (marker accuracy 0.1 pix / tie point accuracy 1 pix) to go further in the workflow !
Hello Yoann Courtois,
yes, I'm aware of this solution, but I was not sure whether PhotoScan uses the variances in order to weight the observations like it is done in weighted least squares. Thanks for pointing it out, it is indeed a quick fix.
Still, in this case the optimization process will use all points in order to create the normal equation matrix. By omitting several 100 or 1000 points it is possible to reduce the computation time in future versions.
Nevertheless, I guess a well-cleaned tie point cloud would give you the possibility to get a longer polynomial distortion model (using k3-k4 & p3-p4), whereas using only targets would give you, maybe a more accurate, but a shorter polynomial distortion model (only until k2 & p2)
At least in industrial photogrammetry there is no need for many coefficients. In most cases the lenses have a quite low distortion (unless it's a special lens like fisheye which need a special treatment anyway) and are well calibrated with 3 radial and 2 asymmetric coefficients. If necessary, one can take 2 affinity coefficients into account. For some special cases, 2 distance dependent coefficients can play a role. If we sum this up, even the worst case produces 12 unknowns (c,x0,y0,r1,r2,r3,b1,b2,c1,c2,d1,d2). Given a usual photogrammetric calibration board with roughly 1000 targets, there is enough over-determination in each image to reconstruct the distortion.
Apart from that, I'm not aware that fourth taylor-elements had any improvement when calibrated scales (and not the reprojection error) has been used to judge the accuracy.
Greetings