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Author Topic: Using lens model with GCP alignment  (Read 1829 times)

aneverman

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Using lens model with GCP alignment
« on: March 16, 2016, 02:17:52 AM »
Hi all,

I am using PhotoScan for SfM models. I have 12 GCPs in the scene which have been surveyed using a total station. I have been adding the lens calibration file from AgiSoft Lens to the project prior to photo alignment. I then add the GCPs after sparse cloud generation, update the georeferencing and optimise the cameras.

My question is: is it with importing the lens model or do my GCP registrations essentially "over-ride" the lens calibration loaded from a file? Or does the lens model help with initial alignment and then get over-written?

Thanks,

Andrew

James

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Re: Using lens model with GCP alignment
« Reply #1 on: March 16, 2016, 01:41:02 PM »
Yes it will get overwritten unless you check the 'fix calibration' box in camera calibration screen.

Even unchecked it should help alignment, as it provides a better starting point from which to refine the parameters. it is subsequently overwritten, but hopefully by a more refined distortion model, rather than a worse one.

In short check the 'fix calibration' box if you are completely confident that your imported calibration file is as good as it can be.

*Edit: the above refers only to camera alignment. I'm not sure what happens if you then add GCPs and run an optimization with 'fix calibration' checked. It could be easily tested by checking the 'fix calibration' box, running the optimization and then looking to see if anything changed in the adjusted tab within camera calibration.

**Edit 2: I just tested it. With 'fix calibration' checked you can not optimize any camera distortion coefficients as they are disabled, so they stay the same as when you imported them, but photoscan still modifies the camera positions and orientations to improve the alignment based on your GCP coordinates.
« Last Edit: March 16, 2016, 02:00:03 PM by James »