Photoscan 9.0 produces broken camera tracks

[adjablon]

Hi,

I'm using Photoscan on an academic project and noticed a peculiarity with Photoscan 9.0. The camera tracks produced after the point cloud is generated are different between versions, and more problematically produces broken camera paths in 9.0

I uploaded an image to imgur showing the problem. Is there any explanation for this? Or any solution other than relying on an older version of the software?

http://i.imgur.com/EdmnJ36.jpg?1

[RalfH]

Is this the only time this happened, or do you have this problem repeatedly? When I have misaligned camera groups (but that has happened in all versions, usually because of poor texture), I usually reset alignment for those which appear wrong and re-align only those cameras. This usually works, but sometimes only if it is done sequentially (re-align photos one by one).

[adjablon]

Hi RalfH,

I ended up doing a re-alignment on the set of photos where the problem occurred and it created a uniform camera track this time. So it seems something was buggy when I tried to run the whole set of photos (it's something around 1200 images). I'd have to re-run alignment on the whole set of images to see if it replicates the problem, but that would take about 10-12 hours or so.

Could Photoscan be having problems when large sets of photos are being processed, at least in 9.0? I've never had issues when running 8.4 (I just recently upgraded upon realizing how old 8.4 was).

[RalfH]

I have seen misalignments in all versions, not just in 0.9.0. As for the problem occuring only with large projects, I don't have this impression. I have had misalignments with 30 images and have had perfect alignments with 700 photos in the first run. I think this might simply be due to more photos meaning more possibilities where things can go wrong (e.g. higher chances of some photos having poor texture).

Regarding the time you need to re-align all photos: most of the processing time in the alignment  is used for (1) finding points, (2) selecting image pairs if you have chosen "pair preseletion" and (3) matching points. For large numbers of images, pair preseletion already reduces processing time a lot. Also, after you have run photo alignment once, PhotoScan remembers the matched points. So if you then select all or some images and then right-click "re-align photos", PhotoScan will use the matched points and recalculate only the photo alignment itself (i.e. perform the actual bundle adjustment). This takes only a fraction of the time you would need for the complete alignment. On the other hand, using the menu item to align photos will start the entire process.

Also, if you de-group the cameras under "camera calibration" (i.e., choose "separate"), this can help to improve alignment, in particular if anything moves within your camera/lens system (e.g. focussing, optical image stabilisation).

As a final note, right-clicking on one image and choosing to re-align that one image will cause PhotoScan to re-align that one image to the existing project AND to re-optimize (but I believe not truly re-align) the bundle adjustment and camera calibration for the entire project (you can see this when comparing refined camera calibration parameters before/after doing this).  This can sometimes be helpful when you see minor flaws in your final model.

[bisenberger]

Some good information there RalfH. Thanks for posting this.