Hi Igor,
Yes i meant using the Pair pre selection Generic. Sorry i should have clarified this. In my experience the alligenment is not worse or better if using the pair pre selection. This does however applies to a aerial data set with plenty of overlap.
I did notice however with some data sets that have less ideal overlap or difficult geometry that disabling the pre pair selection helped in getting more images aligned. But this is more a sign of that either need to add more pictures, get more overlap or re-shoot it entirely.
Conserning the speed increase, it can be pretty drastic, 10x or more is possible (i think). Also depends on your dataset. It takes relatively long to compute the pre selection but after that the actual alignment is really quick. Have a look below at the results i got using a aerial dataset.
Total cameras: 4.000
Effective overlap: 6.7
Reprojection error: 1.4
Alignment paramters:
Accuracy: Medium
Pair preselection: Generic
Key points: 40.000
Tie point: 1.000
Matching time: 14 hours 40 minutes
Alignment time: 9 minutes 37 seconds
I'll do a quick test with a smaller datset to give your a idea of the time savings that can be had using the prepair selection. I will update this post with the results of that test.
Update
Dataset with 38 35Mpx images
Pre pair selection disabled:
Camera's matched 38/38
Effective overlap: 5.46
Reprojection error: 0.96
Alignment paramters:
Accuracy: Medium
Pair preselection: disabled
Key points: 40.000
Tie point: 1.000
Matching time: 3 minutes 4 seconds
Alignment time: 1 seconds
Pre pair selection enabled:
Camera's matched 38/38
Effective overlap: 4.5
Reprojection error: 0.84
Alignment paramters:
Accuracy: Medium
Pair preselection: Generic
Key points: 40.000
Tie point: 1.000
Matching time: 1minutes 30 seconds
Alignment time: 1 seconds
New dataset with 301 Camera's
Pre pair selection disabled:
Camera's matched 301/301
Effective overlap: 8.98
Reprojection error: 1.28
Alignment paramters:
Accuracy: Medium
Pair preselection: disabled
Key points: 40.000
Tie point: 1.000
Matching time: 2 hours 26 minutes
Alignment time: 27 seconds
Pre pair selection enabled:
Camera's matched 240/301
Effective overlap: 5.94
Reprojection error: 1.1
Alignment paramters:
Accuracy: Medium
Pair preselection: Generic
Key points: 40.000
Tie point: 1.000
Matching time: 19 minutes 25 seconds
Alignment time: 31 seconds
Oke so with Pre pair selection enabled it's a lot quicker! Using the same data and the same parameters, it's 7.3 time quicker then disabled (2 hours 26 minutes = 146 minutes -- 146/20=7.3)
There is only one drawback i found, using the pre pair selection enabled it would match 240 camera out of the 301. And disabeling the pre pair selection it would match all of the cameras. This is probably due to the outer camera's not having enough overlap with the rest of the camera's.
So there you have it, it's clear that it is a lot faster but it might not solve all of your camera's. (because of insufficient camera overlap at the edge of the model.)