Hard to comment on all of this without seeing the data set in detail. 80% overlap should be enough .. that said - if you have tall trees and you are flying over the top of them at the same height - the algorithm will struggle. Firstly the tie points on the trees are all moving (wind) and the distance from the UAV to the top of the tree is substantially less than the distance from the UAV to the ground - ie changing your overlap. The camera calibration is a PDF somewhere. Basically do an orbit around a complex shape and run multipass on the optical calcs. Google contextcapture camera calibration and it will doubt turn up. So with the tie points .. create some near where your are having issues .. nominate in the photos .. re-run the AT. If you are going across vast expanses of crops, sand .. this without much unique detail - you run into issues .. or tops of trees.
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