This is more out of interest for the inner workings of Photoscan than anything else, but I've repeatedly found myself in a situation where Photoscan can't align a couple of cameras, but can align these cameras among themselves if I start with them.
Which makes sense, of course.
(Group meaning simply group, here, not any special function of Photoscan.)
But more interesting and the point of my question: Sometimes there are photos which will align with either of the groups, but not at the same time. (So if photo B aligns with group A it's no longer possible to get group C to align with photo B, which is possible if photo B is on its own.)
The photos are of pretty poor quality, so it's not a big deal and the obvious answer is to shoot better and more photos, I just wonder what might be the problem, here. There is no zoom or movement of the object itself happening, as far as I can tell. (Unfortunately I can't share the photos.)