align selected cameras

[William Ringle]

I have a general question. I ran a model with 684 photos, going all the way through including creating texture for the mesh model. Took a long time. About 30 of the photos did not align, so I ran align selected cameras, which then aligned about half of the aligned cameras. My question is at what stage am I after doing this? Must I run create dense cloud again (a very long part of the process), or does align selected photos add to the existing cloud, in which case I can go directly to mesh build?

I've asked this before, but why doesn't photoscan do an automatic align check on the unaligned photos after completion of the initial alignment? In other words, why isn't 'align selected photos' performed automatically?

[n@sk]

Chances are that it tried at some point to align these 30 images, individually or at small subsets, with the rest but it failed.
Bare in mind that feature detection is not a deterministic process and that the quality setting also implicitly affects the acceptance thresholds for feature correspondence.
Once you have the sparse point cloud,  it's probably easier to confirm that some of the detected points are indeed reliable matches; thus, half of them were successfully realigned.
For the rest of the images, which were not aligned, an incremental alignment is required before the dense matching.
Depending on the quality of the images within the overlapping areas, you might have to repeat this process so that enough features, which can be matched, are detected.
In some cases you might have to incrementally align some of the images that were aligned successfully in order to generate features that will be detected in the problematic images.
In any case,  you will have to run the dense matching and mesh generation again because the alignment/optmisation only estimates the exterior orientation and does not update the depth maps.