Important clarification/qualification on one of my assertions.
In a new session, with freshly loaded pristine images, GUI will indeed give an error if one tries to use "Align Selected Cameras".
(I was mistaken about this point, my power user who showed me this working, wasn't working with a completely clean slate. She has been working with some scenes that had some initial processing, that was strategically aborted and "Reset" via the interface so it "appeared pristine" when it was not.)
So here's how my Power user manually gets to place where she can process heavy sessions involving 8,000 50 Mp images and do manual "Align Selected Cameras" as follows. (I share because I think it is an interesting and insightful technique for breaking through huge solves.)
0) Start with a strong machine with 120 Gb ram, lots of cores, and strong graphics card such as Titan-X
1) Into new session load 8000 images.
2) Manually (via GUI) run "Align Photos" and let it
a) Detect points (which takes her about an hour)
b) Matching Points (which takes her about an hour)
c) Finding Pair (which goes fairly quickly)
d) it starts the section "Estimating Camera Locations" but she could leave it in this step more than a week with no apparent signs of progress because there is something quite non-linear in this step, So she aborts Manual processing when it enters this phase.
3) Then she saves out the scene in this state.
4) Now, you can select some sane number of images (50-100) and run "Align Selected Cameras" on them a group at a time,
and you eventually get all 8000 cameras aligned and you save that scene to file. (This is the part I'm trying to Automate via API script)
We plan to use our standard tools to do these later steps (but I'd be lying if I said we have completed these for solves over 2500 images thus far.
5) Then we plan to standard Chunking tools to break it into between 30-50 sections and save
6) Then we plan to leverage Network Cluster batch processing of the Chunks to generate dense point Cloud.
7) Generate Model
Merge chunks
9) Final Texture and output.
-Jay-