Working with camera station metadata

[bigben]

I ran a larger test using a pano rig as a camera station over the weekend.  First pass around the building with a 35mm lens (24-70mm zoom) and then a second lap closer to the building with  a 15mm full frame fisheye. Ran a few quick projects (https://skfb.ly/DnvY, https://skfb.ly/DnKX) with some of the images and learnt a few things.
1. GPS occasionally drifted while shooting, so embedded GPS metadata was a bad idea as it threw out the alignment.
2. Grouping the cameras manually is a bit of a pain. I at least had the forethought to shoot an image of my hand in between groups... most of the time.

Given those two, I obviously need to do some preparation of the metadata before I add the images, so I'm wondering what the best way of doing this is.

  Can I create a structured file to import the images and assign them to groups?  I tried exporting the cameras from a project with camera stations configured. Importing that file loaded the images fine but they weren't in groups. The number of images within a camera station varies so scripting the grouping probably isn't practical.

What to do with the GPS?  Clear the GPS from all but the first camera in each group (or would all cameras need coordinates set the same)... average the coordinates within a group ... If I can import the groups via a metadata file I'd probably handle that externally

Any suggestions/tips?

[bigben]

Leaving only a single camera with GPS in each camera station didn't seem to work.  Alignment failed after 13 cameras. Not sure why... possibly differences in GPS altitude?  Deleted all GPS and the alignment is running slowly (as expected). The result (https://skfb.ly/D6yJ) is very promising though.  Plenty to think about just with that.

  Wondering if every camera should have (the same) GPS settings within a camera station?

[Alexey Pasumansky]

Hello bigben,

I don't think Reference preselection will work in you case, as it was designed mostly for near vertical survey (and oblique aerial imagery starting from version 1.1, if Ground Altitude parameter is used and Yaw, Pitch, Roll data for cameras is present).

So for you project GPS coordinates could be only used for model referencing and optimization.

[bigben]

Thanks Alexey

I've disabled pair preselection, but I thought GPS helped it with providing starting positions for the images.  Working without GPS in the EXIF (or clearing it after importing) will simplify the workflow somewhat and using camera stations with an fov of 90° appears to require much less optimisation than working with single images of similar fov.
 
For georeferencing the scenes I take a reference pic looking vertically down at markers I've chosen, and averaging GPS position over time to improve the accuracy.  The pic makes it easier to find in the scene.

That just leaves me with the grouping step.  For panoramas I record that start and end times for shooting a panorama (= camera station) in a Filemaker Go database on my phone.  I then transfer all of the images and data to my PC and get the database to generate a script to sort the images automatically into folders for each panorama.  It would be great if it was possible to do a similar thing with Photoscan, with either a XML import to define camera station groups or a python script to explicitly create the groups and move the cameras into them... so much to learn