I was writing a blog post about the architecture of a system I built when I found a bug in it. This is that bug, and the much more interesting thing standing behind it.
The system ingests mobile mapping surveys — LiDAR trajectories with spherical photos along them, driven along roads. The files arrive in whatever coordinate system the surveyor was working in, which in this part of the world is not a settled question. So the upload form asks the user to pick one:
SOURCE_SRID_CHOICES = [
(32634, 'UTM zone 34N (EPSG:32634)'),
(31277, 'Gauss-Kruger zone 7 (EPSG:31277)'),
