acts: bug: interpolation out of bounds with ATLAS B-field map

Using the propagator with the ATLAS B-field map can give error messages:

TrackFinding ERROR Step failed with MagneticFieldError:1: Interpolation out of bounds was requested

This can give a lot of messages: ~259 MagneticFieldErrors per ttbar+μ=200 event, each of which produces 2 errors, and 4 warnings (1.6 GB logfile for 1000 events)!

This error is due to InterpolatedBFieldMap::getField() called for a position outside the mapped ATLAS B-field

• The ATLAS B-field is mapped in (-10000,-10000,-15000) to (10000,10000,15000)
• but I see, calls for e.g. getField({-2849, -2486, 54450})
  • These are presumably for extension of seeds that will eventually be cut or rejected

#1467 removes these error messages by trying to return the edge-bin values instead of giving an error. That is still WiP because I couldn’t yet get it to pass the unit tests: seems to work with B=(0,0,0) at the edges (as for ATLAS), but not otherwise.

Even if that can be resolved, the question remains: why is getField() called for points so far outside the detector? @Corentin-Allaire suggested (ACTS-ITk meeting) that the world volume is too large. If so, it may be an ATLAS-specific error, but I hope it’s OK to discuss here.