beam_center_x/y is the PONI - the foot of the perpendicular from the sample - so on a tilted
detector it is not where the beam lands, and the two are distance*tan(tilt)/pixel apart (~8 px on
a real in-house setup). A consumer that wants the beam position, which is what most of them mean,
had to redo the tilt arithmetic or get it wrong.
Add optional direct_beam_x/direct_beam_y to StartMessage, filled from the geometry's own
GetDirectBeam_pxl() so there is no second formula, and put them at the top level of the CBOR start
map beside beam_center_x/y. Optional keys, so a consumer that does not know them skips them.
No _pxl suffix: the stream2 neighbours (beam_center_x, pixel_size_x, detector_distance) carry none
and the units are in docs/CBOR.md. The API's calibration schema spells it direct_beam_x_pxl because
its neighbours there are beam_x_pxl - same quantity, each matching its own neighbourhood.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01EFEJG6WBQv8th4UJFNe53N
leonarski_fandClaude Opus 5
336fafffd0