Slamtec devices count their angle clockwise viewed from the top
(Interface Protocol spec; the official rplidar_ros node mirrors the
angles for the same reason), but the decode used the raw ascending
angles as CCW for a right-side-up unit and mirrored them for an
upside-down one — exactly backwards. Field-verified 2026-07-23: a
right-side-up C1 produced a left-right mirrored sweep against a
verified right-handed reference lidar.
Now: right-side-up mirrors (angle' = 2π − raw, nodes walked backwards);
upside-down uses the raw ascending angles, because the physical flip
already reverses the apparent rotation. The mountedUpsideDown flag
finally carries its true physical meaning.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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