Per-segment absolute registration of the per-tile terrain models
(*_SZXY.tiff: S/Z/X/Y slices) against a 3DEP DEM using the ground_planes
geodetic anchor (lat/lon/alt + qenu with the validated axis adapter
perm(2,0,1) signs(1,-1,-1)). Reports vertical offset (= IMS altitude error
trace; observed -43..+19 m across passes), optional dx/dy/scale search,
robust 2x25% trim. Validated on the pond segment 1763233023_625897:
placement rms 0.17 m at scale 1.0; scale fitting documented as valid only
on temporally stable relief (the 2020-flooded pond trims itself out).
Co-authored-by: Claude <claude@elphel.com>