det_index_mask

NOTE: A2D_INDEX_MASK is bytarr(27) which should be all 1s. The user should never set this. Selection is done through the following parameters for each type of object:

For Imaging:
DET_INDEX_MASK - bytarr(9,3) for the 9 detectors, 3 harmonics. Set to 1 to select.
FRONT - If set, then use front segment.
REAR - If set, then use rear segment.

For Spectrum and Lightcurve:
SEG_INDEX_MASK - bytarr(18) first 9 are for front segments of the 9 detectors, second 9 are for rear segments.
DET_INDEX_MASK - bytarr(9) for the 9 detectors. If set, selects front and rear segments
NOTE: Use SEG_INDEX_MASK or DET_INDEX_MASK, not both

For SRM :
USE_SEGMENT - bytarr(18) controls the detector segments used (first 9 front, second 9 rear) if using the SRM object directly. If creating the SRM through the spectrum object, use_segment will be set internally to be the same as seg_index_mask, so setting use_segment has no effect.