OBSCON
OBSCON designates the observational conditions (or “layer”) in which targets
will be observed. Possible values include “dark” and “bright” for dark-time and
bright-time targets, respectively. Under each observing condition, targets are
stored in files that are grouped by (nested) HEALPixel number in filenames that
resemble {PHASE}targets-{OBSCON}-{RESOLVE}-hp-{HP}.fits . For
targets that are not resolved RESOLVE is omitted from the filename. For
targets that are part of the DESI Main Science Survey PHASE is omitted from
the filename.
There is a special case of secondary targets that were not merged
with primary targets — these secondary targets have no concept of a “resolve”. Such
“standalone” secondary targets are written to monolithic files with names resembling
targets-{OBSCON}-secondary.fits .