The ccds- and survey- files described on the DR4 files page contain a column bitmask, which is defined as:
|0001||this exposure is flagged in the bad_expid file|
|0010||a zeropoint solution was not computed for these exposures, and so the ccdname disagrees with the hdu number|
|0100||these ccds had outlying values for astrometric or photometric offsets (\(\sqrt(\) ccdrarms \(^2 +\) ccddecrms \(^2) > 0.1\) OR ccdphrms \(> 0.2\))|
The CCDs used by legacypipe can be determined via:
photometric == True AND bitmask == 0
Note that photometric, ccdrarms, ccddecrms and ccdphrms are all columns in the ccds- and survey- files described on the DR4 files page.