Finding calibration frames

When a frame is reduced and files as a calibration, it is added to an index file located in ORAC_DATA_OUT named after the type of calibration, e.g., dark frames are filed in index.dark. When the pipeline is run up and needs a calibration frame but has not been asked to reduce one in that session it will look in the index files for one that may have been reduced at a previous time.

If the pipeline is unable to find a suitable calibration it will complain vociferously and exit. This may seem extreme, but remember that ORAC-DR is designed for online use at an observatory. If an observer has not taken appropriate calibrations, we wish to point it out to them in the strongest terms because we do not want them to end up with un-reduceable data.