C The ORAC-DR Calibration Selection

An ORAC-DR HOWTO

Description

ORAC-DR has a totally flexible system for controlling the automatic selection of calibration frames. This note describes how it works and how to override it

What happens

The type of calibrations used depend, obviously, on the instrument and the data reduction recipes used. Typically there are three kinds of calibration frames:

ORAC-DR treats the first two kinds rather differently.

Library frames reside ORAC_DATA_CAL and their selection is hardwired either in the instrument class or in a DR primitive. The users are unlikely to be concerned with them unless they want to override them with their own.

Nightly frames are handled in a more complicated way. A DR recipe that generates a calibration frame is responsible for filing it with the pipeline. The pipeline will hand it back to recipes that require calibration recipes according to a set of rules that are defined on a per-instrument basis by the ORAC-DR infrastructure as well as a per-frame basis by the calibration rules files.

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.

Overriding defaults

You can override the pipeline’s selection of calibration frame by using the ORAC-DR -calib command line option. Use this override judiciously, as in general the pipeline does a fine job.

The ORAC-DR -calib command line option is used by giving comma separated key=value pairs (e.g. ’-calib dark=file1,bias=file2’). The following keys can be used for general instruments. Specific instruments may have extra calibration overrides that can be used.

When files are given the extension should be left off. As an example, if you have made a new bad pixel mask and wish to use it with ORAC-DR, the following command would be used:

 oracdr -calib mask=new_bpm