In nearly all cases, rgssources requires information from the CCF. (The exceptions are trivial cases such as running with filemode=`modify' but with both addusersource and withepicset = `no'.) Because the exceptions are insignificant and involve complicated logic to disentangle, it has been made mandatory to supply a CCF to the task. The location of the CCF is pointed to in the usual way, ie via the environment variable SAS_CCF.
The CCF interface needs to know whether the instrument is RGS1 or RGS2 in order to provide the correct boresight etc. Although the instexpid parameter has not been made mandatory, the task will fail with an error if the information is not ultimately available. See the algorithm section 7 for details of the way the task attempts to deduce the instrument.
The task may also require information from the ODF summary file, in which case the variable SAS_ODF must be set before running the task. This information may be necessary for one of two reasons:
Every attempt has been made to avoid this requirement where possible and thus cater to the user who does not have the entire ODF at their fingertips.
XMM-Newton SOC -- 2023-04-16