The task clearly needs to know the direction in space of the focal axis of the relevant instrument at the time of the observation of interest. There are three necessary pieces of information: the name of the instrument, the date-time of the observation and the spacecraft pointing direction (attitude) at this time. The task processes these as follows: the instrument identification and the observation date-time are used together to calculate (from values stored in the CCF) the instrument boresight correction at the time of the observation; this correction is then applied to the spacecraft pointing.
There are two ways to pass the `cal' information to esky2det, governed by the parameter calinfostyle:
In order to be able to apply the correct boresight correction, as well as to have access to the instrument specifications, the task requires access to the CCF components relevant to the dates of observation and analysis. This is achieved in the usual way by constructing a cif file with cifbuild and pointing to it with the environment variable SAS_CCF.