Initialisation

• From parameter settings and the relevant attributes in the spectral file, set the state of the arfgen data server before processing is performed. For example, if a detector map is specified, read in that detector map. If a particular factor is requested to be included in the ARF by the user, set the data server (ie create the relevant objects) to provide that correction. Also perform various checks, such as ensuring that the correct global attributes are present in the spectrum dataset, and ensuring that the extents of the selected regions lie inside the bounds of the detector map.

• Convert the input detector map into a pixel list, and filter this using the Data SubSpace information stored in the input spectum dataset as detailed below. The result is an internal, filtered detector map that is used in the subsequent processing.
  • From the detector map, generate a table containing the columns DETX, DETY and VALUE, describing the DET coordinates and value for each pixel in the detector map.
  • Add a dummy TIME column (required by attcalc, although not used directly, as attcalc is called with attitudelabel `user`. )
  • Run attcalc on table, generating sky (X, Y) columns
  • Get the DSS information from the spectrum dataset, and 'project' this information onto the planes that contain the POS and the DET axes pairs.
  • filter the table using the projected DSS information.