This task needs as input, in addition to the spectrum and detector map, the position of the source in question. This is currently used to determine the effective area (7.1), to calculate the encircled energy correction (7.5), to compute bounds for the flat and psf-type internal detector maps, and to construct the psf detector map distribution.
The task gets this information from one of two sources: from the centre of the source region in the input spectrum (if the parameter withsourceposfalse), or explicitly from the user (withsourcepostrue).
If the latter, the user can choose to specify the position in one of four coordinate systems: EQPOS, POS, TEL and DET. The coordinate system is specified through the parameter sourcecoords. The actual coordinates of the source can be inputted though the parameters sourcex and sourcey.