Comments

• The atthkgen output file is accessed by attcalc for the mean and median pointing values over the observation (nothing else, when attitudelabel=ahf, attcalc calls the OAL anew). If this file (default name: atthk.dat) doesn't exist in the current directory, a warning message is given, and no PNT attributes are propagated. A boolean parameter withatthkgen exists to determine whether the task should use any atthkgen output file.

• It is still unclear at present how the OM tracking history file will look, and how the attitude information will be accessed from this file (perhaps through a combination of omatt and OAL_getAttitude).

• The parameter imagesize (default 0.36 degrees [= 21.6 arcminutes]) is needed to define the range of the X and Y coordinates and all the WCS attributes. For normal pointings the default value should be used. Larger numbers can be used for instance when constructing a dataset over several pointings over a large field.

• The `position angle' used is in actuality an `astronomical position angle' (see XMM-MOC-TN-0109-OAD and INT-SYS-FD-TN-0004-OAD). This angle is counted from the celestial north in the mathematically positive sense around the axis pointing from the object towards the observer (i.e. anticlockwise from the observer's point of view, looking towards the sky). This is now in line with SciSim.