The data routines are the most important part of the psf system. Given a psf identifier, a detector position in radians, bin sizes and dimensions a data routine returns a 2-D probability array. An offset may also be applied to shift the psf centre from the centre of the 2-D array. It is important to realise that when writing the data routine it could be called with any bin size and not just some default detector pixel size, or multiply thereof. After writing a new data routine evaluate the psf using the CREPSF application using different bin sizes and image extents to check whether the normalisation is being computed correctly. Extra information beyond that supplied as input arguments should be passed using the psf instance data described in the previous section.
The data routine signature is,
SUBROUTINE psf_data_rtn( INTEGER psid, REAL x0, REAL y0, REAL qx, REAL qy,
REAL dx, REAL dy, LOGICAL integ,
INTEGER nx, INTEGER ny, REAL array[],
INTEGER status )
where x0,y0 is the detector position in radians, qx,qy is the offset
from the centre of the output probability array to the psf centre,
dx,dy are the bin sizes in radians and nx,ny the dimensions of
the output array. The integ flag is historical and is not currently
used.