The eposcorr
task reads the X-ray source positions from an input
fits-file and correlates those with the positions from an optical source
catalogue.
The correlation algorithm checks whether there are offsets in RA and DEC
which optimize the correlation. To do this a particular statistic is used and
its value calculated for a grid of 30x30 offset values with a resolution, which
can be controled by input parameters. If demanded a similar grid search
is done for roll angle errors. In that case, first a 3dimensional grid search
will be done and then several iterations with alternating RA/DEC offsets and
rotational offsets are made.
The optimum offsets are then used to correct the
input source positions which will be added as seperate columns to
input X-ray source catalogue.
