XMM-Newton Science Analysis System
omsrclistcomb (omsrclistcomb-2.23) [xmmsas_20211130_0941-20.0.0]
If the parameter alignaxes is set to true (default) then the program
will try to shift the RA/DEC origins of each source-list file to a common
origin. This facility is included to try to remove any slight misalignment between
the input source coordinates of each input source-list files due to small OM
pointing errors. Omsrclistcomb uses the astrometrically uncorrected
celestial coordinates to produce the merged source-list, and this routine
can reduce mis-matching and improve the astrometric accuracy.
The routine works in the following way:
- Get a list of the number of unique “windows” in the input source-list files
(a window has a unique set of WINDOWX0, WINDOWDX, WINDOWY0, WINDOWDY and BINBPE
- For each window do the following:
- Find the source-list that has the most sources in that window.
- For each other source-list in the window, compute the RA/DEC offsets
that are needed to be added to their RAs/Decs to align with the reference source-list coordinates.
- Compute the mean offsets.
- Subtract the mean offsets from the RA/Dec coordinates of the reference source-list.
- Subtract the mean offsets from the computed offsets.
- Add these offsets to the RAs/Decs of the other source-lists.
- having aligned the source-lists of each window with a reference source-list, the
algorithm then tries to align the windows using the following algorithm:
- Loop from i=1 to i=the number of windows
- Loop from j=i+1 to the number of windows
- If all the windows have been aligned exit the routine.
- If both windows have been aligned move on to the next j
- Otherwise, try to align window j with window i, by matching the source-list in window i having
the maximum number of sources with the source-list in window j having the maximum number pf sources.
- if neither window has been aligned, or window j has been aligned, add the offsets to the RA/Decs to all
the sources in the source-list files of window j. Record that windows i and j have been aligned and move on to the next j.
- If window j has been aligned, but not window i, subtract the offsets from the RA/Decs to all
the sources in the source-list files of window i. Record that windows i has been aligned and move on to the next j.
XMM-Newton SOC -- 2021-11-30