Asociation Mode

Similar to SExtractor there is the possibility to run SourceXtractor++ in the so called ASSOCiation mode. In this processing mode the user provides a catalog of target objects as input, and SourceXtractor++ measurements are then restricted to objects matched with those provided by the user.

The association between objects detected on the detection image and user targets is established by measuring the distance between their coordinates.

The relevant parameters for the association mode are:

--assoc-catalog arg                   Path to the file containing the association objects. Plain catalogs in ASCII
                                      or FITS format are accepted.
--assoc-columns arg (=1,2)            Column index in the association catalog  for x/ra,y/dec[,weight].
                                      The index of the first column is 1.
--assoc-mode arg (=NEAREST)           Mode to establish the association between input catalog and the detected
                                      objects. Accepted values are [FIRST, NEAREST, MEAN,  MAG_MEAN,
                                      SUM, MAG_SUM, MIN, MAX].
--assoc-radius arg (=2)               Association radius. The unit is always in pixels of the detection image.

--assoc-filter arg (=ALL)             Association filter. Accepted values are [ALL, MATCHED, UNMATCHED].

--assoc-copy arg                      List of indices of the columns from the input catalog that will be copied to
                                      the output catalog for associated objects .The index of the first column is 1.
                                      Only columns with numerical values can be copied.
--assoc-coord-type arg (=PIXEL)       Coordinate type for the association. Can be [PIXEL, WORLD].

Note that the association mode of SourceXtractor++ is not a forced photometry mode since the objects must be detected on the detection image to establish an association and to trigger the requested measurements. It is also worth noting that even if measurements are only done for the associated objects, these measurements are done taking into account all the surrounding detections, not only those that are associated.