q_identify_src calculates the distance between each pair consisting of an expected catalogue source and a source found in the FOV by the ISSW. This distance and the error radii of the sources are used to calculate the relative distance, . It is therefore essential that the quoted position error has a meaningful value. The relative distances are then stored in an array. Two new arrays are then created one ranking each catalogue source with relDist (the largest value of relative distance considered when matching sources) for its proximity to each found source, and the other ranking each found source with relDist for its proximity to each catalogue source. These two arrays are compared and five classes of source matches are found:
In the case of the two ambiguous categories (Multiple and Confused) the program makes no attempt to separate sources further or resolve conflicts between various possible matches - this should be done by a human. More details on the format of the output result is given in Appendix C.6.2.