High-level data (catalogs) of a single astronomical source can come come from different telescopes, filters, software (detection, segmentation and cataloging tools on the same image) and even different configurations for a single software. As a result, one of the first things we usually do after generating or querying catalog data (for example, with MakeCatalog or Query), is to find which sources in one catalog correspond to which in the other(s). In other words, to ‘match’ the two catalogs with each other. Within Gnuastro, the Match program is in charge of such operations. The matching rows are defined within an aperture, which can be a circle or an ellipse with any orientation.
Before digging into the usage and command-line execution details (in Invoking Match), it is important to discuss several concepts in detail. If this is the first time you are using Match, please take the time to read these three sections (before Invoking Match) in detail to optimize your usage of Match and understanding its outputs. The first is Arranging match output which introduces how the matched rows should be arranged in the outputs and is determined by the purpose/context of your analysis (there are examples in that section). When you want an “inner” or “full” match, some matches can become ambiguous; in Unambiguous matching Gnuastro’s Match strategy for those is discussed. We will then review the Matching algorithms.
GNU Astronomy Utilities 0.24 manual, November 2025.