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7.4.8.3 MakeCatalog output HDUs ¶

After it has completed all the requested measurements (see MakeCatalog measurements on each label), MakeCatalog writes them in table(s) that are stored into a FITS file. This is necessary because the number of output tables and the metadata that MakeCatalog provides can be numerous. If any of the output tables are necessary in another format (for example plain-text), you can use Gnuastro’s Table program (with executable name asttable, see Table).

This section focuses on the HDUs of the output, for the keywords, see MakeCatalog output keywords. The name of the output FITS table can be given to the --output option, with a recognized FITS suffix (as defined in Arguments). When it is not given, the input name will be appended with a -cat.fits suffix (see Automatic output) and its format (ASCII or Binary FITS table) will be determined from the --tableformat option, which is also discussed in Input/Output options. By default (when --spectrum, --checkuplim or --clumpscat are not called) only a single catalog/table will be created for the labeled objects.

• When --clumpscat is called, a secondary catalog/table HDU will also be created for “clumps” (one of the outputs of the Segment program, for more on “objects” and “clumps”, see Segment). In short, if you only have one labeled image, you do not have to worry about clumps and just ignore this.
• When --checkuplim is called, a HDU is added to the output FITS file and is fully described in the description of this option in Upper-limit settings.

The full list of MakeCatalog’s options relating to the output file format and keywords are listed below. See MakeCatalog measurements on each label for specifying which columns you want in the final catalog.

-C

--clumpscat

Do measurements on clumps and produce a second catalog (only devoted to clumps). When this option is given, MakeCatalog will also look for a secondary labeled dataset (identifying substructure) and produce a catalog from that. For more on the definition on “clumps”, see Segment.

When the output is a FITS file, the objects and clumps catalogs/tables will be stored as multiple extensions of one FITS file. You can use Table to inspect the column meta-data and contents in this case. However, in plain text format (see Gnuastro text table format), it is only possible to keep one table per file. Therefore, if the output is a text file, two output files will be created, ending in _o.txt (for objects) and _c.txt (for clumps).

--noclumpsort

Do not sort the clumps catalog based on object ID (only relevant with --clumpscat). This option will benefit the performance²³² of MakeCatalog when it is run on multiple threads and the position of the rows in the clumps catalog is irrelevant (for example, you just want the number-counts).

MakeCatalog does all its measurements on each object independently and in parallel. As a result, while it is writing the measurements on each object’s clumps, it does not know how many clumps there were in previous objects. Each thread will just fetch the first available row and write the information of clumps (in order) starting from that row. After all the measurements are done, by default (when this option is not called), MakeCatalog will reorder/permute the clumps catalog to have both the object and clump ID in an ascending order.

If you would like to order the catalog later (when it is a plain text file), you can run the following command to sort the rows by object ID (and clump ID within each object), assuming they are respectively the first and second columns:

$ awk '!/^#/' out_c.txt | sort -g -k1,1 -k2,2

--cnl-check

Add an extra HDU to the output of MakeCatalog that contains the positions of every clump as well as the positions of that clump’s nearest clump and the distance between the two (in both units of arcseconds and pixels).