====== gsm.py ======
BBS needs a local sky model of the observed field. This sky model is stored in a source table created by [[makesourcedb]] from a text input file.

The script ''gsm.py'' can be used to extract known VLSS sources in the observed field from the GSM and store them in a text file that can directly be used as input by ''makesourcedb''. The parameters for the script need to be given at the command line. The spatial selection can be done using a cone in RA,DEC to be given in J2000.

The sources found will also be extracted from other catalogs (NVSS, WENSS) which are used to fit a spectral index.

By default each source will be its own patch (see [[makesourcedb]]), but using the ''-p'' option it is possible to create a single patch for the sources found.

The command
  use MonetDB
has to be given first in order to make it work well.

=== Cone selection ===
''gsm.py [-p patchname] filename ra dec radius [vlssFluxCutoff [assocTheta]]''

| ''-p patchname'' | if given, all sources will be given the same patch name |
| ''filename'' | the path-name of the file to generate |
| ''ra''       | the RA part of the cone center (degrees) |
| ''dec''      | the DEC part of the cone center (degrees) |
| ''radius''   | the radius of the cone (degrees) |
| ''vlssFluxCutoff'' | minimum flux (Jy) of VLSS sources to use; default = 4 |
| ''assocTheta''     | uncertainty in matching (degrees); default = 0.00278 (10 arcsec) |


=== Output file ===
The generated file is in the ''makesourcedb'' format. The following fields are extracted:

  * source name
  * source type (POINT or GAUSSIAN)
  * RA and DEC
  * Flux I, Q, U, and V (the latter 3 are currently always 0)
  * Major and minor axis and orientation(for gaussian sources)
  * Reference frequency
  * Spectral index

=== Example ===
<code>
  gsm.py /home/username/field1.src 23.175 45.978 1 0.1
</code>
searches in the WENSS catalog using a cone of 1 degree around (23.175, 45.978) degrees.
VLSS sources with a flux >= 0.1 Jy are selected. Implicitly ''makesourcedb'' will create a patch for each source with the same name as the source. Note it is possible to tell ''makesourcedb'' to add a prefix and/or suffix to this patch name.

<code>
  gsm.py -p grp1 /home/username/field1.src 23.175 45.978 1
</code>
searches in the WENSS catalog using a cone of 1 degree around (23.175, 45.978) degrees.
VLSS sources with a flux >= 4 Jy are selected. It will create a line defining patch ''grp1'', where the patch center is the given RA/DEC and its brightness is the summed fluxes. All sources found will belong to this patch.