The catalog descriptor describes how catalog information is to be loaded. It can point to a local catalog (one that lives in the file system) or one that is to be queried over the web.
The catalog descriptor is stored in a text file. The lines are of the form
key => valueThe text file can contain comments. Comments lines begin with the # character.
Loading the catalog data may require additional software. Note that the StarID::SearchCat type of catalog uses the scat WCS Tool. The WCS Tools can be downloaded from
http://tdc-www.harvard.edu/software/wcstools/
1. Here are the contents of a sample star catalog descriptor for querying the USNO B1 catalog over the web:
# Catalog descriptor for USNO B1 over the web. # Note that the StarID::SearchCat uses the scat WCS Tool. type => StarID::SearchCat fields => ID,RA,DEC,MAG,TYPE packed => 0 data => Default catalog/type => Indexed catalog/n => 4 envvar => UB1_PATH location => http://tdc-www.harvard.edu/cgi-bin/scat # a USNO A server: # http://archive.eso.org/skycat/servers/usnoa-server limit => 1000 sort => m3
Note that it provides the URL of an alternate scat server in a comment.
2. Here are the contents of a sample star catalog descriptor for querying the USNO B1 catalog which is stored in the local file system at /catalog/usnob1:
# Catalog descriptor for USNO B1 in a local directory. # Note that the StarID::SearchCat uses the scat WCS Tool. type => StarID::SearchCat fields => ID,RA,DEC,MAG,TYPE packed => 0 data => Default catalog/type => Indexed catalog/n => 4 envvar => UB1_PATH location => /catalog/usnob1 limit => 1000 sort => m3
3. Here are the contents of a sample star catalog descriptor which indicates that the reference objects are contained in a local file:
# Catalog descriptor for user supplied objects in a local file type => StarID::UserCat fields => ID,RA_deg,DEC_deg,MAG,TYPE data => User catalog/type => Indexed catalog/n => 4 path => ./user.cat
Using this type of catspec requires that the file indicated by path contains one object per line; whitespace delimited columns: ID, RA, DEC, MAG, TYPE. RA and DEC are in degrees. ID and TYPE are strings that do not affect whether matching is successful. Here is some example data:
BW64.0320413 278.1938239 26.4173519 10.04 STAR BW62.0315690 278.1260833 26.2875605 11.04 STAR BW62.0315312 278.0138511 26.2678780 11.51 QX BW62.0315660 278.1156484 26.2966887 11.68 GALAXY BW63.0324944 278.0568533 26.3480521 11.71 QX BW63.0325130 278.1059088 26.3247064 11.85 BLEND BW63.0325512 278.2192295 26.3465382 11.89 RALPH BW62.0315721 278.1342799 26.2701978 12.03 JOE BW61.0309996 278.1427828 26.1890667 12.12 SUE BW62.0315820 278.1588183 26.2081613 12.55 OTHER
4. Here are the contents of a sample star catalog descriptor which shows how to use the SearchCat type for other scat supported catalogs:
Consider the 2MASS catalog. First run a sample search to determine what columns scat returns for 2MASS:
$ TMC_PATH=http://tdc-www.harvard.edu/cgi-bin/scat \ scat -d -h -c tmc -n 3 -r 1000 286.1 -8.16 scat WCSTools 3.6.8, 13 March 2007, Doug Mink SAO 2MASS PSC 286.1000000 -8.1600000 J2000 r= 0.28 at epoch 2000.0000 2MASS_num. RA2000 Dec2000 MagJ MagH MagK Arcsec 0817.272819 285.8295583 -8.2269556 5.593 4.695 4.495 993.34 0818.275423 286.2266583 -8.1224500 5.605 5.097 4.943 471.18 0818.274315 286.0375167 -8.1608111 6.072 5.401 5.217 222.68 $Now create a catspec file that identifies the scat output columns left to right in the fields entry:
# Catalog descriptor for user supplied objects in a local file type => StarID::SearchCat fields => ID,RA,DEC,MAGH,MAGJ,MAGK,DIST data => SCAT catalog/type => Indexed catalog/n => 4 subtype => tmc sort => m2 mag => MAGH envvar => TMC_PATH location => http://tdc-www.harvard.edu/cgi-bin/scatThere are five fields that matter: ID, RA, DEC, MAG, TYPE. ID is the unique identifier for the object. RA and DEC give the position in degrees. By default, the field named MAG gives the magnitude, but the mag entry can override that. In the example, it says to use the MAGH field for MAG. The TYPE field is an optional string. Not all scat catalog types return something that represents an object type. If there is no TYPE field, the default value is UNKNOWN.