Catalog descriptors

Several tools requiring star catalog information accept a catspec parameter which gives the catalog descriptor.

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 => value
The 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/

EXAMPLES

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/scat
There 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.

SEE ALSO

aspcorr, tristarid, tristarid1, uvotskycorr

LAST MODIFIED

September 2008