uvotstarid - match a source list against a star catalog


uvotstarid infile=sources.fits outfile=starid.fits


uvotstarid reads a source table and then attempts to identify particular sources in a star catalog.

Provided there are sufficient sources of the minimum brightness, star identification is attempted. The phases of the star identification algorithm are:

direct match
Each source is tested against objects in the catalog with relatively loose magnitude and position constraints.
doublet match
For each pair of sources, the distance between those sources is compared to the distance between direct matches for each of the sources.
doublet validation
Sets of doublets for each source are checked to ensure that there are no conflicting or duplicate assignments of catalog objects to sources.
thesis rating
The q Method is applied to valid sets of doublets to find the optimal quaternion / rotation - the rotation that minimizes a loss function given by the sum squared difference between references and rotated observations. Each thesis is given a rating of loss per doublet.

The thesis with the lowest mean loss is then assumed to be the correct match. If the optimal rotation is less than the tolerance given by the poscorr and rotcorr parameters, the observed source positions are updated.

uvotstarid was developed primarily for the Swift mission which has small fields of view (order of 10 arcminutes on a side). In order to hope to identify several stars in such a field, it is necessary to have a large star catalog (10s of millions of stars). Catalog partitioning was needed to accomodate the large catalog. Currently, the sky is divided into spherical squares of RA and DEC. Changing to another partitioning scheme should only require a change to the driver (and implementing the new partitioning).


infile [filename]
Name of the input source table.
outfile [filename]
Name of the output file.
partition [directory]
Specifies the directory holding the catalog partition.
matchtol [real]
Specifies the radius within which catalog objects are listed as matched to the observed source [arcsec].
radius [real]
Specifies the circle within which all catalog objects will be included in the output [arcsec].
(magtol = 3) [real]
Specifies the magnitude tolerance during direct match.
(postol = 10) [real]
Specifies the position tolerance during direct match [arcsec].
(difftol = 3) [real]
Specifies the difference tolerance during doublet match [arcsec].
(magmin = 20) [real]
Specifies the minimum magnitude source to attempt to match.
(nsrcmin = 3) [integer]
Specifies the minimum number of sources to attempt star identification.
(nsrcmax = 20) [integer]
Specifies the maximum number of sources to pass to star identification. If more sources than this exceed the magmin only the brightest are used.
(poscorr = 5) [real]
Specifies the maximum position correction to apply [arcsec].
(rotcorr = 1) [real]
Specifies the maximum rotation correction to apply [arcmin].
(chatter = 1) [integer, 0 - 10]
Controls the amount of informative text written to standard output. chatter values above 5 are probably only useful for testing.


Execute uvotstarid specifying the direct match position and magnitude tolerances:

	uvotstarid magtol=0.5 postol=8




February 2005