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
- 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
- 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