REVISIONS · SEE_ALSO

## NAME

msccmatch -- match coordinates and adjust WCS

## SYNOPSIS

A list of reference celestial coordinates, either from an astrometry catalog or measured from a reference image, for stars in the field is matched against objects in the mosaic data. A linear relation between the observed positions and the reference coordinates is fit. The relation may include a zero point shift, scale change, and axis rotation for both coordinate axes. The removes pointing errors, rotation errors, and atmospheric refraction effects. The fit is used to update the image world coordinate system to register the WCS to the input coordinate system.

## USAGE

msccmatch input coords

## PARAMETERS

- input
- List of input mosaic exposures to be calibrated.

- coords
- Coordinate filename or command to execute to produce a coordinate file.
The file contains the right ascension and declination in the first two
columns. Any other columns are ignored. When an explicit file is
specified it used for all input exposures.
A command to execute is specified by beginning the parameter string with "!". The special arguments $I will be replaced by the input mosaic exposure and $C by the filename for the coordinate file to be used. A typical command is

!mscgetcatalog $I $C

Note that any hidden parameters either need to be set first or be given explicitly as part of the command.

- outcoords = ""
- Optional list of updated coordinate files to output. The list is matched with the input list of mosaic exposures. If the list is shorter than the input list then no output files are created for the remaining exposures. The output coordinate file consists of those lines in the input coordinates which were used; i.e. were found to be in the field, were not rejected due to bad pixels, and which where centered without error.

- usebpm = yes
- Use bad pixel masks given by the BPM header keywords to reject sources that contain bad pixels?

The following parameters are for a coarse correlation search with large offsets but small rotation.

- nsearch = 50
- Maximum number of positions to use in search. If this is zero then the coarse search is skipped and the coordinates are assumed to be close enough to centroid directly on the objects. If the coarse search is selected then this number should not be too large, otherwise the execution time will become long.

- search = 0.
- Translation search radius in arcsec. If this is zero then the coarse
serach is skipped and the coordinates are assumed to be close enough to
centroid directly. This defines how far from the initial coordinates to
search using the
*nsearch*objects. It should be just large enough to include the expected error in the initial coordinates.

- rsearch = 0.
- Rotation search radius in degrees. This defines a range of rotations about the current tangent point that might be needed to find the correlation match. The correlation algorithm only works with small rotations or order a degree.

The follwoing parameters are for the fine centroiding and coordinate solution based on the centroiding.

- nfit = 4
- The minimum number of sources which must be found and centroided for an acceptable coordinate fit. If the value is negative then this is the maximum number of objects which failed to be found for an acceptable solution.

- rms = 2.
- The maximum RMS in arcsec for an acceptable solution.

- maxshift = 5
- Maximum centering shift in arcsec when centroiding. Sources that produce
centroids (from the
**center**task) that differ from the initial position by more than this amount are considered to have failed to be centroided.

- fitgeometry = "general" (shift|xyscale|rotate|rscale|rxyscale|general)
- Fitting geometry for the coordinate adjustment. This should normally be "general" to all allow for all effects of atmospheric refraction. The other options are only used when looking for specific effects.

- reject = 3.
- Iterative rejection sigma for fitting the position residuals as a function of arcsec from the field tangent point.

- update = yes
- Update the coordinate system in the mosaic exposures? If the value is no then
the input data is not modified. This option might be used just to check
the coordinate system. If the the value is yes and the fit satisfies the
parameters defining an acceptable solution the coordinate system will be
updated if
*interactive*=no, otherwise there is a query whether to accept the solution and update the input data.

- interactive = yes
- Is this task to be run interactively? If yes then the fitting can be
examined and adjusted interactively if the
*fit*parameter is yes and the final solution will be printed followed by a query to accept the solution provided the*update*parameter is yes.

- fit = yes
- Do the coordinate fitting interactively? This required the
*interactive*parameter to be yes. If the fitting is done interactively the**geomap**task used to do the fitting will be executed interactively. The graphical fitting is exited using the`q`key. See the help for**geomap**for more on the interactive fitting.

- verbose = yes
- Verbose output? This determines whether various terminal output is produced.

- listcoords = yes
- List centroiding results for all sources in verbose mode?

- graphics = "stdgraph"
- Graphics device for the interactive fitting.

- cursor = ""
- Graphics cursor input for the interactive fitting. The default null string value selects the graphics window cursor.

- accept = yes
- This is a query parameter when
*update*and*interactive*are yes. You are queried after printing the statistics of the coordinate fit whether to accept the solution and update the coordinate system of the mosaic exposure.

## DESCRIPTION

A list of reference celestial coordinates, either from an astrometry catalog or measured from a reference image, for stars in the field is matched against objects in the mosaic data. A linear relation between the observed positions and the reference coordinates is fit. The relation may include a zero point shift, scale change, and axis rotation for both coordinate axes. The removes pointing errors, rotation errors, and atmospheric refraction effects. The fit is used to update the image world coordinate system to register the WCS to the input coordinate system.

A full description of this task remains to be written.

## EXAMPLES

## REVISIONS

- MSCCMATCH - V4.0: August 22, 2000
- This version includes the ability to get the list of catalogs directly from a web-based catalog server and to find large offsets (provided any rotation is small) using a correlation algorithm.

- MSCCMATCH - V2.external package
- First release.

## SEE ALSO

msczero, mscgetcatalog, geomap, center