awcspars: Default image wcs parameters

Package: astcat

Usage

awcspars

Parameters

wxref = "INDEF", wyref = "INDEF"

The image header keyword names or the numerical values of the x and y reference point in pixels. If wxref = "INDEF" and wyref = "INDEF" the reference point defaults to the center of the image.

wxmag = "INDEF", wymag = "INDEF"

The image header keyword names or the numerical values of the x and y scale factors in arcseconds per pixel. If wxmag or wymag = are undefined a new wcs cannot be created.

wxrot = "180.0", wyrot = "0.0"

The image header keyword names or the numerical values of the x and y rotation angles in degrees measured counter-clockwise to the positive x and y image axes. The default orientation is east=left, north=up. Wxrot values of 0.0, 90.0, 180.0, and 270.0 correspond to east=right, up, left, and down respectively. Wyrot values of 0.0, 90.0, 180.0, and 270.0 correspond to north=up, left, down, and right respectively.

wraref = "RA", wdecref = "DEC"

The image header keyword names or the numerical values of the reference point in celestial coordinates. If wraref and wdecref are undefined a new wcs cannot be created.

wraunits = "", wdecunits = ""

The units of the reference point celestial coordinates. The options are "hours", "degrees", and "radians" for the ra coordinate and "degrees" and "radians" for the dec coordinate. If wraunits and wdecunits are undefined they default to the preferred units of the reference system.

wproj = "tan"

The sky projection geometry. The most commonly used projections are "tan", "arc", "sin", and "lin". Other supported projections are "ait","car", "csc", "gls", "mer", "mol", "par", "pco", "qsc", "stg", "tsc", and "zea".

wsystem = "EQUINOX"

The image header keyword name or string defining the celestial coordinate system of the reference point. The most common values for wsystem are "2000.0", "1950.0", "J2000.0", and "B1950.0". Type "help ccssytems" to get a full list of options.

Description

The default wcs parameters are used to create an approximate FITS wcs for an images which do not have one. Creating an approximate header from the telescope pointing position and the known scale and orientation of the detector can make later steps like locating the catalog stars for computing an accurate plate solution simpler.

In coordinates of the reference point in pixels and celestial coordinates wxref, wyref, wraref, wdecref, the scale factors wxmag and wymag, and the orientation wxrot and wyrot can be read from the image header or set by value. The coordinate system and units of the celestial coordinates of the reference point wsystem and wraunits and wdecunits must be set explicitly. The image projection function wproj must also be set separately.

Examples

1. List the default wcs parameters.

cl> lpar awcspars

2. Edit the default wcs parameters.

cl> awcspars

3. Edit the default wcs parameters from the agetim task.

cl> epar agetim

4. Save the current awcspars parameter values in a text file called awcs1.par. Use the saved parameter set in the next call to the agetim task.

cl> epar awcspars
cl> agetim ... awcspars=awcs1.par ...

Time requirements

Bugs

See also

agetim, ahedit