WCSTools header utilities

cphead
WCS Keywords

The following keywords related to an image's world coordinate system (WCS) are copied from one image header to another by cphead when the -w command line argument is used. No keyword entry is created in the output image header if that keyword is not found in the input image header.
RA Right Ascension, usually set at the observatory and not formally part of WCS It is usually in sexigesimal format (hh:mm:ss.ss), but may be in degrees. WCSTools imwcs writes out a value approximating the center of the image.
DEC Declination, usually set at the observatory and not formally part of WCS It is usually in sexigesimal format (hh:mm:ss.ss), but may be in degrees. WCSTools imwcs writes out a value approximating the center of the image.
EPOCH By the FITS standard, this is the equinox of the observation coordinates in years, but if the EQUINOX keyword is present, it may be the epoch of the observation in years
EQUINOX The equinox of the observation coordinates in years
RADECSYS The system of the coordinates: ICRS, J2000, B1950, GALACTIC, ECLIPTIC
SECPIX Arcseconds per pixel for assumed square pixels. This is an observatory keyword and may be from the instrument model. WCSTools imwcs writes out a value approximating the fit image scale.
SECPIX1 Arcseconds per pixel in the horizontal dimension. This is an observatory keyword and may be from the instrument model.
SECPIX2 Arcseconds per pixel in the vertical dimension. This is an observatory keyword and may be from the instrument model.
CTYPE1 WCS Type of the horizontal coordinate, including coordinate and projection, each allowed four characters, such as RA---TAN.
CTYPE2 WCS Type of the vertical coordinate, including coordinate and projection, each allowed four characters, such as DEC--TAN.
CRPIX1 Reference pixel on the horizonal axis
CRPIX2 Reference pixel on the vertical axis
CRVAL1 Horizonal axis WCS value at the reference pixel
CRVAL2 Vertical axis WCS value at the reference pixel
CDELT1 Change per pixel in horizonal axis WCS value at the reference pixel
CDELT2 Change per pixel in vertical axis WCS value at the reference pixel
CROTA1 Rotation angle of image around the reference pixel in degrees (same as CROTA2 and unnecessary)
CROTA2 Rotation angle of image around the reference pixel in degrees (same as CROTA1, if it is present)
CD1_1 CD1_2
CD2_1 CD2_2
Rotation and scaling matrix
PC1_1 PC1_2
PC2_1 PC2_2
Rotation matrix, used with CDELT1 and CDELT2 in the final version of the FITS-WCS standard as an alternative to the CD_j matrix.
PC001001 PC001002
PC002001 PC002002
Rotation matrix, used with CDELT1 and CDELT2 in draft versions of the FITS-WCS standard. Some data files were written using these keywords before they were dropped from the standard in favor of PCi_j.
LATPOLE Latitude of the pole of the coordinate system. In the final FITS-WCS standard, this may also be set by PVi_4.
LONPOLE Longitude of the pole of the coordinate system. In the final FITS-WCS standard, this may also be set by PVi_3.
IMWCS If the WCS is set by imwcs, the value of this keyword is a string giving the version of the program which was used.
CO1_1 CO1_2 CO1_3
CO1_4 CO1_5 CO1_6
CO1_7 CO1_8 CO1_9
CO1_10 CO1_11 CO1_12
These keywords are the horizontal axis coefficients of a set of polynomial expansions of the CD matrix which can be fit by imwcs.
CO2_1 CO2_2 CO2_3
CO2_4 CO2_5 CO2_6
CO2_7 CO2_8 CO2_9
CO2_10 CO2_11 CO2_12
These keywords are the horizontal axis coefficients of a set of polynomial expansions of the CD matrix which can be fit by imwcs.
PROJP0 PROJP1 PROJP2
PROJP3 PROJP4 PROJP5
PROJP6 PROJP7 PROJP8
PROJP9
These are projection parameters used by draft versions of the FITS WCS standard, but dropped in favor of PVi_j in the final standard.
PV1_0 PV1_1 PV1_2
PV1_3 PV1_4 PV1_5
PV1_6 PV1_7 PV1_8
PV1_9
Projection parameters if axis 1 is latitute/declination
PV2_0 PV2_1 PV2_2
PV2_3 PV2_4 PV2_5
PV2_6 PV2_7 PV2_8
PV2_9
Projection parameters if axis 1 is latitute/declination

Last updated 23 October 2003 by Doug Mink

Telescope Data Center