Appendix
Sample WCSDVARR extension header:
XTENSION= 'IMAGE ' / Image extension
BITPIX = -32 / array data type
NAXIS = 2 / number of array dimensions
NAXIS1 = 65
NAXIS2 = 33
PCOUNT = 0 / number of parameters
GCOUNT = 1 / number of groups
EXTVER = 1 / Distortion array version number
EXTNAME = 'WCSDVARR' / WCS distortion array
CRVAL2 = 0.0 / Coordinate system value at reference pixel
CRPIX1 = 0.0 / Coordinate system reference pixel
CRPIX2 = 0.0 / Coordinate system reference pixel
CRVAL1 = 0.0 / Coordinate system value at reference pixel
CDELT1 = 64 / Coordinate increment along axis
CDELT2 = 64 / Coordinate increment along axis
Sample science extension keywords defining a lookup table distortions:
CPERROR1= 0.058602706 / Maximum error of dgeo correction for axis 1
CPDIS1 = 'Lookup ' / Prior distortion function type
DP1 = 'EXTVER: 1.0' / Version number of WCSDVARR extension
DP1 = 'NAXES: 2.0' / Number of independent variables in CPDIS function
DP1 = 'AXIS.1: 1.0' / Axis number of the 1st variable in a CPDIS function
DP1 = 'AXIS.2: 2.0' / Axis number of the 2nd variable in a CPDIS function
CPERROR2= 0.072911568 / Maximum error of dgeo correction for axis 2
CPDIS2 = 'Lookup ' / Prior distortion function type
DP2 = 'EXTVER: 2.0' / Version number of WCSDVARR extension
DP2 = 'NAXES: 2.0' / Number of independent variables in CPDIS function
DP2 = 'AXIS.1: 1.0' / Axis number of the 1st variable in a CPDIS function
DP2 = 'AXIS.2: 2.0' / Axis number of the 2nd variable in a CPDIS function