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