WCSAXESa&Ignored.&Set to the number of axes in the WCS
Frame - only written if different to NAXIS.
CRVALia&Used to create the pixel to WCS
MappingMapping.&Always written (see “Choice of Reference
Point” below).
CRPIXja&Used to create the pixel to WCS Mapping.&Always
written (see “Choice of Reference Point” below).
CDELTia&Used to create the pixel to WCS Mapping.&Only
written if the CDMatrixCDMatrix attribute of the FitsChan is
set to zero.
CROTAi&Used to create the pixel to WCS Mapping.&Only
written in FITS-AIPS and FITS-AIPS++ encodings.
CTYPEia&Used to choose the class and attributes of the
WCS Frame, and to create the pixel to WCS Mapping (note, “STOKES” and
“COMPLEX” axes are treated as unknown linear axes).&Always written
(see “Use and Choice of CTYPE keywords” below).
CUNITia&Used to set the Units attributes
of the WCS Frame.&Only written if the Units attribute of the WCS Frame
has been set explicitly. If so, the Units value for each axis is used as
the CUNIT value.
PCi_ja&Used to create the pixel to WCS
Mapping.&Only written if the CDMatrix attribute of the FitsChan is set to
zero.
CDi_ja&Used to create the pixel to WCS
Mapping.&Only written if the CDMatrix attribute of the FitsChan is set to
a non-zero value.
PVi_ma&Ignored for linear axes.&Not written if the axes
are linear.
PSi_ma&Ignored.&Not used.
WCSNAMEa&Used to set the DomainDomain attribute
of the WCS Frame.&Only written if the Domain attribute of the WCS Frame
has been set explicitly. If so, the Domain value is used as the WCSNAME
value.
CRDERia&Ignored.&Not used.
CSYERia&Ignored.&Not used.
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