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Table 22

Reserved WCS keywords.

Keyword Primary BINTABLE vector Pixel List
itemize Array primary alternative primary alternative

Coordinate dimensionality WCSAXESa WCAXna ...
Axis type CTYPEia iCTYPn iCTYna TCTYPn TCTYna
Axis units CUNITia iCUNIn iCUNna TCUNIn TCUNna
Reference value CRVALia iCRVLn iCRVna TCRVLn TCRVna
Coordinate increment CDELTia iCDLTn iCDEna TCDLTn TCDEna
Reference point CRPIXja jCRPXn jCRPna TCRPXn TCRPna
Coordinate rotation1 CROTAi iCROTn TCROTn
Transformation matrix2 PCi_ja ijPCna TPCn_ka or TPn_ka
Transformation matrix2 CDi_ja ijCDna TCDn_ka or TCn_ka
Coordinate parameter PVi_ma iPVn_ma or iVn_ma TPVn_ma or TVn_ma
Coordinate parameter array ... iVn_Xa ...
Coordinate parameter PSi_ma iPSn_ma or iSn_ma TPSn_ma or TSn_ma
Coordinate name WCSNAMEa WCSNna WCSna or TWCSna
Coordinate axis name CNAMEia iCNAna TCNAna
Random error CRDERia iCRDna TCRDna
Systematic error CSYERia iCSYna TCSYna
WCS cross-reference target ... WCSTna ...
WCS cross reference ... WCSXna ...
Coordinate rotation LONPOLEa LONPna LONPna
Coordinate rotation LATPOLEa LATPna LATPna
Coordinate epoch EQUINOXa EQUIna EQUIna
Coordinate epoch3 EPOCH EPOCH EPOCH
Date of observation MJD-OBS MJDOBn MJDOBn
Average date of observation MJD-AVG MJDAn MJDAn
Date/time of observation DATE-OBS DOBSn DOBSn
Average date/time of obs DATE-AVG DAVGn DAVGn
Reference frame RADESYSa or RADEna RADEna
Line rest frequency (Hz) RESTFRQa or RFRQna RFRQna
RESTFREQ4 ... ...
Line rest vacuum wavelength (m) RESTWAVa RWAVna RWAVna
Spectral reference frame SPECSYSa SPECna SPECna
Spectral reference frame SSYSOBSa SOBSna SOBSna
Spectral reference frame SSYSSRCa SSRCna SSRCna
Observation X (m) OBSGEO-X OBSGXn OBSGXn
Observation Y (m) OBSGEO-Y OBSGYn OBSGYn
Observation Z (m) OBSGEO-Z OBSGZn OBSGZn
Radial velocity (m s-1) VELOSYSa VSYSna VSYSna
Redshift of source ZSOURCEa ZSOUna ZSOUna
Angle of true velocity VELANGLa VANGna VANGna

Notes. The indexes j and i are pixel and intermediate world coordinate axis numbers, respectively. Within a table, the index n refers to a column number, and m refers to a coordinate parameter number. The index k also refers to a column number. The indicator a is either blank (for the primary coordinate description) or a character A through Z that specifies the coordinate version. See text.


CROTAi form is deprecated but still in use. It must not be used with PCi_j, PVi_m, and PSi_m.


PCi_j and CDi_j forms of the transformation matrix are mutually exclusive, and must not appear together in the same HDU.


EPOCH is deprecated. Use EQUINOX instead.


These 8-character keywords are deprecated; the 7-character forms, which can include an alternate version code letter at the end, should be used instead.

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