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7. SUMMARY

The changes to FITS-header keywords are summarized in Table 8. As described in Paper II, for one purpose, CROTAi may in some cases be used instead of the new keywords so that the coordinate information may be understood by software systems which have yet to be converted to these new conventions.

Table 8. Coordinate keywords: see also Table 2 for alternate types used in binary tables.

Keyword Type Sect. Use Status Comments

WCSAXESa integer 2.2 WCS dimensionality new allows WCS specification for degenerate axes, to be explicit rather than implicit.
CRVALia floating 2.1.1 value at reference point extended meaning of reference point forced by coord. type.
CRPIXja floating 2.1.1 pixel of reference point extended meaning of reference point forced by coord. type.
CDELTia floating 2.1.1 increment at ref. point retained meaning of increment clarified.
CROTAi floating 1 rotation at ref. point deprecated replaced by PCi_j and CDi_j.
CTYPEia character 2.1.1 coord./algorithm type extended Non-linear types have "4-3" form: characters 1-4 specify the coordinate type, character 5 is "-", and characters 6-8 specify an algorithm code for computing the world coordinate value; case dependent.
CUNITia character 2.3 units of coord. values new case dependent, allowed values and combinations are described in Sect. 4.
PCi_ja floating 2.1.2 transformation matrix new linear conversion of pixel number to pixels along coordinate axes; default = 0 (i neq j), = 1 (i = j).
CDi_ja floating 2.1.2 transformation matrix new linear conversion of pixel number to relative coordinates; default all 0 if any given, else PCi_j applies.
PVi_ma floating 2.1.4 parameter m new parameters required in some coordinate types; defaults are algorithm-specific; see Papers II and III for usage examples and default conventions
PSi_ma character 2.1.4 parameter m new parameters required in some coordinate types; defaults are algorithm-specific; see Paper III for usage example and default conventions
WCSNAMEa character 2.5 coord. version name new optional documentation
CRDERia floating 2.6 random error new uncertainty in coordinate due to random errors; default = 0
CSYERia floating 2.6 systematic error new uncertainty in coordinate due to systematic errors; default = 0

where j is a pixel axis number 1 through 99, i is an intermediate world coordinate axis number 1 through 99, m is a parameter number 0
2 through 99, and a is a coordinate description version character blank and A through Z. PC i_ja and CD i_ja may not occur in the same header data unit.

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