FITS-WCS projection type
The values used are represented by symbolic constants with names of the form "
AST__XXX"
, where
"
XXX"
is the (upper case) 3-character code used by the FITS-WCS "
CTYPEi"
keyword to
identify the projection. For example, possible values are AST__TAN (for the tangent plane or
gnomonic projection) and AST__AIT (for the Hammer-Aitoff projection). AST__TPN is an
exception in that it is not part of the FITS-WCS standard (it represents a TAN projection with
polynomial correction terms as defined in an early draft of the FITS-WCS paper).
For a list of available projections, see the FITS-WCS paper.