Plate.ProjectionType Property

Plate.ProjectionType (read-write, ProjectionType)

The plane projection type for mapping XY to RA/Dec coordinates for the image (default = ppTAN)

Syntax

Plate.ProjectionType [= ProjectionType]

The property syntax has these parts:

Part	Description
Value (ProjectionType)	The plane projection type for mapping XY to RA/Dec coordinates for the image (default = ppTAN)

Remarks

The projective geometry used for mapping XY coordinates to RA and Dec. PinPoint implements the 7 projections supported by the professional AIPS system, plus the projections used in the Digital Sky Survey (POSS) plates. For virtually all of the work done by amateurs using their optical telescopes with typical fields of view, the TAN projection is the appropriate one. A Schmidt camera or other wide-field instrument may use another projection. The ppDSS projection is read-only, it is used only for attached DSS plates.

For information on AIPS and the meanings of these projections, see the following:

ftp://fits.cv.nrao.edu/fits/documents/wcs/aips27.ps.Z
ftp://fits.cv.nrao.edu/fits/documents/wcs/aips46.ps.Z

Footnotes in these two documents describe the differences between these algorithms and the 1993-94 WCS draft proposal (see URL below). In particular, these algorithms support ordinary field rotation, but not skew geometries (CD or PC matrix cases). Also, the MER and AIT algorithms work correctly only for CRVALi=(0,0). Users should note that GLS projections with yref!=0 will behave differently in this code than in the draft WCS proposal. The NCP projection is now obsolete (it is a special case of SIN). WCS syntax and semantics for various advanced features is discussed in the draft WCS proposal by Greisen and Calabretta at:

ftp://fits.cv.nrao.edu/fits/documents/wcs/wcs.all.ps.Z

Symbolic Constants

The (symbolic) values for ProjectionType are:

Constant	Value	Description
ppAIT	6	The Hammer-Aitoff projection (AIT)
ppARC	2	The zenithal/azimuthal equidistant projection (ARC)
ppDSS	7	The Digital Sky Survey (POSS) transformation (DSS)
ppGLS	4	The Sanson-Flamsteed (global sinusoidal) projection (GLS)
ppMER	5	The mercator projection (MER)
ppNCP	3	(obsolete) Special case of SIN used by old AIPS versions
ppSIN	0	The orthographic/synthesis (sinusoidal) projection (SIN)
ppTAN	1	The gnomonic (tangent plane) projection (TAN, default)