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The basic concept of a Mapping (
) is rather
generic and obviously it is necessary to have specific Mappings that
implement specific relationships between coordinate systems. AST
provides a range of these, to perform transformations such as the
following and, where appropriate, their inverses:
- Conversions between various celestial coordinate systems (the
SlaMap).
- Conversions between various spectral coordinate systems (the
SpecMap).
- Conversion between 2-dimensional spherical celestial coordinates
(longitude and latitude) and a 3-dimensional vectorial positions (the SphMap).
- Various projections of the celestial sphere on to 2-dimensional
coordinate spaces--i.e. map projections (the DssMap and WcsMap).
- Permutation, introduction and elimination of coordinates (the
PermMap).
- Various linear coordinate transformations (the MatrixMap, WinMap
and ZoomMap).
- Lookup tables (the LutMap).
- General-purpose transformations expressed using arithmetic
operations and functions similar to those available in C (the
MathMap).
- Transformations for internal use within a program, based on
private transformation functions which you write yourself in C (the
IntraMap).
Further reading: For a more complete description of each of the
Mappings mentioned above, see its entry in
. In addition, see the discussion of the
PermMap in
, the UnitMap in
and the IntraMap in
. The ZoomMap is used as an example throughout
.
Next: Compound Mappings
Up: Overview of AST Concepts
Previous: Relationships Between Coordinate Systems
AST A Library for Handling World Coordinate Systems in Astronomy
Starlink User Note 211
R.F. Warren-Smith & D.S. Berry
30th April 2003
E-mail:ussc@star.rl.ac.uk
Copyright (C) 2003 Central Laboratory of the Research Councils