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coordsys.projection - Function

	Package	general
	Module	images
	Tool	coordsys

Recover the direction coordinate projection

Synopsis
projection(type)

Arguments

type	in	Type of projection
		Allowed:	String
		Default:	Current

Returns
Record, Vector string, Int or fail

Description

If the Coordinate System contains a direction coordinate, this function (short-hand name p) can be used to recover information about the projection. For discussion about celestial coordinate systems, including projections, see the papers by Mark Calabretta and Eric Greisen. The initial draft from 1996 (implemented in AIPS++Background information can be found here.

What this function returns depends upon the value you assign to type.

• type=unset. In this case (the default), the actual projection type and projection parameters are returned in a Glish record with fields type and parameters, respectively.

• type='all'. In this case, a vector of strings containing all of the possible projection codes is returned.

• type=code. If you specify a valid projection type code (see list by setting type='all') then what is returned is the number of parameters required to describe that projection (useful in function setprojection).

You can change the projection with setprojection.

If the Coordinate System does not contain a direction coordinate, an exception is generated.

Example

- cs := coordsys(direction=T)
- cs.projection()
[type=SIN, parameters=[0 0] ] 
-
- cs.projection('all')
AZP TAN SIN STG ARC ZPN ZEA AIR CYP CAR MER CEA COP 
COD COE COO BON PCO GLS PAR AIT MOL CSC QSC TSC 
-
- cs.projection('ZPN')
10

We first recover the projection type and parameters from the direction coordinate. Then we find the list of all possible projection types. FInally, we recover the number of parameters required to describe the 'ZPN' projection.