1.1.3.0 coordsys.projection

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coordsys.projection - Function

1.1.3 Recover the direction coordinate projection

Description

If the Coordinate System contains a direction coordinate, this function 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 CASA. 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 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.

Arguments


Inputs
type	Type of projection. Defaults to current projection.
	allowed:	string
	Default:

Returns
record

Example

"""
#
print "\t----\t projection Ex 1 \t----"
csys = cs.newcoordsys(direction=True)
print csys.projection()
#{’type’: ’SIN’, ’parameters’: [0.0, 0.0]}
print csys.projection(’all’)
#{’all’: True, ’types’: [’AZP’, ’TAN’, ’SIN’, ’STG’, ’ARC’, ’ZPN’, ’ZEA’,
# ’AIR’, ’CYP’, ’CAR’, ’MER’, ’CEA’, ’COP’, ’COD’, ’COE’, ’COO’, ’BON’,
# ’PCO’, ’SFL’, ’PAR’, ’AIT’, ’MOL’, ’CSC’, ’QSC’, ’TSC’]}
print csys.projection(’ZPN’)
#{’nparameters’: 100}
#
"""

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.

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