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Position generators define the angular extent and position of a
source. Each function has both mandatory and optional arguments.
Optional arguments are usually set to a reasonable default. Mandatory
arguments are explicitly included in the argument list; optional
arguments are passed via a lua
table (an associative array, or hash
in Perl lingo). For example, here are two equivalent methods of
creating a rectangular source at a specific off-axis location:
optargs = { } optargs.theta = '2 arcmin' optargs.phi = '3 arcmin' optargs.z = '-2 parsec' rect( 'square in the sky', '1 arcsec', '1 arcsec', optargs ) rect( 'square in the sky', '1 arcsec', '1 arcsec', { theta = '2 arcmin', phi = '3 arcmin', z = '-2 parsec' } )
Note that z is negative; the Z coordinate increases towards the focal plane.