6.1 Position Generators

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.