[Last Change: 15 Mar 2019 (rev 3)]

How to raytrace Lots and Lots of Sources

If you are attempting to simulate a complex field with many sources in it, there are better ways of doing this than simply repeating

point{ ... }
point{ ... }
point{ ... }

ad nauseum.

Parameters in a Lua list

If all of your sources are points, you could do something like this:

sources = {
       -- theta, phi, spectrum
       { 0, 0, 1.49},
       { {10, "arcseconds"} , 0, 6.4 },
}

for _, src in pairs(sources) do
  point{ position = { theta = src[1], phi = src[2] }, spectrum = src[3] }
end

which is slightly less nauseating.

Parameters in an RDB file

An improvement might be to store your positions and spectra in a separate file, say an RDB formatted file . That file might have columns "theta", "phi", and "file", and "scale", where the file column contains the name of a file containing a spectrum and scale is a scale factor to apply to the spectrum:

theta	phi	file	scale
N	N	S	N
0	0	spec_6.80.rdb	1.0
1	170	spec_6.80.rdb	0.5
0.5	120	spec_6.80.rdb	3.0

(Those are single tab characters between the columns, not spaces; here's the source file and the spectrum file)

The following code would read that file in and generate a set of point sources:

RDB = require('rdb')

srcfile = 'sources.rdb'

rdb = RDB( srcfile )
if nil == rdb then
   error( "error opening up ".. srcfile )
end

row = rdb:read()

while row ~= nil do

   point{ position = { theta = row.theta,
		       phi = row.phi },
	  spectrum = { { type = 'file',
			 format = 'rdb',
			 scale = row.scale,
			 file = row.file,
			 units = 'photons/s/cm2'
		   } }
       }

   row = rdb:read()

end

Parameters in an XML file

For the ultimate in flexibility, SAOTrace provides the load_sources function, which can load sources from an XML formatted file

with the following code:

load_sources( 'ngc2516-small.xml', { ra_aimpt = 1.1953549452648E+02,
				     dec_aimpt = -6.0763660833014E+01
				  } )