Conversion from geographic to geomagnetic coordinates

Question

I'm trying to convert between geographic and geomagnetic coordinates. I've found the following Prolog script, but I don't understand it enough to convert it myself. The target language is Java, but anything understandable is fine (C, Python, VB, whatever).

http://idlastro.gsfc.nasa.gov/ftp/pro/astro/geo2mag.pro

If someone could either help with the conversion of this script or explain what exactly it is doing (those array operations are baffling to me), I'd really appreciate it.

Thanks

Answer 1

Depending on the application, altitude can be an important variables in this coordinate conversion since geomagnetic coordinates are a mapping of the Earth's dipole magnetic field.

In Python you can easily convert geographic coordinates to geomagnetic (and vice versa) with SpacePy (http://sourceforge.net/projects/spacepy/).

Since you are looking for the source code to convert to Java, SpacePy is implementing the Fortran International Radiation Belt Environment Modeling (IRBEM) library, the source of which is available (http://irbem.svn.sourceforge.net/viewvc/irbem/web/index.html)

In Python, in case others are looking for a quick solution:

import spacepy.coordinates as coord
from spacepy.time import Ticktock
import numpy as np
def geotomag(alt,lat,lon):
    #call with altitude in kilometers and lat/lon in degrees 
    Re=6371.0 #mean Earth radius in kilometers
    #setup the geographic coordinate object with altitude in earth radii 
    cvals = coord.Coords([np.float(alt+Re)/Re, np.float(lat), np.float(lon)], 'GEO', 'sph',['Re','deg','deg'])
    #set time epoch for coordinates:
    cvals.ticks=Ticktock(['2012-01-01T12:00:00'], 'ISO')
    #return the magnetic coords in the same units as the geographic:
    return cvals.convert('MAG','sph')