geo.rb

#!/usr/bin/env ruby
=begin
    Andrew Turner, ruby distance calculation
    Copyright (C) 2005 Andrew Turner

    This program is free software; you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
    the Free Software Foundation; either version 2 of the License, or
    (at your option) any later version.

    This program is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with this program; if not, write to the Free Software
   Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA

   Please send patches / bug reports to andrew@highearthorbit.com

=end


class Geo
  def deg2rad(deg)
  	(deg * Math::PI / 180)
  end

  def rad2deg(rad)
  	(rad * 180 / Math::PI)
  end

  def abs(x)
    if x >= 0
      x
    else
      -x
    end
  end

  def acos(rad)
  	Math.atan2(Math.sqrt(abs(1 - rad**2)), rad)
  end

  def distance_in_km(lat1, lon1, lat2, lon2)
  	theta = lon1 - lon2

  	dist = Math.sin(self.deg2rad(lat1)) * Math.sin(deg2rad(lat2)) + Math.cos(self.deg2rad(lat1)) * Math.cos(self.deg2rad(lat2)) * Math.cos(deg2rad(theta))

  	dist = self.rad2deg(self.acos(dist))

  	(dist * 60.0 * 1.1515 * 1.609344) #distance in km
  end
  
  def distance_in_m(lat1, lon1, lat2, lon2)
  	distance_in_km(lat1, lon1, lat2, lon2) * 1000
  end
  
  
end