Handy example for working out distance between two sets of latitude and longitude points.... The start of a geo fence!

DistanceLatLon.py

import math

def distance_on_unit_sphere(lat1, long1, lat2, long2):
    # modified by Matthew Bordignon @bordignon Oct 2013
    #
    # handy example for finding distance between two sets of co-oridinates 
    # modified from http://www.johndcook.com/python_longitude_latitude.html
    # handy tool to chk calculations, http://www.johndcook.com/lat_long_distance.html
    # Convert latitude and longitude to 
    # spherical coordinates in radians.
    degrees_to_radians = math.pi/180.0
        
    # phi = 90 - latitude
    phi1 = (90.0 - lat1)*degrees_to_radians
    phi2 = (90.0 - lat2)*degrees_to_radians
        
    # theta = longitude
    theta1 = long1*degrees_to_radians
    theta2 = long2*degrees_to_radians
        
    # Compute spherical distance from spherical coordinates.
        
    # For two locations in spherical coordinates 
    # (1, theta, phi) and (1, theta, phi)
    # cosine( arc length ) = 
    #    sin phi sin phi' cos(theta-theta') + cos phi cos phi'
    # distance = rho * arc length
    
    cos = (math.sin(phi1)*math.sin(phi2)*math.cos(theta1 - theta2) + 
           math.cos(phi1)*math.cos(phi2))
    arc = math.acos( cos ) 
    # Remember to multiply arc by the radius of the earth 
    # in your favorite set of units to get length.
    # We assume the radius of the earth is 3960 miles or 6373 kilometers
    arc = arc * 6373 #kilometers here
    #arc = arc * 3960 #miles here
    
    arc = '%.1f' % arc #reduce to one deciminal point
    return arc

#example on how to use it
#home
lon1a = 145.359013
lat1a = -37.913301

#work
lon2b = 144.950333
lat2b = -37.832111


print str(distance_on_unit_sphere(lat1a, lon1a, lat2b, lon2b)) +" kilometers between the two points"