# Based on the formula for great-circle distance# (http://en.wikipedia.org/wiki/Great-circle_distance)## Note that this is not 100% accurate as the earth isn't a "true" sphere, but# for our purposes it's plenty (guaranteed within 0.5%).import mathdef GeoDistance(lat1, lon1, lat2, lon2): """ Calculate the distance between two points on earth in km Positive values represent north and east, negative values represent west and south. """ phi1 = math.radians(90.0 - lat1) phi2 = math.radians(90.0 - lat2) theta1 = math.radians(lon1) theta2 = math.radians(lon2) arc = math.acos(math.sin(phi1) * math.sin(phi2) * math.cos(theta1 - theta2) + math.cos(phi1) * math.cos(phi2)) # 6371.01 is the average radius of the earth in km. return arc * 6371.01