Haversine Distance

gistfile1.py

'''See http://en.wikipedia.org/wiki/Haversine_formula for more details'''

from math import sin, cos, sqrt, asin, radians

RADIUS_EARTH_M = 6371200.0 #The Earth's mean radius in meters

def haversine_distance(a, b):
    '''Operates on two lat,lngs and returns the distance in meters'''
    
    lng1, lat1 = map(radians, a) #lng, lat to radians
    lng2, lat2 = map(radians, b) #lng, lat to radians
    
    sin_dlat_over_2 = sin((lat2 - lat1) / 2.0)
    sin_dlng_over_2 = sin((lng2 - lng1) / 2.0)
    
    f = sin_dlat_over_2 * sin_dlat_over_2 
    f += cos(lat1) * cos(lat2) * sin_dlng_over_2 * sin_dlng_over_2        
    return RADIUS_EARTH_M * 2.0 * asin(sqrt(f))