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# gabesmed/distance.py

Created February 14, 2012 11:43
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great circle distance in python
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 """Distance helpers.""" import math EARTH_CIRCUMFERENCE = 6378137 # earth circumference in meters def great_circle_distance(latlong_a, latlong_b): """ >>> coord_pairs = [ ... # between eighth and 31st and eighth and 30th ... [(40.750307,-73.994819), (40.749641,-73.99527)], ... # sanfran to NYC ~2568 miles ... [(37.784750,-122.421180), (40.714585,-74.007202)], ... # about 10 feet apart ... [(40.714732,-74.008091), (40.714753,-74.008074)], ... # inches apart ... [(40.754850,-73.975560), (40.754851,-73.975561)], ... ] >>> for pair in coord_pairs: ... great_circle_distance(pair[0], pair[1]) # doctest: +ELLIPSIS 83.325362855055... 4133342.6554530... 2.7426970360283... 0.1396525521278... """ lat1, lon1 = latlong_a lat2, lon2 = latlong_b dLat = math.radians(lat2 - lat1) dLon = math.radians(lon2 - lon1) a = (math.sin(dLat / 2) * math.sin(dLat / 2) + math.cos(math.radians(lat1)) * math.cos(math.radians(lat2)) * math.sin(dLon / 2) * math.sin(dLon / 2)) c = 2 * math.atan2(math.sqrt(a), math.sqrt(1 - a)) d = EARTH_CIRCUMFERENCE * c return d

### gardiner commented Oct 19, 2012

EARTH_CIRCUMFERENCE should be EARTH_RADIUS. At least that's what the number is.

### joeatbayes commented Jul 1, 2015

Your code returns the wrong answer for the test ((47.64828, -122.52963), (47.61168, -122.33326)) compare it to google and several others. Your code understates the distance. Your code returns 15.284 km while other libraries returned 21.944km and google returned 12.7 miles which converts to 20.43km

### kannes commented Apr 12, 2017

joeatbayes, that is to be expected. There are different formulas based on different earth models with different accuracies.