I found this code on stack overflow:
from math import radians, cos, sin, asin, sqrt, atan2
def haversine(lon1, lat1, lon2, lat2):
"""
Calculate the great circle distance between two points
on the earth (specified in decimal degrees)
"""
# convert decimal degrees to radians
lon1, lat1, lon2, lat2 = map(radians, [lon1, lat1, lon2, lat2])
print(lon1, lat1, lon2, lat2)
# haversine formula
dlon = abs(lon2 - lon1)
dlat = abs(lat2 - lat1)
a = sin(dlat/2)**2 + cos(lat1) * cos(lat2) * sin(dlon/2)**2
c = 2 * atan2(sqrt(a), sqrt(1-a))
r = 6371 # Radius of earth in kilometers. Use 3956 for miles
return c * r
When I use the function with these coordinates: haversine(-94.5930, 39.1230, -94.4839, 39.1561), it returns 10.103458011601726.
When I run those coordinates through online gps coordinate distance calculators, they all produce an answer around 12 kilometers.
I can't find any differences between this code and the haversine formula found here, so I do not know why it is producing answers different than those from the online calculators (including the one in the link)
Between your online validation and the use of your function, you are mixing up the order of latitude and longitude. This function expects it in lon/lat pairs, while lat/long is the more typical ordering of pairs. Your observation is repeatable if you enter them incorrectly online here.
print haversine(-94.5930, 39.1230, -94.4839, 39.1561) # 10.1034580116
print haversine(39.1230, -94.5930, 39.1561, -94.4839) # 12.1348612974