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from math import radians, cos, sin, asin, sqrt
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def haversine(lon1, lat1, lon2, lat2):
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"""
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Calculate the great circle distance between two points
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on the earth (specified in decimal degrees)
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"""
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# convert decimal degrees to radians
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lon1, lat1, lon2, lat2 = map(radians, [lon1, lat1, lon2, lat2])
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# haversine formula
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dlon = lon2 - lon1
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dlat = lat2 - lat1
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a = sin(dlat/2)**2 + cos(lat1) * cos(lat2) * sin(dlon/2)**2
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c = 2 * asin(sqrt(a))
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r = 6371 # Radius of earth in kilometers. Use 3956 for miles
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return c * r
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