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; Haversine formula | |
; a = sin²(Δφ/2) + cos φ1 ⋅ cos φ2 ⋅ sin²(Δλ/2) | |
; c = 2 ⋅ atan2( √a, √(1−a) ) | |
; d = R ⋅ c | |
; where φ is latitude, λ is longitude, R is earth’s radius (mean radius = 6,371km); | |
(defn haversine | |
"Implementation of Haversine formula. Takes two sets of latitude/longitude pairs and returns the shortest great circle distance between them (in km)" | |
[{lon1 :lng lat1 :lat} {lon2 :lng lat2 :lat}] | |
(let [R 6378.137 ; Radius of Earth in km | |
dlat (Math/toRadians (- lat2 lat1)) | |
dlon (Math/toRadians (- lon2 lon1)) | |
lat1 (Math/toRadians lat1) | |
lat2 (Math/toRadians lat2) | |
a (+ (* (Math/sin (/ dlat 2)) (Math/sin (/ dlat 2))) (* (Math/sin (/ dlon 2)) (Math/sin (/ dlon 2)) (Math/cos lat1) (Math/cos lat2)))] | |
(* R 2 (Math/asin (Math/sqrt a))))) |
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