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Haversine Formula implementation in Clojure
; 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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