haversine.clj

(def earth-radius 6371)

(defn degree-to-radian [deg]
  (* deg (/ Math/PI 180)))

(defn distance [lata lnga latb lngb]
  (let [lata-r    (degree-to-radian lata)
        lnga-r    (degree-to-radian lnga)
        latb-r    (degree-to-radian latb)
        lngb-r    (degree-to-radian lngb)
        delta-lat (- latb-r lata-r)
        delta-lng (- lngb-r lnga-r)]
    (* earth-radius 2 (Math/asin (Math/sqrt (+ (Math/pow (Math/sin
	    (/ delta-lat 2)) 2) (* (Math/cos lata-r) (Math/cos latb-r)
	    (Math/pow (Math/sin (/ delta-lng 2)) 2))))))))