maidenhead.clj

;; https://en.wikipedia.org/wiki/Maidenhead_Locator_System
;; http://no.nonsense.ee/qth/map.html
;; http://ham.stackexchange.com/questions/221/how-can-one-convert-from-lat-long-to-grid-square


(defn to-maidenhead
  [lat long]
  (let [long (-> long (+ 180) (/ 2))
        lat  (-> lat (+ 90))
        funs [#(* 10 (mod % 1)) #(* 24 (mod % 1)) #(* 10 (mod % 1)) #(* 24 (mod % 1))]
        cars [\A \0 \a \0 \a]]
    (map (fn [geo]
           (map (fn [n car] (char (+ (int car) n)))
                (reductions (fn [n fun] (fun n))
                            (/ geo 10)
                            funs)
                cars))
         [long lat])))

(def to-maidenhead-str (comp #(apply str %) #(apply interleave %) to-maidenhead))

(comment
  
  (apply str
    (apply interleave
      (to-maidenhead 36.165926 -86.723285)))
    
  ;; => "EM66pd39et"
  
  (and
    (= "EM66pd39et" (to-maidenhead-str 36.165926 -86.723285))
    (= "OF86cx76ql" (to-maidenhead-str -33.014673 116.230695))
    (= "FD54oq44oh" (to-maidenhead-str -55.315349 -68.794971))
    (= "PM85ge79vh" (to-maidenhead-str 35.205535 136.56579)))

 ;; => true
 
 
 ;; Just a simple test at various coordinates around the globe.
 ;; Maidenhead Locator taken from http://no.nonsense.ee/qth/map.html
 
)