Tile Server Quad Tree Math

tiles.clj

(import 'java.lang.Math)

(defn tile-count [z]
  (Math/pow 2 z))

(defn deg2num [lat_deg lon_deg z]
  (let [lat_rad (Math/toRadians lat_deg)
        n (tile-count z)
        x (int (* (/ (+ lon_deg 180.0) 360.0) n))
        y (int
                (*
                (/  
                (- 1.0
                   (/
                      (Math/log
                        (+ 
                          (Math/tan lat_rad)
                          (/ 1.0 
                             (Math/cos lat_rad))))
                     Math/PI))
                  2)
                  n))]
    (list x y z)))


(defn tilelink [lat lon z]
  (let [u "http://a.tile.openstreetmap.org"
        url (fn [x y z] (str u "/" z "/" x "/" y ".png"))
        ]
    (apply url (deg2num lat lon z))))


(defn num2deg [x y z]
  (let [n (tile-count z)
        lon (- (* (/ x n) 360.0) 180.0)
        lat_rad (Math/atan
                  (Math/sinh
                    (* Math/PI
                       (- 1
                          (/ (* 2 y) n)))))
        lat (Math/toDegrees lat_rad)]
    (list lat lon)))

(defn num2deg-bb [x y z]
  (let [nw (num2deg x y z)
        sw (num2deg x (+ 1 y) z)
        ne (num2deg (+ 1 x) y z)
        se (num2deg (+ 1 x) (+ 1 y) z)]
    (list nw sw se ne)))


(defn bb-extents [bb]
  (let [lats (map first bb)
        lons (map second bb)
        minlat (reduce min lats)
        maxlat (reduce max lats)
        minlon (reduce min lons)
        maxlon (reduce max lons)]
    (list minlat maxlat minlon maxlon)))

(defn deg2extents [lat lon z]
  (bb-extents 
    (apply 
      num2deg-bb 
      (deg2num 
        lat lon z))))

(defn num2extents [x y z]
  (bb-extents 
    (num2deg-bb x y z)))