npmap.js/src/util/tilemath.js

A JavaScript web mapping library, built as a Leaflet plugin, for the National Park Service.

'use strict';

/**
 * http://wiki.openstreetmap.org/wiki/Slippy_map_tilenames#ECMAScript_.28JavaScript.2FActionScript.2C_etc..29
 */
module.exports = ({
  lat2tile: function(lat, zoom) {
    return (Math.floor((1-Math.log(Math.tan(lat*Math.PI/180) + 1/Math.cos(lat*Math.PI/180))/Math.PI)/2 *Math.pow(2,zoom)));
  },
  long2tile: function(lon, zoom) {
    return (Math.floor((lon+180)/360*Math.pow(2,zoom)));
  },
  tile2lat: function (y, z) {
    var n=Math.PI-2*Math.PI*y/Math.pow(2,z);
    return (180/Math.PI*Math.atan(0.5*(Math.exp(n)-Math.exp(-n))));
  },
  tile2long: function(x, z) {
    return (x/Math.pow(2,z)*360-180);
  }
});