geohash.js

// geohash.js
// Geohash library for Javascript
// (c) 2008 David Troy
// Distributed under the MIT License
(function(globals) {

  var BITS = [16, 8, 4, 2, 1];

  var BASE32 = "0123456789bcdefghjkmnpqrstuvwxyz";
  var NEIGHBORS = { right  : { even :  "bc01fg45238967deuvhjyznpkmstqrwx" },
  							    left   : { even :  "238967debc01fg45kmstqrwxuvhjyznp" },
  							    top    : { even :  "p0r21436x8zb9dcf5h7kjnmqesgutwvy" },
  							    bottom : { even :  "14365h7k9dcfesgujnmqp0r2twvyx8zb" } };

  var BORDERS   = { right  : { even : "bcfguvyz" },
  							    left   : { even : "0145hjnp" },
  							    top    : { even : "prxz" },
  							    bottom : { even : "028b" } };

  NEIGHBORS.bottom.odd = NEIGHBORS.left.even;
  NEIGHBORS.top.odd = NEIGHBORS.right.even;
  NEIGHBORS.left.odd = NEIGHBORS.bottom.even;
  NEIGHBORS.right.odd = NEIGHBORS.top.even;

  BORDERS.bottom.odd = BORDERS.left.even;
  BORDERS.top.odd = BORDERS.right.even;
  BORDERS.left.odd = BORDERS.bottom.even;
  BORDERS.right.odd = BORDERS.top.even;

  function refineInterval(interval, cd, mask) {
  	if (cd&mask)
  		interval[0] = (interval[0] + interval[1])/2;
    else
  		interval[1] = (interval[0] + interval[1])/2;
  }

  globals.calculateAdjacent = function(srcHash, dir) {
  	srcHash = srcHash.toLowerCase();
  	var lastChr = srcHash.charAt(srcHash.length-1);
  	var type = (srcHash.length % 2) ? 'odd' : 'even';
  	var base = srcHash.substring(0,srcHash.length-1);
  	if (BORDERS[dir][type].indexOf(lastChr)!=-1)
  		base = calculateAdjacent(base, dir);
  	return base + BASE32[NEIGHBORS[dir][type].indexOf(lastChr)];
  }

  globals.decodeGeoHash = function(geohash) {
  	var is_even = 1;
  	var lat = []; var lon = [];
  	lat[0] = -90.0;  lat[1] = 90.0;
  	lon[0] = -180.0; lon[1] = 180.0;
  	lat_err = 90.0;  lon_err = 180.0;

  	for (i=0; i<geohash.length; i++) {
  		c = geohash[i];
  		cd = BASE32.indexOf(c);
  		for (j=0; j<5; j++) {
  			mask = BITS[j];
  			if (is_even) {
  				lon_err /= 2;
  				refineInterval(lon, cd, mask);
  			} else {
  				lat_err /= 2;
  				refineInterval(lat, cd, mask);
  			}
  			is_even = !is_even;
  		}
  	}
  	lat[2] = (lat[0] + lat[1])/2;
  	lon[2] = (lon[0] + lon[1])/2;

  	return { latitude: lat, longitude: lon};
  }

  globals.encodeGeoHash = function(latitude, longitude) {
  	var is_even=1;
  	var i=0;
  	var lat = []; var lon = [];
  	var bit=0;
  	var ch=0;
  	var precision = 12;
  	geohash = "";

  	lat[0] = -90.0;  lat[1] = 90.0;
  	lon[0] = -180.0; lon[1] = 180.0;

  	while (geohash.length < precision) {
  	  if (is_even) {
  			mid = (lon[0] + lon[1]) / 2;
  	    if (longitude > mid) {
  				ch |= BITS[bit];
  				lon[0] = mid;
  	    } else
  				lon[1] = mid;
  	  } else {
  			mid = (lat[0] + lat[1]) / 2;
  	    if (latitude > mid) {
  				ch |= BITS[bit];
  				lat[0] = mid;
  	    } else
  				lat[1] = mid;
  	  }

  		is_even = !is_even;
  	  if (bit < 4)
  			bit++;
  	  else {
  			geohash += BASE32[ch];
  			bit = 0;
  			ch = 0;
  	  }
  	}
  	return geohash;
  }

}(window));