Useful geo functions

Haversine.js

function haversineDistance(lat1, lon1, lat2, lon2) {
    'use strict';
    var R = 6378100; // metres
    var dLat = this.deg2rad(lat2 - lat1);
    var dLon = this.deg2rad(lon2 - lon1);
    var a =
        Math.sin(dLat / 2) * Math.sin(dLat / 2) +
        Math.cos(this.deg2rad(lat1)) * Math.cos(this.deg2rad(lat2)) *
        Math.sin(dLon / 2) * Math.sin(dLon / 2);
    var c = 2 * Math.atan2(Math.sqrt(a), Math.sqrt(1 - a));
    var d = R * c;
    return d;
}

function deg2rad(deg) {
  'use strict';
  return deg * (Math.PI / 180);
}

Quadkey.js

//Convert Latitude/Longitude to Quadkey

function tileXYToQuadKey(tile, zoom) {
    var quadKey='', i, digit, mask;
    for (i = zoom; i > 0; i--) {
        digit = '0';
        mask = 1 << (i - 1);
        if ((tile.x & mask) !== 0) {
            digit++;
        }
        if ((tile.y & mask) !== 0) {
            digit++;
            digit++;
        }
        quadKey+= "" + digit;
    }
    return quadKey;
}

function tileSystem(latitude, longitude) {
    var sinLatitude = Math.sin(latitude * Math.PI/180);
    var x = ((longitude + 180) / 360) * 256 * Math.pow(2,16);
    var y = (0.5 - Math.log((1 + sinLatitude) / (1 - sinLatitude)) / (4 * Math.PI)) * 256 * Math.pow(2, 16);
    return {x: Math.round(x/256), y: Math.round(y/256)};
}

var quadkey = tileXYToQuadKey(tileSystem(latitude, longitude), 16);