Clustering algorithm

cluster.js

var MAX_ZOOM = 21;
var OFFSET = 268435456;
var RADIUS = 85445659.4471;
    
var latToY = function(value) {
	return Math.round(OFFSET - RADIUS * Math.log((1 + Math.sin(value * Math.PI / 180)) / (1 - Math.sin(value * Math.PI / 180))) / 2);
};

var lngToX = function(value) {
    return Math.round(OFFSET + RADIUS * value * Math.PI / 180);        
};

var pixelDistance = function(p1, p2, zoom) {
    var x1 = lngToX(p1.lng);
    var y1 = latToY(p1.lat);
    var x2 = lngToX(p2.lng);
    var y2 = latToY(p2.lat);
        
    return Math.sqrt(Math.pow((x1 - x2), 2) + Math.pow((y1 - y2), 2)) >> (MAX_ZOOM - zoom);
};

exports.walks = function(walks, minDistance, zoom) {
	var clusters = [];
	
	while (walks.length > 0) {
		var walk = walks.pop();
		var cluster = [];
		
		walks.forEach(function(adjacent, i) {
			var distance = pixelDistance(walk.startPoint, adjacent.startPoint, zoom);
			
			if (minDistance > distance) {
				walks.splice(i, 1);
				cluster.push(adjacent);
			}
		});
		
		if (cluster.length > 0) {
			cluster.push(walk);
			clusters.push(cluster);
		} else {
			clusters.push(walk);
		}
	}
	
	return clusters;
};