gistfile1.js

//point in polygon algorithm
var inside = function (point, polygon) {
    // ray-casting algorithm based on
    // http://www.ecse.rpi.edu/Homepages/wrf/Research/Short_Notes/pnpoly.html
    
    var x = point[0], y = point[1];
    
    var inside = false;
    for (var i = 0, j = polygon.length - 1; i < polygon.length; j = i++) {
        var xi = polygon[i][0], yi = polygon[i][1];
        var xj = polygon[j][0], yj = polygon[j][1];
        
        var intersect = ((yi > y) != (yj > y))
            && (x < (xj - xi) * (y - yi) / (yj - yi) + xi);
        if (intersect) inside = !inside;
    }
    
    return inside;
};