Detect a point is inside a polygon with google maps

// Thanks to App Delegate Inc

// For API V2

GPolygon.prototype.contains = function(latLng) {

 var inPolygon = false;

// Exclude points outside of bounds as there is no way they are in the polygon

var bounds = this.getBounds();

if  (bounds!=null && bounds.contiansLatLng) {

// Raycast point in polygon method

var numPoints = this.getVertexCount();

var j = numPoints - 1;

var P = latLng;

for (var i = 0; i < numPoints; i++) {

var P1 = this.getVertex(i);

var P2 = this.getVertex(j);

if (P1.lng()<P.lng() && P.lng()<=P2.lng()) {

if ( (P2.lng()-P1.lng())*(P.lat()-P1.lat()) < (P.lng()-P1.lng())*(P2.lat()-P1.lat()) ) {

inPolygon = !inPolygon;

}

}

j = i;

}

}

return inPolygon;

}

// For API V3

google.maps.Polygon.prototype.contains = function(latLng) {

var inPolygon = false;

var path = this.getPath();

if (path) {

// Raycast point in polygon method

var numPoints = path.getLength();

        var j = numPoints - 1;
        var P = latLng;
        for (var i = 0; i < numPoints; i++) {
            var P1 = path.getAt(i);
            var P2 = path.getAt(j);
            if (P1.lng()<P.lng() && P.lng()<=P2.lng()) {
                if ( (P2.lng()-P1.lng())*(P.lat()-P1.lat()) < (P.lng()-P1.lng())*(P2.lat()-P1.lat()) ) {
                    inPolygon = !inPolygon;
                }
            }
            j = i;
        }

}

return inPolygon;

}