OpenLayers.Geometry.LineString.prototype.getCentroid = function() {
	var vertices = this.getVertices();
	if (vertices.length == 2) {
		var center_x = (vertices[0].x + vertices[1].x)/2;
		var center_y = (vertices[0].y + vertices[1].y)/2;
        return new OpenLayers.Geometry.Point( center_x, center_y );
	} else {
		// The original getCentroid-method
        return this.components.length && this.components[0].getCentroid();
	}
};