estore();
    }

    function drawCentroidGuidewire(loc, polygon) {
        var angle = Math.atan( (loc.y - polygon.y) / (loc.x - polygon.x) ),
            radius, endpt;

        radius = polygon.radius + TRACKING_RING_MARGIN;
        angle = angle - rotatingLockAngle;

        if (loc.x >= polygon.x) {
            endpt = { x: polygon.x + radius * Math.cos(angle),
                y: polygon.y + radius * Math.sin(angle)
            };
        }
        else {
            endpt = { x: polygon.x - radius * M