public RectangleEdge getRangeAxisEdge(int index) {
        AxisLocation location = getRangeAxisLocation(index);
        RectangleEdge result = Plot.resolveRangeAxisLocation(location,
                this.orientation);
        if (result == null) {
            result = RectangleEdge.opposite(getRangeAxisEdge(0));
        }
        return result;