if (data.length == 2) {
            if (idx == 0) {
                gd = [
                    [xp.call(this._xaxis, data[0][0]), yp.call(this._yaxis, data[0][1])], 
                    [xp.call(this._xaxis, data[1][0]), yp.call(this._yaxis, data[1][1]),