Method point2

CvPlot/examples/DoublePendulum.h:26–28

		return { l * sin(t1), l * -cos(t1) };
	}
	cv::Point2d point2() const {
		return point1() + cv::Point2d{ l * sin(t2), l * -cos(t2) };
	}
	const std::vector<cv::Point2d>& trace() const {
		return traceVec;
	}