Method untransform

CvPlot/examples/examples_core.cpp:317–319

            return{ std::cos(p.x)*p.y,std::sin(p.x)*p.y };
        }
        cv::Point2d untransform(const cv::Point2d &p)const override {
            return{ std::atan2(p.y, p.x), std::sqrt(p.x *p.x + p.y*p.y) };
        }
        cv::Rect2d transformBoundingRect(const cv::Rect2d &r)const override{
            double radius = r.y + r.height;
            return cv::Rect2d(-radius, -radius, 2 * radius, 2 * radius);