版本：opencv-4.7.0-windows
Opencv中，大多数时候，逆时针旋转是正方向，但在RotatedRect和ellipse中，顺时针旋转是正方向。

//RotatedRect的角度参数是顺时针为正方向
RotatedRect(const Point2f& center, const Size2f& size, float angle);

//ellipse的angle、startAngle、endAngle都是顺时针为正方向
void ellipse(InputOutputArray img, Point center, Size axes,
                        double angle, double startAngle, double endAngle,
                        const Scalar& color, int thickness = 1,
                        int lineType = LINE_8, int shift = 0);

源码说明：

代码测试：

#include <opencv2/opencv.hpp>
int main()
{
#pragma region RotatedRect顺时针为正
	cv::Mat image = cv::Mat(500, 500, CV_8UC3, cv::Scalar(255,255,255));

	cv::Scalar color(0, 0, 255); 
	cv::Point2f center1 = cv::Point2f(100, 100);
	cv::Size2f axes1 = cv::Size2f(100, 50);

	cv::RotatedRect rotatedRect(center1, axes1, 0);
	cv::Point2f vertices[4];
	rotatedRect.points(vertices);
	for (int i = 0; i < 4; i++) {
		cv::line(image, vertices[i], vertices[(i + 1) % 4], color, 1, cv::LINE_AA);
	}


	cv::Point2f center2 = cv::Point2f(300, 100);
	cv::RotatedRect rotatedRect1(center2, axes1, 5);
	rotatedRect1.points(vertices);
	for (int i = 0; i < 4; i++) {
		cv::line(image, vertices[i], vertices[(i + 1) % 4], color, 1, cv::LINE_AA);
	}
#pragma endregion

#pragma region ellipse顺时针为正
	cv::Point center3 = cv::Point(50,300);
	int radius1 = 50;
	int startAngle = 0;
	int endAngle = 90;
	cv::ellipse(image, center3, cv::Size(radius1, radius1), 0, startAngle, endAngle, color, 5, cv::LINE_AA);

	cv::Point center4 = cv::Point(250, 300);
	endAngle = 180;
	cv::ellipse(image, center4, cv::Size(radius1, radius1), 0, startAngle, endAngle, color, 5, cv::LINE_AA);

	cv::Point center5 = cv::Point(400, 300);
	cv::ellipse(image, center5, cv::Size(radius1, radius1), 30, startAngle, endAngle, color, 5, cv::LINE_AA);
	
	cv::imshow("Image", image);
	cv::waitKey(0);
	cv::destroyAllWindows();
#pragma region ellipse顺时针为正
}

测试结果：