OpenCV4探索学习：基础功能与技巧

（长期更新）

1、Mat中数据传递、赋值，操作clone() 与copyto()的区别。

Mat imageSrc = imread("1.png" , 0) ;
Mat imageDst(imageSrc) ;//仅是创建了Mat的头部分，共享数据区
Mat imageDst = imageSrc ;//仅是创建了Mat的头部分，共享数据区
Mat imageDst = imageSrc.clone() ;//完全拷贝，把imageSrc中的所有信息拷贝到imageDst中
Mat imageDst ;imageSrc.copyTo(imageDst) ;//拷贝imageSrc的数据区到imageDst中，在拷贝数据前会有一步：imageDst.create(this->size , this->type)

2、vector转存到Mat：

Mat VecToMat(vector vecPoint)
{
    int nSize = vecPoint.size();
    Mat matOut = Mat(nSize, 2, CV_64F);
    for (int i = 0; i < matOut.rows; i++)
    {
        matOut.at(i, 0) = vecPoint[i].x;
        matOut.at(i, 1) = vecPoint[i].y;
    }	
    return matOut
}

3、画闭合点连线

Point2f vertices[4];
rRect.points(vertices);
for (int i = 0; i < 4; i++)
	line(test_image, vertices[i], vertices[(i+1)%4], Scalar(0,255,0), 2);

4、捕获异常

try
{
	
}  
catch (cv::Exception& e)  
{      
   char* msg_e = e.what();  
   return -1;
}

5、绘制带方向箭头的直线

void drawAxis(Mat& img, Point p, Point q, Scalar colour, const float scale = 0.2)
{
    //! [visualization1]
    double angle = atan2( (double) p.y - q.y, (double) p.x - q.x ); // angle in radians
    double hypotenuse = sqrt( (double) (p.y - q.y) * (p.y - q.y) + (p.x - q.x) * (p.x - q.x));

    // Here we lengthen the arrow by a factor of scale
    q.x = (int) (p.x - scale * hypotenuse * cos(angle));
    q.y = (int) (p.y - scale * hypotenuse * sin(angle));
    line(img, p, q, colour, 1, LINE_AA);

    // create the arrow hooks
    p.x = (int) (q.x + 9 * cos(angle + CV_PI / 4));
    p.y = (int) (q.y + 9 * sin(angle + CV_PI / 4));
    line(img, p, q, colour, 1, LINE_AA);

    p.x = (int) (q.x + 9 * cos(angle - CV_PI / 4));
    p.y = (int) (q.y + 9 * sin(angle - CV_PI / 4));
    line(img, p, q, colour, 1, LINE_AA);
    //! [visualization1]
}