opencv图像坐标点检测出来后，怎么进行点与点间实际距离与角度换算？

[berlinpand]

进行了角点检测把图像上一条线上的角点检测出来了，但是输出的是像素坐标点，想问问如何进行点与点像素距离到实际距离的转换，和点与点连线间直线夹角的计算，算法是了解一些，可是实现不太懂，请大家赐教

[赵4老师]

仅供参考：

double angle( Point pt1, Point pt2, Point pt0 ) {// finds a cosine of angle between vectors from pt0->pt1 and from pt0->pt2
    double dx1 = pt1.x - pt0.x;
    double dy1 = pt1.y - pt0.y;
    double dx2 = pt2.x - pt0.x;
    double dy2 = pt2.y - pt0.y;
    double ratio;//边长平方的比
    ratio=(dx1*dx1+dy1*dy1)/(dx2*dx2+dy2*dy2);
    if (ratio<0.8 || 1.2<ratio) {//根据边长平方的比过小或过大提前淘汰这个四边形，如果淘汰过多，调整此比例数字
//      Log("ratio\n");
        return 1.0;//根据边长平方的比过小或过大提前淘汰这个四边形
    }
    return (dx1*dx2 + dy1*dy2)/sqrt((dx1*dx1 + dy1*dy1)*(dx2*dx2 + dy2*dy2) + 1e-10);
}
void findSquares( const Mat& gray0, vector<vector<Point> >& squares ) {// returns sequence of squares detected on the gray0. the sequence is stored in the specified memory storage
    squares.clear();

    Mat pyr,gray1,timg;

    // down-scale and upscale the gray0 to filter out the noise
    pyrDown(gray0, pyr, Size(gray0.cols/2, gray0.rows/2));
    pyrUp(pyr, timg, gray0.size());
    vector<vector<Point> > contours;

    // try several threshold levels
    for (int l = 0; l < N; l++ ) {
        // hack: use Canny instead of zero threshold level.
        // Canny helps to catch squares with gradient shading
//      if (l == 0 ) {//可试试不对l==0做特殊处理是否能在不影响判断正方形的前提下加速判断过程
//          // apply Canny. Take the upper threshold from slider
//          // and set the lower to 0 (which forces edges merging)
//          Canny(timg, gray1, 0, thresh, 5);
//          // dilate canny output to remove potential
//          // holes between edge segments
//          dilate(gray1, gray1, Mat(), Point(-1,-1));
//      } else {
            // apply threshold if l!=0:
            //     tgray(x,y) = gray1(x,y) < (l+1)*255/N ? 255 : 0
            gray1 = timg >= (l+1)*255/N;
//      }

        // find contours and store them all as a list
        findContours(gray1, contours, CV_RETR_LIST, CV_CHAIN_APPROX_SIMPLE);

        vector<Point> approx;

        // test each contour
        for (size_t i = 0; i < contours.size(); i++ ) {
            // approximate contour with accuracy proportional
            // to the contour perimeter
            approxPolyDP(Mat(contours[i]), approx, arcLength(Mat(contours[i]), true)*0.02, true);//0.02为将毛边拉直的系数，如果对毛边正方形漏检，可试试调大

            // square contours should have 4 vertices after approximation
            // relatively large area (to filter out noisy contours)
            // and be convex.
            // Note: absolute value of an area is used because
            // area may be positive or negative - in accordance with the
            // contour orientation
            if (approx.size() == 4 && isContourConvex(Mat(approx))) {
                double area;
                area=fabs(contourArea(Mat(approx)));
                if (4000.0<area && area<30000.0) {//当正方形面积在此范围内……，如果有因面积过大或过小漏检正方形问题，调整此范围。
//                  printf("area=%lg\n",area);
                    double maxCosine = 0.0;

                    for (int j = 2; j < 5; j++ ) {
                        // find the maximum cosine of the angle between joint edges
                        double cosine = fabs(angle(approx[j%4], approx[j-2], approx[j-1]));
                        maxCosine = MAX(maxCosine, cosine);
                        if (maxCosine==1.0) break;// //边长比超过设定范围
                    }

                    // if cosines of all angles are small
                    // (all angles are ~90 degree) then write quandrange
                    // vertices to resultant sequence
                    if (maxCosine < 0.1 ) {//四个角和直角相比的最大误差，可根据实际情况略作调整，越小越严格
                        squares.push_back(approx);
                        return;//检测到一个合格的正方形就返回
//                  } else {
//                      Log("Cosine>=0.1\n");
                    }
                }
            }
        }
    }
}

[沐阳2100]

你说的实际坐标，实际距离是指现实中地理位置空间的坐标和距离还是相对于客户区现实界面的坐标距离啊？

[berlinpand]

引用 2 楼 m0_37901643 的回复:

你说的实际坐标，实际距离是指现实中地理位置空间的坐标和距离还是相对于客户区现实界面的坐标距离啊？

其实我想知道的是单幅（图像中的距离和现实中比例是1：1的）图像上测出两个像素点的像素距离后如何换成cm等长度单位，不知道这样说您了解了吗。

[李吉吉吉吉]

最近有啥进展吗？我最近也在弄坐标问题

[一只酸奶瓶]

有进展了咩？opecv下的坐标是从左上角开始的 这样如何求解点对的距离哇