1.

鼠标左键按下选择起点，拖动鼠标，左键放开，确定终点。

实现效果1

实现效果2

2.

在linux下使用libfreenect2开源多平台驱动来获取kinect2.0的传感器信息，得到深度信息，并通过libfreenect2提供的函数，来得到相机坐标系中某一点的空间坐标。

3.

运用鼠标操作函数（setMouseCallback），来获取画面中的两个点，并用直线将他们连接起来，通过（2）中的方法得到两点的空间坐标：A(x1,y1,z1)，B(x2,y2,z2)。通过简单计算，便可以求得两点的实际距离。

4.

关键代码：

while(!protonect_shutdown)    {        listener.waitForNewFrame(frames);        libfreenect2::Frame *rgb = frames[libfreenect2::Frame::Color];        libfreenect2::Frame *depth = frames[libfreenect2::Frame::Depth];        cv::Mat(rgb->height, rgb->width, CV_8UC4, rgb->data).copyTo(rgbmat);        cv::Mat(depth->height, depth->width, CV_32FC1, depth->data).copyTo(depthmat);        cv::Mat(registered.height, registered.width, CV_8UC4, registered.data).copyTo(rgbd);        registration->apply(rgb, depth, &undistorted, &registered, true, &depth2rgb);        cv::Mat(registered.height, registered.width, CV_8UC4, registered.data).copyTo(rgbd);        //resize(rgbmat, dst1, Size(), c, d, INTER_NEAREST);        inRange(depthmat,Scalar(a),Scalar(b),dst);        //morphologyEx(dst,dst,MORPH_OPEN,kernel);        findContours(dst,contours,hireachy,RETR_EXTERNAL,CHAIN_APPROX_SIMPLE,Point(0,0));        if (contours.size() > 0)        {            double maxArea=0;            for (int i = 0; i < contours.size(); i++)            {                double area = contourArea(contours[static_cast
     
      (i)]);                if (area > maxArea)                {                    maxArea = area;                    rect = boundingRect(contours[static_cast
      
       (i)]);                    minEnclosingCircle(contours[static_cast
       
        (i)], center, radius);                }            }        }        setMouseCallback("main",on_MouseHandle);     // 鼠标操作        registration->getPointXYZ(&undistorted, pt11.y, pt11.x,x1, y1, z1);  // 像素坐标转化为空间坐标        registration->getPointXYZ(&undistorted,pt21.y,pt21.x,x2, y2, z2);        //rectangle(rgbd, rect, Scalar(0,255,0),2);        line(rgbd, pt11, pt21, Scalar(0,255,0));   //  划线        l = sqrt(pow((x1-x2),2) + pow((y1-y2),2) + pow((z1-z2),2));        cout << "length:" << l << "m" <
        
          0 && ((key & 0xFF) == 27)); // shutdown on escape         listener.release(frames);    }     dev->stop();    dev->close();     delete registration; #endif     std::cout << "stop!" << std::endl;    return 0;}void on_MouseHandle(int event, int x, int y, int flags, void* ustc){    if (event == EVENT_LBUTTONDOWN)    {        Point pt1 = Point(x, y);        pt11 = pt1;    }    else if (event == EVENT_LBUTTONUP)    {        Point pt2 = Point(x, y);        pt21 = pt2;    }}