Explanation

• Create a visualization window.

• Get camera pose from camera position, camera focal point and y direction.

• Obtain transform matrix knowing the axes of camera coordinate system.

• Create a cloud widget from bunny.ply file

• Given the pose in camera coordinate system, estimate the global pose.

• If the view point is set to be global, visualize camera coordinate frame and viewing frustum.

• Visualize the cloud widget with the estimated global pose

• If the view point is set to be camera’s, set viewer pose to cam_pose.

Code

#include <opencv2/viz/vizcore.hpp>#include <iostream>#include <fstream>using namespace cv;using namespace std;/** * @function cvcloud_load * @brief load bunny.ply */Mat cvcloud_load(){    Mat cloud(1, 1889, CV_32FC3);    ifstream ifs("bunny.ply");    string str;    for(size_t i = 0; i < 12; ++i)        getline(ifs, str);    Point3f* data = http://www.mamicode.com/cloud.ptr();"Usage: " << endl << "./transformations [ G | C ]" << endl;        return 1;    }    bool camera_pov = (argv[1][0] == ‘C‘);    /// Create a window    viz::Viz3d myWindow("Coordinate Frame");    /// Add coordinate axes    myWindow.showWidget("Coordinate Widget", viz::WCoordinateSystem());    /// Let‘s assume camera has the following properties    Point3f cam_pos(3.0f,3.0f,3.0f), cam_focal_point(3.0f,3.0f,2.0f), cam_y_dir(-1.0f,0.0f,0.0f);    /// We can get the pose of the cam using makeCameraPose    Affine3f cam_pose = viz::makeCameraPose(cam_pos, cam_focal_point, cam_y_dir);    /// We can get the transformation matrix from camera coordinate system to global using    /// - makeTransformToGlobal. We need the axes of the camera    Affine3f transform = viz::makeTransformToGlobal(Vec3f(0.0f,-1.0f,0.0f), Vec3f(-1.0f,0.0f,0.0f), Vec3f(0.0f,0.0f,-1.0f), cam_pos);    /// Create a cloud widget.    Mat bunny_cloud = cvcloud_load();    viz::WCloud cloud_widget(bunny_cloud, viz::Color::green());    /// Pose of the widget in camera frame    Affine3f cloud_pose = Affine3f().translate(Vec3f(0.0f,0.0f,3.0f));    /// Pose of the widget in global frame    Affine3f cloud_pose_global = transform * cloud_pose;    /// Visualize camera frame    if (!camera_pov)    {        viz::WCameraPosition cpw(0.5); // Coordinate axes        viz::WCameraPosition cpw_frustum(Vec2f(0.889484, 0.523599)); // Camera frustum        myWindow.showWidget("CPW", cpw, cam_pose);        myWindow.showWidget("CPW_FRUSTUM", cpw_frustum, cam_pose);    }    /// Visualize widget    myWindow.showWidget("bunny", cloud_widget, cloud_pose_global);    /// Set the viewer pose to that of camera    if (camera_pov)        myWindow.setViewerPose(cam_pose);    /// Start event loop.    myWindow.spin();    return 0;}

OpenCV Tutorials —— Transformations