1 Transformations {#tutorial_transformations}
7 In this tutorial you will learn how to
9 - How to use makeTransformToGlobal to compute pose
10 - How to use makeCameraPose and Viz3d::setViewerPose
11 - How to visualize camera position by axes and by viewing frustum
16 You can download the code from [here ](https://github.com/opencv/opencv/tree/3.4/samples/cpp/tutorial_code/viz/transformations.cpp).
17 @include samples/cpp/tutorial_code/viz/transformations.cpp
22 Here is the general structure of the program:
24 - Create a visualization window.
27 viz::Viz3d myWindow("Transformations");
29 - Get camera pose from camera position, camera focal point and y direction.
31 /// Let's assume camera has the following properties
32 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);
34 /// We can get the pose of the cam using makeCameraPose
35 Affine3f cam_pose = viz::makeCameraPose(cam_pos, cam_focal_point, cam_y_dir);
37 - Obtain transform matrix knowing the axes of camera coordinate system.
39 /// We can get the transformation matrix from camera coordinate system to global using
40 /// - makeTransformToGlobal. We need the axes of the camera
41 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);
43 - Create a cloud widget from bunny.ply file
45 /// Create a cloud widget.
46 Mat bunny_cloud = cvcloud_load();
47 viz::WCloud cloud_widget(bunny_cloud, viz::Color::green());
49 - Given the pose in camera coordinate system, estimate the global pose.
51 /// Pose of the widget in camera frame
52 Affine3f cloud_pose = Affine3f().translate(Vec3f(0.0f,0.0f,3.0f));
53 /// Pose of the widget in global frame
54 Affine3f cloud_pose_global = transform * cloud_pose;
56 - If the view point is set to be global, visualize camera coordinate frame and viewing frustum.
58 /// Visualize camera frame
61 viz::WCameraPosition cpw(0.5); // Coordinate axes
62 viz::WCameraPosition cpw_frustum(Vec2f(0.889484, 0.523599)); // Camera frustum
63 myWindow.showWidget("CPW", cpw, cam_pose);
64 myWindow.showWidget("CPW_FRUSTUM", cpw_frustum, cam_pose);
67 - Visualize the cloud widget with the estimated global pose
70 myWindow.showWidget("bunny", cloud_widget, cloud_pose_global);
72 - If the view point is set to be camera's, set viewer pose to **cam_pose**.
74 /// Set the viewer pose to that of camera
76 myWindow.setViewerPose(cam_pose);
82 -# Here is the result from the camera point of view.
84 ![](images/camera_view_point.png)
86 -# Here is the result from global point of view.
88 ![](images/global_view_point.png)