vendor: OpenCV 5.0.0 snapshot at 755e50675d97db9b7d449d8bd6b09888646f6c6e

2026-08-22 00:11:13 +08:00
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+Transformations {#tutorial_transformations}
+===============
+
+@prev_tutorial{tutorial_widget_pose}
+@next_tutorial{tutorial_creating_widgets}
+
+Goal
+----
+
+In this tutorial you will learn how to
+
+-   How to use makeTransformToGlobal to compute pose
+-   How to use makeCameraPose and Viz3d::setViewerPose
+-   How to visualize camera position by axes and by viewing frustum
+
+Code
+----
+
+You can download the code from [here ](https://github.com/opencv/opencv_contrib/tree/master/modules/viz/samples/transformations.cpp).
+@include viz/samples/transformations.cpp
+
+Explanation
+-----------
+
+Here is the general structure of the program:
+
+-   Create a visualization window.
+    @code{.cpp}
+    /// Create a window
+    viz::Viz3d myWindow("Transformations");
+    @endcode
+-   Get camera pose from camera position, camera focal point and y direction.
+    @code{.cpp}
+    /// 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);
+    @endcode
+-   Obtain transform matrix knowing the axes of camera coordinate system.
+    @code{.cpp}
+    /// 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);
+    @endcode
+-   Create a cloud widget from bunny.ply file
+    @code{.cpp}
+    /// Create a cloud widget.
+    Mat bunny_cloud = cvcloud_load();
+    viz::WCloud cloud_widget(bunny_cloud, viz::Color::green());
+    @endcode
+-   Given the pose in camera coordinate system, estimate the global pose.
+    @code{.cpp}
+    /// 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;
+    @endcode
+-   If the view point is set to be global, visualize camera coordinate frame and viewing frustum.
+    @code{.cpp}
+    /// 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);
+    }
+    @endcode
+-   Visualize the cloud widget with the estimated global pose
+    @code{.cpp}
+    /// Visualize widget
+    myWindow.showWidget("bunny", cloud_widget, cloud_pose_global);
+    @endcode
+-   If the view point is set to be camera's, set viewer pose to **cam_pose**.
+    @code{.cpp}
+    /// Set the viewer pose to that of camera
+    if (camera_pov)
+        myWindow.setViewerPose(cam_pose);
+    @endcode
+
+Results
+-------
+
+-#  Here is the result from the camera point of view.
+
+![](images/camera_view_point.png)
+
+-#  Here is the result from global point of view.
+
+![](images/global_view_point.png)