OpenCV/opencv_contrib/modules/viz/tutorials/transformations/transformations.markdown

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 . @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.

-# Here is the result from global point of view.