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