transformations tutorial rst

doc/tutorials/viz/transformations.rst

+.. _transformations:
+
+Transformations
+***************
+
+Goal
+====
+
+In this tutorial you will learn how to
+
+.. container:: enumeratevisibleitemswithsquare
+
+  * 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 <../../../../samples/cpp/tutorial_code/viz/transformations.cpp>`_.
+
+.. code-block:: cpp
+
+    #include <opencv2/viz.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 = cloud.ptr<cv::Point3f>();
+        float dummy1, dummy2;
+        for(size_t i = 0; i < 1889; ++i)
+            ifs >> data[i].x >> data[i].y >> data[i].z >> dummy1 >> dummy2;
+        
+        cloud *= 5.0f;
+        return cloud;
+    }
+
+    /**
+     * @function main
+     */
+    int main(int argn, char **argv)
+    {        
+        if (argn < 2)
+        {
+            cout << "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::CoordinateSystemWidget());
+        
+        /// 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::CloudWidget 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::CameraPositionWidget cpw(0.5); // Coordinate axes
+            viz::CameraPositionWidget 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;
+    }
+
+    
+Explanation
+===========
+
+Here is the general structure of the program:
+
+* Create a visualization window.
+
+.. code-block:: cpp
+
+    /// Create a window
+    viz::Viz3d myWindow("Transformations");
+    
+* Get camera pose from camera position, camera focal point and y direction.
+
+.. code-block:: 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);
+    
+* Obtain transform matrix knowing the axes of camera coordinate system.
+
+.. code-block:: 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);
+    
+* Create a cloud widget from bunny.ply file
+
+.. code-block:: cpp
+
+    /// Create a cloud widget.
+    Mat bunny_cloud = cvcloud_load();
+    viz::CloudWidget cloud_widget(bunny_cloud, viz::Color::green());
+    
+* Given the pose in camera coordinate system, estimate the global pose.
+    
+.. code-block:: 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;
+    
+* If the view point is set to be global, visualize camera coordinate frame and viewing frustum.
+
+.. code-block:: cpp
+
+    /// Visualize camera frame
+    if (!camera_pov)
+    {
+        viz::CameraPositionWidget cpw(0.5); // Coordinate axes
+        viz::CameraPositionWidget cpw_frustum(Vec2f(0.889484, 0.523599)); // Camera frustum
+        myWindow.showWidget("CPW", cpw, cam_pose);
+        myWindow.showWidget("CPW_FRUSTUM", cpw_frustum, cam_pose);
+    }
+    
+* Visualize the cloud widget with the estimated global pose
+    
+.. code-block:: cpp
+
+    /// Visualize widget
+    myWindow.showWidget("bunny", cloud_widget, cloud_pose_global);
+    
+* If the view point is set to be camera's, set viewer pose to **cam_pose**.
+    
+.. code-block:: cpp
+
+    /// Set the viewer pose to that of camera
+    if (camera_pov)
+        myWindow.setViewerPose(cam_pose);
+        
+Results
+=======
+
+#. Here is the result from the camera point of view.
+
+    .. image:: images/camera_view_point.png
+        :alt: Camera Viewpoint
+        :align: center
+
+#. Here is the result from global point of view.
+
+    .. image:: images/global_view_point.png
+        :alt: Global Viewpoint
+        :align: center

samples/cpp/tutorial_code/viz/transformations.cpp

@@ -6,6 +6,7 @@
 
 #include <opencv2/viz.hpp>
 #include <iostream>
+#include <fstream>
 
 using namespace cv;
 using namespace std;
@@ -22,10 +23,32 @@ void help()
     << "how to use makeCameraPose and Viz3d::setViewerPose. You can observe the scene "
     << "from camera point of view (C) or global point of view (G)"                    << endl
     << "Usage:"                                                                       << endl
-    << "./coordinate_frame [ G | C ]"                                                 << endl
+    << "./transformations [ G | C ]"                                                 << endl
     << endl;
 }
 
+/**
+ * @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 = cloud.ptr<cv::Point3f>();
+    float dummy1, dummy2;
+    for(size_t i = 0; i < 1889; ++i)
+        ifs >> data[i].x >> data[i].y >> data[i].z >> dummy1 >> dummy2;
+    
+    cloud *= 5.0f;
+    return cloud;
+}
+
 /**
  * @function main
  */
@@ -48,20 +71,23 @@ int main(int argn, char **argv)
     myWindow.showWidget("Coordinate Widget", viz::CoordinateSystemWidget());
     
     /// 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(-1.0,0.0,0.0);
+    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.
-    viz::SphereWidget sphere_widget(Point3f(0.0,0.0,0.0), 0.5, 10, viz::Color::red());
+    Mat bunny_cloud = cvcloud_load();
+    viz::CloudWidget cloud_widget(bunny_cloud, viz::Color::green());
     
     /// Pose of the widget in camera frame
-    Affine3f sphere_pose = Affine3f().translate(Vec3f(0.0f,0.0f,3.0f));
+    Affine3f cloud_pose = Affine3f().translate(Vec3f(0.0f,0.0f,3.0f));
     /// Pose of the widget in global frame
-    Affine3f sphere_pose_global = transform * sphere_pose;
+    Affine3f cloud_pose_global = transform * cloud_pose;
     
     /// Visualize camera frame
     if (!camera_pov)
@@ -73,7 +99,7 @@ int main(int argn, char **argv)
     }
     
     /// Visualize widget
-    myWindow.showWidget("sphere", sphere_widget, sphere_pose_global);
+    myWindow.showWidget("bunny", cloud_widget, cloud_pose_global);
     
     /// Set the viewer pose to that of camera
     if (camera_pov)