opencv/doc/tutorials/viz/transformations/transformations.markdown

Transformations

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 . @code{.cpp} #include <opencv2/viz.hpp> #include #include

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.ptrcv::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::WCoordinateSystem());

  /// 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::WCloud 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::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); }

  /// 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; } @endcode Explanation

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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

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1. Here is the result from the camera point of view.

   

2. Here is the result from global point of view.