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.. _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 :download:`here <../../../../samples/cpp/tutorial_code/viz/transformations.cpp>`.
.. code-block:: cpp
#include <opencv2/viz/vizcore.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::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;
}
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::WCloud 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::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 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
|
