| OpenCV 5.0.0alpha Open Source Computer Vision

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Pose of a widget

Prev Tutorial: Launching Viz
Next Tutorial: Transformations

# Goal

In this tutorial you will learn how to

- Add widgets to the visualization window
- Use Affine3 to set pose of a widget
- Rotating and translating a widget along an axis

# Code

You can download the code from here.

#include <opencv2/viz.hpp>
#include <opencv2/3d.hpp>
#include <iostream>
using namespace cv;
using namespace std;
static void help()
{
cout
<< "--------------------------------------------------------------------------" << endl
<< "This program shows how to visualize a cube rotated around (1,1,1) and shifted "
<< "using Rodrigues vector." << endl
<< "Usage:" << endl
<< "./widget_pose" << endl
<< endl;
}
int main()
{
help();
viz::Viz3d myWindow("Coordinate Frame");
myWindow.showWidget("Coordinate Widget", viz::WCoordinateSystem());
viz::WLine axis(Point3f(-1.0f,-1.0f,-1.0f), Point3f(1.0f,1.0f,1.0f));
axis.setRenderingProperty(viz::LINE_WIDTH, 4.0);
myWindow.showWidget("Line Widget", axis);
viz::WCube cube_widget(Point3f(0.5,0.5,0.0), Point3f(0.0,0.0,-0.5), true, viz::Color::blue());
cube_widget.setRenderingProperty(viz::LINE_WIDTH, 4.0);
myWindow.showWidget("Cube Widget", cube_widget);
Mat rot_vec = Mat::zeros(1,3,CV_32F);
float translation_phase = 0.0, translation = 0.0;
rot_vec.at<float>(0, 0) += (float)CV_PI * 0.01f;
rot_vec.at<float>(0, 1) += (float)CV_PI * 0.01f;
rot_vec.at<float>(0, 2) += (float)CV_PI * 0.01f;
translation_phase += (float)CV_PI * 0.01f;
translation = sin(translation_phase);
Mat rot_mat;
Rodrigues(rot_vec, rot_mat);
cout << "rot_mat = " << rot_mat << endl;
Affine3f pose(rot_mat, Vec3f(translation, translation, translation));
Affine3f pose2(pose.matrix);
cout << "pose = " << pose.matrix << endl;
cout << "pose = " << pose2.matrix << endl;
while(!myWindow.wasStopped())
{
/* Rotation using rodrigues */
rot_vec.at<float>(0,0) += (float)CV_PI * 0.01f;
rot_vec.at<float>(0,1) += (float)CV_PI * 0.01f;
rot_vec.at<float>(0,2) += (float)CV_PI * 0.01f;
translation_phase += (float)CV_PI * 0.01f;
translation = sin(translation_phase);
Mat rot_mat1;
Rodrigues(rot_vec, rot_mat1);
Affine3f pose1(rot_mat1, Vec3f(translation, translation, translation));
myWindow.setWidgetPose("Cube Widget", pose1);
myWindow.spinOnce(1, true);
}
return 0;
}
3d.hpp
cv::Affine3< float >
cv::Mat
n-dimensional dense array class
Definition mat.hpp:951
cv::Mat::at
_Tp & at(int i0=0)
Returns a reference to the specified array element.
cv::Point3_
Template class for 3D points specified by its coordinates x, y and z.
Definition types.hpp:255
cv::Vec< float, 3 >
cv::viz::Viz3d
The Viz3d class represents a 3D visualizer window. This class is implicitly shared.
Definition viz3d.hpp:68
cv::viz::WCoordinateSystem
Compound widgets.
Definition widgets.hpp:514
cv::viz::WCube
This 3D Widget defines a cube.
Definition widgets.hpp:373
cv::viz::WLine
Simple widgets.
Definition widgets.hpp:236
CV_32F
#define CV_32F
Definition interface.h:81
CV_PI
#define CV_PI
Definition cvdef.h:382
main
int main(int argc, char *argv[])
Definition highgui_qt.cpp:3
cv
Definition core.hpp:107
std
STL namespace.
viz.hpp

# Explanation

Here is the general structure of the program:

- Create a visualization window.
  viz::Viz3d myWindow("Coordinate Frame");
- Show coordinate axes in the window using CoordinateSystemWidget.
  myWindow.showWidget("Coordinate Widget", viz::WCoordinateSystem());
- Display a line representing the axis (1,1,1).
  viz::WLine axis(Point3f(-1.0f,-1.0f,-1.0f), Point3f(1.0f,1.0f,1.0f));
  axis.setRenderingProperty(viz::LINE_WIDTH, 4.0);
  myWindow.showWidget("Line Widget", axis);
- Construct a cube.
  viz::WCube cube_widget(Point3f(0.5,0.5,0.0), Point3f(0.0,0.0,-0.5), true, viz::Color::blue());
  cube_widget.setRenderingProperty(viz::LINE_WIDTH, 4.0);
  myWindow.showWidget("Cube Widget", cube_widget);
- Create rotation matrix from rodrigues vector
  rot_vec.at<float>(0,0) += CV_PI * 0.01f;
  rot_vec.at<float>(0,1) += CV_PI * 0.01f;
  rot_vec.at<float>(0,2) += CV_PI * 0.01f;
  ...
  Mat rot_mat;
  Rodrigues(rot_vec, rot_mat);
- Use Affine3f to set pose of the cube.
  Affine3f pose(rot_mat, Vec3f(translation, translation, translation));
  myWindow.setWidgetPose("Cube Widget", pose);
- Animate the rotation using wasStopped and spinOnce
  while(!myWindow.wasStopped())
  {
  ...
  myWindow.spinOnce(1, true);
  }

# Results

Here is the result of the program.