| OpenCV 4.3.0 Open Source Computer Vision

Pose of a widget

## 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/calib3d.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;
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_mat;
Rodrigues(rot_vec, rot_mat);
Affine3f pose(rot_mat, Vec3f(translation, translation, translation));
myWindow.setWidgetPose("Cube Widget", pose);
myWindow.spinOnce(1, true);
}
return 0;
}

## 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.