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;

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) += CV_PI * 0.01f;
 rot_vec.at<float>(0,1) += CV_PI * 0.01f;
 rot_vec.at<float>(0,2) += CV_PI * 0.01f;

 translation_phase += 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.