Pose of a widget

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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.