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;

/**
 * @function main
 */
int main()
{
    /// Create a window
    viz::Viz3d myWindow("Coordinate Frame");

    /// Add coordinate axes
    myWindow.showWidget("Coordinate Widget", viz::WCoordinateSystem());

    /// Add line to represent (1,1,1) axis
    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 widget
    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);

    /// Display widget (update if already displayed)
    myWindow.showWidget("Cube Widget", cube_widget);

    /// Rodrigues vector
    Mat rot_vec = Mat::zeros(1,3,CV_32F);
    float translation_phase = 0.0, translation = 0.0;
    while(!myWindow.wasStopped())
    {
        /* Rotation using rodrigues */
        /// Rotate around (1,1,1)
        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;

        /// Shift on (1,1,1)
        translation_phase += CV_PI * 0.01f;
        translation = sin(translation_phase);

        Mat rot_mat;
        Rodrigues(rot_vec, rot_mat);

        /// Construct pose
        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.

/// Create a window
viz::Viz3d myWindow("Coordinate Frame");

• Show coordinate axes in the window using CoordinateSystemWidget.

/// Add coordinate axes
myWindow.showWidget("Coordinate Widget", viz::WCoordinateSystem());

• Display a line representing the axis (1,1,1).

/// Add line to represent (1,1,1) axis
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.

/// Construct a cube widget
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

/// Rotate around (1,1,1)
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.

/// Construct pose
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.