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 <opencv2/3d.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();

    /// 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);
    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;

    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;

    /// Shift on (1,1,1)
    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;
    /// Construct pose
    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 */
        /// Rotate around (1,1,1)
        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;

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

        Mat rot_mat1;
        Rodrigues(rot_vec, rot_mat1);

        /// Construct pose
        Affine3f pose1(rot_mat1, Vec3f(translation, translation, translation));

        myWindow.setWidgetPose("Cube Widget", pose1);

        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.

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