Visual Servoing Platform  version 3.2.1 under development (2019-09-17) under development (2019-09-17)

Example that shows how to simulate a visual servoing on a Pioneer mobile robot equipped with a camera able to move along the pan axis. The current visual features that are used are s = (x, log(Z/Z*)). The desired one are s* = (x*, 0), with:

The degrees of freedom that are controlled are (vx, wz), where wz is the rotational velocity and vx the translational velocity of the mobile platform at point M located at the middle between the two wheels.

The feature x allows to control wy, while log(Z/Z*) allows to control vz.

#include <iostream>
#include <visp3/core/vpHomogeneousMatrix.h>
#include <visp3/core/vpVelocityTwistMatrix.h>
#include <visp3/gui/vpPlot.h>
#include <visp3/robot/vpSimulatorPioneerPan.h>
#include <visp3/visual_features/vpFeatureBuilder.h>
#include <visp3/visual_features/vpFeatureDepth.h>
#include <visp3/visual_features/vpFeaturePoint.h>
#include <visp3/vs/vpServo.h>
int main()
try {
// Set the position the camera has to reach
cdMo[1][3] = 1.2; // t_y should be different from zero to be non singular
cdMo[2][3] = 0.5;
// Set the initial camera position
cMo[0][3] = 0.3;
cMo[1][3] = cdMo[1][3];
cMo[2][3] = 1.;
vpRotationMatrix cdRo(0, atan2(cMo[0][3], cMo[1][3]), 0);
// Get robot position world frame
// Compute the position of the object in the world frame
wMo = wMc * cMo;
// Define the target
vpPoint point(0, 0, 0); // Coordinates in the object frame
vpServo task;
cVe = robot.get_cVe();
vpMatrix eJe;
// Current and desired visual feature associated later to the x coordinate
// of the point
vpFeaturePoint s_x, s_xd;
// Create the current x visual feature
// Create the desired x* visual feature
s_xd.buildFrom(0, 0, cdMo[2][3]);
// Add the feature
task.addFeature(s_x, s_xd, vpFeaturePoint::selectX());
// Create the current and desired log(Z/Z*) visual feature
vpFeatureDepth s_Z, s_Zd;
// Initial depth of the target in front of the camera
double Z = point.get_Z();
// Desired depth Z* of the target.
double Zd = cdMo[2][3];
s_Z.buildFrom(s_x.get_x(), s_x.get_y(), Z, log(Z / Zd));
s_Zd.buildFrom(0, 0, Zd,
0); // log(Z/Z*) = 0 that's why the last parameter is 0
// Add the feature
task.addFeature(s_Z, s_Zd);
// Create a window (800 by 500) at position (400, 10) with 3 graphics
vpPlot graph(3, 800, 500, 400, 10, "Curves...");
// Init the curve plotter
graph.initGraph(0, 3);
graph.initGraph(1, 2);
graph.initGraph(2, 1);
graph.setTitle(0, "Velocities");
graph.setTitle(1, "Error s-s*");
graph.setTitle(2, "Depth");
graph.setLegend(0, 0, "vx");
graph.setLegend(0, 1, "wz");
graph.setLegend(0, 2, "qdot_pan");
graph.setLegend(1, 0, "x");
graph.setLegend(1, 1, "log(Z/Z*)");
graph.setLegend(2, 0, "Z");
int iter = 0;
for (;;) {
cMo = wMc.inverse() * wMo;
// Update the current x feature
// Update log(Z/Z*) feature. Since the depth Z change, we need to update
// the intection matrix
Z = point.get_Z();
s_Z.buildFrom(s_x.get_x(), s_x.get_y(), Z, log(Z / Zd));
// Compute the control law. Velocities are computed in the mobile robot
// reference frame
// Send the velocity to the robot
graph.plot(0, iter, v); // plot velocities applied to the robot
graph.plot(1, iter, task.getError()); // plot error vector
graph.plot(2, 0, iter, Z); // plot the depth
if (task.getError().sumSquare() < 0.0001) {
std::cout << "Reached a small error. We stop the loop... " << std::endl;
const char *legend = "Click to quit...";
vpDisplay::displayText(graph.I, (int)graph.I.getHeight() - 60, (int)graph.I.getWidth() - 150, legend, vpColor::red);
// Kill the servo task
} catch (const vpException &e) {
std::cout << "Catch an exception: " << e << std::endl;