Visual Servoing Platform  version 3.5.1 under development (2023-05-30)

Example of dots tracking in an image sequence and pose computation.

* ViSP, open source Visual Servoing Platform software.
* Copyright (C) 2005 - 2022 by Inria. All rights reserved.
* This software is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
* See the file LICENSE.txt at the root directory of this source
* distribution for additional information about the GNU GPL.
* For using ViSP with software that can not be combined with the GNU
* GPL, please contact Inria about acquiring a ViSP Professional
* Edition License.
* See for more information.
* This software was developed at:
* Inria Rennes - Bretagne Atlantique
* Campus Universitaire de Beaulieu
* 35042 Rennes Cedex
* France
* If you have questions regarding the use of this file, please contact
* Inria at
* This file is provided AS IS with NO WARRANTY OF ANY KIND, INCLUDING THE
* Description:
* Pose computation on an object made of dots.
* reading of PGM image
* Display image using either the X11 or GTK or GDI display
* track 4 dots (vpDots) in the image
* compute the pose
#include <iomanip>
#include <sstream>
#include <stdio.h>
#include <stdlib.h>
#include <visp3/core/vpConfig.h>
#include <visp3/core/vpDebug.h>
#if (defined(VISP_HAVE_X11) || defined(VISP_HAVE_GTK) || defined(VISP_HAVE_GDI) || defined(VISP_HAVE_OPENCV)) && \
(defined(VISP_HAVE_LAPACK) || defined(VISP_HAVE_EIGEN3) || defined(VISP_HAVE_OPENCV))
#include <visp3/core/vpImage.h>
#include <visp3/core/vpImagePoint.h>
#include <visp3/io/vpImageIo.h>
#include <visp3/gui/vpDisplayGDI.h>
#include <visp3/gui/vpDisplayGTK.h>
#include <visp3/gui/vpDisplayOpenCV.h>
#include <visp3/gui/vpDisplayX.h>
#include <visp3/blob/vpDot.h>
#include <visp3/core/vpIoTools.h>
#include <visp3/core/vpPixelMeterConversion.h>
#include <visp3/io/vpParseArgv.h>
#include <visp3/vision/vpPose.h>
// List of allowed command line options
#define GETOPTARGS "cdi:p:hf:l:s:"
void usage(const char *name, const char *badparam, std::string ipath, std::string ppath, unsigned first,
unsigned last, unsigned step)
std::string ext("png");
std::string ext("pgm");
fprintf(stdout, "\n\
Test dot tracking.\n\
%s [-i <input image path>] [-p <personal image path>]\n\
[-f <first image>] [-l <last image>] [-s <step>][-c] [-d] [-h]\n",
fprintf(stdout, "\n\
OPTIONS: Default\n\
-i <input image path> %s\n\
Set image input path.\n\
From this path read images \n\
Setting the VISP_INPUT_IMAGE_PATH environment\n\
variable produces the same behaviour than using\n\
this option.\n\
-p <personal image path> %s\n\
Specify a personal sequence containing images \n\
to process.\n\
By image sequence, we mean one file per image.\n\
The format is selected by analysing the filename extension.\n\
Example : \"/Temp/visp-images/cube/image.%%04d.%s\"\n\
%%04d is for the image numbering.\n\
-f <first image> %u\n\
First image number of the sequence.\n\
-l <last image> %u\n\
Last image number of the sequence.\n\
-s <step> %u\n\
Step between two images.\n\
Disable the mouse click. Useful to automaze the \n\
execution of this program without humain intervention.\n\
-d \n\
Turn off the display.\n\
Print the help.\n",
ipath.c_str(), ext.c_str(), ppath.c_str(), ext.c_str(), first, last, step);
if (badparam)
fprintf(stdout, "\nERROR: Bad parameter [%s]\n", badparam);
bool getOptions(int argc, const char **argv, std::string &ipath, std::string &ppath, unsigned &first, unsigned &last,
unsigned &step, bool &click_allowed, bool &display)
const char *optarg_;
int c;
while ((c = vpParseArgv::parse(argc, argv, GETOPTARGS, &optarg_)) > 1) {
switch (c) {
case 'c':
click_allowed = false;
case 'd':
display = false;
case 'i':
ipath = optarg_;
case 'p':
ppath = optarg_;
case 'f':
first = (unsigned)atoi(optarg_);
case 'n':
last = (unsigned)atoi(optarg_);
case 's':
step = (unsigned)atoi(optarg_);
case 'h':
usage(argv[0], NULL, ipath, ppath, first, last, step);
return false;
usage(argv[0], optarg_, ipath, ppath, first, last, step);
return false;
if ((c == 1) || (c == -1)) {
// standalone param or error
usage(argv[0], NULL, ipath, ppath, first, last, step);
std::cerr << "ERROR: " << std::endl;
std::cerr << " Bad argument " << optarg_ << std::endl << std::endl;
return false;
return true;
int main(int argc, const char **argv)
try {
std::string env_ipath;
std::string opt_ipath;
std::string ipath;
std::string opt_ppath;
std::string dirname;
std::string filename;
unsigned opt_first = 0;
unsigned opt_last = 80;
unsigned opt_step = 1;
bool opt_click_allowed = true;
bool opt_display = true;
int i;
std::string ext("png");
std::string ext("pgm");
std::cout << "-------------------------------------------------------" << std::endl;
std::cout << " poseVirtualVS.cpp" << std::endl << std::endl;
std::cout << " Example of dots tracking in an image sequence and pose "
<< std::endl;
std::cout << "-------------------------------------------------------" << std::endl;
std::cout << std::endl;
// Get the visp-images-data package path or VISP_INPUT_IMAGE_PATH
// environment variable value
// Set the default input path
if (!env_ipath.empty())
ipath = env_ipath;
// Read the command line options
if (getOptions(argc, argv, opt_ipath, opt_ppath, opt_first, opt_last, opt_step, opt_click_allowed,
opt_display) == false) {
// Get the option values
if (!opt_ipath.empty())
ipath = opt_ipath;
// Compare ipath and env_ipath. If they differ, we take into account
// the input path comming from the command line option
if (opt_ipath.empty() && opt_ppath.empty()) {
if (ipath != env_ipath) {
std::cout << std::endl << "WARNING: " << std::endl;
std::cout << " Since -i <visp image path=" << ipath << "> "
<< " is different from VISP_IMAGE_PATH=" << env_ipath << std::endl
<< " we skip the environment variable." << std::endl;
// Test if an input path is set
if (opt_ipath.empty() && env_ipath.empty() && opt_ppath.empty()) {
usage(argv[0], NULL, ipath, opt_ppath, opt_first, opt_last, opt_step);
std::cerr << std::endl << "ERROR:" << std::endl;
std::cerr << " Use -i <visp image path> option or set VISP_INPUT_IMAGE_PATH " << std::endl
<< " environment variable to specify the location of the " << std::endl
<< " image path where test images are located." << std::endl
<< " Use -p <personal image path> option if you want to " << std::endl
<< " use personal images" << std::endl
<< std::endl;
// Declare an image, this is a gray level image (unsigned char)
// it size is not defined yet, it will be defined when the image will
// read on the disk
unsigned iter = opt_first;
std::ostringstream s;
char cfilename[FILENAME_MAX];
if (opt_ppath.empty()) {
// Warning : the datset is available on
dirname = vpIoTools::createFilePath(ipath, "cube");
// Build the name of the image file
s.setf(std::ios::right, std::ios::adjustfield);
s << "image." << std::setw(4) << std::setfill('0') << iter << "." << ext;
filename = vpIoTools::createFilePath(dirname, s.str());
} else {
snprintf(cfilename, FILENAME_MAX, opt_ppath.c_str(), iter);
filename = cfilename;
// define the vpDot structure, here 4 dots will tracked
vpDot d[4];
for (i = 0; i < 4; i++) {
// by using setGraphics, we request to see the all the pixel of the dot
// in green on the screen.
// It uses the overlay image plane.
// The default of this setting is that it is time consuming
if (opt_display) {
} else {
// Read image named filename and put the bitmap into in I.
try {
vpImageIo::read(I, filename);
} catch (...) {
if (opt_ppath.empty()) {
std::cerr << std::endl << "ERROR:" << std::endl;
std::cerr << " Cannot read " << filename << std::endl;
std::cerr << " Check your -i " << ipath << " option, " << std::endl
<< " or VISP_INPUT_IMAGE_PATH environment variable" << std::endl;
} else {
std::cerr << std::endl << "ERROR:" << std::endl;
std::cerr << " Cannot read " << filename << std::endl;
std::cerr << " or your -p " << opt_ppath << " option " << std::endl << std::endl;
// We open a window using either the X11 or GTK or GDI window manager
// it will be located in 100,100 and titled "tracking using vpDot"
// its size is automatically defined by the image (I) size
#if defined VISP_HAVE_X11
vpDisplayX display;
#elif defined VISP_HAVE_GTK
vpDisplayGTK display;
#elif defined VISP_HAVE_GDI
vpDisplayGDI display;
#elif defined VISP_HAVE_OPENCV
vpDisplayOpenCV display;
if (opt_display) {
// Display size is automatically defined by the image (I) size
display.init(I, 100, 100, "tracking using vpDot");
// display the image
// The image class has a member that specify a pointer toward
// the display that has been initialized in the display declaration
// therefore is is no longer necessary to make a reference to the
// display variable.
// Flush the display
vpImagePoint cog[4]; // Center of gravity of the dot
if (opt_display && opt_click_allowed) {
// dot coordinates (u,v) = (column,row)
std::cout << "Click the four white dots on the object corner clockwise" << std::endl;
for (i = 0; i < 4; i++) {
// tracking is initalized if no other parameters are given
// to the iniTracking(..) method a right mouse click on the
// dot is expected dot location can also be specified
// explicitly in the initTracking method :
// d.initTracking(I,ip) where ip is the image point from
// where the dot need to be searched.
// track the dot and returns its coordinates in the image
// results are given in float since many many are usually considered
// an expcetion is thrown by the track method if
// - dot is lost
// - the number of pixel is too small
// - too many pixels are detected (this is usual when a "big"
// specularity
// occurs. The threshold can be modified using the
// setMaxDotSize() method
d[i].track(I, cog[i]);
} else {
d[0].initTracking(I, cog[0]);
d[0].track(I, cog[0]);
d[1].initTracking(I, cog[1]);
d[1].track(I, cog[1]);
d[2].initTracking(I, cog[2]);
d[2].track(I, cog[2]);
d[3].initTracking(I, cog[3]);
d[3].track(I, cog[3]);
if (opt_display) {
// display a red cross (size 10) in the image at the dot center
// of gravity location
// in the vpDisplay class member's when pixel coordinates
// are considered the first element is the row index and the second
// is the column index:
// vpDisplay::displayCross(Image, row index, column index, size,
// color) therefore u and v are inverted wrt to the vpDot
// specification
// Alternatively, to avoid this problem another set of member have
// been defined in the vpDisplay class.
// If the method name is postfixe with _uv the specification is :
// vpDisplay::displayCross_uv(Image, column index, row index, size,
// color)
for (i = 0; i < 4; i++)
// flush the X11 buffer
// --------------------------------------------------------
// Now wil compute the pose
// The pose will be contained in an homogeneous matrix cMo
// We need a structure that content both the 3D coordinates of the point
// in the object frame and the 2D coordinates of the point expressed in
// meter the vpPoint class is ok for that
vpPoint P[4];
// The vpPose class mainly contents a list of vpPoint (that is (X,Y,Z, x,
// y) )
vpPose pose;
// the list of point is cleared (if that's not done before)
// we set the 3D points coordinates (in meter !) in the object/world frame
double L = 0.04;
P[0].setWorldCoordinates(-L, -L, 0); // (X,Y,Z)
P[1].setWorldCoordinates(L, -L, 0);
P[2].setWorldCoordinates(L, L, 0);
P[3].setWorldCoordinates(-L, L, 0);
// set the camera intrinsic parameters
// see more details about the model in vpCameraParameters
double px = 600;
double py = 600;
double u0 = 192;
double v0 = 144;
vpCameraParameters cam(px, py, u0, v0);
// pixel-> meter conversion
for (i = 0; i < 4; i++) {
// u[i]. v[i] are expressed in pixel
// conversion in meter is achieved using
// x = (u-u0)/px
// y = (v-v0)/py
// where px, py, u0, v0 are the intrinsic camera parameters
double x = 0, y = 0;
// The pose structure is build, we put in the point list the set of point
// here both 2D and 3D world coordinates are known
for (i = 0; i < 4; i++) {
pose.addPoint(P[i]); // and added to the pose computation point list
// compute the initial pose using Dementhon method followed by a non
// linear minimisation method
// Pose by Dementhon or Lagrange provides an initialization of the non linear virtual visual-servoing pose estimation
if (opt_display) {
// display the compute pose
pose.display(I, cMo, cam, 0.05, vpColor::red);
// Covariance Matrix Computation
// Uncomment if you want to compute the covariance matrix.
// pose.setCovarianceComputation(true); //Important if you want
// tracker.getCovarianceMatrix() to work.
// this is the loop over the image sequence
while (iter < opt_last) {
// set the new image name
if (opt_ppath.empty()) {
s << "image." << std::setw(4) << std::setfill('0') << iter << "." << ext;
filename = vpIoTools::createFilePath(dirname, s.str());
} else {
snprintf(cfilename, FILENAME_MAX, opt_ppath.c_str(), iter);
filename = cfilename;
// read the image
vpImageIo::read(I, filename);
if (opt_display) {
// Display the image
// Flush the display
// kill the point list
// track the dot
for (i = 0; i < 4; i++) {
// track the point
d[i].track(I, cog[i]);
if (opt_display) {
// display point location
// pixel->meter conversion
double x = 0, y = 0;
// and added to the pose computation point list
// the pose structure has been updated
// the pose is now updated using the virtual visual servoing approach
// Dementhon or lagrange is no longer necessary, pose at the
// previous iteration is sufficient
if (opt_display) {
// display the compute pose
pose.display(I, cMo, cam, 0.05, vpColor::red);
// Covariance Matrix Display
// Uncomment if you want to print the covariance matrix.
// Make sure pose.setCovarianceComputation(true) has been called
// (uncomment below). std::cout << pose.getCovarianceMatrix() <<
// std::endl << std::endl;
iter += opt_step;
} catch (const vpException &e) {
std::cout << "Catch a ViSP exception: " << e << std::endl;
#elif !(defined(VISP_HAVE_LAPACK) || defined(VISP_HAVE_EIGEN3) || defined(VISP_HAVE_OPENCV))
int main()
std::cout << "Cannot run this example: install Lapack, Eigen3 or OpenCV" << std::endl;
int main()
std::cout << "You do not have X11, or GTK, or GDI (Graphical Device Interface) functionalities to display images..."
<< std::endl;
std::cout << "Tip if you are on a unix-like system:" << std::endl;
std::cout << "- Install X11, configure again ViSP using cmake and build again this example" << std::endl;
std::cout << "Tip if you are on a windows-like system:" << std::endl;
std::cout << "- Install GDI, configure again ViSP using cmake and build again this example" << std::endl;
Generic class defining intrinsic camera parameters.
static const vpColor red
Definition: vpColor.h:217
Display for windows using GDI (available on any windows 32 platform).
Definition: vpDisplayGDI.h:129
The vpDisplayGTK allows to display image using the GTK 3rd party library. Thus to enable this class G...
Definition: vpDisplayGTK.h:135
The vpDisplayOpenCV allows to display image using the OpenCV library. Thus to enable this class OpenC...
Use the X11 console to display images on unix-like OS. Thus to enable this class X11 should be instal...
Definition: vpDisplayX.h:135
static void display(const vpImage< unsigned char > &I)
static void displayCross(const vpImage< unsigned char > &I, const vpImagePoint &ip, unsigned int size, const vpColor &color, unsigned int thickness=1)
static void flush(const vpImage< unsigned char > &I)
This tracker is meant to track a dot (connected pixels with same gray level) on a vpImage.
Definition: vpDot.h:116
error that can be emited by ViSP classes.
Definition: vpException.h:72
Implementation of an homogeneous matrix and operations on such kind of matrices.
static void read(vpImage< unsigned char > &I, const std::string &filename, int backend=IO_DEFAULT_BACKEND)
Definition: vpImageIo.cpp:148
Class that defines a 2D point in an image. This class is useful for image processing and stores only ...
Definition: vpImagePoint.h:89
void set_u(double u)
Definition: vpImagePoint.h:335
void set_v(double v)
Definition: vpImagePoint.h:346
static std::string getViSPImagesDataPath()
Definition: vpIoTools.cpp:1399
static std::string createFilePath(const std::string &parent, const std::string &child)
Definition: vpIoTools.cpp:1764
static bool parse(int *argcPtr, const char **argv, vpArgvInfo *argTable, int flags)
Definition: vpParseArgv.cpp:69
static void convertPoint(const vpCameraParameters &cam, const double &u, const double &v, double &x, double &y)
Class that defines a 3D point in the object frame and allows forward projection of a 3D point in the ...
Definition: vpPoint.h:82
void set_x(double x)
Set the point x coordinate in the image plane.
Definition: vpPoint.cpp:511
void setWorldCoordinates(double oX, double oY, double oZ)
Definition: vpPoint.cpp:113
void set_y(double y)
Set the point y coordinate in the image plane.
Definition: vpPoint.cpp:513
Class used for pose computation from N points (pose from point only). Some of the algorithms implemen...
Definition: vpPose.h:90
void addPoint(const vpPoint &P)
Definition: vpPose.cpp:149
Definition: vpPose.h:110
Definition: vpPose.h:104
void clearPoint()
Definition: vpPose.cpp:134
bool computePose(vpPoseMethodType method, vpHomogeneousMatrix &cMo, bool(*func)(const vpHomogeneousMatrix &)=NULL)
Definition: vpPose.cpp:414
static void display(vpImage< unsigned char > &I, vpHomogeneousMatrix &cMo, vpCameraParameters &cam, double size, vpColor col=vpColor::none)
Definition: vpPose.cpp:655