tutorial-franka-real-ibvs-apriltag.cpp

Example of eye-in-hand image-based control law. We control here a real robot, the Franka Emika Panda robot (arm with 7 degrees of freedom). The velocity is computed in the camera frame. The inverse jacobian that converts cartesian velocities in joint velocities is implemented in the robot low level controller. Visual features are the image coordinates of 4 points corresponding too the corners of an AprilTag.

The device used to acquire images is a Realsense D435 device.

Camera extrinsic (eMc) parameters are set by default to a value that will not match Your configuration. Use –eMc command line option to read the values from a file. This file could be obtained following extrinsic camera calibration tutorial: https://visp-doc.inria.fr/doxygen/visp-daily/tutorial-calibration-extrinsic.html

Camera intrinsic parameters are retrieved from the Realsense SDK.

The target is an AprilTag that is by default 12cm large. To print your own tag, see https://visp-doc.inria.fr/doxygen/visp-daily/tutorial-detection-apriltag.html You can specify the size of your tag using –tag_size command line option.

/****************************************************************************
 *
 * ViSP, open source Visual Servoing Platform software.
 * Copyright (C) 2005 - 2021 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.
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 * 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 https://visp.inria.fr for more information.
 *
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 * Inria Rennes - Bretagne Atlantique
 * Campus Universitaire de Beaulieu
 * 35042 Rennes Cedex
 * France
 *
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 * Inria at visp@inria.fr
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#include <iostream>
 
#include <visp3/core/vpCameraParameters.h>
#include <visp3/detection/vpDetectorAprilTag.h>
#include <visp3/gui/vpDisplayOpenCV.h>
#include <visp3/gui/vpPlot.h>
#include <visp3/io/vpImageIo.h>
#include <visp3/visual_features/vpFeatureBuilder.h>
#include <visp3/visual_features/vpFeaturePoint.h>
#include <visp3/vs/vpServo.h>
#include <visp3/vs/vpServoDisplay.h>
 
#include <visp3/robot/vpRobotFranka.h>
#include <visp3/sensor/vpRealSense2.h>
 
#if defined( VISP_HAVE_REALSENSE2 ) && ( VISP_CXX_STANDARD >= VISP_CXX_STANDARD_11 ) &&                                \
    ( defined( VISP_HAVE_OPENCV ) ) && defined( VISP_HAVE_FRANKA )
 
void
display_point_trajectory( const vpImage< unsigned char > &I, const std::vector< vpImagePoint > &vip,
                          std::vector< vpImagePoint > *traj_vip )
{
  for ( size_t i = 0; i < vip.size(); i++ )
  {
    if ( traj_vip[i].size() )
    {
      // Add the point only if distance with the previous > 1 pixel
      if ( vpImagePoint::distance( vip[i], traj_vip[i].back() ) > 1. )
      {
        traj_vip[i].push_back( vip[i] );
      }
    }
    else
    {
      traj_vip[i].push_back( vip[i] );
    }
  }
  for ( size_t i = 0; i < vip.size(); i++ )
  {
    for ( size_t j = 1; j < traj_vip[i].size(); j++ )
    {
      vpDisplay::displayLine( I, traj_vip[i][j - 1], traj_vip[i][j], vpColor::green, 2 );
    }
  }
}
 
int
main( int argc, char **argv )
{
  double opt_tagSize           = 0.08;
  std::string opt_robot_ip     = "192.168.1.1";
  std::string opt_eMc_filename = "";
  bool display_tag             = true;
  int opt_quad_decimate        = 2;
  bool opt_verbose             = false;
  bool opt_plot                = false;
  bool opt_adaptive_gain       = false;
  bool opt_task_sequencing     = false;
  double convergence_threshold = 0.00005;
 
  for ( int i = 1; i < argc; i++ )
  {
    if ( std::string( argv[i] ) == "--tag_size" && i + 1 < argc )
    {
      opt_tagSize = std::stod( argv[i + 1] );
    }
    else if ( std::string( argv[i] ) == "--ip" && i + 1 < argc )
    {
      opt_robot_ip = std::string( argv[i + 1] );
    }
    else if ( std::string( argv[i] ) == "--eMc" && i + 1 < argc )
    {
      opt_eMc_filename = std::string( argv[i + 1] );
    }
    else if ( std::string( argv[i] ) == "--verbose" )
    {
      opt_verbose = true;
    }
    else if ( std::string( argv[i] ) == "--plot" )
    {
      opt_plot = true;
    }
    else if ( std::string( argv[i] ) == "--adaptive_gain" )
    {
      opt_adaptive_gain = true;
    }
    else if ( std::string( argv[i] ) == "--task_sequencing" )
    {
      opt_task_sequencing = true;
    }
    else if ( std::string( argv[i] ) == "--quad_decimate" && i + 1 < argc )
    {
      opt_quad_decimate = std::stoi( argv[i + 1] );
    }
    else if ( std::string( argv[i] ) == "--no-convergence-threshold" )
    {
      convergence_threshold = 0.;
    }
    else if ( std::string( argv[i] ) == "--help" || std::string( argv[i] ) == "-h" )
    {
      std::cout
          << argv[0] << " [--ip <default " << opt_robot_ip << ">] [--tag_size <marker size in meter; default "
          << opt_tagSize << ">] [--eMc <eMc extrinsic file>] "
          << "[--quad_decimate <decimation; default " << opt_quad_decimate
          << ">] [--adaptive_gain] [--plot] [--task_sequencing] [--no-convergence-threshold] [--verbose] [--help] [-h]"
          << "\n";
      return EXIT_SUCCESS;
    }
  }
 
  vpRobotFranka robot;
 
  try
  {
    std::cout << "Try to connect to robot ip: " << opt_robot_ip << std::endl;
    robot.connect( opt_robot_ip );
    std::cout << "Panda robot connected" << std::endl;
 
    vpRealSense2 rs;
    rs2::config config;
    unsigned int width = 640, height = 480;
    config.enable_stream( RS2_STREAM_COLOR, 640, 480, RS2_FORMAT_RGBA8, 30 );
    config.enable_stream( RS2_STREAM_DEPTH, 640, 480, RS2_FORMAT_Z16, 30 );
    config.enable_stream( RS2_STREAM_INFRARED, 640, 480, RS2_FORMAT_Y8, 30 );
    std::cout << "Try to connect to Realsense camera " << std::endl;
    rs.open( config );
    std::cout << "Camera connected" << std::endl;
 
    // Get camera extrinsics
    vpPoseVector ePc;
    // Set camera extrinsics default values corresponding to
    // - an Intel RealSense D435 camera
    // - attached to the Franka end-effector using the mechanical interface corresponding to
    //   the cad model given in franka-rs-D435-camera-holder.stl file
    ePc[0] = 0.0564668;
    ePc[1] = -0.0375079;
    ePc[2] = -0.150416 ;
    ePc[3] = 0.0102548;
    ePc[4] = -0.0012236;
    ePc[5] = 1.5412;
 
    // If provided, read camera extrinsics from --eMc <file>
    if ( !opt_eMc_filename.empty() )
    {
      ePc.loadYAML( opt_eMc_filename, ePc );
    }
    else
    {
      std::cout << "Warning, opt_eMc_filename is empty! Use hard coded values."
                << "\n";
    }
    vpHomogeneousMatrix eMc( ePc );
    std::cout << "eMc:\n" << eMc << "\n";
    std::cout << "ePc:\n" << vpPoseVector(eMc).t() << "\n";
 
    // Get camera intrinsics
    vpCameraParameters cam =
        rs.getCameraParameters( RS2_STREAM_COLOR, vpCameraParameters::perspectiveProjWithDistortion );
    std::cout << "cam:\n" << cam << "\n";
 
    vpImage< unsigned char > I( height, width );
 
    vpDisplayOpenCV dc( I, 10, 10, "Color image" );
 
    vpDetectorAprilTag::vpAprilTagFamily tagFamily                  = vpDetectorAprilTag::TAG_36h11;
    vpDetectorAprilTag::vpPoseEstimationMethod poseEstimationMethod = vpDetectorAprilTag::HOMOGRAPHY_VIRTUAL_VS;
    // vpDetectorAprilTag::vpPoseEstimationMethod poseEstimationMethod = vpDetectorAprilTag::BEST_RESIDUAL_VIRTUAL_VS;
    vpDetectorAprilTag detector( tagFamily );
    detector.setAprilTagPoseEstimationMethod( poseEstimationMethod );
    detector.setDisplayTag( display_tag );
    detector.setAprilTagQuadDecimate( opt_quad_decimate );
 
    // Servo
    vpHomogeneousMatrix cMo, oMo;
 
    // Desired pose used to compute the desired features
    vpHomogeneousMatrix cdMo( vpTranslationVector( 0, 0, opt_tagSize * 3 ), // 3 times tag with along camera z axis
                              vpRotationMatrix( { 1, 0, 0, 0, -1, 0, 0, 0, -1 } ) );
 
    // Create visual features
    std::vector< vpFeaturePoint > p( 4 ), pd( 4 ); // We use 4 points
 
    // Define 4 3D points corresponding to the CAD model of the Apriltag
    std::vector< vpPoint > point( 4 );
    point[0].setWorldCoordinates( -opt_tagSize / 2., -opt_tagSize / 2., 0 );
    point[1].setWorldCoordinates( opt_tagSize / 2., -opt_tagSize / 2., 0 );
    point[2].setWorldCoordinates( opt_tagSize / 2., opt_tagSize / 2., 0 );
    point[3].setWorldCoordinates( -opt_tagSize / 2., opt_tagSize / 2., 0 );
 
    vpServo task;
    // Add the 4 visual feature points
    for ( size_t i = 0; i < p.size(); i++ )
    {
      task.addFeature( p[i], pd[i] );
    }
    task.setServo( vpServo::EYEINHAND_CAMERA );
    task.setInteractionMatrixType( vpServo::CURRENT );
 
    if ( opt_adaptive_gain )
    {
      vpAdaptiveGain lambda( 1.5, 0.4, 30 ); // lambda(0)=4, lambda(oo)=0.4 and lambda'(0)=30
      task.setLambda( lambda );
    }
    else
    {
      task.setLambda( 0.5 );
    }
 
    vpPlot *plotter = nullptr;
    int iter_plot   = 0;
 
    if ( opt_plot )
    {
      plotter = new vpPlot( 2, static_cast< int >( 250 * 2 ), 500, static_cast< int >( I.getWidth() ) + 80, 10,
                            "Real time curves plotter" );
      plotter->setTitle( 0, "Visual features error" );
      plotter->setTitle( 1, "Camera velocities" );
      plotter->initGraph( 0, 8 );
      plotter->initGraph( 1, 6 );
      plotter->setLegend( 0, 0, "error_feat_p1_x" );
      plotter->setLegend( 0, 1, "error_feat_p1_y" );
      plotter->setLegend( 0, 2, "error_feat_p2_x" );
      plotter->setLegend( 0, 3, "error_feat_p2_y" );
      plotter->setLegend( 0, 4, "error_feat_p3_x" );
      plotter->setLegend( 0, 5, "error_feat_p3_y" );
      plotter->setLegend( 0, 6, "error_feat_p4_x" );
      plotter->setLegend( 0, 7, "error_feat_p4_y" );
      plotter->setLegend( 1, 0, "vc_x" );
      plotter->setLegend( 1, 1, "vc_y" );
      plotter->setLegend( 1, 2, "vc_z" );
      plotter->setLegend( 1, 3, "wc_x" );
      plotter->setLegend( 1, 4, "wc_y" );
      plotter->setLegend( 1, 5, "wc_z" );
    }
 
    bool final_quit                           = false;
    bool has_converged                        = false;
    bool send_velocities                      = false;
    bool servo_started                        = false;
    std::vector< vpImagePoint > *traj_corners = nullptr; // To memorize point trajectory
 
    static double t_init_servo = vpTime::measureTimeMs();
 
    robot.set_eMc( eMc ); // Set location of the camera wrt end-effector frame
    robot.setRobotState( vpRobot::STATE_VELOCITY_CONTROL );
 
    while ( !has_converged && !final_quit )
    {
      double t_start = vpTime::measureTimeMs();
 
      rs.acquire( I );
 
      vpDisplay::display( I );
 
      std::vector< vpHomogeneousMatrix > cMo_vec;
      detector.detect( I, opt_tagSize, cam, cMo_vec );
 
      {
        std::stringstream ss;
        ss << "Left click to " << ( send_velocities ? "stop the robot" : "servo the robot" )
           << ", right click to quit.";
        vpDisplay::displayText( I, 20, 20, ss.str(), vpColor::red );
      }
 
      vpColVector v_c( 6 );
 
      // Only one tag is detected
      if ( cMo_vec.size() == 1 )
      {
        cMo = cMo_vec[0];
 
        static bool first_time = true;
        if ( first_time )
        {
          // Introduce security wrt tag positionning in order to avoid PI rotation
          std::vector< vpHomogeneousMatrix > v_oMo( 2 ), v_cdMc( 2 );
          v_oMo[1].buildFrom( 0, 0, 0, 0, 0, M_PI );
          for ( size_t i = 0; i < 2; i++ )
          {
            v_cdMc[i] = cdMo * v_oMo[i] * cMo.inverse();
          }
          if ( std::fabs( v_cdMc[0].getThetaUVector().getTheta() ) <
               std::fabs( v_cdMc[1].getThetaUVector().getTheta() ) )
          {
            oMo = v_oMo[0];
          }
          else
          {
            std::cout << "Desired frame modified to avoid PI rotation of the camera" << std::endl;
            oMo = v_oMo[1]; // Introduce PI rotation
          }
 
          // Compute the desired position of the features from the desired pose
          for ( size_t i = 0; i < point.size(); i++ )
          {
            vpColVector cP, p_;
            point[i].changeFrame( cdMo * oMo, cP );
            point[i].projection( cP, p_ );
 
            pd[i].set_x( p_[0] );
            pd[i].set_y( p_[1] );
            pd[i].set_Z( cP[2] );
          }
        }
 
        // Get tag corners
        std::vector< vpImagePoint > corners = detector.getPolygon( 0 );
 
        // Update visual features
        for ( size_t i = 0; i < corners.size(); i++ )
        {
          // Update the point feature from the tag corners location
          vpFeatureBuilder::create( p[i], cam, corners[i] );
          // Set the feature Z coordinate from the pose
          vpColVector cP;
          point[i].changeFrame( cMo, cP );
 
          p[i].set_Z( cP[2] );
        }
 
        if ( opt_task_sequencing )
        {
          if ( !servo_started )
          {
            if ( send_velocities )
            {
              servo_started = true;
            }
            t_init_servo = vpTime::measureTimeMs();
          }
          v_c = task.computeControlLaw( ( vpTime::measureTimeMs() - t_init_servo ) / 1000. );
        }
        else
        {
          v_c = task.computeControlLaw();
        }
 
        // Display the current and desired feature points in the image display
        vpServoDisplay::display( task, cam, I );
        for ( size_t i = 0; i < corners.size(); i++ )
        {
          std::stringstream ss;
          ss << i;
          // Display current point indexes
          vpDisplay::displayText( I, corners[i] + vpImagePoint( 15, 15 ), ss.str(), vpColor::red );
          // Display desired point indexes
          vpImagePoint ip;
          vpMeterPixelConversion::convertPoint( cam, pd[i].get_x(), pd[i].get_y(), ip );
          vpDisplay::displayText( I, ip + vpImagePoint( 15, 15 ), ss.str(), vpColor::red );
        }
        if ( first_time )
        {
          traj_corners = new std::vector< vpImagePoint >[corners.size()];
        }
        // Display the trajectory of the points used as features
        display_point_trajectory( I, corners, traj_corners );
 
        if ( opt_plot )
        {
          plotter->plot( 0, iter_plot, task.getError() );
          plotter->plot( 1, iter_plot, v_c );
          iter_plot++;
        }
 
        if ( opt_verbose )
        {
          std::cout << "v_c: " << v_c.t() << std::endl;
        }
 
        double error = task.getError().sumSquare();
        std::stringstream ss;
        ss << "||error||: " << error;
        vpDisplay::displayText( I, 20, static_cast< int >( I.getWidth() ) - 150, ss.str(), vpColor::red );
 
        if ( opt_verbose )
          std::cout << ss.str() << std::endl;
 
        if ( !has_converged && error < convergence_threshold )
        {
          has_converged = true;
          std::cout << "Servo task has converged"
                    << "\n";
          vpDisplay::displayText( I, 100, 20, "Servo task has converged", vpColor::red );
        }
        if ( first_time )
        {
          first_time = false;
        }
      } // end if (cMo_vec.size() == 1)
      else
      {
        v_c = 0;
      }
 
      if ( !send_velocities )
      {
        v_c = 0;
      }
 
      // Send to the robot
      robot.setVelocity( vpRobot::CAMERA_FRAME, v_c );
 
      {
        std::stringstream ss;
        ss << "Loop time: " << vpTime::measureTimeMs() - t_start << " ms";
        vpDisplay::displayText( I, 40, 20, ss.str(), vpColor::red );
      }
      vpDisplay::flush( I );
 
      vpMouseButton::vpMouseButtonType button;
      if ( vpDisplay::getClick( I, button, false ) )
      {
        switch ( button )
        {
        case vpMouseButton::button1:
          send_velocities = !send_velocities;
          break;
 
        case vpMouseButton::button3:
          final_quit = true;
          v_c        = 0;
          break;
 
        default:
          break;
        }
      }
    }
    std::cout << "Stop the robot " << std::endl;
    robot.setRobotState( vpRobot::STATE_STOP );
 
    if ( opt_plot && plotter != nullptr )
    {
      delete plotter;
      plotter = nullptr;
    }
 
    if ( !final_quit )
    {
      while ( !final_quit )
      {
        rs.acquire( I );
        vpDisplay::display( I );
 
        vpDisplay::displayText( I, 20, 20, "Click to quit the program.", vpColor::red );
        vpDisplay::displayText( I, 40, 20, "Visual servo converged.", vpColor::red );
 
        if ( vpDisplay::getClick( I, false ) )
        {
          final_quit = true;
        }
 
        vpDisplay::flush( I );
      }
    }
    if ( traj_corners )
    {
      delete[] traj_corners;
    }
  }
  catch ( const vpException &e )
  {
    std::cout << "ViSP exception: " << e.what() << std::endl;
    std::cout << "Stop the robot " << std::endl;
    robot.setRobotState( vpRobot::STATE_STOP );
    return EXIT_FAILURE;
  }
  catch ( const franka::NetworkException &e )
  {
    std::cout << "Franka network exception: " << e.what() << std::endl;
    std::cout << "Check if you are connected to the Franka robot"
              << " or if you specified the right IP using --ip command line option set by default to 192.168.1.1. "
              << std::endl;
    return EXIT_FAILURE;
  }
  catch ( const std::exception &e )
  {
    std::cout << "Franka exception: " << e.what() << std::endl;
    return EXIT_FAILURE;
  }
 
  return 0;
}
#else
int
main()
{
#if !defined( VISP_HAVE_REALSENSE2 )
  std::cout << "Install librealsense-2.x" << std::endl;
#endif
#if ( VISP_CXX_STANDARD < VISP_CXX_STANDARD_11 )
  std::cout << "Build ViSP with c++11 or higher compiler flag (cmake -DUSE_CXX_STANDARD=11)." << std::endl;
#endif
#if !defined( VISP_HAVE_FRANKA )
  std::cout << "Install libfranka." << std::endl;
#endif
  return 0;
}
#endif