calibrateTsai.cpp

Example of Tsai calibration to estimate extrinsic camera parameters, ie hand-eye homogeneous transformation.

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 * Description:
 * Tsai calibration example to estimate hand to eye transformation.
 *
 * Authors:
 * Fabien Spindler
 *
 *****************************************************************************/


#include <stdio.h>
#include <sstream>
#include <iomanip>
#include <vector>

#include <visp3/core/vpDebug.h>
#include <visp3/io/vpParseArgv.h>
#include <visp3/core/vpIoTools.h>
#include <visp3/vision/vpCalibration.h>
#include <visp3/core/vpExponentialMap.h>

int main()
{
  try {
    // We want to calibrate the hand to eye extrinsic camera parameters from 6 couple of poses: cMo and wMe
    const unsigned int N = 6;
    // Input: six couple of poses used as input in the calibration proces
    std::vector<vpHomogeneousMatrix> cMo(N) ; // eye (camera) to object transformation. The object frame is attached to the calibrartion grid
    std::vector<vpHomogeneousMatrix>  wMe(N) ; // world to hand (end-effector) transformation
    // Output: Result of the calibration
    vpHomogeneousMatrix  eMc; // hand (end-effector) to eye (camera) transformation

    // Initialize an eMc transformation used to produce the simulated input transformations cMo and wMe
    vpTranslationVector etc(0.1, 0.2, 0.3);
    vpThetaUVector erc;
    erc[0] = vpMath::rad(10); // 10 deg
    erc[1] = vpMath::rad(-10); // -10 deg
    erc[2] = vpMath::rad(25); // 25 deg

    eMc.buildFrom(etc, erc);
    std::cout << "Simulated hand to eye transformation: eMc " << std::endl ;
    std::cout << eMc << std::endl ;
    std::cout << "Theta U rotation: " << vpMath::deg(erc[0]) << " " << vpMath::deg(erc[1]) << " " << vpMath::deg(erc[2]) << std::endl;

    vpColVector v_c(6) ; // camera velocity used to produce 6 simulated poses
    for (unsigned int i=0 ; i < N ; i++)
    {
      v_c = 0 ;
      if (i==0) {
        // Initialize first poses
        cMo[0].buildFrom(0, 0, 0.5, 0, 0, 0); // z=0.5 m
        wMe[0].buildFrom(0, 0, 0, 0, 0, 0); // Id
      }
      else if (i==1)
        v_c[3] = M_PI/8 ;
      else if (i==2)
        v_c[4] = M_PI/8 ;
      else if (i==3)
        v_c[5] = M_PI/10 ;
      else if (i==4)
        v_c[0] = 0.5 ;
      else if (i==5)
        v_c[1] = 0.8 ;

      vpHomogeneousMatrix cMc; // camera displacement
      cMc = vpExponentialMap::direct(v_c) ; // Compute the camera displacement due to the velocity applied to the camera
      if (i > 0) {
        // From the camera displacement cMc, compute the wMe and cMo matrices
        cMo[i] = cMc.inverse() * cMo[i-1];
        wMe[i] = wMe[i-1] * eMc * cMc * eMc.inverse();
      }
    }

    if (0) {
      for (unsigned int i=0 ; i < N ; i++) {
        vpHomogeneousMatrix wMo;
        wMo = wMe[i] * eMc * cMo[i];
        std::cout << std::endl << "wMo[" << i << "] " << std::endl ;
        std::cout << wMo << std::endl ;
        std::cout << "cMo[" << i << "] " << std::endl ;
        std::cout << cMo[i] << std::endl ;
        std::cout << "wMe[" << i << "] " << std::endl ;
        std::cout << wMe[i] << std::endl ;
      }
    }

    // Reset the eMc matrix to eye
    eMc.eye();

    // Compute the eMc hand to eye transformation from six poses
    // - cMo[6]: camera to object poses as six homogeneous transformations
    // - wMe[6]: world to hand (end-effector) poses as six homogeneous transformations
    vpCalibration::calibrationTsai(cMo, wMe, eMc) ;

    std::cout << std::endl << "Output: hand to eye calibration result: eMc estimated " << std::endl ;
    std::cout << eMc << std::endl ;
    eMc.extract(erc);
    std::cout << "Theta U rotation: " << vpMath::deg(erc[0]) << " " << vpMath::deg(erc[1]) << " " << vpMath::deg(erc[2]) << std::endl;
    return 0 ;
  }
  catch(vpException &e) {
    std::cout << "Catch an exception: " << e << std::endl;
    return 1 ;
  }
}