samples/cpp/tutorial_code/features2D/Homography/homography_from_camera_displacement.cpp

An example program about homography from the camera displacement

Check the corresponding tutorial for more details

#include <iostream>
#include <opencv2/core.hpp>
#include <opencv2/imgproc.hpp>
#include <opencv2/highgui.hpp>
#include <opencv2/calib3d.hpp>
 
using namespace std;
using namespace cv;
 
namespace
{
enum Pattern { CHESSBOARD, CIRCLES_GRID, ASYMMETRIC_CIRCLES_GRID };
 
void calcChessboardCorners(Size boardSize, float squareSize, vector<Point3f>& corners, Pattern patternType = CHESSBOARD)
{
    corners.resize(0);
 
    switch (patternType)
    {
    case CHESSBOARD:
    case CIRCLES_GRID:
        for( int i = 0; i < boardSize.height; i++ )
            for( int j = 0; j < boardSize.width; j++ )
                corners.push_back(Point3f(float(j*squareSize),
                                          float(i*squareSize), 0));
        break;
 
    case ASYMMETRIC_CIRCLES_GRID:
        for( int i = 0; i < boardSize.height; i++ )
            for( int j = 0; j < boardSize.width; j++ )
                corners.push_back(Point3f(float((2*j + i % 2)*squareSize),
                                          float(i*squareSize), 0));
        break;
 
    default:
        CV_Error(Error::StsBadArg, "Unknown pattern type\n");
    }
}
 
Mat computeHomography(const Mat &R_1to2, const Mat &tvec_1to2, const double d_inv, const Mat &normal)
{
    Mat homography = R_1to2 + d_inv * tvec_1to2*normal.t();
    return homography;
}
 
Mat computeHomography(const Mat &R1, const Mat &tvec1, const Mat &R2, const Mat &tvec2,
                      const double d_inv, const Mat &normal)
{
    Mat homography = R2 * R1.t() + d_inv * (-R2 * R1.t() * tvec1 + tvec2) * normal.t();
    return homography;
}
 
void computeC2MC1(const Mat &R1, const Mat &tvec1, const Mat &R2, const Mat &tvec2,
                  Mat &R_1to2, Mat &tvec_1to2)
{
    //c2Mc1 = c2Mo * oMc1 = c2Mo * c1Mo.inv()
    R_1to2 = R2 * R1.t();
    tvec_1to2 = R2 * (-R1.t()*tvec1) + tvec2;
}
 
void homographyFromCameraDisplacement(const string &img1Path, const string &img2Path, const Size &patternSize,
                                      const float squareSize, const string &intrinsicsPath)
{
    Mat img1 = imread( samples::findFile( img1Path ) );
    Mat img2 = imread( samples::findFile( img2Path ) );
 
    vector<Point2f> corners1, corners2;
    bool found1 = findChessboardCorners(img1, patternSize, corners1);
    bool found2 = findChessboardCorners(img2, patternSize, corners2);
 
    if (!found1 || !found2)
    {
        cout << "Error, cannot find the chessboard corners in both images." << endl;
        return;
    }
 
    vector<Point3f> objectPoints;
    calcChessboardCorners(patternSize, squareSize, objectPoints);
 
    FileStorage fs( samples::findFile( intrinsicsPath ), FileStorage::READ);
    Mat cameraMatrix, distCoeffs;
    fs["camera_matrix"] >> cameraMatrix;
    fs["distortion_coefficients"] >> distCoeffs;
 
    Mat rvec1, tvec1;
    solvePnP(objectPoints, corners1, cameraMatrix, distCoeffs, rvec1, tvec1);
    Mat rvec2, tvec2;
    solvePnP(objectPoints, corners2, cameraMatrix, distCoeffs, rvec2, tvec2);
 
    Mat img1_copy_pose = img1.clone(), img2_copy_pose = img2.clone();
    Mat img_draw_poses;
    drawFrameAxes(img1_copy_pose, cameraMatrix, distCoeffs, rvec1, tvec1, 2*squareSize);
    drawFrameAxes(img2_copy_pose, cameraMatrix, distCoeffs, rvec2, tvec2, 2*squareSize);
    hconcat(img1_copy_pose, img2_copy_pose, img_draw_poses);
    imshow("Chessboard poses", img_draw_poses);
 
    Mat R1, R2;
    Rodrigues(rvec1, R1);
    Rodrigues(rvec2, R2);
 
    Mat R_1to2, t_1to2;
    computeC2MC1(R1, tvec1, R2, tvec2, R_1to2, t_1to2);
    Mat rvec_1to2;
    Rodrigues(R_1to2, rvec_1to2);
 
    Mat normal = (Mat_<double>(3,1) << 0, 0, 1);
    Mat normal1 = R1*normal;
 
    Mat origin(3, 1, CV_64F, Scalar(0));
    Mat origin1 = R1*origin + tvec1;
    double d_inv1 = 1.0 / normal1.dot(origin1);
 
    Mat homography_euclidean = computeHomography(R_1to2, t_1to2, d_inv1, normal1);
    Mat homography = cameraMatrix * homography_euclidean * cameraMatrix.inv();
 
    homography /= homography.at<double>(2,2);
    homography_euclidean /= homography_euclidean.at<double>(2,2);
 
    //Same but using absolute camera poses instead of camera displacement, just for check
    Mat homography_euclidean2 = computeHomography(R1, tvec1, R2, tvec2, d_inv1, normal1);
    Mat homography2 = cameraMatrix * homography_euclidean2 * cameraMatrix.inv();
 
    homography_euclidean2 /= homography_euclidean2.at<double>(2,2);
    homography2 /= homography2.at<double>(2,2);
 
    cout << "\nEuclidean Homography:\n" << homography_euclidean << endl;
    cout << "Euclidean Homography 2:\n" << homography_euclidean2 << endl << endl;
 
    Mat H = findHomography(corners1, corners2);
    cout << "\nfindHomography H:\n" << H << endl;
 
    cout << "homography from camera displacement:\n" << homography << endl;
    cout << "homography from absolute camera poses:\n" << homography2 << endl << endl;
 
    Mat img1_warp;
    warpPerspective(img1, img1_warp, H, img1.size());
 
    Mat img1_warp_custom;
    warpPerspective(img1, img1_warp_custom, homography, img1.size());
    imshow("Warped image using homography computed from camera displacement", img1_warp_custom);
 
    Mat img_draw_compare;
    hconcat(img1_warp, img1_warp_custom, img_draw_compare);
    imshow("Warped images comparison", img_draw_compare);
 
    Mat img1_warp_custom2;
    warpPerspective(img1, img1_warp_custom2, homography2, img1.size());
    imshow("Warped image using homography computed from absolute camera poses", img1_warp_custom2);
 
    waitKey();
}
 
const char* params
    = "{ help h         |       | print usage }"
      "{ image1         | left02.jpg | path to the source chessboard image }"
      "{ image2         | left01.jpg | path to the desired chessboard image }"
      "{ intrinsics     | left_intrinsics.yml | path to camera intrinsics }"
      "{ width bw       | 9     | chessboard width }"
      "{ height bh      | 6     | chessboard height }"
      "{ square_size    | 0.025 | chessboard square size }";
}
 
int main(int argc, char *argv[])
{
    CommandLineParser parser(argc, argv, params);
 
    if (parser.has("help"))
    {
        parser.about("Code for homography tutorial.\n"
            "Example 3: homography from the camera displacement.\n");
        parser.printMessage();
        return 0;
    }
 
    Size patternSize(parser.get<int>("width"), parser.get<int>("height"));
    float squareSize = (float) parser.get<double>("square_size");
    homographyFromCameraDisplacement(parser.get<String>("image1"),
                                     parser.get<String>("image2"),
                                     patternSize, squareSize,
                                     parser.get<String>("intrinsics"));
 
    return 0;
}