OpenCV/opencv_contrib/modules/aruco/samples/aruco_samples_utility.hpp

#include <opencv2/highgui.hpp>
#include <opencv2/aruco.hpp>
#include <opencv2/calib3d.hpp>
#include <ctime>

namespace {
inline static bool readCameraParameters(std::string filename, cv::Mat &camMatrix, cv::Mat &distCoeffs) {
    cv::FileStorage fs(filename, cv::FileStorage::READ);
    if (!fs.isOpened())
        return false;
    fs["camera_matrix"] >> camMatrix;
    fs["distortion_coefficients"] >> distCoeffs;
    return true;
}

inline static bool saveCameraParams(const std::string &filename, cv::Size imageSize, float aspectRatio, int flags,
                                    const cv::Mat &cameraMatrix, const cv::Mat &distCoeffs, double totalAvgErr) {
    cv::FileStorage fs(filename, cv::FileStorage::WRITE);
    if (!fs.isOpened())
        return false;

    time_t tt;
    time(&tt);
    struct tm *t2 = localtime(&tt);
    char buf[1024];
    strftime(buf, sizeof(buf) - 1, "%c", t2);

    fs << "calibration_time" << buf;
    fs << "image_width" << imageSize.width;
    fs << "image_height" << imageSize.height;

    if (flags & cv::CALIB_FIX_ASPECT_RATIO) fs << "aspectRatio" << aspectRatio;

    if (flags != 0) {
        sprintf(buf, "flags: %s%s%s%s",
                flags & cv::CALIB_USE_INTRINSIC_GUESS ? "+use_intrinsic_guess" : "",
                flags & cv::CALIB_FIX_ASPECT_RATIO ? "+fix_aspectRatio" : "",
                flags & cv::CALIB_FIX_PRINCIPAL_POINT ? "+fix_principal_point" : "",
                flags & cv::CALIB_ZERO_TANGENT_DIST ? "+zero_tangent_dist" : "");
    }
    fs << "flags" << flags;
    fs << "camera_matrix" << cameraMatrix;
    fs << "distortion_coefficients" << distCoeffs;
    fs << "avg_reprojection_error" << totalAvgErr;
    return true;
}

}