OpenCV 错误:相机校准:断言在matrix_wrap.cpp失败

错误：

OpenCV(3.4.1) Error: Assertion failed (i < 0) in cv::debug_build_guard::_InputArray::getMat_, 
file C:buildmaster_winpack-build-win64-vc15opencvmodulescoresrcmatrix_wrap.cpp, line 50

"matrix_wrap.cpp"中触发错误的代码：

if( k == STD_VECTOR )
{
CV_Assert( i < 0 );
int t = CV_MAT_TYPE(flags);
const std::vector<uchar>& v = *(const std::vector<uchar>*)obj;
return !v.empty() ? Mat(size(), t, (void*)&v[0]) : Mat();
}

整个代码：

#include <iostream>    
#include <opencv2/opencv.hpp>  

int main(int argc, char *argv[])
{
cv::Mat img = cv::imread(argv[1], CV_LOAD_IMAGE_GRAYSCALE);
cv::Size imageSize = cv::Size(img.size[0], img.size[1]);
cv::Mat cameraMatrix, distCoeffs;
double squareSize = 30;
cv::Size boardSize = cv::Size(6, 11);
std::vector<cv::Point2f> imagePoints;
std::vector<cv::Point3f> objectPoints;
for (int i = 0; i < boardSize.height; i++) {
for (int j = 0; j < boardSize.width; j++) {
objectPoints.push_back(
cv::Point3f(float(j * squareSize), float(i * squareSize), 0));
}
}
std::vector<cv::Mat>  rvecs, tvecs;
bool found = false;
if (img.size[0] > 1)
{
bool found = findChessboardCorners(img, boardSize, imagePoints, cv::CALIB_CB_ADAPTIVE_THRESH);
if (found)
{
drawChessboardCorners(img, boardSize, imagePoints, found);
}
objectPoints.resize(imagePoints.size(), objectPoints[0]);
double rms = calibrateCamera(objectPoints, imagePoints, imageSize, cameraMatrix, distCoeffs, rvecs, tvecs);
cv::namedWindow("My Image");
cv::imshow("My Image", img);
cv::waitKey(1000);
}
return 0;
}

我想使用带有杂散棋盘的基本相机校准。 在"校准相机"功能之前一切正常，但我无法弄清楚为什么会出现此错误。

"objectPoints"和"imagePoints"的大小是相同的。 提前谢谢你。

附言： 我是这个论坛的新手，也是OpenCV;)