I’m trying to undistort points using the fish-eye camera model. I got it working perfectly fine in python3 using

```
distorted = np.array([[list(target[0].pt)]], dtype=np.float32)
new_xy = cv2.fisheye.undistortPoints(
distorted,
cam_cal.camera_matrix,
cam_cal.distortion_coefficients,
P=cam_cal.new_camera_matrix,
)
```

Where “target” is a sequence of keypoints. Now I’m trying to do the equivalent in C++

```
cv::Point2f points_in = {800, 700};
cv::Point2f point_out;
std::vector<cv::Point2f> vec_in = {};
vec_in.push_back(points_in);
std::cout << vec_in << std::endl;
std::vector<cv::Point2f> vec_out = {};
cv::fisheye::undistortPoints(
vec_in,
vec_out,
m_camera_matrix,
m_dist_coeffs,
cv::Mat::eye(3, 3, CV_64FC1),
m_new_camera_matrix
);
std::cout << vec_out << std::endl;
point_out = vec_out[0];
vec_out.pop_back();
```

But the result is `[-nan, -nan]`

. I also tried using `cv::Mat`

instead of `std::vector<cv::Point2f>`

but get the same result.

However, the following works and I get the expected results, so I really have no clue what I’m doing wrong.

```
m_new_camera_matrix = cv::Mat(3, 3, CV_64F);
cv::fisheye::estimateNewCameraMatrixForUndistortRectify(
m_camera_matrix,
m_dist_coeffs,
cv::Size(image_width, image_height),
cv::Mat::eye(3, 3, CV_64F),
m_new_camera_matrix
);
cv::fisheye::initUndistortRectifyMap(
m_camera_matrix,
m_dist_coeffs,
cv::Mat::eye(3, 3, CV_64F),
m_new_camera_matrix,
cv::Size(image_width, image_height),
CV_32FC1,
m_map_1,
m_map_2
);
cv::remap(
frame,
output,
m_map_1,
m_map_2,
cv::InterpolationFlags::INTER_LINEAR,
cv::BorderTypes::BORDER_CONSTANT
);
```

where

```
m_camera_matrix =
[695.84766, 0, 823.49;
0, 697.85657, 704.2644;
0, 0, 1]
m_distortion_coefficients =
[-0.00358979;
0.01170594;
-0.008970209999999999;
0.00252217],
image_width = 1600
image_height = 1300
```