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Author SHA1 Message Date
s-trinh e258f2595e Merge pull request #26299 from s-trinh:feat/getClosestEllipsePoints_2 
Add getClosestEllipsePoints() function to get the closest point on an ellipse #26299

Following https://github.com/opencv/opencv/issues/26078, I was thinking that a function to get for a considered 2d point the corresponding closest point (or maybe directly the distance?) on an ellipse could be useful.
This would allow computing the fitting error with `fitEllipse()` for instance.

Code is based from:
- https://stackoverflow.com/questions/22959698/distance-from-given-point-to-given-ellipse/46007540#46007540
- https://blog.chatfield.io/simple-method-for-distance-to-ellipse/
- https://github.com/0xfaded/ellipse_demo

---

Demo code:

<details>
  <summary>code</summary>
 
```cpp
#include <iostream>
#include <opencv2/opencv.hpp>

namespace
{
void scaleApplyColormap(const cv::Mat &img_float, cv::Mat &img)
{
  cv::Mat img_scale = cv::Mat::zeros(img_float.size(), CV_8UC3);

  double min_val = 0, max_val = 0;
  cv::minMaxLoc(img_float, &min_val, &max_val);
  std::cout << "min_val=" << min_val << " ; max_val=" << max_val << std::endl;

  if (max_val - min_val > 1e-2) {
    float a = 255 / (max_val - min_val);
    float b = -a * min_val;

    cv::convertScaleAbs(img_float, img_scale, a, b);
    cv::applyColorMap(img_scale, img, cv::COLORMAP_TURBO);
  }
  else {
    std::cerr << "max_val - min_val <= 1e-2" << std::endl;
  }
}

cv::Mat drawEllipseDistanceMap(const cv::RotatedRect &ellipse_params)
{
  float bb_rect_w = ellipse_params.center.x + ellipse_params.size.width;
  float bb_rect_h = ellipse_params.center.y + ellipse_params.size.height;

  std::vector<cv::Point2f> points_list;
  points_list.resize(1);
  cv::Mat pointsf;
  cv::Mat closest_pts;
  cv::Mat dist_map = cv::Mat::zeros(bb_rect_h*1.5, bb_rect_w*1.5, CV_32F);
  for (int i = 0; i < dist_map.rows; i++) {
    for (int j = 0; j < dist_map.cols; j++) {
      points_list[0].x = j;
      points_list[0].y = i;
      cv::Mat(points_list).convertTo(pointsf, CV_32F);
      cv::getClosestEllipsePoints(ellipse_params, pointsf, closest_pts);
      dist_map.at<float>(i, j) = std::hypot(closest_pts.at<cv::Point2f>(0).x-j, closest_pts.at<cv::Point2f>(0).y-i);
    }
  }

  cv::Mat dist_map_8u;
  scaleApplyColormap(dist_map, dist_map_8u);
  return dist_map_8u;
}
}

int main()
{
  std::vector<cv::Point2f> points_list;

  // [1434, 308], [1434, 309], [1433, 310], [1427, 310], [1427, 312], [1426, 313], [1422, 313], [1422, 314],
  points_list.push_back(cv::Point2f(1434, 308));
  points_list.push_back(cv::Point2f(1434, 309));
  points_list.push_back(cv::Point2f(1433, 310));
  points_list.push_back(cv::Point2f(1427, 310));
  points_list.push_back(cv::Point2f(1427, 312));
  points_list.push_back(cv::Point2f(1426, 313));
  points_list.push_back(cv::Point2f(1422, 313));
  points_list.push_back(cv::Point2f(1422, 314));

  // [1421, 315], [1415, 315], [1415, 316], [1414, 317], [1408, 317], [1408, 319], [1407, 320], [1403, 320],
  points_list.push_back(cv::Point2f(1421, 315));
  points_list.push_back(cv::Point2f(1415, 315));
  points_list.push_back(cv::Point2f(1415, 316));
  points_list.push_back(cv::Point2f(1414, 317));
  points_list.push_back(cv::Point2f(1408, 317));
  points_list.push_back(cv::Point2f(1408, 319));
  points_list.push_back(cv::Point2f(1407, 320));
  points_list.push_back(cv::Point2f(1403, 320));

  // [1403, 321], [1402, 322], [1396, 322], [1396, 323], [1395, 324], [1389, 324], [1389, 326], [1388, 327],
  points_list.push_back(cv::Point2f(1403, 321));
  points_list.push_back(cv::Point2f(1402, 322));
  points_list.push_back(cv::Point2f(1396, 322));
  points_list.push_back(cv::Point2f(1396, 323));
  points_list.push_back(cv::Point2f(1395, 324));
  points_list.push_back(cv::Point2f(1389, 324));
  points_list.push_back(cv::Point2f(1389, 326));
  points_list.push_back(cv::Point2f(1388, 327));

  // [1382, 327], [1382, 328], [1381, 329], [1376, 329], [1376, 330], [1375, 331], [1369, 331], [1369, 333],
  points_list.push_back(cv::Point2f(1382, 327));
  points_list.push_back(cv::Point2f(1382, 328));
  points_list.push_back(cv::Point2f(1381, 329));
  points_list.push_back(cv::Point2f(1376, 329));
  points_list.push_back(cv::Point2f(1376, 330));
  points_list.push_back(cv::Point2f(1375, 331));
  points_list.push_back(cv::Point2f(1369, 331));
  points_list.push_back(cv::Point2f(1369, 333));

  // [1368, 334], [1362, 334], [1362, 335], [1361, 336], [1359, 336], [1359, 1016], [1365, 1016], [1366, 1017],
  points_list.push_back(cv::Point2f(1368, 334));
  points_list.push_back(cv::Point2f(1362, 334));
  points_list.push_back(cv::Point2f(1362, 335));
  points_list.push_back(cv::Point2f(1361, 336));
  points_list.push_back(cv::Point2f(1359, 336));
  points_list.push_back(cv::Point2f(1359, 1016));
  points_list.push_back(cv::Point2f(1365, 1016));
  points_list.push_back(cv::Point2f(1366, 1017));

  // [1366, 1019], [1430, 1019], [1430, 1017], [1431, 1016], [1440, 1016], [1440, 308]
  points_list.push_back(cv::Point2f(1366, 1019));
  points_list.push_back(cv::Point2f(1430, 1019));
  points_list.push_back(cv::Point2f(1430, 1017));
  points_list.push_back(cv::Point2f(1431, 1016));
  points_list.push_back(cv::Point2f(1440, 1016));
  points_list.push_back(cv::Point2f(1440, 308));

  cv::Mat pointsf;
  cv::Mat(points_list).convertTo(pointsf, CV_32F);

  cv::RotatedRect ellipse_params = cv::fitEllipseAMS(pointsf);
  std::cout << "ellipse_params, center=" << ellipse_params.center << " ; size=" << ellipse_params.size
    << " ; angle=" << ellipse_params.angle << std::endl;

  cv::TickMeter tm;
  tm.start();
  cv::Mat dist_map_8u = drawEllipseDistanceMap(ellipse_params);
  tm.stop();
  std::cout << "Elapsed time: " << tm.getAvgTimeSec() << " sec" << std::endl;

  cv::Point center(ellipse_params.center.x, ellipse_params.center.y);
  cv::Point axis(ellipse_params.size.width/2, ellipse_params.size.height/2);
  std::vector<cv::Point> ellipse_pts_list;
  cv::ellipse2Poly(center, axis, ellipse_params.angle, 0, 360, 1, ellipse_pts_list);
  cv::polylines(dist_map_8u, ellipse_pts_list, false, cv::Scalar(0, 0, 0), 3);

  // Points to be fitted
  cv::Mat closest_pts;
  cv::getClosestEllipsePoints(ellipse_params, pointsf, closest_pts);
  for (int i = 0; i < closest_pts.rows; i++) {
    cv::Point pt;
    pt.x = closest_pts.at<cv::Point2f>(i).x;
    pt.y = closest_pts.at<cv::Point2f>(i).y;
    cv::circle(dist_map_8u, pt, 8, cv::Scalar(0, 0, 255), 2);
  }

  cv::imwrite("dist_map_8u.png", dist_map_8u);

  return EXIT_SUCCESS;
}
```
</details>

![image](https://github.com/user-attachments/assets/3345cc86-ba83-44f9-ac78-74058a33a7dc)

---

### Pull Request Readiness Checklist

See details at https://github.com/opencv/opencv/wiki/How_to_contribute#making-a-good-pull-request

- [x] I agree to contribute to the project under Apache 2 License.
- [x] To the best of my knowledge, the proposed patch is not based on a code under GPL or another license that is incompatible with OpenCV
- [x] The PR is proposed to the proper branch
- [x] There is a reference to the original bug report and related work
- [x] There is accuracy test, performance test and test data in opencv_extra repository, if applicable
      Patch to opencv_extra has the same branch name.
- [x] The feature is well documented and sample code can be built with the project CMake
 2025-06-03 17:12:16 +03:00
Maxim Smolskiy a2a3f5e86c Merge pull request #26773 from MaximSmolskiy:improve-robustness-for-ellipse-fitting 
Improve robustness for ellipse fitting #26773

### Pull Request Readiness Checklist

Related to #26694 

Current noise addition is not very good because for example it turns degenerate case of one horizontal line into degenerate case of two parallel horizontal lines

Improving noise addition leads to improved robustness of algorithms

See details at https://github.com/opencv/opencv/wiki/How_to_contribute#making-a-good-pull-request

- [x] I agree to contribute to the project under Apache 2 License.
- [x] To the best of my knowledge, the proposed patch is not based on a code under GPL or another license that is incompatible with OpenCV
- [x] The PR is proposed to the proper branch
- [x] There is a reference to the original bug report and related work
- [x] There is accuracy test, performance test and test data in opencv_extra repository, if applicable
      Patch to opencv_extra has the same branch name.
- [x] The feature is well documented and sample code can be built with the project CMake
 2025-01-20 14:25:40 +03:00
MaximSmolskiy 9b85ab0a63 Fix comment for fitEllipse Java case accurracy test 2025-01-06 19:14:57 +03:00
Vadim Pisarevsky 8abb312c20 Merge pull request #17417 from vpisarev:fix_fitellipse 
* improved fitEllipse and fitEllipseDirect accuracy in singular or close-to-singular cases (see issue #9923)

* scale points using double precision

* added normalization to fitEllipseAMS as well; fixed Java test case by raising the tolerance (it's unclear what is the correct result in this case).

* improved point perturbation a bit. make the code a little bit more clear

* trying to fix Java fitEllipseTest by slightly raising the tolerance threshold

* synchronized C++ version of Java's fitEllipse test

* removed trailing whitespaces
 2020-06-01 18:01:20 +00:00
Alexander Alekhin 4a297a2443 ts: refactor OpenCV tests 
- removed tr1 usage (dropped in C++17)
- moved includes of vector/map/iostream/limits into ts.hpp
- require opencv_test + anonymous namespace (added compile check)
- fixed norm() usage (must be from cvtest::norm for checks) and other conflict functions
- added missing license headers
 2018-02-03 19:39:47 +00:00
Rostislav Vasilikhin fb5cd42c6b enabled tests for fitEllipse since the issue is fixed 2017-10-23 16:28:49 +03:00
arybnikov 2deda0e868 Added tests for issues ##4515, 6544 2016-07-18 10:01:13 +03:00