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Maxim Smolskiy
ad560f69f4
Fix checking that point lies inside ellipse #27704 ### Pull Request Readiness Checklist Previous `check_pt_in_ellipse` implementation was incorrect. For points on ellipse `cv::norm(to_pt)` should be equal to `el_dist`. I tested current implementation with following Python script: ``` import cv2 import numpy as np import matplotlib.pyplot as plt from matplotlib.patches import Ellipse def check_pt_in_ellipse(pt, el): center, axes, angle = ellipse to_pt = pt - center el_angle = angle * np.pi / 180 to_pt_r_x = to_pt[0] * np.cos(-el_angle) - to_pt[1] * np.sin(-el_angle) to_pt_r_y = to_pt[0] * np.sin(-el_angle) + to_pt[1] * np.cos(-el_angle) pt_angle = np.arctan2(to_pt_r_y / axes[1], to_pt_r_x / axes[0]) x_dist = 0.5 * axes[0] * np.cos(pt_angle) y_dist = 0.5 * axes[1] * np.sin(pt_angle) el_dist = np.sqrt(x_dist * x_dist + y_dist * y_dist) assert abs(np.linalg.norm(to_pt) - el_dist) < 1e-10 # TEST(Imgproc_FitEllipse_Issue_4515, accuracy) { points = np.array([ [327, 317], [328, 316], [329, 315], [330, 314], [331, 314], [332, 314], [333, 315], [333, 316], [333, 317], [333, 318], [333, 319], [333, 320], ]) ellipse = cv2.fitEllipseDirect(points) center, axes, angle = ellipse angle_rad = np.deg2rad(angle) points_on_ellipse = [] for point_angle_deg in range(0, 360, 10): point_angle = np.deg2rad(point_angle_deg) point = np.array([0., 0.]) point_x = axes[0] * 0.5 * np.cos(point_angle) point_y = axes[1] * 0.5 * np.sin(point_angle) point[0] = point_x * np.cos(angle_rad) - point_y * np.sin(angle_rad) point[1] = point_x * np.sin(angle_rad) + point_y * np.cos(angle_rad) point[0] += center[0] point[1] += center[1] points_on_ellipse.append(point) points_on_ellipse = np.array(points_on_ellipse) for point in points_on_ellipse: check_pt_in_ellipse(point, ellipse) plt.figure(figsize=(8, 8)) plt.scatter(points[:, 0], points[:, 1], c='red', label='points') plt.scatter(points_on_ellipse[:, 0], points_on_ellipse[:, 1], c='yellow', label='ellipse') ellipse = Ellipse(xy=center, width=axes[0], height=axes[1], angle=angle, facecolor='none', edgecolor='b') plt.gca().add_patch(ellipse) plt.gca().set_aspect('equal') plt.legend() plt.show() ``` 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 - [ ] There is a reference to the original bug report and related work - [ ] There is accuracy test, performance test and test data in opencv_extra repository, if applicable Patch to opencv_extra has the same branch name. - [ ] The feature is well documented and sample code can be built with the project CMake
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