Inconsistent orientation of detected/generated ArUco and AprilTags

Start with the provided Python reproduction using ArucoDetector.detectMarkers and generateImageMarker for the AprilTag and ArUco dictionaries. Trace how each dictionary defines corner ordering and generated marker orientation; done means detection and generation use a consistent orientation for both marker families, with the reproduction confirming the corrected ordering.

ArUco and AprilTag detection both uses a clockwise orientation, however, AprilTag corners start with bottom right while ArUco starts with upper left. See the example below:

Code:

import cv2


def draw_markers_with_corners(img, corners):
    for i, marker_corners in enumerate(corners):
        # Get the corners of the marker
        corner_points = marker_corners.reshape((4, 2))
        corner_points = corner_points.astype(int)

        # Draw each corner with its ordinal position
        for j, corner in enumerate(corner_points):
            # Draw corner point
            cv2.circle(img, tuple(corner), 5, (0, 0, 255), -1)
            # Label the corner with its ordinal position (0, 1, 2, 3)
            cv2.putText(
                img,
                str(j),
                (corner[0] + 10, corner[1] + 10),
                cv2.FONT_HERSHEY_SIMPLEX,
                0.5,
                (255, 0, 0),
                2,
            )

    return img


img = cv2.imread("markers.jpeg")

parameters = cv2.aruco.DetectorParameters()

april_dict = cv2.aruco.getPredefinedDictionary(cv2.aruco.DICT_APRILTAG_36h11)
april_detector = cv2.aruco.ArucoDetector(april_dict, parameters)
aruco_dict = cv2.aruco.getPredefinedDictionary(cv2.aruco.DICT_4X4_250)
aruco_detector = cv2.aruco.ArucoDetector(aruco_dict, parameters)

img_marked = img.copy()
april_corners, _, _ = april_detector.detectMarkers(img)
img_marked = draw_markers_with_corners(img_marked, april_corners)

aruco_corners, _, _ = aruco_detector.detectMarkers(img)
img_marked = draw_markers_with_corners(img_marked, aruco_corners)

cv2.imwrite("markers_detected.jpeg", img_marked)

The same issue persists (likely due to pre-defined dictionary configurations) for generation:

The generated AprilTag 36h11 - 0 (wrong orientation, see above)

The generated ArUco 4x4_250 - 0 (correct orientation, see above)

Code:

import cv2

april_dict = cv2.aruco.getPredefinedDictionary(cv2.aruco.DICT_APRILTAG_36h11)
aruco_dict = cv2.aruco.getPredefinedDictionary(cv2.aruco.DICT_4X4_250)

img = cv2.aruco.generateImageMarker(aruco_dict, 0, 200, borderBits=1)
cv2.imwrite("aruco.png", img)

img = cv2.aruco.generateImageMarker(april_dict, 0, 200, borderBits=1)
cv2.imwrite("april.png", img)