AprilTag 25h9
AprilTag 25h9 holds 35 markers of
5×5 bits. In OpenCV it is
cv2.aruco.DICT_APRILTAG_25h9.
Generate a AprilTag 25h9 board
The numbers
| OpenCV name | cv2.aruco.DICT_APRILTAG_25h9 |
| Bits in a marker | 5 × 5 = 25 |
| Markers available | 35, with IDs 0 to 34 |
| Printed width | 7 cells, border included |
| Bits the decoder repairs | 4 |
| Cell size on a 100 mm marker | 14.3 mm |
| Pixels wanted in the image | 84 (floor 28) |
| Range for a 100 mm marker | about 2.0 m |
Range assumes a camera 1920 px wide, 60 degree horizontal field of view, which is a focal length of about 1663 pixels, and a marker seen straight on.
When to use it
Five bit markers are a middle setting: noticeably tougher than four bit markers, and still readable well beyond arm reach. This is an AprilTag family. Pick it when the rest of the stack already uses AprilTag, for example in ROS. OpenCV reads it through cv2.aruco just like an ArUco dictionary. With 35 markers this suits a single board or a small set of tagged objects.
The rest of the family
| Dictionary | Markers | Bits repaired |
|---|---|---|
| AprilTag 25h9 | 35 | 4 |