Apriltag Vision

Apriltag Vision

Setting Up the Apriltag Detector

We need parameters for the Apriltag detector in order to accurately detect tags.

Use the following parameters (tested on Microsoft LifeCam HD-3000)

at_detector = Detector(
   families="tag16h5",
   nthreads=1,
   quad_decimate=0.3,
   quad_sigma=0.35,
   refine_edges=1,
   decode_sharpening=0.25,
   debug=0
)

Recoloring

To detect Apriltags we must be in a grayscale color space.

---

imgGrayscale = cv2.cvtColor(img, cv2.COLOR_BGR2GRAY)

Checking For Apriltag

First we check for apriltags in the image, then we take only the apriltags that the program is most confident in seeing.

****`apriltags = at_detector.detect(imgGrayscale)

apriltags = [x for x in apriltags if x.hamming == 0]`

Locating Apriltag Positions

for i in range(len(apriltags)):
    centerXY = ast.literal_eval((re.sub(" +", " ", ((str(apriltags[i].center).replace("[", "")).replace("]", "")).strip())).replace(" ", ", "))
    centerXY = list(centerXY)
    centerXY[0] = centerXY[0] - 320
    centerXY[1] = centerXY[1] - 240

centerXY[0] is the X position of the Apriltag. centerXY[1] is the Y position of the Apriltag.

Finding Tag ID

for i in range(len(apriltags)):
		tagID = apriltags[i].tag_id