rapid: add marker tracker sample

modules/rapid/samples/track_marker.py

+import numpy as np
+import cv2 as cv
+
+# aruco config
+adict = cv.aruco.Dictionary_get(cv.aruco.DICT_4X4_50)
+cv.imshow("marker", cv.aruco.drawMarker(adict, 0, 400))
+marker_len = 5
+
+# rapid config
+obj_points = np.float32([[-0.5, 0.5, 0], [0.5, 0.5, 0], [0.5, -0.5, 0], [-0.5, -0.5, 0]]) * marker_len
+tris = np.int32([[0, 2, 1], [0, 3, 2]])  # note CCW order for culling
+line_len = 10
+
+# random calibration data. your mileage may vary.
+imsize = (800, 600)
+K = cv.getDefaultNewCameraMatrix(np.diag([800, 800, 1]), imsize, True)
+
+# video capture
+cap = cv.VideoCapture(0)
+cap.set(cv.CAP_PROP_FRAME_WIDTH, imsize[0])
+cap.set(cv.CAP_PROP_FRAME_HEIGHT, imsize[1])
+
+rot, trans = None, None
+while cv.waitKey(1) != 27:
+    img = cap.read()[1]
+
+    # detection with aruco
+    if rot is None:
+        corners, ids = cv.aruco.detectMarkers(img, adict)[:2]
+
+        if ids is not None:
+            rvecs, tvecs = cv.aruco.estimatePoseSingleMarkers(corners, marker_len, K, None)[:2]
+            rot, trans = rvecs[0].ravel(), tvecs[0].ravel()
+
+    # tracking and refinement with rapid
+    if rot is not None:
+        for i in range(5):  # multiple iterations
+            ratio, rot, trans = cv.rapid.rapid(img, 40, line_len, obj_points, tris, K, rot, trans)
+            if ratio < 0.8:
+                # bad quality, force re-detect
+                rot, trans = None, None
+                break
+
+    # drawing
+    cv.putText(img, "detecting" if rot is None else "tracking", (0, 20), cv.FONT_HERSHEY_SIMPLEX, 1.0, (0, 255, 255))
+    if rot is not None:
+        cv.drawFrameAxes(img, K, None, rot, trans, marker_len)
+    cv.imshow("tracking", img)