Added descriptions to PlaneTracker samples

samples/python2/plane_tracker.py

@@ -1,3 +1,24 @@
+'''
+Multitarget planar tracking
+==================
+
+Example of using features2d framework for interactive video homography matching.
+ORB features and FLANN matcher are used. This sample provides PlaneTracker class
+and an example of its usage.
+
+video: http://www.youtube.com/watch?v=pzVbhxx6aog
+
+Usage
+-----
+plane_tracker.py [<video source>]
+
+Keys:
+   SPACE  -  pause video
+   c      -  clear targets
+
+Select a textured planar object to track by drawing a box with a mouse.
+'''
+
 import numpy as np
 import cv2
 from collections import namedtuple
@@ -14,8 +35,22 @@ flann_params= dict(algorithm = FLANN_INDEX_LSH,
 
 MIN_MATCH_COUNT = 10
 
-
+'''
+  image     - image to track
+  rect      - tracked rectangle (x1, y1, x2, y2)
+  keypoints - keypoints detected inside rect
+  descrs    - their descriptors
+  data      - some user-provided data
+'''
 PlanarTarget = namedtuple('PlaneTarget', 'image, rect, keypoints, descrs, data')
+
+'''
+  target - reference to PlanarTarget
+  p0     - matched points coords in target image
+  p1     - matched points coords in input frame
+  H      - homography matrix from p0 to p1
+  quad   - target bounary quad in input frame
+'''
 TrackedTarget = namedtuple('TrackedTarget', 'target, p0, p1, H, quad')
 
 class PlaneTracker: