opencv/samples/python2/plane_tracker.py

'''
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
import video
import common


FLANN_INDEX_KDTREE = 1
FLANN_INDEX_LSH    = 6
flann_params= dict(algorithm = FLANN_INDEX_LSH,
                   table_number = 6, # 12
                   key_size = 12,     # 20
                   multi_probe_level = 1) #2

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:
    def __init__(self):
        self.detector = cv2.ORB( nfeatures = 1000 )
        self.matcher = cv2.FlannBasedMatcher(flann_params, {})  # bug : need to pass empty dict (#1329)
        self.targets = []

    def add_target(self, image, rect, data=None):
        '''Add a new tracking target.'''
        x0, y0, x1, y1 = rect
        raw_points, raw_descrs = self.detect_features(image)
        points, descs = [], []
        for kp, desc in zip(raw_points, raw_descrs):
            x, y = kp.pt
            if x0 <= x <= x1 and y0 <= y <= y1:
                points.append(kp)
                descs.append(desc)
        descs = np.uint8(descs)
        self.matcher.add([descs])
        target = PlanarTarget(image = image, rect=rect, keypoints = points, descrs=descs, data=None)
        self.targets.append(target)

    def clear(self):
        '''Remove all targets'''
        self.targets = []
        self.matcher.clear()

    def track(self, frame):
        '''Returns a list of detected TrackedTarget objects'''
        self.frame_points, self.frame_descrs = self.detect_features(frame)
        if len(self.frame_points) < MIN_MATCH_COUNT:
            return []
        matches = self.matcher.knnMatch(self.frame_descrs, k = 2)
        matches = [m[0] for m in matches if len(m) == 2 and m[0].distance < m[1].distance * 0.75]
        if len(matches) < MIN_MATCH_COUNT:
            return []
        matches_by_id = [[] for _ in xrange(len(self.targets))]
        for m in matches:
            matches_by_id[m.imgIdx].append(m)
        tracked = []
        for imgIdx, matches in enumerate(matches_by_id):
            if len(matches) < MIN_MATCH_COUNT:
                continue
            target = self.targets[imgIdx]
            p0 = [target.keypoints[m.trainIdx].pt for m in matches]
            p1 = [self.frame_points[m.queryIdx].pt for m in matches]
            p0, p1 = np.float32((p0, p1))
            H, status = cv2.findHomography(p0, p1, cv2.RANSAC, 3.0)
            status = status.ravel() != 0
            if status.sum() < MIN_MATCH_COUNT:
                continue
            p0, p1 = p0[status], p1[status]
            
            x0, y0, x1, y1 = target.rect
            quad = np.float32([[x0, y0], [x1, y0], [x1, y1], [x0, y1]])
            quad = cv2.perspectiveTransform(quad.reshape(1, -1, 2), H).reshape(-1, 2)

            track = TrackedTarget(target=target, p0=p0, p1=p1, H=H, quad=quad)
            tracked.append(track)
        tracked.sort(key = lambda t: len(t.p0), reverse=True)
        return tracked

    def detect_features(self, frame):
        '''detect_features(self, frame) -> keypoints, descrs'''
        keypoints, descrs = self.detector.detectAndCompute(frame, None)
        if descrs is None:  # detectAndCompute returns descs=None if not keypoints found
            descrs = []
        return keypoints, descrs


class App:
    def __init__(self, src):
        self.cap = video.create_capture(src)
        self.frame = None
        self.paused = False
        self.tracker = PlaneTracker()

        cv2.namedWindow('plane')
        self.rect_sel = common.RectSelector('plane', self.on_rect)
    
    def on_rect(self, rect):
        self.tracker.add_target(self.frame, rect)

    def run(self):
        while True:
            playing = not self.paused and not self.rect_sel.dragging
            if playing or self.frame is None:
                ret, frame = self.cap.read()
                if not ret:
                    break
                self.frame = frame.copy()
            
            vis = self.frame.copy()
            if playing:
                tracked = self.tracker.track(self.frame)
                for tr in tracked:
                    cv2.polylines(vis, [np.int32(tr.quad)], True, (255, 255, 255), 2)
                    for (x, y) in np.int32(tr.p1):
                        cv2.circle(vis, (x, y), 2, (255, 255, 255))

            self.rect_sel.draw(vis)
            cv2.imshow('plane', vis)
            ch = cv2.waitKey(1)
            if ch == ord(' '):
                self.paused = not self.paused
            if ch == ord('c'):
                self.tracker.clear()
            if ch == 27:
                break

if __name__ == '__main__':
    print __doc__

    import sys
    try: video_src = sys.argv[1]
    except: video_src = 0
    App(video_src).run()