title: How can i use the Object tracking API of vision framework on ios11?
body: <pre><code>// init bounding
  CGRect rect = CGRectMake(0, 0, 0.3, 0.3);
  VNSequenceRequestHandler* reqImages = [[VNSequenceRequestHandler alloc] init];
  VNRectangleObservation* ObserveRect = [VNRectangleObservation observationWithBoundingBox:rect];
  VNTrackRectangleRequest* reqRect = [[VNTrackRectangleRequest alloc] initWithRectangleObservation:ObserveRect];
  NSArray&lt;VNRequest *&gt;* requests = [NSArray arrayWithObjects:reqRect, nil];
  BOOL bsucc = [reqImages performRequests:requests onCGImage:img.CGImage error:&amp;error];
  
  // get tracking bounding
  VNDetectRectanglesRequest* reqRectTrack = [VNDetectRectanglesRequest new];
  NSArray&lt;VNRequest *&gt;* requestsTrack = [NSArray arrayWithObjects:reqRectTrack, nil];
  [reqImages performRequests:requestsTrack onCGImage:img.CGImage error:&amp;error];
  
  VNRectangleObservation* Observe = [reqRectTrack.results firstObject];
  CGRect boundingBox = Observe.boundingBox;
  </code></pre>
  
  <p>Why the boundingBox value is incorrect?</p>
  
  <p>How can i find the demo of vision.framework of ios11 ?</p>