Hello,
I am trying to implement visual odometry via my webcam and the steps I have followed so far are the following:
- Capture video from webcam (2 following frames each loop).
- Undistort the frames with the callibration parameters I got.
- Convert frames to gray scale.
- Apply FAST algorithm for feature detection.
- And now I am at the calcOpticalFlowPyrLK() step.
My issue is that at step 4 when I print the number of keypoints found in the 2 following frames I get different numbers between the frames (which is logical), but when I do the same thing after the calling of calcOpticalFlowPyrLK() I get the exact same number.
To be more specific, I have wrote:
vector<KeyPoint> kpointsframe1;
vector<KeyPoint> kpointsframe2;
vector<Point2f> pointsframe1;
vector<Point2f> pointsframe2;
vector<uchar> status;
vector<float> err;
Size winSize = Size(21,21);
TermCriteria termcrit = TermCriteria(TermCriteria::COUNT+TermCriteria::EPS,30,0.01);
Mat Essential;
capture.read(frame1);
capture.read(frame2);
undistort(frame1,frame1undist,CameraMatrix,distCoeffs);
undistort(frame2,frame2undist,CameraMatrix,distCoeffs);
cvtColor(frame1undist,frame1gray,CV_BGR2GRAY);
cvtColor(frame2undist,frame2gray,CV_BGR2GRAY);
FAST(frame1gray,kpointsframe1,THRESHOLD_DIFFERENCE,false,FastFeatureDetector::TYPE_9_16);
FAST(frame2gray,kpointsframe2,THRESHOLD_DIFFERENCE,false,FastFeatureDetector::TYPE_9_16);
for(int i=0;i<kpointsframe1.size();i++) pointsframe1.push_back(kpointsframe1.at(i).pt);
for(int i=0;i<kpointsframe2.size();i++) pointsframe2.push_back(kpointsframe2.at(i).pt);
calcOpticalFlowPyrLK(frame1gray,frame2gray,pointsframe1,pointsframe2,status,err,winSize,3,termcrit,0,0.0001);
and I print the following in each loop:
cout<<status.size()<<endl;
cout<<pointsframe1.size()<<endl;
cout<<pointsframe2.size()<<endl;
cout<<"-------------------"<<endl;
If I comment the line
calcOpticalFlowPyrLK(frame1gray,frame2gray,pointsframe1,pointsframe2,status,err,winSize,3,termcrit,0,0.0001);
I get different numbers, but if I leave it like that I get 3 numbers which are all the same in each loop. All the above code is in a while loop. I am wondering why this happens? Shouldn't the calcOpticalFlowPyrLK() try to find the matching between the keypoints of the two frames and give the status of their differences or I am understanding something wrong?
Thanks for answering and for your time in advance,
Chris