Question

I am trying to use OpenCV for Android (OpenCV 2.4.3)
I am writing a program to track keypoints. I am trying to use FeatureDetector to detect keypoints and then Video.calcOpticalFlowPyrLK
to track them.
The question that has me stumped is that the FeatureDetector function returns a MatOfKeyPoint while calcOpticalFlowPyrLK takes a MatOfPoint2f.

Note that MatOfKeyPoint is different from MatOfPoint (Conversion from MatOfPoint to MatOfPont2f is straightforward).

Here is my code so far:

//Feature detector for LKT flow estimation
FeatureDetector cvFeatureDetector;
//Vector of keypoints
MatOfKeyPoint keypoints;

...
...

//intitialize detector
cvFeatureDetector = FeatureDetector.create(FeatureDetector.GFTT);

keypoints = new MatOfKeyPoint();

...
...

//mPrevImgMat is a grayscale image - previous frame
//mCurrentImgMat is a grayscale image - current frame

//Run feature detector in previous image
cvFeatureDetector.detect(mPrevImgMat, keypoints);

MatOfPoint2f keypointsFound = new MatOfPoint2f();
MatOfByte keypointsStatus = new MatOfByte();
MatOfFloat err = new MatOfFloat();
Size winSize = new Size(25,25);
int maxLevel = 3;

//Optical flow to find keypoints in current image
Video.calcOpticalFlowPyrLK(mPrevImgMat, mCurrentImgMat, keypoints,
            keypointsFound, keypointsStatus, err, winSize, maxLevel);

//Obviously "keypoints" in the line above does not work. How does one covert
//keypoints to MatOfPoint2f?

Things I have tried unsuccessfully so far:
(1) keypoints.convertTo()
(2) Creating a vector from keypoints and then trying to populate a vector of Point Vector pointList. Then typecast to MatOfPoint2f when calling flow funciton
(MatOfPoint2f) pointList
(3) Trying to populate a MatOfPoint2f from scratch. Cant figure out how to do this
(4) Using fromArray method in MatOfPoint2f – Not sure what this method does. Documentation is blank for this method. Am I missing something obvious?

Answer 1

Answering my own question… I got the answer in another forum. The link to that discussion is below
http://www.answers.opencv.org/question/6206/opencv4android-conversion-from-matofkeypoint-to/