Android:将calcOpticalFlowPyrLK与MatOfPoint2f一起使用

时间:2012-09-24 08:23:48

标签: java android opencv opticalflow feature-tracking

我无法将matOpticalFlowPyrLK与MatOfPoint2f一起使用。我宣布我的类型如下:

private Mat mPreviousGray;                  // previous gray-level image
private List<MatOfPoint2f> points;          // tracked features
private MatOfPoint initial;                 // initial position of tracked points

并使用以下内容查找和跟踪功能 (我的代码基于Robert Laganiere在C ++中的示例光流应用程序。)

// Called whenever a new frame m is captured
private void OpticalFlow(Mat m, int maxDetectionCount, double qualityLevel,
    double minDistance) {

    if (points.get(0).total() < maxDetectionCount/2)                // Check if new points need to be added
    {
        // maxDetectionCount = 500
        // qualityLevel = 0.01
        // minDistance = 10
        Imgproc.goodFeaturesToTrack(m, initial, maxDetectionCount, qualityLevel, minDistance);

        // add the detected features to the currently tracked features
        points.get(0).push_back(initial);
        // Have checked length of points.get(0), is not zero.
    }

    // for first image of the sequence
    if(mPreviousGray.empty())
        m.copyTo(mPreviousGray);

    if( points.get(0).total() > 0 )   // EMG - 09/22/11 - fix optical flow crashing bug 
    {       
        // 2. track features
        Video.calcOpticalFlowPyrLK(mPreviousGray, m, // 2 consecutive images
                points.get(0), // input point position in first image
                points.get(1), // output point postion in the second image
                status,    // tracking success
                error);      // tracking error
    }

    ...

    m.copyTo(mPreviousGray);

    ...
}

以前,变量points的类型为List<List<Point>>,我会通过使用fromList实例化MatOfPoint2f并将其传递给calcOpticalFlowPyrLK来在类型之间进行转换。

但是,我想不再那样做,因为从列表到列表的转换会丢失initialpoints中点之间的对应关系。我想保留这种对应关系,所以我可以通过在两个矩阵中同时迭代来绘制光流线。

不幸的是,现在我有以下断言失败:

09-24 10:04:30.400: E/cv::error()(8216): OpenCV Error: Assertion failed ((npoints = prevPtsMat.checkVector(2, CV_32F, true)) >= 0) in void cv::calcOpticalFlowPyrLK(const cv::_InputArray&, const cv::_InputArray&, const cv::_InputArray&, const cv::_OutputArray&, const cv::_OutputArray&, const cv::_OutputArray&, cv::Size, int, cv::TermCriteria, int, double), file X:\Dev\git\opencv-2.4\modules\video\src\lkpyramid.cpp, line 593
09-24 10:04:30.400: E/AndroidRuntime(8216): FATAL EXCEPTION: Thread-321
09-24 10:04:30.400: E/AndroidRuntime(8216): CvException [org.opencv.core.CvException: X:\Dev\git\opencv-2.4\modules\video\src\lkpyramid.cpp:593: error: (-215) (npoints = prevPtsMat.checkVector(2, CV_32F, true)) >= 0 in function void cv::calcOpticalFlowPyrLK(const cv::_InputArray&, const cv::_InputArray&, const cv::_InputArray&, const cv::_OutputArray&, const cv::_OutputArray&, const cv::_OutputArray&, cv::Size, int, cv::TermCriteria, int, double)
09-24 10:04:30.400: E/AndroidRuntime(8216): ]
09-24 10:04:30.400: E/AndroidRuntime(8216):     at org.opencv.video.Video.calcOpticalFlowPyrLK_2(Native Method)
09-24 10:04:30.400: E/AndroidRuntime(8216):     at org.opencv.video.Video.calcOpticalFlowPyrLK(Video.java:445)

奇怪的是,如果我自己添加这个断言,在调用calcOpticalFlowPyrLK之前,它不会失败。

我希望有人可以帮我弄清楚真正的问题在哪里,以及如何保持帧之间跟踪点之间的这种关系。

编辑:我发现需要做些什么来避免这个断言错误,然后应用程序行为正常,但是:

  • 我不知道为什么
  • 我现在对Calib3d.solvePnP有类似的问题,但将convertTo应用于imagePoints和objectPoints并不能解决问题,CvType.CV_32FC2CvType.CV_32FCvType.CV_64F < / LI>

要在calcOpticalFlowPyrLK的情况下更正断言失败,我已将points.get(0).push_back(initial);更改为以下内容:

Imgproc.goodFeaturesToTrack(m, initial, maxDetectionCount, qualityLevel, minDistance);

MatOfPoint2f initial2f = new MatOfPoint2f();
initial.convertTo(initial2f, CvType.CV_32FC2);
// add the detected features to the currently tracked features
trackedpoints.get(0).push_back(initial2f);

所以我的问题已经改为:有人可以为我解释一般情况,以便我知道如何用Calib3d.solvePnP解决我的问题吗?

2 个答案:

答案 0 :(得分:1)

calcOpticalFlowPyrLK点参数的类型为MatOfPoint2f,内部为CV_32FC2。

solvePnP第一个参数是 MatOfPoint3f ,其内部是 CV_32FC3 。尝试转换为它以查看它是否已修复。

有些opencv函数需要特定的Mat类型,我想出于效率原因你必须手动选择正确的类型,而不是自动进行opencv猜测/转换。

答案 1 :(得分:0)

{p {3}}中有人之前遇到过这个问题。我最近在OpenCV4Android的光流功能中遇到了这个问题(Assertion)。此解决方案仅在您无法处理以前的点矩阵时才有效:

而不是使用convertTo()方法,你应该将你从matOfKeyPoints.ToArray()获得的Keypoint []数组的每个元素放入matOfPoints2f数组。

原因在other thread中解释:

    KeyPoint[] arrayOfkp = keypoints.toArray();
    org.opencv.core.Point[] arrayOfp = new org.opencv.core.Point[arrayOfkp.length];
    for(int j =0;j<arrayOfkp.length;j++)
    {
        arrayOfp[j] = new org.opencv.core.Point(0, 0);
        arrayOfp[j].x = (int) arrayOfkp[j].pt.x;
        arrayOfp[j].y = (int) arrayOfkp[j].pt.y;
    }
    prevPts.fromArray(arrayOfp);