RLOF OptFlow Bug Fix

[matijazigic]

Pull Request Readiness Checklist

See details at https://github.com/opencv/opencv/wiki/How_to_contribute#making-a-good-pull-request

• I agree to contribute to the project under Apache 2 License.
• To the best of my knowledge, the proposed patch is not based on a code under GPL or another license that is incompatible with OpenCV
• The PR is proposed to the proper branch
• There is a reference to the original bug report and related work
• There is accuracy test, performance test and test data in opencv_extra repository, if applicable
  Patch to opencv_extra has the same branch name.
• The feature is well documented and sample code can be built with the project CMake

The bug has already been reported and explained on the OpenCV forum:

• optflow-calcopticalflowsparserlof-giving-assertion-error
• calcopticalflowsparserlof-assertion-error-in-initialflow

The bug is manifested only if 'UseInitialFlow' is set to true and 'ForwardBackwardThreshold' > 0 (enabled).

[alalek]

LGTM 👍

[rangingwaves]

cv::Mat img1 = cv::imread("./image/1.png");
cv::Mat img2 = cv::imread("./image/2.png");
if (img1.empty() || img2.empty()) {
std::cerr << "Error: Could not open images." << std::endl;
return -1;
}

std::vector<cv::Point2f> points1, points2;
cv::Mat img1_gray;
cv::cvtColor(img1, img1_gray, cv::COLOR_BGR2GRAY);
cv::goodFeaturesToTrack(img1_gray, points1, 150, 0.01, 10);

cv::Ptr<cv::optflow::RLOFOpticalFlowParameter> rlof_param = cv::optflow::RLOFOpticalFlowParameter::create();
rlof_param->useInitialFlow= true;

std::vector<uchar> status;
std::vector<float> err;
points2 = points1; 
std::cout<<"point1 size"<<points1.size()<<"   "<<"point2 size"<<points2.size()<<std::endl;
cv::optflow::calcOpticalFlowSparseRLOF(img1, img2, points1, points2, status, err, rlof_param, 0);

// cv::calcOpticalFlowPyrLK(img1, img2, points1, points2, status, err, cv::Size(21, 21), 1,cv::TermCriteria(cv::TermCriteria::COUNT+cv::TermCriteria::EPS, 30, 0.01), cv::OPTFLOW_USE_INITIAL_FLOW);

Why am I still encountering this error：
the Print result is point1 size150 point2 size150，
terminate called after throwing an instance of 'cv::Exception'
what(): OpenCV(4.10.0) /home/hfm/slam_lib/opencv-4.10.0/opencv_contrib-4.10.0/modules/optflow/src/rlof/rlof_localflow.cpp:402: error: (-215:Assertion failed) nextPtsMat.checkVector(2, CV_32F, true) == npoints in function 'calcLocalOpticalFlowCore'。I used // cv::calcOpticalFlowPyrLK(img1, img2, points1, points2, status, err, cv::Size(21, 21), 1,cv::TermCriteria(cv::TermCriteria::COUNT+cv::TermCriteria::EPS, 30, 0.01), cv::OPTFLOW_USE_INITIAL_FLOW);and there was no such error. Did I make a mistake?