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According to cv::MultiTracker Class Reference http://docs.opencv.org/3.1.0/d8/d77/c...

bool update (const Mat &image)

returns just a single boolean, so how to tell which of the objects being tracked returned the false?

Thanks for any help.

NOVICE question: http://docs.opencv.org/3.0-beta/modul... states that AKAZE descriptors can only be used with KAZE or AKAZE keypoints. Try to avoid using extract and detect instead of operator() due to performance reasons.

so I tried to use KAZE detector with AKAZE descriptor extractor:

Ptr<Feature2D> detector = cv::KAZE::create();
Ptr<DescriptorExtractor> extractor = cv::AKAZE::create();

...
vector<KeyPoint> keypoint;
Mat features;
detector->detect(img, keypoint);
extractor->compute(img, keypoint, features);  //<- error at this line

generate the following error:

OpenCV Error: Assertion failed (0 <= kpts[i].class_id && kpts[i].class_id < static_cast<int>(evolution_.size())) 
in cv::AKAZEFeatures::Compute_Descriptors, file ..\..\..\src\opencv\modules\features2d\src\kaze\AKAZEFeatures.cpp, line 712

However, when both detector and extractor are the same, there is no problem. Any help is appreciated, thanks. JC