public class DescriptorManager {

	private static ORBDetector _detector;
	public static ORBDetector Detector
            => _detector ?? (_detector = new ORBDetector(numberOfFeatures: 700, scaleFactor: 1.2F, nLevels: 10, edgeThreshold: 0));

	public static Mat ExtractDescriptor(Mat mat) {
		var descriptors = new Mat();
		var keyPoints = new VectorOfKeyPoint();
		Detector.DetectAndCompute(mat, null, keyPoints, descriptors,false);
		descriptors.ConvertTo(descriptors, DepthType.Cv8U);
		return descriptors;
	}

	public static Mat ConcatDescriptors(IEnumerable<Mat> descriptors) {
            var mat = descriptors.FirstOrDefault();
            if (mat == null) return null;
            descriptors = descriptors.Skip(1);
            foreach(var descriptor in descriptors) {
		var next = new Mat();
                CvInvoke.VConcat(mat, descriptor, next);
                next.ConvertTo(mat, DepthType.Cv8U);
            }
            mat.ConvertTo(mat, DepthType.Cv8U);
            return mat;
        }
}