After reading this paper, as well as many answers.opencv questions, I was wondering if there was any code examples out there of an ORB Bag Of Words? I could only find SURF or SIFT examples.
Unfortunately there is no example of using Bag-Of-Words with binary descriptors (BRIEF, ORB, BRISK, FREAK). Either way the paper you showed explains how you can do it. For traditional descriptors (SIFT, SURF) the k-means clustering technique is used because the vocabulary is generated from a set of real valued descriptors. However to obtain a binary vocabulary, k-means method is not ideal because mean is not defined in binary space, then you can use the k-majority method.