It's hard to draw a line between broad object categories (e.g. "bike","wine bottle") and more specific object classes (e.g. "hartley & zisserman book cover"). This method seems to be targeting the former, while vocab tree methods like Nister et al. seem to be targeting the latter. Do you think this method would scale to a large set of more specific object classes like book or cd covers, or is it more tuned to borad object categories?