If they blanket an area with cameras, as China does, they can use multiple vantage points to get more accurate measurements and, when a positive ID is made, the

If they blanket an area with cameras, as China does, they can use multiple vantage points to get more accurate measurements and, when a positive ID is made, they can persistently track that person crossing from one field of view to another. I think the main advantage of gait analysis (or limb proportion measurement) is that it will encourage a more efficient, decentralized computation that first distills the observed data into a fingerprint that can be more easily transmitted over a wire to a massive database for matching, rather than the alternatives of either replicating that database or transmitting raw, high-bandwidth data. Besides limb measurements, they could also use last known location, residence, and vehicle ownership information to increase the certainty of loose matches.