I have designed the system for visual tracking using a single camera back in 2009. That system has become industry standard. Now days it is a standard practice to use video camera for tracking performer on the stage.
Now, in 2019, new system is designed, world first multicamera tracking system. System has two major advantages. It uses real world coordinates, so that Geo Location using video cameras is enabled for surveillance and geo tagging (no sensors on humans) applications. Second advantage is unlimited field of view. Imagine stage tracking application where you have 4 cameras to use as a standard feature.
Multi Camera systems are patent pending systems.