As I've mentioned previously, this type of mocap system requires multiple cameras. You need at least 2 cameras to see a marker for 3D triangulation to be possible. When capturing a human there is a high chance markers will be obscured, requiring at least 6 cameras to maintain visibility. You could get away with fewer cameras if trying to capture something simpler, like a quad copter or other robotic vehicle. With that said, I have 4 cameras almost complete and I plan to do some testing before committing to another 6 (My ideal setup has 10 cameras).