Mazan: Flash of the Blade
Mazan: Flash of the Blade, was an early commercial electromagnetic tracker based arcade game, released by Japanese firm Namco in 2002.
Gameplay was simple, you stood in front of the machine, grasped a roam-rubber 'sword' in both hands, probably holding it by the solid plastic base, and swung at on-screen enemies. The virtual blade matched your movements precisely.
This system is probably immediately familiar to anyone who has used a Wii. Very different technology, but same interaction paradigm.
Rlectromagnetic trackers are sensitive to electrically or magnetically conductive objects. That was the keystone of the system: inside the handle were two magnets, one at either end of the hilt, and a spring between them. The spring being there to keep the two magnets apart at all times, no matter how the handle was twisted, or deformed. They served as positional markers for the top and bottom of the handle, in real-time.
Tracking the magnets were four trackers, spaced regularly apart inside a plastic loop that extended up from both sides of the console and looped above the player. A mat was also provided, with a line along the sides and back, painted the same colour as the loop. Between them, they denoted the 'game space'. The trackers could not reliably track position without all four engaged, so that was why the sword could not go out to either side. The line behind was just there to ensure good reception, as electromagnetic signals attenuate with distance.
A big problem is that if there is metal near the electromagnetic tracker's transmitter or receiver, the transmitter signals are distorted and the resulting position/orientation measurements contain errors. Thus, anyone with a large amount of steel in them, or around them, had trouble playing the game. This was also why the arcade machine required significant floor space - to keep other machines away from it, and create a buffer zone.
The trackers monitored the sword hilt via linear interpolation; two tracked its horizontal position, two tracked its vertical position. This was necessary art the time, due to the limited processing power available.
The game itself did not need any real input - it was essentially a rail shooter that followed a pre-determined path at a pre-determined speed, with the user trying to use the sword to hit enemies, and to deflect oncoming blows. As a result, sword position was crucial, and all of the trackers functioned together to track position in the z-axis, such that sword strokes could have depth, albeit at a lower resolution than the other axis.
There were specicic moves for special attacks and defences, or you could just flail about like a mad-person; either approach worked. The unit itself was rediculously expensive compared to other arcade units at the time, and whilst some US machines were sold, in the main it was restricted to Japan.
The reason for this cost, was the sheer computing power required to rtrack properly wioth available hardware. Namco actually produced their own custom GPU cards as the power to run the unit, each one was capable of 1.4 gigaflops, and up to 16 could bee inserted into the unit, where they would automatically function as a multi-core system. With three gigabytes of EPROM on each card, they could be assigned dedicated tasks - such as monitoring the trackers in real-time.