1 A multi-player arcade video game platform with a wireless tangible user interface Doo-Seop Eom, Taeyoung Kim, Hyunho Jee, Hyoil Lee, and Junghyun Han IEEE Transaction on Consumer Electronics, Vol. 54, No. 4 November, 2008 Presented by: Chin-Yu, Ou

2 Outline Introduction Arcade Video Game Platform Hardware configuration Computation of distances and acceleration Pose computation Performance analysis in position sensing Implementation and prototype game Conclusion

3 Introduction A recent game development trend is a natural user interface which seamlessly integrates physical space and virtual space. Recognition of a game player’s gesture often replaces traditional pointing devices such a a mouse. Tracking a player’s motion, and representing it in virtual environments.

4 Introduction (cont.) Authors designed and developed a motion tracking system using various off-the-shelf wireless sensor nodes, and built a prototype of an arcade video game. The motion tracking system comprised acceleration sensors and ultrasonic signals. The angular velocities of the devices were computed, to create special effects in the game.

5 Hardware configuration Sink node Beacon Game stick

6 Hardware configuration (cont.) The sink node synchronizes and coordinates the beacons and game sticks, an then collects the distance/acceleration data of the game sticks. The game sticks send ultrasonic signals to the beacons, for measuring the distances between them.

7 Computation of distances and acceleration The sink node broadcasts RF signals to all game sticks. Each game stick responds to the broadcast with an RF message, which contains its ID. The sink node identifies every active game stick. The ID of Beacons are known to the sink node in advance. When a beacon receives an ultrasonic signal, it uses the standard time-of-arrival technique to estimate the distance of the game stick.

8 Computation of distances and acceleration (cont.)

9 Immediately after sending the packet of the last game stick to the PC, the sink node synchronizes the beacons and game sticks, and then performs another iteration to render the next scene. Packet of each game stick

10 Pose computation For computing the position of a game stick, the well- known trilateration method is used.

11 Pose computation (cont.)

12 Pose computation (cont.) The system of equations is solved using Newton- Raphson method. 參閱 運用初始值來求算方程式的近似解，再由近似解代入求 算更精確的解，依此類推。 The initial position (x, y, z) of the game stick is set to the center of the game space.

13 Performance analysis in position sensing For the purpose of performance analysis, a game stick was fixed at a particular position, and the distance from a beacon was measured 1,500 times. The distance between the game stick and the beacon is 100cm. 25ºC

14 Performance analysis in position sensing (cont.) The speed of sound varies with the atmospheric conditions, and the most important factor is the temperature. The speed of sound usually increases with increasing temperature (m/s) represents the speed at 0ºC and t is the temperature.

15 Performance analysis in position sensing (cont.) t = 25ºC. The room temp. is 20ºC

16 Performance analysis in position sensing (cont.) t = 25ºC. The room temp. is 30ºC

17 Implementation and prototype game The beacons are located at the four corners of the screen, and this is a two-player game. The ID and pose of each game stick are sampled at 25Hz(motion data of two game sticks are sampled at 50Hz).

18 Implementation and prototype game (cont.) For approximating the angular velocities, which are used for creating special effects in the game.

19 Conclusion The paper presented an arcade video game platform that can detect the motions of multiple game players. The implementation results proved that various off-the- shelf wireless sensor nodes can be used for VR games that require the tracking of the motions of users or physical objects.