Figure 1 shows playing scene with this system.
Co-located three players surround physical game field and shoot invaders from virtual space at a border between real space and virtual space,
that is mixed reality space. The players are visually armed with helmets and guns in the mixed reality space.
(a) Real space (b) Mixed reality space
Figure 1. Playing scene
Figure 2 shows a player's view.
An enemy is rushing toward the player. Players see stereoscopic video see-through images with their HMDs.
RV-BG takes the advantage of video see-through approach for the flexibility in merging virtual and real scenes.
Virtual invaders cast shadows on physical objects, such as the tables, blocks and the floor.
They also dip in the physical objects and hide behind them.
These visual effects are easily achieved using pre-calibrated geometry of the physical world.
Figure 2. Player's view Figure 3. Gesture commands (a) Load (b) Fire (c) Guard
Players can interact with the system intuitively
using easy gestures as shown in Figure 3.
A position tracker attached to a palm measures position and attitude of the hand.
Movement of a hand relative to a head position identifies gestures, which distinguish commands.
Corresponding visual effect is fed back for each command.
Three gesture commands are below:
(1) Load: Drawing hand back loads a bullet, and emits virtual pointing lasers, which shows a line-of-fire.
Players can aim their gun pointing with them.
(2) Fire: Thrusting hand forward along the lasers launches a bullet.
The line-of-fire is decided by combination of orientation of the hand and direction of movement.
(3) Guard: Covering body with forearm prevents damage from attack by enemies or stray bullets shot by other players.
A player in guarding state is surrounded by glass-like virtual shell.
The HMD is equipped with two CCD cameras for stereoscopic
In addition, an electro-magnetic 6DOF position sensor is attached to the HMD for head-tracking.
In order to compensate the error of the magnetic sensor, registration algorithm that uses vision is implemented .
Landmarks to be tracked are arranged in the game field.
 K. Satoh, T. Ohshima, H. Yamamoto, and H. Tamura, "Case studies of see-through augmentation in mixed reality project,"
Proceedings of IWAR '98 (1998).