Portable Virtual Reality
The PPT-H optical position tracking used in the HIVE includes 12 wall mounted digital cameras and a desktop computer which communicates with each of the cameras via Ethernet cables. The PPT-H camera system cannot be easily moved and requires extensive setup. The purchase price is on the order of $100,000. Thus, the optical tracking system represents the primary limitation of the HIVE relative to both cost and portability.
A portable position tracking system for immersive virtual environment applications must perform two functions:
- Provide a locomotion interface which allows users to change their position in the virtual world.
- Provide the absolute position estimates of each user for use in collision avoidance, to keep users contained in the tracking area, and to support techniques such as redirected walking.
Locomotion interface tracking requires smooth high frequency updates so that movement through the virtual world will appear to be natural and be similar to what the user normally experiences while navigating in daily life. Since immersive VE users have no reference to their physical surroundings, there is no need for absolute accuracy in the locomotion interface. Instead, there is only a requirement for short-term precision and responsiveness
On the other hand, the avoidance of tracking area boundaries, obstacles, and possibly other users requires absolute positional accuracy. Proper functioning of RDW algorithms requires accurate information regarding where the user is physically located within the tracking area, which direction they are moving, how fast they are moving, and where the limits of the physical space lie. Relative to locomotion interface requirements, there is no need for high frequency updates. In outdoor applications, this type of data has been provided by WAAS enabled GPS. For indoor locations, SLAM is an attractive alternative.
Self-contained Position Tracking of Human Movement Using Small Inertial/Magnetic Sensor Modules
Numerous applications require a self-contained personal navigation system that works in indoor and outdoor environments, does not require any infrastructure support, and is not susceptible to noise and interference. Posture tracking with an array of inertial/magnetic sensors attached to individual human limb segments has been successfully demonstrated. The "sourceless" nature of this technique makes possible full body posture tracking in an area of unlimited size with no supporting infrastructure. Such sensor modules contain three orthogonally mounted angular rate sensors, three orthogonal linear accelerometers and three orthogonal magnetometers. This project involves a method for using accelerometer data combined with orientation estimates from the same modules to calculate position during walking and running. The periodic nature of these motions includes short periods of zero foot velocity when the foot is in contact with the ground. This pattern allows for precise drift error correction. Relative position is calculated through double integration of drift corrected accelerometer data. Preliminary experimental results for various types of motion including walking, side stepping, and running have demonstrated the accuracy of distance and position estimates using this method.
