Upper body tracking using the Polhemus Fastrak

1. Introduction This technical report presents the design and implementation of the sensor system used to track the arms and ri BLOCKINe motions with respect to the upper body. This was performed as part of the AUSA`95 dismounted infantry work { an eort to insert humans into NPSNet's distributed virtual environment. The sensor work can be divided into three areas: (1) the Fastrak setup including sensor positions and interface to the computer as well as the device driver software, (2) the software interface to the Jack model and the inverse kinematics algorithm needed to achieve \reasonable" arm tracking, and (3) the implementation of the ri BLOCKINe tracking and the initial attempts at targeting. In the next section, a description of the hardware is presented. This includes the serial cable for the Fastrak unit to the computer, transmitter and receiver (sensor) ports, and DIP switch settings. It also illustrates the coordinate systems associated with each of these hardware components. Section 3 presents the corresponding device driver that was developed. In Section 4, the placement of the sensors on the person to be tracked is illustrated and the organization of the upper body tracking software is introduced. In particular, the top-level interface functions between the NPSNet application and the algorithms developed in this work are described. This section is followed by the inverse kinematics routines for arm tracking (Section 5), and the algorithms for ri BLOCKINe tracking and targeting (Section 6). Following AUSA`95, development of the head-mounted display (HMD) interface to use the new Fastrak device driver was performed. Section 7 describes this work. The report concludes with a summary and discussion of the work that needs to be performed to make this a better system.