A virtual global positioning system for distributed interactive simulation environments

A major shortfall in the fidelity of current military distributed virtual environments (DVEs) is the lack of virtual Global Positioning System (GPS) timing and position signals for entities within the environment. The DVE's usefulness is reduced because positional errors and positional accuracy that would be available in the real world are not present in the DVE. This, in turn, affects the validity of the results of training, analysis, and evaluations involving systems that rely on GPS. The magnitude of the affect depends on the degree that the systems involved in the DVE rely on GPS in the real world. The project reported in this paper addresses this deficit in current military DVEs. The capability we developed to provide a virtual GPS-based navigation capability within a DVE is based upon three components. These components are a complete virtual GPS satellite constellation, a means for broadcasting GPS signals using the Distributed Interactive Simulation (DIS) simulation protocols, and a software system, the Virtual GPS Receiver (VGPSR), to calculate simulation entity position using the virtual GFS time and position signals. The virtual GPS satellites are propagated in their orbits using the Solar System Modeler (SM). The SIM also performs the simulated GPS signal broadcast by transmitting a DIS protocol data unit (PDU) with the data that would appear within a real world GPS satellite broadcast. The VGPSR is a plug-in module available for simulation applications that require virtual GPS navigation. To demonstrate the capability of this system, we used the VGPSR in conjunction with the Virtual Cockpit to simulate virtual weapons deployment. We present the design of the VGPSR and the design of the modules added to the SM for GPS broadcast. We describe the calculations the system performs to calculate position in the virtual environment and we will describe the accuracy and performance the system achieves when calculating virtual environment position using our. system. We conclude with suggestions for further research in this area.