Dead Reckoning in Geodetic Coordinates for Improved LVC Interoperability

摘要

Geodetic Coordinates are the familiar Latitude-Longitude-Altitude coordinates used by almost all simulations for specifying world location. The familiar Yaw-Pitch-Roll angles are also nearly universal for describing entity orientation. However, Live, Virtual, Constructive (LVC) interoperability going back to the 1995 Distributed Interactive Simulation (DIS) standard uses Geocentric Cartesian Coordinates for both location and orientation, requiring coordinate conversion to and from the internal Geodetic Coordinates. The Geocentric Cartesian Coordinate system was originally chosen for DIS because it is rectilinear. It is easier to perform dead reckoning and associated math in X-Y-Z rectilinear coordinates than in Latitude-Longitude polar coordinates. The ongoing development of the new DIS Version 8 standard is considering the use of Geodetic Coordinates instead of Geocentric. This would eliminate the coordinate conversion to and from Geocentric coordinates for the sake of dead reckoning. Many entities are static and require no dead reckoning at all. Dynamic terrain and cultural features are increasingly modeled as simulation entities, meaning many more static entities will be generated as fidelity requirements increase in the future. For moving entities, it is possible to perform dead reckoning in Geodetic Coordinates. It requires some approximation but the error is insignificant. No matter how accurate the algorithm, dead reckoning itself is at best an estimate of the future behavior of an entity, so a slight decrease in accuracy has no effect. The use of the body-axis dead reckoning algorithm is further explored. This has been defined in the DIS standards since 1995 but has seen little use and is generally not well understood. However, it has been found to give a significantly better result for predicting the path of turning vehicles. This algorithm has been adapted to Geodetic Coordinates and tested. This paper describes algorithms for performing dead reckoning in Geodetic Coordinates. The difference in accuracy between the Geodetic and the traditional Geocentric dead reckoning is analyzed and compared. The body-axis dead reckoning algorithm has been found to give the same superior results in Geodetic Coordinates as it does in Geocentric. It is the basis of the Geodetic dead reckoning that is being proposed for DIS Version 8. Simplification of dead reckoning algorithms is also being proposed. This is related but independent of the decision to use GDC coordinates. The first phase of research toward a single dead reckoning algorithm for moving entities is described.