Global Coordinate System in the Improved Computer Generated Forces Terrain Database

摘要

The Improved Computer Generated Forces Terrain Database (ICTDB) project, being developed jointly by TASC and SAIC, is one of four projects in the DARPA/TEC Advanced Distributed Simulation Synthetic Environments program. The goal of this project is to design and develop the next generation terrain database representation for Computer Generated Forces (CGF) systems. One of the major technology developments undertaken by the ICTDB team is the design and implementation of a Global Coordinate System (GCS) for CGF systems. GCS starts with a tiling of the Earth's surface into cells compatible with the GEOREF tiling. Within each cell, a local Cartesian frame of reference is defined whose axes furnish a secant plane to the Earth's surface and a normal vector at the center of the cell. This amounts to an offset and a rotation of the DIS GCC coordinate system. The benefits of moving to GCS include: elimination of projection anomalies, naturality to the application developer, fast conversion to and from GCC and true global scaleability. At the same time, the compactness of the data representation is maintained. A more complete description of the design of GCS is contained in a paper by Evans and Stanzione presented to the 13th DIS Workshop.In the current paper, the details of the ModSAF implementation of GCS are elaborated. To date, the implementation of GCS exists in ModSAF, as additions to the CTDB representation, together with several new libraries to support the tiling scheme and coordinate translations. This GCS framework has infact been integrated into ModSAF 2.1, together with changes to the Persistent Object Protocol which support the extra coordinate used by GCS, the cell ID. We then discuss in detail some issues of scaleability which argue for the use of the Global Coordinate System. Our analysis shows that for the upcoming STOW ACTD, use of GCS seems a strong requirement. Finally, we outline future work needed to make the implementation of GCS complete. This includes changes to the database production process needed to fully support GCS. Currently multi-celled GCS databases have been produced from the Area 2 dataset for demonstration purposes.