In Distributed Interactive Simulation (DIS), each participating node is responsible for maintaining its own model of the synthetic environment. Problems may arise if significant inconsistencies are allowed to exist between these separate world views, resulting in unrealistic simulation results or negative training, and a corresponding degradation of interoperability in a DIS simulation exercise. In the DIS community, this is known as the simulator terrain database (TDB) correlation problem. This is part of the larger synthetic environment correlation problem in DIS, which includes atmosphere, ocean, space, and a wide variety of dynamic effects, behaviors and models. In this article, we investigate the terrain database correlation problem and the resultant effects on interoperability in DIS systems. The fundamental elements of terrain databases designed for real-time distributed simulation are introduced. A generic data pipeline for terrain database generation systems is developed for the purpose of illustrating causes of the correlation problem and issues of terrain database fidelity. Implications of the problem are discussed, and testing methodologies are recommended for its mitigation. Several statistical methods have been developed to analyze consistency between various elements of the synthetic environment across DIS platforms. Correlation metrics have been formulated for terrain elevations and features. Comparisons and consistency of final rendered images have been addressed. Finally, a suite of software tools that has been developed for interoperability investigations and visual comparison of terrain databases is presented.

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