This paper describes the requirements, data structures, and algorithms utilized in the run time Player Unit of the OneTESS program. OneTESS is a combined instrumentation suit designed to satisfy the requirements for both training and operational testing being developed by a team lead by AT&T. Specifically we will describe the terrain services and Player Unit services required for geometric pairing and engagement processing along with the accurate database design and procurement strategy required to build it. The paper will also describe a voxel based visualization engine adapted to perform dynamic terrain updates and high accurate test site preparation. We will also describe the process for procuring and testing the fidelity of the terrain environment and describe the analysis to answer the "what is good enough" question within the context of instrumentation accuracies and development strategies.Lastly we will discuss the implications and opportunities afforded by onboard environment models both for future test and training applications as well as in future deployable units.