46 © 2015 Open Geospatial Consortium
1. Raw source correlation: Is the degree of informational consistency between
two or more sets of raw data
18
i.e., inputs to a modeling station representing aspects of the same environment for instance, the correlation errors arising
from Digital Terrain Elevation Data DTED elevation data that does not perfectly match to satellite raster imagery due to oblique view distortions
induced by the satellite. Correlation errors are intrinsic to the process of gathering data because since there is no means to gather all of the required
data from a single device, at a single instant in time. Instead, datasets e.g., elevation, raster imagery, geometry are each gathered from various devices of
various types with distinct precision, formats, capabilities, fidelity at different times. This in turn leads to a broad range of correlation errors
typically resolved by the modeler during the final assembly of the synthetic environment from its sources.
2. Source database self-correlation: Is the degree of informational consistency
between the internal datasets of a source database produced by a DB generation toolset. To a large extent, the effort expended at DB generation
time consists in eliminating or at least reducing correlation errors arising from miss-correlated raw source data.
3. Runtime database correlation: Is the degree of informational consistency
between two or more runtime client-specific databases representing the same synthetic environment
19
. The likelihood of achieving correlated runtime client-device databases is particularly low when different authoring tools and
possibly different source data are used to assemble each of the compiled runtime databases. In recent years, some authoring tools have been improved
to automatically produce a set of client-device database from one common repository internal to the tools. Nonetheless, it is still current practice within
the simulation community to independently deploy the simulator client-device databases; as a result, correlation errors may occur especially if the master
database repository is constantly evolving. The CDB Specification eliminates database correlation errors since only one database is used to represent the
same synthetic environment. The CDB is a single database that can be accessed simultaneously by all simulator client-devices at runtime. By
definition, it addresses all runtime database-level correlation errors.
4. Numerical accuracy correlation: Is the degree of informational consistency
between the outputs of two or more devices, with each device performing the same algorithms, using the same control parameters but performing internal
computations to a different numerical accuracy. Consider for example two
18
In this context, raw source denotes any input to the modeling workstation that is used to assemble the synthetic environment; consequently, the data may have undergone some level of post-processing such as image color-
balancing, image ortho-rectification, etc. or may be in a specialized source interchange format such as SIF, SEDRIS, etc..
19
A runtime client-specific database is a device-loadable database format that can be processed by a target device.