47 © 2015 Open Geospatial Consortium
devices computing the sin of an angle, one with a series of 10 terms, and another with an interpolation of a look-up table with 100 entries, or one device
using 32-bit signed integers for its internal computations and the other using single-precision floats. The CDB Specification reduces numerical accuracy
correlation errors because a single representation is used for each dataset. Note however that numerical correlation may deteriorate due to the variances
in numerical precision inherent to each client-device.
5. Algorithmic correlation: Is the degree of informational consistency between
the outputs of two or more devices, with each device performing its internal computations to the same numerical accuracy, but using different algorithms
with possibly different control parameters. Consider for example, two devices meshing terrain from a regular grid of elevation points, one using a regular
mesh of right-handed triangles using the elevation points as vertices, and the other with a DeLauney triangulated mesh derived from the grid of elevation
points. Algorithmic correlation errors can be introduced anywhere in the dataset processing chain, ranging from the raw source level right through to
the internals of the simulator client-devices. While it is not possible to mandate complete algorithmic uniformity throughout this elaborate chain, the
CDB Specification offers solutions to this issue
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. Firstly, only one database is produced, so all DB authoring tool algorithmic correlation issues are
eliminated. Note that the implementation of runtime publishers on a simulator can play a role in improving overall algorithmic correlation
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.
6. Parametric correlation: Is the degree of informational consistency between
the outputs of two or more devices, with each device performing the same algorithms with identical numerical precision with different control
parameters e.g., consider two devices generating regular meshes of right- handed triangles based on a regular grid of elevation points organized by
LOD, one using an LOD meshing tolerance parameter of 1m and the other one using 2m. Note that it is clearly possible to create a synthetic environment
database whose content is at a level of resolution, fidelity and accuracy that can overwhelm any client-device; however, the amount and type of data that
is rejected by each type of client-device can vary considerably. For example, a NAVAIDs data server client-device need only be concerned with Digital
Aeronautical Flight Information File DAFIF™, and as a result is virtually unaffected by changes in the resolution of the terrain elevation data which
could easily increase terrain SE content by 100-fold. The implementation of the CDB Specification on a simulator can reduce andor eliminate parametric
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For instance, the CDB does not impose the terrain skinning and meshing conventions that each of the runtime publisher generates for its attached client-device. However, it is understood that if all client-devices would use the
CDB meshing conventions natively, correlation issues between clients would be significantly reduced.
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Since each dataset is uniquely represented, it is possible to share a greater number of algorithms between CDB runtime publishers. This ensures that datasets are processed in an identical fashion whenever two or more
publishers share the same algorithm.