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could be handled by a new SE simulation that dynamically calculates soil moisture content as a function of localized rain precipitation and soil typescomposition. A second simulation would
then derive the resulting soil physics and determine vehicle wheel slippage across the varying terrain conditions.
The modificationnotification approach is well-suited for a broad gamut of SE simulations; however, some simulations are very data intensive and would require excessive broadcasting
bandwidths to other federates. In such cases, these dynamic simulations would have to be replicated in the other client-devices of the federation. Good examples of this are visual system
special effects e.g., rotor downwash effect, missile plumes, muzzle flashes, cast landing lights; typically such simulations are proprietary and intrinsic to the client-devices. Other examples of
this include the varying effects of weather
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local winds, temperature, humidity, particulates, etc. and oceans currents, temperature, etc..
1.4 Key Features and Characteristics of the CDB Specification
The following paragraphs provide an overview of key features and characteristics of the CDB Specification.
1.4.1 Synthetic environment Database for Simulation Applications
The CDB Specification is a simulator-level synthetic environment database Specification for use in real-time. The Specification is open, platform-independent and client-device independent.
The Specification defines all aspects of data representation and organization, and storage structure necessary to support full-mission real-time simulation. The CDB Specification
synthetic environment databases contain datasets that represent the features of a synthetic environment for the purposes of simulation applications. The CDB provides a time-invariant
synthetic environment representation of the earth, composed as terrain, naturalman-made features and moving models for use by SE authoring tools and simulators.
1.4.2 Logical Addressability
The CDB Specification provides for near-infinite addressability. The amount of information associated with a CDB is limited only by available disk storage. The CDB Specification allows
for a nearly infinite number of identifiers within a single CDB. Addressability is not expected to be a limiting factor even if we assume a yearly doubling of storage capacity.
1.4.3 High Spatial Resolution and Scalability
The CDB Specification provides for near-infinite resolution due its organization of data in LODs. The CDB Specification grid-organized data e.g., elevation, ground raster imagery,
ground properties is structured into an LOD hierarchy consisting of up to 34 LODs. Grid- organized data can be represented to a resolution of 13 microns.
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Time-varying weather simulation effects could be simulated by a “weather server” simulation subsystem which in turn can rely on the terrain elevation and terrain material datasets to perform its simulation of weather in
real-time.
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The CDB Specification also provides for near-infinite cultural content. The CDB Specification for vector data 3D point, lineal and areal features is also structured into a LOD hierarchy
consisting of up to 34 LODs. At the finest possible LOD, a CDB can contain in excess of 100 million cultural features per square meter.
The CDB Specification permits each geographic area to be modeled at a distinct LOD in accordance to the availability of source data. Since this capability is provided at a tile-level, it is
storage-efficient.
1.4.4 Earth Geodetic Spatial Representation Model
Geo-referenced data constitute a major aspect of the CDB Specification synthetic environment data. It uses a geographic coordinate representation WGS-84 latlong, elevation for the earth’s
terrain surfaces and ocean floor. Furthermore, natural and man-made objects are positioned and oriented using geodetic coordinates. The CDB Specification provides geodetic coverage for the
entire earth.
1.4.5 TileLayerLevel-of-Detail Structure
The CDB Specification offers a structure that is well suited for the efficient access of its contents. To this end, it relies on three important means to organize the synthetic environment
data:
Tiles Layers
Level-of-Detail LOD
1.4.5.1 Tiles
The CDB Specification relies on a top-level tile structure designed to organize the data for efficient access in real-time. The tile structure provides an effective means for simulator client-
devices to access the datasets of a geographical area at a selected LOD. Since the spatial dimension of tiles varies inversely with LOD i.e., resolution, client-devices can readily predict
the amount of data contained within the tile; as a result, the management of memory within client-devices is simplified and much more deterministic.
The CDB Specification Data Representation Model DRM is logically organized as a strip of geo-unit aligned tiles along each earth slice. Each earth slice is divided into a decreasing number
of tiles to account for the fact that the length of an earth slice decreases with increasing latitude.
1.4.5.2 Layers
The CDB Specification DRM is also logically organized as distinct layers of information. The layers are theoretically independent from each other, i.e., changes in one layer do not impose
changes in other layers.
Layers are additive in fidelity, i.e., the achievable level of the simulation fidelity increases with the number of layers.
