2.2 
Two-Dimensional Features 
A variety of terrestrial features, typically derived from two-dimensional (2D) cartographic sources, are used to 
populate the synthetic environment. These include roadbeds, railbeds, rivers, streams, lakes and land cover. In the 
past, these have been scaled to appropriate dimensions and projected as 2D “ribbons” onto the 3D surface. While 
this technique has been successfully employed to support many “fast-moving” high-altitude flight simulations, 
spatial anomalies such as rivers running uphill or roads lying on undrivable slopes that may be inconsequential in 
a flight simulator can be unacceptable or even pathological in ground vehicle operations. Currently, much progress 
is being made in incorporating such cartographic features into integrated TIN surfaces invoking the appropriate 
spatial constraints (i.e., lakes at a constant elevation, streams in local terrain minima, cut-and-fill roads) directly 
in the TIN generation process. 
2.3 Three-Dimensional Objects 
Unlike the traditional cartographic representations constrained to 2D symbolization, the virtual world supports 
three-dimensional (3D) representation of objects such as buildings, bridges, towers and pipelines. Typically, wire 
frame models of 3D objects are generated a variety of computer-aided design (CAD) environments to include both 
generic models (i.e., typical school, church, mosque, farmhouse, power tower, telephone pole) and site-specific 
models with unique models such as the Pentagon, White House, Golden Gate Bridge, or Hoover Dam. 
2.4 Texture Maps 
Visualization of synthetic environments require texture maps, computer graphic analogs to the traditional 
cartographic tint and screen patterns assembled for depicting features on paper maps (i.e., forest, swamp and 
built-up areas). Characterization of dynamic processes—shading to represent time-of-day, terrestrial and cloud 
shadowing, and non-visual (i.e., rigorous thermal infrared or synthetic aperture radar modeling)—represents 
work that is largely in progress. Use of mapping, Earth resources or reconnaissance imagery as a special case 
of geo-specific “photo-texture map” supports a growing set of both real-time and non-real-time visualization 
applications. 
3 Value-Adding Strategy 
Construction of a useful synthetic environment requires integration of these cartographic components into 
spatially coherent, three-dimensional representation of the geographic area of interest. To meet the technical 
challenges associated with Advanced Distributed Simulation, a “Value-Added Strategy” builds on operational 
digital terrain products using softcopy workstations to exploit mapping, Earth resources and reconnaissance 
imagery. 
3.1 Building on Operational Products 
Building on operational digital terrain products is critical for interoperability and responsivenes as well as 
economy. Military digital terrain data products from the Defense Mapping Agency (DMA) include Digital Terrain 
Elevation Data (DTED), Digital Chart of the World (DCW), Digital Feature Analysis Data (DFAD), Interim 
Terrain Data (ITD), Digital Nautical Chart (DNC) and Tactical Terrain Data (TTD). For the United States, 
similar digital terrain data products are available from the U.S. Geological Survey. Like any map product, 
however, digital terrain data represents an abstraction of the real world with fundamental limitations of currency, 
metric accuracy and level of generalization. 
3.2 Enhancement with Imagery 
While some applications can be met by direct exploitation of such standard digital terrain data, more demand 
ing applications—particularly those supporting operations “close to the ground”—are well-served by emerging 
capabilities for “value-adding” by the user working with controlled imagery. Advanced softcopy workstations, 
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