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models is appropriate if the modeler wishes to fully replicate all of the unique characteristics e.g., shape, size, texture of a feature, as they are in the real-world. As a result, a geospecific
model usually corresponds to a unique real-world recognizable cultural feature. Real-world features such as the Eiffel Tower, the Pentagon, or the CN Tower, to name a few, are usually
modeled as geospecific.
3.3.3 T2DModel Tiled 2D Model
A feature is said to have a 2D modeled representation if it is associated with a modeled representation that has no significant height with respect to the underlying terrain and generally
conforms to the terrain profile. It is convenient to think of the 2D Models as a complement and as an extension to the Primary Elevation and VSTI Imagery datasets. 2D Models provide the
means to represent 2D surface features that are conformed to the underlying terrain:
a Modeled representation of geotypical and geospecific 2D lineal-features such as roads, runways and taxiways, stripes.
b Modeled representation of geotypical and geospecific 2D polygon-features such as aprons, surface markings, contaminants, land usage campgrounds, farms, etc..
2D Models can also be used to model geotypical terrain textures as a mesh of 2D textured polygons overlaying the terrain. This modeling technique replicates approaches used in early
Image Generators which had limited ability to page-in geospecific terrain textures.
3.3.4 MModel Moving 3D Model
A moving model is typically characterized as such if it can move on its own or be moved. More specifically within the context of this standard, the model is not required to be attached to a
cultural point feature.
During the course of a multi-player simulation
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, each client-device is typically solicited to provide a modeled representation of each of the players. The activation of such players requires
that the client-device access the appropriate modeled representation for each of players. There are a large number of military simulations where the player types are characterized by their DIS
code. To this end, the CDB data store provides a moving model library whose structure provides a convenient categorization of models by their DIS code.
3.3.5 Use of GSModels and GTModels
Sections 3.3.1 and 3.3.2 illustrate cases where the choice to represent a feature with either a geotypical GTModels or a geospecific model GSModels is more clear-cut. This section gives
additional insight into the considerations and tradeoffs that go with associating a point-feature with either a geotypical or a geospecific modeled representation. By characterizing a feature as
geotypical, the modeler makes a statement as to the expected usage of the feature and its associated modeled representation within the CDB.
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The players may be virtual e.g., other simulators, synthetic e.g., computer-generated simulations or may be live real-world players playing alongside virtual or synthetic players.
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When a feature is tagged as geotypical… a the modeler is making a statement about his knowledge of the very high
probability of repeatedly encountering that model type within the CDB and…
b the modeler is making a statement that he will likely associate the same modeled representation same shape, size, texture, materials, or attributes, etc. for the
feature type – as a result, the client-devices can count on the fact that the model will be heavily replicated throughout the CDB. The characterization of a model
as geotypical tells the consumers of the CDB that the model is heavily used throughout the CDB and that it may be cached in memory for re-use.
The manner in which geotypical models are stored accessed differs from their geospecific counterparts. Geotypical models are stored in their own directory structure; this group of models
is referred collectively as the GTModel library. The storage structure of the GTModel library provides a convenient categorization of models by their feature codes and their level-of-detail.
As a result, geotypical models can be managed as a global library of 3D models that are used to fill the CDB with cultural detail.
The above discussion applies equally to statically-positioned moving models. The manner in which statically-positioned moving model features and their modeled representations are stored
and accessed is similar to geotypical models; it differs however in the fact that the MModel library provides a categorization of models by their DIS code. The model is fetched from the
MModel library regardless of whether it is used as statically-positioned model by the modeler or whether it is dynamically-positioned by the client-device during the simulation.
Conversely, when a feature is tagged as geospecific… a the modeler is making a statement about his knowledge of the very low
probability of encountering typically only once that feature type within the CDB or…
b the modeler is making a statement regarding his intention to associate a unique modeled representation different shape, size, texture, materials, or attributes, etc.
for that feature – as a result, the client-devices can assume that the feature will never share the same modeled representation with other features e.g., no model
replication within the CDB. Real-world recognizable cultural point features say the Eiffel Tower, the Pentagon, the CN Tower are usually modeled as
geospecific.
GSModels have a storage organization that is consistent with Tiled datasets. The storage organization of tiled datasets has been optimized to efficiently access CDB content by its lat-long
location, its level-of-detail and its dataset component type.
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Requirement 40
http:opengis.netspecCDB1.0cor egeospecific-storage
Like all of the CDB Tiled datasets, geospecific models SHALL be stored in the \CDB\Tiles\ directory. As a result, client-devices can reference each model with a unique
directory path and a unique file name which is derived from the model’s unique position, level-of-detail, and its feature code
See section 6.4.7.2, Volume 10 OGC CDB Implementation Guidance for more implementation guidance on this topic.
3.3.6 Organizing Models into Levels of Detail
