22
© 2016 Open Geospatial Consortium
Section 5: CDB Datasets provides a detailed description of all CDB datasets. The current CDB standard relies on established industry formats:
• The TIFF format. TIFF encoding rules are defined in Volume 10: OGC CDB
Implementation Guidance; •
The Best Practice use of the OpenFlight
6
format Volume 6: OGC CDB Rules for Encoding Data using OpenFlight;
• The RGB format. Included in the Gamma Tutorial Section, Volume 10: OGC CDB
Implementation Guidance •
The Best Practice use of the Shapefile format in a CDB data store. The Shapefile table content encoding rules are in Volume 4. Volume 4: OGC CDB Best Practice use of
Shapefiles for Vector Data Storage; •
JPEG 2000 file format Volume 2: OGC CDB Core Model and Physical Structure Annexes, Annex H.
Each of these documents has been annotated to reflect the conventions established by the CDB standard. The Best Practice conventions currently define how TIFF, OpenFlight, RGB,
Shapefile and JPEG 2000 formatted files are to be interpreted by CDB-compliant simulator readers. Additional encoding formats and conventions will be defined for future versions of the
CDB standard.
Annexes J and F of Volume 2 provide the CDB light type naming hierarchy and the CDB model component hierarchies respectively while \CDB\Metadata\Materials.xml provides the material
list for the CDB standard.
Other Annexes in Volume 2 further describe additional aspects of the CDB standard: •
Providing the CDB Directory Naming and Structure Annex M, •
List of Texture Component Selectors Annex O see footnote 32
7
, •
SGI Image File Format http:paulbourke.netdataformatssgirgbsgiversion.html, •
Table of Dataset Codes Annex Q
8
• How some datasets are derived from others Annex R see footnote 32.
1.6.3 What is the CDB Standard: An Overview
The CDB standard defines a conceptual model that models the organization, and storage structure of a data store to support real time simulation applications. A data store that conforms
to the CDB standard contains datasets organized in layers and tiles that represent the features of the earth for the purposes of distributed simulation applications. A CDB data store can be
readily used by existing simulation client-devices legacy IGs, Radars, CGF, etc. through a
6
Other 3d formats will be evaluated and considered for best practice specification in future versions of CDB. These include CityGML, InDoorGML, COLLADA, and so forth.
7
Annex O can be found in Volume 2 CDB Core Model and Physical Structure Annexes
8
OGC CDB Core: Model and Physical Structure: Informative Annexes
23
© 2016 Open Geospatial Consortium
publishing process performed in real-time. The CDB conceptual model would allow an implementation if a CDB compliant data store in a relational database. However, the data
structures used in CDB structured data stores are somewhat different than those used in relational databases because 1. of the use of standardized data formats adopted by the simulation
community and 2. the CDB storage structure is optimized for near real time simulation applications. The approach defined in this CDB Core standard facilitates the work required to
adapt existing authoring tools to readwritemodify data into the CDB and the task to develop runtime publishers RTP designed to operate on these data structures.
The CDB standard is fundamentally about: ● A representation of the earth and man-made environment for use in real time simulations.
● A turnkey, as-is representation of the Synthetic Environment SE for use in real-time distributed simulation applications.
Currently, the majority of a CDB conformant internal data storage representation is based on five well known and supported data formats endorsed by leaders of the simulation database tools
industry. The CDB Best Practices associated with the Core standard are currently recommended for implementation of a CDB data store:
● For the representation of terrain altimetry, terrain surface characteristics relevant to simulation: TIFFGeoTIFF
● For the representation of 3D culture and moving models: OpenFlight ● For the textures associated with 3D culture and moving models RGB
● For the instancing and attribution of statically positioned point, lineal and polygon 2D3D
culture features. ● For a representation of terrain raster imagery comprising a well-defined and accepted
compression method that allows both lossy and lossless schemes: JPEG 2000. Please note that the OGC CDB Standards Working Group is considering developing best
practice guidance for using other industry standard formats and encodings, such as OGC CityGML, OGC InDoorGML, and OGC GeoPackage.
NOTE: Due to the real time requirement, the CDB standard limits the number of units of measure for each physical quantity. For instance, all coordinates are represented in latitude
longitude and all distances are in meters.
NOTE: In the future, the CDB standard will evolve to enable the use of other international and de-facto geospatial encoding structures.
The CDB specified storage structure allows efficient searching, retrieval and storage of any information contained within a CDB structured data store. Storage structure aspects include
descriptions of each information field used within CDB conformant files, including data types and data type descriptions.
The CDB standard relies on three important concepts to organize the geospatial data:
24
© 2016 Open Geospatial Consortium
● Tiles: The CDB defined storage structure allows efficient searching, retrieval and
storage of any information contained within the CDB. The storage structure portion of this standard geographically divides the world into geodetic tiles each tile bounded by
latitude and longitude, each tile containing a specific set of features such as terrain altimetry, vectors and models such as 3d models and radar cross section models, which
are in turn represented by the datasets. The datasets define the basic storage unit used in a CDB data store. The geographic granularity is at the tile level while the information
granularity is at the dataset level. As a result, the CDB storage structure permits flexible and efficient updates due to the different levels of granularity with which the information
can be stored or retrieved
● Layers: The CDB model is also logically organized as distinct layers of information.
The layers are notionally independent from each other i.e., changes in one layer do not impose changes in other layers.
● Levels-of-Detail LODs: The availability of LOD representations is critical to real-time
performance. Most simulation client-devices can readily take advantage of an LOD structure because, in many cases, less detailinformation is necessary at increasing
distances from the simulated own-ship. As a result, many client-devices can reduce by 100-fold or more the required bandwidth to access environmental data in real-time. The
availability of levels-of-detail permits client-devices to deal with data stores having big- data levels of content. The CDB storage model supports a LOD hierarchy consisting of
up to 34 LODs. The CDB standard requires that each geographic area be reduced into a LOD hierarchy in accordance to the availability of source data.
The standard does not define or enforce an operating system or file system.
1.6.4 What the CDB Standard is Not
