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140 © 2015 Open Geospatial Consortium
141 © 2015 Open Geospatial Consortium
Chapter 4
4
CDB File Formats
The CDB Specification internal formats are based on the formats used by industry-standard toolsets. As a result, the Specification eliminates the time-consuming off-line database assembly
and database publishing process usually imposed by each of the clients. Refer to Section 1.6.4.2, Database Generation Flow for a more comprehensive discussion of this topic.
Furthermore, the translation step into CDB format is typically trivial since the CDB Specification is based on industry-standard native tool formats.
The CDB Specification permits any CDB to run “as-is”, without any offline assembly aka compilation, translation, conversion, on any CDB-compliant simulator client-device platform.
This allows the simulator user community AND the database creation community to freely exchange CDBs across simulators and database generation facilities either through the exchange
of physical media or entire storage subsystems or via network. As a result, a CDB can be run and exchanged without change on any CDB-compliant simulator client-devices or any database
generation workstations, regardless of the computer platforms, simulator system software.
The storage structure of the CDB Specification allows for efficient searching, retrieval and storage of any information contained within the database. The storage structure portion of the
Specification is defined in Chapter 3.
This chapter concerns itself with the formats used by the CDB. The formats used by the CDB Specification are:
1. TIFF .tif: used for the representation of all datasets whose inherent
structure reflects that of a two-dimensional regular grid in a Cartesian coordinate system. The primary use of TIFF within a CDB is for the
representation of terrain elevation and raster imagery. To qualify as a CDB-compliant TIFF reader, the reader must satisfy the requirements
described in Appendix B of this Specification. It is to be noted that the LZW compression algorithm within the TIFF format is supported and
encouraged by the CDB Specification when the data type of the content of the file is of integral type. As a consequence, it is strongly recommended
to compress TIFF files containing integer values but to avoid compression if the file contains floating-point values.
2. GeoTIFF .tif: used for the representation of all datasets whose
inherent structure reflects that of a two-dimensional regular grid of a Geographic coordinate system. The primary use of GeoTIFF within a
CDB is for the representation of terrain elevation note: the use GeoTIFF is preferred over TIFF in the case of terrain elevation. CDB-compliant
GeoTIFF readers do not concerns themselves with any of the GeoTIFF specific tags because the CDB Specification provides all of the
conventions to geo-reference each geographic dataset. However, it is
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strongly recommended that database generation tools be fully compliant to GeoTIFF; this provision eliminates the need for the tools to be aware of
the CDB conventions governing the content of each geo-referenced dataset.
3. SGI Format .rgb: used for the representation of 3D model textures.
The file format allows for the representation of an image with 1, 2, 3, or 4 channels. A single channel image represents a grey-shaded texture; a two-
channel image represents a grey-shaded texture with an alpha component providing the transparency; a three-channel image represents a color
RGB texture; finally, a four-channel image is a color RGB texture with an alpha channel providing the transparency. CDB-compliant RGB
readers must be fully compliant with the SGI Image File Format Specification. Its use is limited to 3D models.
4. JPEG 2000 .jp2: used for the representation of an image encoded in
accordance to the JPEG 2000 standard. CDB-compliant JPEG 2000 readers must be fully compliant with the JPEG 2000 standard while
reading such still image file types. JPEG 2000 encoded images can be used for the representation of geo-referenced terrain imagery with some
degree of compression levels and is only applicable in the case of terrain raster imagery.
5.
OpenFlight .flt: used for the representation of 3-dimensional geometric representation of all models statically positioned cultural
models, moving models. To qualify as a CDB-compliant OpenFlight reader, the reader must satisfy the requirements described in Appendix C
of this Specification.
6. Shape .shp, .shx, .dbf, .dbt: used for the representation and
attribution of the vector feature datasets in a CDB. To qualify as a CDB- compliant Shape reader, the reader must satisfy the requirements
described in Appendix D of this Specification.
7. Extensible Mark-up Language .xml: used to store metadata that
describes CDB versioning, describes CDB Composite and Base material structure, defines CDB light type naming conventions and hierarchy, and
defines CDB model component hierarchy.
8. Cross-platform and interoperable file storage and transfer format
.zip: used to archive and store geospecific 3D model datasets. Appendices B, C, D of this Specification define the required compliancy of CDB readers for the
TIFF, OpenFlight and Shape formats. Appendix T describes the JPEG 2000 file format and the last section of Appendix D describes the dBASE III+ file format used by the Shapefile standard.
For all other formats used by this Specification, CDB readers must be fully compliant.
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Table 4-1: CDB File Format Compatibility
File Format Versions Supported by
CDB CDB Client-device Behavior
for Prior Versions
.tif 6.0
Ignores data .rgb
1.0 Ignores data
.jp2 1.0
Ignores data .flt
16.0 Ignores data
.shp, .shx ERSI White Paper, July 98 Ignores data
.dbf, .dbt dBASE III+ and above
Ignores data .xml
1.0 Ignores data
.zip 6.3.1
Ignores data
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Chapter 5
5
CDB Datasets
This chapter provides the description of the content of CDB datasets, except OpenFlight and RCS models that are covered in the following chapters. Chapter 5 also provides the Component
Selectors necessary to complete the file names associated with all CDB datasets.