GDF 3.0, a European standard created by Comité Européen de Normalisation (CEN), is emerging as the de facto international standard for exchanging navigable databases. GDF has multiple versions, which prevent usage of a single GDF compiler worldwide to serve all map suppliers. Highlights are as follows:
The GDF conceptual data model comprises three entities: levels, attributes, and relationships.
The GDF levels represent real-life objects that have locations, such as roads, railways, states, and water elements. GDF has three feature levels:
Level 0 describes the geometry of the map in terms of the cartographic primitives. It breaks the map down into its most basic form for representation. Geometric features (level 0) are nodes, edges, and faces. XYZ coordinate records define the longitude, latitude, and relative altitude of the nodes and/or shape points of an edge. One XYZ record for each node identifies its geometric location, while a single XYZ record identifies the location of all shape points of an edge. An edge is bound by two nodes identifying its end points. A face consists of one or more edges identifying its boundaries.
Level 1 describes the map in terms of simple features, which can take the form of points, lines, or areas. For example, a road element is a line feature; a junction is a point feature. On level 1, the level 0 elements receive "real world" significance. The following relationships exist between
level 1 and level 0:
Complex features comprise a group of simple or complex features. For example, the United States is a country, which is made up of a group of states. This is Level 2 of the GDF. The GDF feature representation schema specifies how the individual features should be represented by nodes, edges, and faces—the cartographic primitives.
The properties of features are referred to as attributes. A feature can have zero or more attributes. Except for a few cases, attributes apply to specific features. For instance, the Form of Way attribute is valid only for the feature category "roads and ferries," while the Official Name attribute may apply to the feature categories "roads and ferries," "services," and the like.
The two types of attributes are simple and composite. Simple attributes have one component. For instance, form of way is a simple attribute. Composite attributes have more than one attribute, each of which can be a simple attribute or another composite attribute. All components of a composite attribute have to be taken into account; otherwise, the incorrect representation may result. Each set of composite attributes is represented by its own Segmented Attribute (SATT) record. House number rangeis an example of a composite attribute, which consists of:
CEN GDF 3.0 also allows user-defined attributes and their associated values.
A relationship consists of two or more features and identifies an association among those features. For instance, the prohibited manoeuvre relationship consists of a line feature (road element), a point feature (junction), and one or more line features. Relationships can have attributes of their own. For instance, the attribute Vehicle Typeis associated with a given Prohibited Manoeuvre relationship.
NAVTEQ customers may have a proprietary data structure for publishing navigable map contents, as used by their application. Data contained in an extraction format must be converted into this proprietary data structure. Customers must build or buy a compiler that reads the extraction format, interprets the data in the format, and publishes the content into their proprietary data structure.
The CEN standard allows the creation of user-defined entities. NAVTEQ has added user-defined records, features, attributes, and relationships to ensure a complete representation of the NAVTEQ® Core Map in GDF. The CEN standard defines attributes, features, and relationships that are not included in the NAVTEQ GDF, although to conform to the standard, some NAVTEQ attributes are forced into CEN representation.
All attributes in the NAVTEQ Core Map database are represented in the NAVTEQ GDF. The feature types are different (e.g., airport is 4581 in the NAVTEQ internal database and 7383 in the NAVTEQ GDF) and the terminology is different:
GDF also supports supplemental data options not currently available in the NAVTEQ internal database (i.e., Long Haul, NAVTEQ Map Voice Data™, and the like).
NAVTEQ map data are available in GDF 3.0 format as follows:
The region counts listed are based on second quarter 2006 databases and are published as a reference only; regions are expected to grow with continued increased coverage worldwide. China is available through the NAVTEQ/NavInfo joint venture NAV2.
For more technical information or questions about the GDF 3.0 data format, content, and representation, please review the the GDF Reference Manual or contact a Technical Customer Support representative in our discussion forums.
