Geographic Data Files
Geographic Data Files ( GDF ) is a system developed by the car navigation industry conceptual and logical data model with definition of a non-binary standard file exchange format for vector map data, in particular for road maps. It was 14825:2011 described under the Standard ISO / DIS ( GDF5.0 edition of the standards replaced GDF4.0 of 2004). Traditionally, GDF files fixed width fields and 80 characters per line. The individual records can be continued by continuation Records. The recent revision of the GDF standards by ISO looks recently also XML and SQL - based formats.
Structure
The map objects are stored in three levels:
- Level 0: The geometry
- Level 1: Simple Features
- Level 2: Complex Features
Level 0
Here the geometry is in the form of points (nodes ), lines ( Edges ) and surfaces (faces ), the Edges of nodes and shape points are formed and multiple edges are combined into faces.
Level 1
At this level, map objects are decorated with attributes. There may be features without topology by some manufacturers, but in general the features with one or more Nodes, Edges or Faces are provided, so can the features divided by their geometry in line, point and area features.
The map objects are categorized with feature codes; Feature codes are specified to a part already in the GDF standard and can be defined for the other part of the GDF individual manufacturers ( this, a Feature Specification record is created in the GDF- header). An example of the four-digit numeric code: Feature code " 4110 " Road Element. The attributes are stored in Segmented attributes Records and included, similar to the feature codes, partly by GDF, in part, by the GDF- manufacturer -specified codes. Example: " FW" = Form of Way
Level 2
Complex features are summarized from one or more features or complex features and get a new set of attributes. For example, can a state as Complex Feature composed capture of counties, where the circles Complex may be features from cities and these in turn Complex features from districts. Complex features can also consist of several Relationships. In addition, features relationships can be represented by Relationships between all features and Complex.
GDF differs from simple exchange formats, not least through the instructions that determine are how to structure data and capture.
There are also GDF z coordinates, but rarely used in current implementations (eg as height information of buildings, but there is not Cartesian, but as the number of aufzutürmenden, fixed height units).
The format is very scalable and has no limit on the accuracy of the data because the fields in which the coordinates are written, can be adjusted by Field Definition Records and Record Definition Records all needs; but there are also no minimum accuracy or minimal feature requirements. With the option of creating your own individual feature by feature definition Records of the use of GDF is not limited to road maps.
Manufacturer
The company Navteq and TomTom are the two main creators of navigation data sets.