Geographic Data Files
Geographic Data Files ( GDF , German Geographical data files ) has been 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 under the standard ISO / DIS 14825: 2011 describes (GDF5.0 issue of standards replaced GDF4.0 2004). Traditionally, GDF files have fixed-width fields of 80 characters per line. The individual records can be continued with continuation records . The latest revision of the GDF standard by ISO now also provides for 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 ), whereby the edges are formed from nodes and shape points and several edges are combined to form faces .
Level 1
At this level, map objects are provided with attributes . Some manufacturers may have features without a topology, but the features are usually provided with one or more nodes, edges or faces so that the features can be divided into line , point and area features according to their geometry .
The map objects are categorized with feature codes ; Some feature codes are already specified in the GDF standard and some can be defined by the individual GDF manufacturer (for this purpose 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 in Segmented attributes Records filed and contain, similar to the feature codes , in part, by GDF, in part, by the GDF manufacturer specified codes . Example: "FW" = Form of Way
Level 2
Complex features are made up of one or more features or complex features and are given a new set of attributes. For example, a federal state can be recorded as a complex feature composed of rural districts , whereby the districts can be complex features from cities and these in turn can be complex features from city districts. Complex features can also consist of different relationships . In addition, among all the features and features Complex relationships through Relationships are represented.
GDF differs from simple exchange formats not least in the instructions that define how data is to be structured and recorded.
There are also z-coordinates in the GDF, which are rarely used in current implementations (e.g. as height information for buildings, but not in Cartesian, but as the number of fixed height units to be piled up).
The format is very scalable and has no limit to the accuracy of the data, since the fields in which the coordinates are written can be adapted to all needs using Field Definition Records and Record Definition Records ; but there is also no minimum accuracy or minimum feature requirements. Due to the possibility of individual creation of your own features using feature definition records , the use of GDF is not limited to street maps.
Manufacturer
The companies Navteq and TomTom are the two most important producers of navigation data sets.