General Information
Geographic Data Files (GDF) is a standard mainly used in vehicle navigation for the exchange of digital maps between map manufacturers and navigation system integrators. Additionally, GDF provides numerous rules for data capture and representation, in regard to many street space objects. The current specification GDF5.0 was published in 2011 by ISO and is divided into several sections (ISO 14825, 2011). Real world objects called ‘Features’ and their database representation form the core of the general GDF data model. Furthermore, topological and non-topological relations between these features as well as their characteristics are described. Additionally, these features are organized semantically by categorizing them into different thematic feature themes defined in the so-called Feature Catalogue. Possible attributes and relationships of these features are specified in the corresponding attribute catalogue and relationship catalogue. Features can also be subdivided based on the topology of the underlying graph by which the features are defined. Moreover, all objects can be conceptually divided over three levels called Level-0, Level-1 and Level-2. This concept shall be illustrated by explaining the most relevant thematic category with regard to street space called ‘Roads and Ferries’. This contains a so called ‘Road Network’ which can be represented in Level-1 and Level-2 respectively. A representation in Level-0 would consist of basic topological building blocks such as nodes, edges or faces but is not available for road network representations. Simple features such as ‘Road Elements’ or ‘Junctions’ make up Level-1 objects and can be aggregated to form more complex features called ‘Road’ or ‘Intersection’ in Level-2. Road networks are represented by linear structures. Enclosed traffic areas, defined as areas within unstructured traffic movements such as car parks, can be represented as areas. GDF supports a mechanism of linearly referencing points along line features. Furthermore, all geodetic parameters needed for the correct interpretation of X, Y and Z-values shall be described explicitly to make a transformation into any other coordinate system possible. While many basic concepts of GDF are explained using UML diagrams, there is also a complete XML schema defined within the standard document.