Location Reference
This section of NDW Docs provides information on various methods of location referencing used by NDW.
Definition within the Context
The definition of location reference is: characterization of the location of an entity in space-time relative to a location reference system. In the context of NDW, this refers to the location of an event (situationPublication) or the collection of measurement data (measuredDataPublication) in relation to the applicable location reference system.
Applicable Location Reference Systems
Within the Dutch Profile, the following three location reference systems are in use:
The usage principles are:
- For Real-time Traffic Data (AVG), only location references based on VILD / ALERT-C are allowed, supplemented as much as possible with WGS84 / X,Y coordinates. Optionally, location references based on OpenLR may be included.
- For Status Data, location references based on VILD / ALERT-C should be applied where possible, supplemented as much as possible with WGS84 / X,Y coordinates. Optionally, location references based on OpenLR may be included.
Explanation of Multiple Location Reference Systems
Multiple location reference systems are used because NDW information must support different target audiences simultaneously.
Location reference based on VILD / ALERT-C is aimed at users who utilize NDW information to inform road users. The predefined VILD location table is leading. VILD contains locations that are recognizable to road users. The location of an event or measurement data collection is indicated as a relative location in relation to a VILD location.
Location reference based on WGS84 / X,Y coördinates is intended for users who need to quickly and easily display NDW information geographically. The widely known WGS84 coordinate reference system is leading. The location of an event or measurement data collection is indicated as an absolute location on the WGS84 ellipsoid.
Location reference based on OpenLR is aimed at users who want to "plot" NDW information onto a geographic base network of their choice, generally to establish relationships with other information linked to this base network. OpenLR, developed by TomTom, is based on the shortest path algorithm on a network/graph, where only essential route-determining locations are included alongside the start and endpoint. The location of an event or measurement data collection is indicated as a relative location in relation to a "node" in the network.
Location Reference is Road-Oriented
All mentioned location reference systems share the characteristic of being road-oriented. This means they can be used to derive on which road, and if possible, in which direction the event or measurement data collection takes place. Additional information is required to determine with certainty the exact lane and/or roadway of the event or measurement data collection. This information is provided in the supplementary DATEX II attributes and elements specified for this purpose.
For more information, see Explanation of the Supplementary Location Reference