A location reference describes a location. A location can be a particular point, curve or two-dimensional shape on the surface of the earth. Quite often, when a location is used in an application, it refers to a particular anthropogenic or geographic feature, such as a road, building, mountain or body of water.
The core challenge for creating location references is to describe the location unambiguously, while at the same time keeping the size of the encoded reference to a minimum.
The location referencing functionality in the Location Library supports use cases in the field of traveller information. The specific challenge here is to ensure that the receiver of location referencing information can interpret the information in the context of a map that is not shared between sender and receiver. For example, the receiver of a message describing a road closure needs to match that information to its own map. This way, the receiver can determine a new route that avoids the closed stretch of road.
The Location Library provides modules to work with different location referencing methods that are part of the ISO 21219 series TPEG2 standard.
The Location Library includes the following modules for working with location references:
tpeg2 defines a Java/Scala representation of TPEG2 location references and messages, as well as providing the ability to marshall and unmarshal these references and messages to the binary and XML encodings specified in the standard.
referencing provides the ability to represent given location references in the Optimized Map for Location Library as well as creating location references from locations given in terms of vertices in the Optimized Map for Location Library.
The location referencing schemes that are supported are TMC and OLR.
TMC vs OLR
TMC is a pre-coded location referencing scheme while OLR uses characteristic points in the road network to describe paths in the road network.
Advantages of TMC
- Creating and resolving a reference is computationally cheap.
- References are very small.
- References are unambiguous.
Advantages of OLR
- Sender and receiver do not need to share a location table, which avoids issues of distribution, versioning and licensing.
- You can reference arbitrary paths in the road network, not only paths along highways and major roads.