Location Library location referencing

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.