Navigation and Positioning

Digital maps are a pre-requisite for satellite navigation and many other ITS applications, such as automated driving and traveller information systems. Many technologies are currently available for creating and updating digital maps. For example, digital maps can be created by collecting raw network data, digitising paper maps, from aerial photographs and other sources. An initiative called OpenStreetMap (http://www.openstreetmap.org) intends to develop digital mapping for the whole world. The maps are developed from GPS traces collected by ordinary people and uploaded to the website. Aerial imagery and low-tech field maps are often used to verify that the resulting maps are accurate and up to date.

A navigation database is a commercially developed database used in satellite navigation systems. It is often based on a Network Gazetteer (See Basic Info-structure) and will contain all the elements needed to construct a travel plan or a route from a specific origin to a specific destination. Additional criteria may be added such as the route passes through a specific point, that it avoids tolls, that it is the fastest or shortest available, or that it minimises fuel consumption or emissions.

A navigation database is multi-layered and requires more than the basic coordinates for the road network links and nodes, although that is an important starting point.

Additional features necessary for navigation include:

• the complete road network geometry, which must be regularly updated
• a full and complete functional classification of the roads
• toll roads
• freeways/ expressways
• major urban arterial roads
• main streets
• residential streets
• low access streets (private roads, unpaved roads)
• accurate information on street and highway interconnections
• details of all motorway overpasses and underpasses
• road characteristics, including one-way information, turn restrictions, divided lanes, number of lanes and lane-use restrictions, stop lights, stop signs and construction status
• street, village, town and city names and alternative (alias) names where appropriate
• address ranges for both sides of the street
• postal location codes (postcodes, ZIP codes)
• "vanity" names for buildings and locations as well as the postal address

Navigation databases also contain information on points of interest and landmarks, such as public transport facilities, major office buildings by name, hotels, restaurants and tourist attractions, post offices, government buildings, military bases, hospitals, schools, petrol stations, convenience stores, shopping centres and malls, toll-booths – and in some countries, the location of speed cameras.

Crowd-sourcing and social networking has enabled the creation of navigation databases that are adapted to the needs of specific groups of road-users, such as truck drivers and cyclists. There are also important developments taking place in pedestrian navigation.

Further information

Infromation on pedestrian navigation: http://www.insidegnss.com/node/513 and http://www.navipedia.net/index.php/Pedestrian_Navigation

Location-based services are computer applications that use location data to control features or the information displayed to the user. They have several applications in health, entertainment, mobile commerce, and transport. In road transport, for instance, location-based services can be used to provide point of interest information (using data held in a navigation database – such as the closest fuel station or restaurant. Location-based services can also be used to display congestion or weather information according to the location of the user (See Location-Based Services).

In co-operative systems, vehicles share data with each other and with the road infrastructure using vehicle to vehicle (V2V) and vehicle to infrastructure (V2I) communications. Vehicles that are connected in this way can make use of real-time information on moving objects (such as other vehicles nearby), and on stationary objects that might be transitory (traffic cones, parked vehicles and warning signs). This highly detailed, constantly changing information is held in a data store known as a Local Dynamic Map (LDM). The LDM supports various ITS applications by maintaining information on objects that influence, or are part of, the traffic. Data can be received from a range of different sources such as vehicles, infrastructure units, traffic centres and on-board sensors. The LDM offers mechanisms to grant safe and secure access to this data by means of V2V and V2I communications.

The data structure for the LDM is made of four layers:

• the first layer stores the static map information. This is data about the road network, provided by a map data supplier, that is permanent
• the second layer extends the static map with information that is important for co-operative systems – for example road signs, intersection features and landmarks for referencing and positioning
• the third layer contains information that is dynamic and transient, such as weather, traffic attributes and road conditions
• the top layer contains highly dynamic information about the position of vehicles and road users – detected by in-vehicle and other sensors. It also keeps track of the available communication nodes. This fourth layer is particularly important for Connected Vehicle applications

Location referencing and object positioning for the upper layers of the LDM is complex and requires adequate location referencing methods. Since not all ITS applications need location referenced information, the use of this data is not mandatory.

These technologies allow the location of vehicles to be ascertained in real-time as they travel across the network. AVL has many useful applications for vehicle fleet management, such as improving emergency management services by helping to locate and dispatch emergency vehicles. AVL can be used for probe vehicle detection and on buses to locate vehicles in real-time and determine their expected arrival time at bus stops.

A number of technologies are available for AVL systems including dead reckoning, ground-based radio, signpost and odometer, and Global Positioning Systems. GPS is currently the most commonly used technology.

Fixed point transponder-based systems

Another system for tracking and locating vehicles uses fixed point transponders which can read and communicate with other equipment – for example, toll tags on-board vehicles. These systems can determine when a vehicle passes by a certain point, and provide useful information on travel times and speeds.

Mobile phone triangulation

A third method for locating vehicles is through mobile phone triangulation. The location of a mobile phone user is identified by measuring the distance to several cell phone towers within whose range the user is located. Using this technology, the location of the vehicle can be identified within an accuracy of about 120 meters. In rural areas, where few cell towers are located, the tower can measure the angle of transmission, which – along with the distance – can be used to locate the phone user even though the user might only be within the range of single cell phone tower. The estimated location in this case is not very accurate (within about 1.6 km).