Editing Automatic vehicle location (section)

== Types of systems ==
=== Simple direction finding ===
[[Amateur radio]] and some cellular or [[Personal Communications Service|PCS]] wireless systems use '''direction finding or triangulation''' of transmitter signals radiated by the mobile. This is sometimes called '''radio direction finding''' or '''RDF'''. The simplest forms of these systems calculate the bearing from two fixed sites to the mobile. This creates a triangle with endpoints at the two fixed points and the mobile. Trigonometry tells you roughly where the mobile transmitter is located. In wireless telephone systems, the phones transmit continually when off-hook, making continual tracking and the collection of many location samples possible. This is one type of location system required by [[Federal Communications Commission]] Rules for wireless [[Enhanced 911]].

=== Former LORAN-based locating ===
Motorola offered a 1970s-era system based on the [[United States Coast Guard]] [[LORAN]] maritime navigation system. The LORAN system was intended for ships but signal levels on the US east- and west-coast areas were adequate for use with receivers in automobiles. The system may have been marketed under the Motorola model name ''Metricom''. It consisted of an [[Low frequency|LF]] LORAN receiver and data interface box/modem connected to a separate two-way radio. The receiver and interface calculated a latitude and longitude in degrees, decimal degrees format based on the LORAN signals. This was sent over the radio as [[MDC-1200]] or MDC-4800 data to a system controller, which plotted the mobile's approximate location on a map. The system worked reliably but sometimes had problems with electrical [[noise]] in urban areas. Sparking electric [[trolley pole]]s or industrial plants which radiated electrical noise sometime overwhelmed the LORAN signals, affecting the system's ability to determine the mobile's geolocation. Because of the limited resolution, this type of system was impractical for small communities or operational areas such as a pit mine or port.

=== Signpost systems ===
To track and locate vehicles along fixed routes, a technology called '''Signpost transmitters''' is employed. This is used on transit routes and rail lines where the vehicles to be tracked continually operated on the same linear route. A [[transponder]] or RFID chip along the vehicle route would be polled as the train or bus traverses its [[Thoroughfare|route]]. As each transponder was passed, the moving vehicle would query and receive an [[acknowledgement (data networks)|ack]], or handshake, from the signpost transmitter. A transmitter on the mobile would report passing the signpost to a system controller. This allows supervision, a [[call center]], or a [[dispatcher|dispatch]] center to monitor the progress of the vehicle and assess whether or not the vehicle was ''on schedule''. These systems are an alternative inside tunnels or other conveyances where GPS signals are blocked by terrain.<ref>For an example of one US signpost system, see its service manual: ''T1919A Metrocom II 150.8-174 MHz Vehicle Location Receiver'', (Schaumburg, Illinois: Motorola Communications and Electronics, 1979).</ref>

=== Today's GPS-based locating ===
The low price and ubiquity of [[Global Positioning System|Global Positioning System or GPS]] equipment has lent itself to more accurate and reliable telelocation systems. GPS signals are impervious to most electrical noise sources and do not require the user to install an entire system. Usually only a receiver to collect signals from the satellite segment is installed in each vehicle and radio or GSM to communicate the collected location data with a dispatch point.<ref>{{cite web |title=GPS-based location feature |url=https://logistimatics.com/blog/5-things-to-consider-when-purchasing-a-vehicle-gps-tracker/ |date= 2017-09-08}}</ref>

Large private telelocation or AVL systems send data from GPS receivers in vehicles to a dispatch center over their private, user-owned radio backbone. These systems are used for businesses like parcel delivery and ambulances. Smaller systems which do not justify building a separate radio system use cellular or PCS data services to communicate location data from vehicles to their dispatching center. Location data is periodically polled from each vehicle in a fleet by a central controller or computer. In the simplest systems, data from the GPS receiver is displayed on a map allowing humans to determine the location of each vehicle. More complex systems feed the data into a computer assisted dispatch system which automates the process. For example, the computer assisted dispatch system may check the location of a call for service and then pick a list of the four closest ambulances. This narrows the dispatcher's choice from the entire fleet to an easier choice of four vehicles.

Some wireless carriers such as [[Sprint Nextel|Nextel]] have decided GPS was the best way to provide the mandated location data for wireless Enhanced 9-1-1. Newer [[Integrated Digital Enhanced Network|Nextel radios]] have embedded GPS receivers which are polled if 9-1-1 is dialed. The 9-1-1 center is provided with latitude and longitude from the radio's GPS receiver. In centers with [[computer-aided dispatch]], the system may assign an address to the call based on these coordinates or may project an icon depicting the caller's location onto a map of the area.

=== Sensor-augmented AVL ===
The main purpose of using AVL is not only to locate the vehicles, but also to obtain information about engine data, fuel consumption, driver data and sensor data from i.e. doors, freezer room on trucks or air pressure. Such data can be obtained via the [[CAN-bus]], via direct connections to AVL systems or via open bus systems such as [[UFDEX]] that both sends and receives data via SMS or [[GPRS]] in pure [[ASCII]] text format. Because most AVL consists of two parts, [[GPS]] and [[GSM]] modem with additional embedded AVL software contained in a [[microcontroller]], most AVL systems are fixed for its purposes unless they connect to an open bus system for expansion possibilities.

With an open bus system the users can send invoices based on goods delivered with exact location, time and date data where if connected to scale, [[RFID]] or barcode readers, can make a fairly good automated system to avoid human errors.

In countries with high prices on gasoline external fuel sensors are used to prevent cases of fuel theft.<ref>{{cite web|url=http://www.rfidsb.com/tm/2008/04/24/fuel-theft-in-the-usa-reaches-8-billion-in-2008/|title=fuel theft in the usa reaches 8 billion in 2008 – RFID Switchboard|website=www.rfidsb.com|access-date=23 April 2018|archive-url=https://archive.today/20120720214117/http://www.billboard.com/album/madonna/sticky-sweet-tour/1330476%23/album/madonna/sticky-sweet-tour/1330476|archive-date=2012-07-20|url-status=live}}</ref>

=== Logbook functions ===
Another scenario for sensor functions is to connect the AVL to driver information, to collect data about driving time, stops,  or even driver absence from the vehicle. If the driver/worker conditions is such as the hourly rates for driving and working outside is not the same, this can be monitored by sensors, by using [[iButton]] or other personal identification devices. Later by analyzing log-file it is possible to get reports on any kind of events, like stops, visited streets, speed limits violations, etc.<ref>{{Cite web |url=https://gurtam.com/en/wialon |title=GPS fleet management system; |access-date=2010-06-28 }}</ref>