GPS tracking unit
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A GPS tracking unit is a device that uses the Global Positioning System to determine the precise location of a vehicle, person, or other asset to which it is attached and to record the position of the asset at regular intervals. The recorded location data can be stored within the tracking unit, or it may be transmitted to a central location data base, or internet-connected computer, using a cellular (GPRS), radio, or satellite modem embedded in the unit. This allows the asset's location to be displayed against a map backdrop either in real-time or when analysing the track later, using customized software.

Types of GPS trackers
Usually, a GPS tracker will fall into one of these three categories:

Data loggers
A GPS logger simply logs the position of the device at regular intervals in its internal memory. Modern GPS loggers have either a memory card slot, or internal flash memory and a USB port. Some act as a USB flash drive. This allows downloading of the track log data for further analyzing in a computer. The tracklist or point of interest list may be in GPX or other format.
Most digital cameras save the time a photo was taken. Provided the camera clock was reasonably accurate, this time can be correlated with GPS log data, to provide an accurate location. This can be added to the Exif metadata in the picture file, thus geotagging it.
In some Private Investigation cases, these data loggers are used to keep track of the vehicle or the fleet vehicle. The reason for using this device is so that a PI will not have to follow the target so closely and always has a backup source of data.

Data pushers
Also known as a GPS transponder, this kind of device is used by the security industry, which pushes (i.e. "sends") the position of the device, at regular intervals, to a determined server, that can instantly analyze the data.
These devices started to become popular and cheaper at the same time as mobile phones. Falling prices of SMS services, and smaller sizes of phone allowed to integrate the technologies at a fair price. A GPS receiver and a mobile phone sit side-by-side in the same box, powered by the same battery. At regular intervals, the phone sends a text message via SMS, containing the data from the GPS receiver. Newer GPS-integrated smartphones running GPS tracking software can turn the phone into a data pusher (or logger) device; as of 2009 open source and proprietary applications are available for iPhone and Android.[1] [2] [3][4]
Some companies provide data "push" technology, enabling sophisticated GPS tracking in business environments, specifically organizations that employ a mobile workforce, such as a commercial fleet.[5] Typical GPS tracking systems used in commercial fleets have two core parts: location hardware (or tracking device) and tracking software. This combination is often referred to as an Automatic Vehicle Tracking system. The tracking device is most often hardwire installed in the vehicle; connected to the ignition switch, battery and antennae. The typical tracking hardware for a fleet management solution uses GPS to pinpoint its location and then transmits updates at regular intervals or after an event trigger, e.g. ignition on / off. These location updates are commonly transmitted, coverage permitting, in Europe and increasingly in North America using GPRS. The location data are made available for viewing, in most cases via a website accessed over the internet, where fleet activity can be viewed live or historically using digital maps and reports.
GPS tracking systems used in commercial fleets are often configured to transmit location and telemetry input data at a set update rate or when an event (door open/close, auxiliary equipment on/off) triggers the unit to transmit data. Live GPS Tracking used in commercial fleets, generally refers to systems which update regularly at 1 minute, 2 minute or 5 minute intervals, whilst the ignition status is on. Some tracking systems combine timed updates with heading change triggered updates.
The applications of these kind of trackers include:
* Law enforcement. An arrested criminal out on bail may have to wear a GPS tracker, usually on the ankle, as a bail condition.
* Fleet control. For example, a delivery or taxi company may put such a tracker in every of its vehicles, thus allowing the staff to know if a vehicle is on time or late, or is doing its assigned route. The same applies for armored trucks transporting valuable goods, as it allows to pinpoint the exact site of a possible robbery.
* Stolen vehicle searching. Owners of expensive cars can install a tracker, and "activate" it in case of theft. "Activate" means that a command is issued to the tracker, via SMS or otherwise, to act as a fleet control device, allowing the user to know where the vehicle is.
* Animal control. When put on a wildlife animal (e.g. in a collar), it allows scientists to study its activities and migration patterns. Vaginal implant transmitters mark the location where pregnant females give birth.[6] Animal tracking collars may also be put on domestic animals, to locate them in case they get lost.
* Race control. In some sports, such as gliding, participants are required to carry a tracker. This allows, among other applications, for race officials to know if the participants are cheating, taking unexpected shortcuts or how far apart they are. This use has been featured in the movie "Rat Race".
* Espionage/surveillance. When put on a person, or on his personal vehicle, it allows the person monitoring the tracking to know his/her habits. This application is used by private investigators.
* These devices are also used by some parents to track their children.[7]. The supporters claim that if cleverly used, this actually allows children more independence.
* Internet Fun. Some Web 2.0 pioneers have created their own personal web pages that show their position constantly, and in real-time, on a map within their website. These usually use data push from a GPS enabled cell phone.

Data pullers
Contrary to a data pusher, that sends the position of the device at regular intervals (push technology), these devices are always-on and can be queried as often as required (pull technology). This technology is not in widespread use, but an example of this kind of device is a computer connected to the Internet and running gpsd.
These can often be used in the case where the location of the tracker will only need to be known occasionally e.g. placed in property that may be stolen.
Data Pullers are coming into more common usage in the form of devices containing a GPS receiver and a cell phone which, when sent a special SMS message reply to the message with their location.

Tags: GPS Tracker, Vehicle tracking system, GPS tracking, GPS Tracking System, GPS Tracking Device, GPS TrackMaker, Fleet Management, Satellite GPS, GPS Vehicle Tracking, GPS for Pet, GPR for Kids