The Global Positioning System (GPS) is a technology that locates the exact position of an entity on the earth anywhere, anytime and in any weather. The GPS is a constellation of twenty four satellites, which orbit around the earth and send continuous stream of signals to the ground stations enabling a GPS receiver to exactly locate the position of a vehicle.
A GPS receiver's job is to locate four or more of these satellites, figure out the distance to each satellite, and use this information to determine its own location, this operation is based on a simple mathematical principle called trilateration. Once the receiver makes this calculation, it provides the latitude, longitude co-ordinates of its current position.
The installed GPS devices in your vehicles are vehicle tracking units/hardware. Vehicle tracking system uses GPS technology to find the location of the monitored or tracked vehicle and then uses cellular networks to send the location data to the monitoring center.
GPS (Global Positioning System) is for fixing the location where as GSM/CDMA is for sending the data to the monitoring centers
There are two types of tracking, they are as follows:
ctive Tracking (Online Tracking)
Passive Tracking (Offline Tracking)
This tracking involves collecting the data such as latitude, longitude, speed etc, and transmits the information in real time through cellular networks.
Here, in this tracking the device collects the data such as date, time, latitude, longitude, speed and stores this data in the memory. Then this data can be accessed to on the computer for purposes like mapping and other calculations.
A GPS receiver calculates its position by precisely timing the signals sent by the GPS satellites high above the earth. Each satellite continually transmits messages containing the time the message was sent, precise orbital information (the ephemeris), and the general system health and rough orbits of all GPS satellites (the almanac).
The receiver measures the transit time of each message and computes the distance to each satellite. Geometric trilateration is used to combine these distances with the location of the satellites to determine the receiver's location.
The position is displayed, perhaps with a moving map display or latitude and longitude; elevation information may be included.
GPS units also show derived information such as direction and speed, calculated from position changes. It might seem three satellites are enough to solve for position, since space has three dimensions. However a very small clock error multiplied by the very large speed of light—the speed at which satellite signals propagate—results in a large positional error.
The receiver uses a fourth satellite to solve for x, y, z, and t, which is used to correct the receiver's clock. While most GPS applications use the computed location only and effectively hide the very accurately computed time, it is used in a few specialized GPS applications such as time transfer and traffic signal timing.
Although four satellites are required for normal operation, fewer apply in special cases. If one variable is already known for example, a ship or plane may have known elevation; a receiver can determine its position, using only three satellites.
