Differential GPS or DGPS increases the accuracy of the GPS reading. The United States Military owns and operates the GPS system so naturally they will want to keep effective readings to a minimum. Selective Availability or SA is used to limit the accuracy of the commercial grade GPS devices that civilians use. Selective Availability creates errors to the time the signal is sent between the satellite and the GPS receiver, so you’ll get an inaccurate position reading on the GPS device by about 100 meters. Introducing the differential GPS will narrow down the error and give you a better reading, one that is about ten meters from the real position. Through this system you will get a more precise reading.
- Base stations. For the Differential GPS to work, two receivers are used to collect data. The first GPS base station is fixed in one position and works just like any other GPS device wherein signals from 4 satellites must be received to establish position. Naturally the first station will get errors and display an inaccurate position. The second base station isn’t stationary; it is a roving station that collects the data from the first station. The data from the first station contains the signal received from the satellites and the actual position the station is in, then the roving station calculates the information and corrects it. The process can be done in real time.
- Reprocessing. Software is provided by manufacturers of GPS devices to help process and correct the real time data. The software will take away any event that affects the signal while it is being received, such as blocked satellites. The software reprocesses the data to present a more accurate reading.
- Correction through Postprocessing. As opposed to real time processing, the data taken from the stations are collected then processed at a later time through a processing software that calculates the corrected locations. This is later sent to a Geographical Information System and the information can then be viewed and analyzed. The information can be presented with three views, the first being the database view which present the data with street or road names and latitude and longitude information. The second view displays geographical features on map, and the third view is a model view, where the information on land conditions is presented through a model form.
The differential GPS gives its users a more accurate reading of position and additional information on geographical conditions that can be analyzed and used by different agencies.