High Precision GPS
To achieve higher precision positioning results with GPS, more signals from maximum numbers of satellites have to be recorded for computation. Usually, this would mean longer occupancy time and reduction in the noise that interfere with the signals from the satellites.
Specially external antenna mounted on pole or tripod are used when high precision GPS results are required. Such setup is usually seen with land survey GPS or geodetic GPS.
As for engineering applications, multiple receivers linked via wireless modems and radio frequency transmitters. The satellites signals from these receivers are computed on-the-fly with portable field computers to provide highly accurate measurements for construction of structures.
Differential GPS
Differential Global Positioning System (DGPS) is an enhancement that uses a network of fixed ground based reference stations. Each base station computes the difference between the positions indicated by the satellite systems and the known fixed position and transmits this correction via terrestrial radio broadcast. GPS receiver will require an additional radio(external or integrated) to receive such broadcast to make use of such correction.
Postprocessing GPS
As the name implies, this technique involves additional processing of the collected satellites signals, usually over period of time at 2 or more fixed points. Sophisticated algorithm also known as post-processing software, attempts to resolve uncertainties and errors in noisy signals by estimating a combination of the GPS satellite states, station locations, clock parameters, troposphere parameters, earth orientation parameters and etc. The relative distance between 2 points can be calculated to within 0.005m.
Real-time Kinematic GPS - RTK
With the advent of microships technology and wireless communication, satellites signals received by 2 or more GPS receivers are compared and computed to give high precision result in shorter time span.
Usually, there is a base station and a roving unit. The 2 units are linked wirelessly - via UHF radio or mobile phone networks such as GSM and GPRS. The roving unit will combine the data from the base station and compute its own position on-the-fly.
You can imagine having a GPS receiver, a computer and a radio/mobile phone integrated in the roving unit to achieve such a technological feat.
More information on RTK, click here.
