GPS CORRECTION SERVICE – GLOBAL ASSETS
DOES YOUR SYSTEM OFFER SATELLITE-BASED AUGMENTATION SYSTEM?
Satellite-based augmentation systems (SBAS) support wide-area augmentation through the use of additional satellite-broadcast messages. This involves an additional carrier signal and your GPS has to be able to receive this additional signal. Such systems are commonly composed of multiple ground stations, located at accurately-surveyed points. The ground stations take measurements of one or more of the GNSS satellites, the satellite signals, or other environmental factors which may impact the signal received by the users. Using these measurements, information messages are created and sent to one or more satellites for broadcast to end users.
SBA Accuracy is 0.3m horizontally/ 0.8m vertically
For information on International GNSS Service (IGS) https://www.igs.org
NATIONAL REGIONAL SYSTEMS
In the US we use The Wide Area Augmentation System (WAAS), operated by the United States Federal Aviation Administration (FAA).
Multi-functional Satellite Augmentation System (MSAS) is a Japanese GPS augmentation system.
GLONASS , GPS Navigation system in Russian. is it a second GPS system for many navigation systems in the world.
The European Geostationary Navigation Overlay Service (EGNOS) was developed by the European Space Agency on behalf of the European Commission. It supplements the GPS, GLONASS and Galileo GPS constellations.
GPS-aided GEO augmented navigation (GAGAN) is an implementation by the Indian government.
StarFire navigation system
Starfix DGPS System
WHY DO YOU USE RTK IN MAPPING?
Real Time Kinematic (RTK) satellite navigation is a technique used to enhance the precision of position data derived from satellite-based positioning systems (global navigation satellite systems, GNSS) such as GPS, GLONASS. This method provides up to single digit centimeter-level accuracy
In practice, RTK systems use a single base station receiver and a number of mobile units. The base station re-broadcasts the phase of the carrier that it observes, and the mobile units compare their own phase measurements with the one received from the base station. There are several ways to transmit a correction signal from base station to mobile station. The most popular way to achieve real-time, low-cost signal transmission is to use a radio modem.
This allows the units to calculate their relative position to within millimeters, although their absolute position is accurate only to the same accuracy as the computed position of the base station. The typical nominal accuracy for these systems is 5 centimeter horizontally and 2 centimeters vertically.
This means a LiDAR operator would not have to geo-correct their data on the ground. This is an advantage for firms that need corrected geospatial data really fast.
However this technique does come with limitations. If you are flying longer distances, closer to the earth, like most mapping drones do, then you are likely to loose the carrier signal.
WHY POST PROCESSING KINEMATIC?
Post processed kinematic (PPK) is a GPS is a position location process whereby signals received from a mobile location receiving device stores position data that can be adjusted using corrections from a reference station after the data has collected.
Just like RTK, PPK does require a base station. However if you are operating in the US, you may be able to use the public CORS network.
Using PPK 5-6 cm of absolute accuracy can be achieved. However it too comes with a cost, unlike RTK, the data must first be downloaded and then the corrections processed.
For an industry that can afford a few minutes to process their data, the trade off in accuracy, reliability, and cost is very attractive.
Continuously Operating Reference Stations (CORS)