What is RTK and why do I Need it?
Centimetre-grade Real Time Kinematic (RTK) GPS and GNSS receivers have been available for a long time, but only in Bluetooth format for mobile GIS for a few years. As such, the use of that high precision equipment in the field is a newer phenomenon for field workers outside licensed land surveyors or the construction industry. RTK GPS receivers are traditionally very expensive and their accuracy has been thought of as beyond the field mapping needs of most environmental and engineering firms, and government land management groups. However, with the introduction of Bluetooth RTK receivers for use with field tablets and mobile GIS, RTK’s potential has become less expensive to achieve and much desired. Add to that the availability of Bluetooth RTK receiver rentals from Anatomic Field Solutions, and the continued progression of many companies into mobile GIS workflows with tablets becomes much easier and more affordable. Using a Bluetooth RTK receiver for the ultimate level of accuracy is now an obvious choice for field mapping tasks.
Bluetooth GPS and GNSS receivers (sub-meter vs centimetre)
Currently, most mobile GIS field users are utilizing sub-meter receivers. These receivers achieve that level of accuracy with assistance from SBAS (WAAS or Wide Area Augmentation System) satellite corrections. This system was developed by the FAA for the GPS constellation to increase accuracy and availability. WAAS uses a network of ground-based reference stations in North America to measure small variations in the GPS satellite’s signals. These are then routed to master stations to send corrections to the WAAS satellites in geosynchronous orbit above North America to then be broadcast down to GPS receivers capable of receiving and applying these corrections to compute the GPS receivers’ location with improved accuracy. This gets the sub-meter receivers accuracy down to under 1 meter. You can review our field test article comparing the capabilities of these receivers.
The way this technology works with SBAS corrections from the WAAS network over North America looks like the diagram below. A tablet is Bluetooth paired to a GNSS receiver. The Bluetooth sub-meter receiver is acquiring location data transmissions from satellites in the GPS and Glonass constellations, which is providing approximately 2 to 4-meter accuracy. Then, the SBAS satellites in the GPS constellation are broadcasting corrections to the GNSS receiver to increase accuracy down to the sub-meter levels we see in our field test data.
Transitioning away from that handheld GNSS unit to a Bluetooth RTK receiver and tablet will:
Give your field teams increased confidence they are getting their required accuracy in real-time
Provide your GIS staff with a simpler workflow since all location, photographic, and asset data will come from the tablet
Eliminate the need for time-consuming post-processing of location data
Provide the project manager with more accurate data and project cost savings to better compete on job proposals
For consulting firms with clients that require post-processing, utilizing a Bluetooth RTK receiver can eliminate that requirement through an information sharing discussion with your client. Essentially, the same types of calculations done with the post-processing method to increase the accuracy of field location data is being done in real-time by RTK base station networks if your RTK receiver is connected through cellular service to your local RTK network. The RTK network is pulling the same satellite data used in post-processing and conducting corrections analyses, and then broadcasting those corrections from an NTRIP Castor live right to your Bluetooth RTK receiver connected to your field tablet! The project savings over legacy post-processing methods are truly significant.
What about working in remote regions or areas without a local RTK network?
There are currently three Mobile GIS options in this kind of scenario;
Use the RTK unit as an SBAS unit for sub-meter data when you have poor cellular service and cannot connect to the network, and then utilize the RTK network for centimetre data when cellular service is available.
Setup your own base station to use with a rover unit for centimetre accuracy.
Use a RTK receiver with a paid correction service from the satellites. In this case, for example, the Arrow Gold RTK or Basic could be used with paid SBAS corrections via Atlas for either sub-foot (30cm) or sub-decimetre (10cm). In this case, the diagram would look the same as the SBAS (WAAS) solution except they would be Atlas satellites and not WAAS satellites providing the high-accuracy solution.
