Achieving Centimeter Accuracy in RTK
For centimeter accuracy a GNSS Receiver unit will need to have access to GNSS corrections. There are two ways to achieve this. Either by sourcing NTRIP corrections over the internet or by pairing with another GNSS Receiver unit in RTK mode.
Networked Transport of RTCM via Internet Protocol (NTRIP) is a method which allows a RTK GNSS receiver (client) to communicate with a base station (caster) over the internet in order to achieve centimeter accuracy.
When a Base Station is set to a known latitude, longitude and height, this is referred to as a ‘known’ point. This base will monitor the satellites above and will calculate position corrections and sending them to the Rover.
Using Emlid as an example, their Reach RS+ or Reach RS2 can be used as a Base Station, it can be set up on a ‘known’ point at a static location and ‘transmit’ corrections over the Internet. It can also be set up locally, if this is the case all results will be cm accurate relative to the base station position, they may not be absolute.
The Baseline is an important factor to consider when receiving corrections over the internet. Whether this is from an NTRIP provider or from your own unit which is transmitting corrections.
The baseline is the distance between the GNSS Client and the Base Station. The further the rover is from the base station the less accuracy it will have. This is due to different atmospheric conditions at different locations. The Baseline for the Emlid Reach RS+ is 10km for RTK whereas the baseline for the Reach RS2 is 60km.