How Accurate is RTK GNSS Really?

In RTK GNSS Accuracy Test: Emlid Reach RS2 vs. Topcon Hiper VR, the aim was to determine whether the RS2 was able to achieve comparable results to the VR in varying environmental challenges. However, the study did not answer the question of the accuracies we should expect in an RTK GNSS receiver. In this discussion we aim to answer the question: in reality, how accurate is our RTK GNSS data?

We begin by looking at the position accuracy specifications published by major manufacturers. 

Taken at face value, the most accurate GNSS receivers for post processed static sessions are the Topcon, Trimble and Leica receivers. The Reach RS2 claim of being 1 mm worse is, in nearly every case, negligible.

The most accurate RTK setup in this group is the Reach RS2. Again, with negligible differences. 

Looking at this table alone, it would be quite reasonable to say that multi-constellation GNSS accuracy does not change based on the receiver used.

The truth is that all GNSS receivers will run into similar inconsistencies because of the process by which RTK GNSS determines a position. This is not to mention the reality that, because of expediency and purpose, an element of human error may also be involved. An example of this would be mounting a receiver on an ATV and not understanding the inaccuracies that it introduces. 

So how accurate is our RTK GNSS data? The table below shows the elevations at the same point with variations of satellite constellations used and some instances repeated. 

There is a difference of 0.07 ft. on the same point with all constellations at a later time in the day. When GPS only is repeated, we see a difference of 0.12 ft. GPS and GLONASS produce the highest elevation. Static OPUS processes are consistent and show the lowest elevation. Static processing should be the most accurate base on the specifications of GNSS RTK receivers. This seems completely reasonable given a two-hour static session observing at 1 Hz would yield 7,200 observations compared to 50 observations if an RTK coordinate is stored averaging over 10 seconds at 5 Hz. 

All told, the conclusion is that most everyone agrees regarding RTK GNSS receivers; they are a great tool for a vast number of jobs, but they have their inconsistencies. If you look at a spec that says you will receive 7 mm horizontal accuracy in RTK, you may receive that on occasion, and you may receive 35 mm accuracy on occasion.

Simply looking at specifications is a good starting point to determining what equipment is right for you, but doesn't always paint the clearest picture or always give the most realistic idea of the results you will achieve. At E38 Survey Solutions, our technical team is up to date on current equipment and processes that occur in the field. Consult with us when you’re looking for equipment and we will point you in the right direction. And if it’s our equipment, we offer reliable support and service.