Collecting Ground Control Points With The Reach RS2

by Kali Fencl

There are a few methods to get a globally accurate base coordinate:

  • RTK Network Service Provider (NTRIP)
  • NGS Survey Marks
  • OPUS
  • OPUS + PPK

RTK Network Service Provider (NTRIP)

When searching for one of these service providers, be sure you have adequate coverage in your area and that you have RTCM3 messages being sent out. Many states offer free networks, so if you search your state’s DOT you may find you have a free network you can use. The process is simple – you’ll need to ensure your RS2 is connected to the internet, then you’ll enter your correction input to the network service provider and pull down their corrections.

NGS Survey Marks

Another way to obtain globally accurate ground control points is to set your base up over a known point. There are survey marks throughout the US that are published online and an interactive map on the NGS website where you can find these marks. If you have a mark close to your site, you can set your base over that mark, enter that survey mark coordinate in the base mode section of your RS2, and that will provide globally accurate coordinates on your rover.

OPUS (PPP)

To obtain a known point using OPUS, we’ll set our base to log data for 90+ minutes. Then, upload that data log to OPUS and about 45 minutes later, OPUS will send an accurate coordinate back in an email, which will then be used as our base coordinate.

OPUS (PPP) + PPK

In conjunction with OPUS, we can do PPK processing, which is beneficial if we don’t have much time to expend on site, we can complete all surveying in one trip. In this process, we can complete all surveying in one shot, then process on OPUS, and then in PPK later. We will store data in our base (again, likely 90+ minutes), and we’ll also log data on our rover. We’ll collect GCPs as normal, which should be relatively accurate, but back in the office we can process that data with OPUS to obtain that coordinate and then process our GCPs against the new coordinate with our rover log and the result will be a globally accurate ground control point.

Relative Accuracy

There are plenty of cases where all you’ll need is relative accuracy. For example, if you’re completing stockpile volume calculations, it’s unnecessary to know the location of those piles in the world; you only need the accurate tonnage. Or if you’re on someone else’s jobsite where they have their own assumed coordinate system – not an actual coordinate system, you may need to localize it.

In order to localize an assumed coordinate system, you can use a program like FieldGenius, which will allow you to localize to any arbitrary or assumed local coordinate system.

Emlid Reach RS2 Capabilities

The RS2 is a reliable, accurate, and inexpensive tool to collect ground control points. We recently completed a study comparing the RS2 versus Topcon’s latest receiver, the Hyper VR. We knew where the trouble spots were located on the land in question as well as where older receivers weren’t ever able to obtain a fix. The study was done with the equipment side by side and we found both the VR and the RS2 were able to get a fix. In terms of results, the products were essentially identical, and the RS2 performed a little better across board.

Reach RS2 Specs

One of the reasons the RS2 was able to obtain comparable accuracy to the Hiper VR is we’re tracking all four global constellations. Some of the other specifications of the RS2 to highlight include the internal radio (up to a five-mile range), a long battery life, and it’s IP67 waterproof.

Customers Using Reach RS2

McSteen Land Surveyors – 17 RS2 Receivers

Campbell & Associates – 9 RS2 Receivers

Minnesota Department of Natural Resources – 30 RS2 Receivers

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