RTK, correction networks and working with a base

RTK (Real-Time Kinematic) is a method by which a GNSS receiver obtains its position with centimeter-level accuracy in real time. The idea is simple: the moving receiver (the rover) gets differential corrections from a fixed point, which compensate for some of the satellite signal errors. The practical question is where these corrections come from.

Two sources of corrections

• A network of permanent stations (CORS) over mobile internet, using the NTRIP protocol
• Your own base, which sends corrections to the rover by radio or over the internet

The two options do not exclude each other: many teams use the network as the main option and their own base in areas without coverage.

The correction network in Moldova

Moldova has the MOLDPOS correction network, operated by a state institution (INGEOCAD), with access by subscription. There are several subscription types with different rates. Rates and conditions may change, so clarify them directly with the operator. The same goes for the compatibility of your receiver: a receiver with a 4G module can in principle receive NTRIP corrections over mobile internet, but confirm the specific terms with the network operator.

The advantages of a network: you do not need to carry and set up a base, and the rover is ready as soon as it has internet. The limits: you depend on mobile coverage and on the availability of the service.

When you need your own base

Your own base is useful in several situations:

• you work in areas without stable mobile internet
• several rovers work on the site at the same time
• you want independence from an external provider
• you need corrections outside the network's coverage area

Models in the catalog: the MBase, with a 5 W radio and a range of up to 35 km according to the manufacturer, and the SuperBase, with two hot-swappable batteries. Real results depend on terrain, obstacles and the radio antenna. The M7 with a 5 W radio is described by the manufacturer as suitable for the base role too. All of them are in the Base stations section.

How to work with a base

The general principles are the same for any base:

• Set up the base in an open place with a good view of the sky, away from reflective surfaces and sources of interference
• The base coordinates must be correct: either a point with known coordinates or a carefully determined position. All points surveyed by the rover are referenced to it
• The rover and the base must use the same coordinate system and the same transmission settings
• Before work, check the result on a known control point

Checking the result

A practical tip: at the start of the season and when changing work site, survey a known control point and compare the coordinates. A large difference immediately shows a mistake in the base setup or the coordinate system, before the mistake spreads through the whole volume of work.

Radio or internet

Radio does not depend on mobile operators, but its range is limited by terrain and obstacles. Mobile internet gives practically unlimited range but depends on coverage. Receivers such as the M20L have both a built-in radio and 4G, and the MS80 uses dual RTK (NTRIP and a 2 W radio). For the use of radio frequencies we recommend checking the requirements that apply in Moldova.

What to choose

• You work mostly where there is internet and access to a network: a receiver with 4G and a network subscription
• You work in remote places or with several rovers: your own base with a radio
• You need both: a rover with radio and 4G plus a base

For help choosing a configuration (rover, base, controller) add the models to the quote cart or write to us on the Contacts page. See also the GNSS receivers section.