RTK GPS - When You Need Centimetre-Level Accuracy

Standard GPS in your phone shows your location with 5-10 metres error. Fine for walking around. Try planting a field or marking out a construction site with that though. RTK GPS solves the problem and delivers 1-2 centimetre accuracy.

What RTK is and why you need it

RTK stands for Real-Time Kinematic. In simple terms - it's GPS on steroids. The system has two parts: a base station and a receiver (also called a rover).

The base sits at a point with known coordinates. It receives signals from satellites and calculates how much they're off. These corrections get sent to your receiver via internet or radio. And just like that, instead of 5 metres error you've got 2 centimetres.

Why regular GPS isn't accurate

The signal from a satellite travels through the atmosphere. There it gets delayed, reflected, distorted. Plus the satellites themselves don't fly perfectly along their orbits either. All this creates error.

RTK compares what arrived at the base (where coordinates are precisely known) with what should have arrived. It sends the difference to your receiver. The receiver accounts for the correction and outputs accurate coordinates.

How accurate is it really

If the base is nearby (up to 10 km), horizontal accuracy works out to 8 mm plus 1 mm per kilometre. Vertical is slightly worse - 15 mm plus 1 mm/km.

Say you're working 5 km from the base. Error will be 8 + 5 = 13 mm horizontally. That's just over a centimetre. For most tasks that's plenty.

There's also network RTK. Instead of one base, there's a whole network of stations. They cover a large area and provide corrections via internet subscription. Accuracy is the same or even better.

Where it's used

Surveying

Land surveyors hardly carry heavy theodolites anymore. RTK receiver on a pole - and in a minute you've got a point with centimetre accuracy. Property boundaries, topographic surveys, setting out - all done with RTK.

Agriculture

This is where RTK delivers real savings. A tractor with autopilot drives straight, no overlaps. Seeds aren't sown twice in the same spot, fertiliser isn't wasted. Farmers report 10-15% savings on materials.

Plus you can work at night or in fog. The system guides the tractor, the driver just monitors.

Construction

An excavator with RTK digs the foundation pit exactly to plan. No need to constantly call a surveyor with a staff. The operator sees on screen how much more to dig and where to move the bucket.

On road works this is especially critical. Five centimetres error over a kilometre of road - that's already a drainage problem.

Other applications

RTK goes on drones for precision agriculture and mapping. Researchers use it for monitoring landslides and glacier movement. Autonomous vehicles also need this accuracy for navigation.

How to choose equipment

Receivers come in single and dual frequency. Dual frequency costs more but locks onto RTK faster and works better near buildings. They receive GPS, GLONASS, Galileo, BeiDou - the more satellites visible, the better.

There are classic surveying receivers - large, on a tripod, with a controller. There are compact ones for drones - weighing about 200 grammes. There are modules for embedding into machinery.

Own base or subscription

If you're working on one site - get your own base. Buy once and work. A base costs from $1000 for a basic one to $10000 for professional.

If you move between different sites - network RTK is more convenient. You pay $30-100 monthly for access, but don't need to haul the base around and set it up each time. These systems work through NTRIP protocol and only need internet.

What you need to work

First, open sky. Trees, buildings, canopies - all interfere. The antenna needs to see as many satellites as possible.

Second, connection to the base or internet. Without corrections the receiver works like regular GPS. Some models can store data and post-process it later, but that's not RTK anymore.

Third, correct settings. NTRIP server, port, mount point - one mistake and the system won't work. Though modern receivers are fairly simple to set up.

What it costs

A basic single-frequency receiver - from $500. Professional dual-frequency - $3000 to $15000. Your own base - from $1000. Network RTK subscription - $30-100 per month.

For agriculture there are budget solutions based on modules like ZED-F9P. They cost $200-300 but require self-assembly and configuration.

Real limitations

RTK doesn't work in forests under dense tree canopy. Works poorly in cities between tall buildings - signals reflect and get distorted.

Distance to base matters. Beyond 20 km accuracy drops. For large sites you need either network RTK or several bases.

Magnetic storms can degrade signal quality. It's rare but happens.

Practical tips

Always check work on control points. Measure the same spot several times - coordinates should match to the centimetre.

Keep the antenna level. A 5 degree tilt with 2 metre pole height gives 17 cm horizontal error.

Watch the solution status. "Float" is bad, accuracy is metre-level. "Fixed" is good, RTK is working. If it's constantly float, look for problems in settings or connection.

Bottom line

RTK made centimetre accuracy accessible. 15 years ago the equipment cost as much as a car. Now - as much as a decent laptop.

The technology works, it's proven, it's reliable. If your work requires better than 10-20 cm accuracy - you need RTK. If you can live with a metre error - no point overpaying.