Explaining How RTK Positioning Works

Why High Precision is Achieved in Civil Engineering Surveying

In modern civil engineering surveying, satellite positioning technologies like GPS are indispensable. However, conventional GPS positioning can introduce errors of several meters or more, leaving challenges for precise surveying. This is where RTK positioning comes into play. RTK stands for Real Time Kinematic, an advanced technology capable of measuring positions with centimeter-level accuracy.

This article clearly explains what RTK positioning is, its mechanism and differences from GPS, and the benefits RTK brings to civil engineering surveying. Furthermore, it touches on the latest RTK technology, “LRTK,” and introduces how to request free materials.

1. What is RTK Positioning?

RTK positioning is a technology that dramatically improves positioning accuracy in real time by using two GNSS receivers: a base station and a rover.

• Base Station: Installed at a location with a known, precise position (coordinates)

• Rover: Installed at the location where positioning is desired

Both units simultaneously observe signals from GNSS satellites. By canceling out common positioning errors, they can calculate highly accurate position information in real time—accuracy unattainable with standard standalone positioning.

Commonly referred to as “RTK-GNSS positioning” or “interference positioning,” this technology originated in surveying. Today, it's widely used in applications like automated construction machinery control, agriculture, and drone surveying.

2. Differences Between Standard GPS Positioning and RTK Positioning

To understand the power of RTK positioning, let's first examine how it differs from standard GPS positioning (standalone GNSS positioning).

• Standard GPS: A single receiver receives signals from multiple satellites and calculates position → Various factors like atmospheric effects and satellite clock errors cause errors of about 5 to 10 meters

This is why your current location may appear off on smartphone map apps or car navigation systems.

In contrast, RTK positioning uses correction data from reference stations to cancel out these errors, enabling positioning accuracy within a few centimeters.

• RTK Accuracy Examples - Horizontal Position Error: Approximately 2–3 cm - Vertical Error: Approximately 3–4 cm

In other words, RTK offers significantly higher precision compared to conventional GPS.

Why RTK is Highly Accurate

• Relative Positioning and Correction Data are Key

• RTK is a type of “relative positioning” that determines position between a reference station and a rover station

• The reference station knows its precise position, so it calculates the positioning error (error factors) in real time from the satellite signals it receives

• This error information is sent to the rover station, which applies the correction values to its own measured position

• This cancels out the errors, yielding a highly accurate position

In this way, RTK, which uses reference station data to improve accuracy, can also be called “real-time differential positioning,” and the difference from conventional GPS is clear.

3. How RTK Achieves High Precision

Let's take a closer look at how RTK positioning achieves centimeter-level accuracy.

Keywords

• Carrier Phase Measurement

• Flow of Correction Data

Carrier Phase Measurement

• RTK performs positioning using the satellite signal's carrier wave in addition to standard code positioning (a method using the pseudorange code contained in the satellite signal).

• The L1 band carrier wave emitted by GPS satellites has an extremely short wavelength of approximately 19 cm.

• By precisely counting the phase of this wave (the position of wave crests and troughs), millimeter-level distance changes can be detected

Measurement Process

• The receiver continuously tracks the phase of the carrier wave received from satellites

• It measures “exactly how many wave lengths arrived (integer wave count)” and “how much arrived as a fractional remainder (decimal part)”

• Since the integer part of “how many wavelengths” is unknown using only the carrier wave, the position is first roughly determined via code positioning (with an error of several meters). From there, the integer number of carrier wave wavelengths is solved (resolving the integer bias).

• By comparing data from the reference station and the mobile station, periodic carrier wave shifts are canceled out, allowing the unknown integer part to be correctly estimated.

By utilizing the phase difference of the carrier wave in this manner, distance can be measured with accuracy down to the millimeter range, not just centimeters, resulting in highly precise position coordinates.

Exchange of Correction Data

• In RTK positioning, the base station and rover communicate in real-time, exchanging error correction information

• The rover applies the received correction data to its own calculated positioning results, obtaining a high-precision position with errors canceled out

• Think of it as subtracting the “error calculated by the base station” from the “rover's positioning value”

• This cancels out common error factors like atmospheric effects, satellite orbit errors, and clock errors, leaving only an error of a few centimeters

4. Benefits of Using RTK in Civil Engineering Surveying

Now that you understand the mechanism and high precision of RTK positioning, let's explain the practical benefits of using RTK in civil engineering surveying sites.

From large-scale projects by general contractors to small-to-medium civil works and infrastructure inspections like roads and railways, the benefits RTK brings to surveying operations are substantial.

Key Benefits of Using RTK

• Significantly Increased Survey Efficiency RTK enables rapid surveying of points across large areas in a short time. Where traditional methods required measuring each point individually with a total station or multiple personnel for positioning, RTK-GNSS allows you to simply walk with the receiver and continuously acquire point coordinates. This dramatically reduces work time, especially on sites with numerous measurement points like topographic surveys. Furthermore, RTK maintains accuracy even several kilometers away from the base station, reducing the need for frequent receiver relocation compared to total stations, especially on large construction sites or road surveys.

• Labor Savings (One-Person Surveying) With RTK surveying, a single operator can acquire point coordinates by operating the receiver mounted on a pole. In some cases, this allows one person to complete the entire survey. Even when setting up your own base station, it requires no manual intervention once fixed in place, as it automatically transmits data. Using a network RTK service (discussed later) eliminates the need for a physical base station altogether, offering the convenience of surveying with just one instrument. This leads to reduced staffing and labor savings, enabling efficient operations even on sites where skilled surveyors are scarce.

• Instant High-Precision Positioning As a real-time positioning system, RTK provides high-precision measurements on-site, enabling immediate checks and decisions. For example, you can instantly compare design drawings with actual positions on-site or verify the precise placement of structures during construction. Traditional static surveying methods required bringing data back for processing to achieve high accuracy, but RTK allows verification as you measure. This helps prevent rework and ensures quality.

• Applications Beyond Surveying (Construction DX) The advantage of obtaining high-precision positional information in real time extends beyond mere surveying tasks. For example, attaching a GNSS receiver to heavy machinery and managing the height of the blade (dozer blade) with RTK enables earthwork with centimeter-level accuracy, eliminating reliance on the operator's intuition. Overseas case studies report examples where two RTK receivers mounted on a bulldozer's blade automatically controlled excavation and embankment work, leveling the ground with millimeter-level precision.

Within the civil engineering industry's initiatives like i-Construction and ICT Construction, RTK has become a key technology. Its applications are expanding, including labor-saving formwork management and automated operation of heavy machinery.

Summary RTK positioning brings three key advantages to civil engineering surveying: speed, ease, and high accuracy. The traditional measurement error of several meters has now shrunk to just a few centimeters, fundamentally transforming the way field surveying is conducted. This truly represents a revolution in civil engineering surveying enabled by RTK.

5. Even Easier and More Accurate with the Latest RTK Technology: “LRTK”

To maximize the benefits of RTK positioning, having field-friendly equipment is crucial. Recently, devices and services have emerged to make RTK positioning more accessible. A prime example is the latest technology called “LRTK”.

What is LRTK?

• Developed by Refixia Inc., a Tokyo Institute of Technology spin-off

• A solution consisting of a pocket-sized high-precision GNSS terminal and its companion app

• The “LRTK Phone” is particularly notable as an RTK receiver that attaches directly to smartphones - Simply attach it to the back of your smartphone (Android or iPhone) to enable satellite-based RTK positioning - Instantly acquires centimeter-level positioning data by launching the dedicated app - Features built-in antenna and battery, eliminating the cumbersome setup of traditional stationary GNSS receivers - A groundbreaking device that truly turns “your smartphone into a surveying instrument”

LRTK Use Cases & Features

• Makes RTK positioning, previously requiring specialized surveying equipment, dramatically more accessible

• Example: Tagging photos taken with a smartphone during concrete structure crack inspections with precise location coordinates and storing them in the cloud

• Enables one-touch collection of location-tagged data for disaster site documentation, infrastructure inspection photo management, and more

• Accelerates field DX (Digital Transformation)

• LRTK also supports the Centimeter-Level Augmentation Service (CLAS) provided by Japan's Quasi-Zenith Satellite “Michibiki” - Maintains high-precision positioning even in areas with poor internet connectivity using satellite augmentation signals

• Compact and lightweight equipment - Enables unique applications like attaching to helmets to track worker locations, not just dedicated poles