RTK GNSS and GPS Comparison: Meter-level vs Centimeter-level (half-inch accuracy) – High-precision Positioning Achieved by LRTK

Table of Contents

• Differences between GNSS and GPS

• Characteristics of GPS standalone positioning accuracy (meter-level)

• What is RTK positioning? The mechanism for achieving centimeter-level (half-inch accuracy) accuracy

• What is the difference between meter-level and centimeter-level?

• Why high-precision positioning is required in surveying and construction

• Challenges of conventional RTK positioning

• High-precision positioning realized by LRTK

• What is simplified surveying with LRTK?

• FAQ (Frequently Asked Questions)

Differences between GNSS and GPS

First, let’s clarify the meanings of the terms GNSS and GPS. GNSS stands for “Global Navigation Satellite System” and refers to satellite systems in general used to determine positions on Earth. Systems operated by various countries and regions—such as the US GPS, Russia’s GLONASS, Europe’s Galileo, and China’s BeiDou—are collectively referred to as GNSS. GPS (Global Positioning System), on the other hand, is the name of the satellite positioning system operated by the United States and is one component of GNSS. In Japan, the term “GPS” is often used informally to refer to satellite positioning in general, but strictly speaking GPS is only one part of GNSS.

In satellite positioning, signals from multiple navigation satellites overhead are received, and distances are measured to compute the receiver’s coordinates. A GNSS receiver (GPS receiver) derives its latitude, longitude, and altitude by capturing signals from at least four satellites. Because navigation satellite signals can be received anywhere on Earth, a key advantage of GNSS/GPS is that positional information can be obtained without special infrastructure. However, it is also known that there are limits to the positional accuracy when measuring directly from satellites. The next section explains the typical accuracy of GPS standalone positioning and the sources of its errors.

Characteristics of GPS standalone positioning accuracy (meter-level)

Positioning using ordinary GPS (standalone positioning) yields what is called meter-level accuracy. This means errors are on the order of several meters. In practice, position information obtained from simple GPS receivers built into smartphones or consumer car navigation systems is known to deviate by an average of about 5〜10 m (16.4〜32.8 ft). For example, when you use GPS on a road, the displayed position may sometimes appear to be in the adjacent lane or on the sidewalk. However, for casual use such as route guidance in map apps, this degree of deviation is usually not a practical problem, so meter-level accuracy suffices for everyday use.

So why does standalone GPS positioning produce errors of several meters? Major error sources include the following:

• Satellite and receiver clock errors: slight discrepancies in satellite atomic clocks or errors in the receiver clock affect distance measurements and cause positional offsets.

• Signal delays in the atmosphere: as radio waves pass through the ionosphere and troposphere they are refracted or slowed, introducing errors into distance measurements.

• Multipath: when satellite signals reflect off buildings or the ground and arrive by longer paths, measured distances become artificially long, causing errors.

• Satellite geometry: if the distribution of satellites overhead is uneven, the dilution of precision (DOP) increases and accuracy decreases.

Because these factors combine, standalone GNSS positioning inevitably incurs errors on the order of meters. As described above, ordinary GPS positioning is convenient and does not require infrastructure, but its accuracy is subject to meter-level deviations. A positional uncertainty of several meters means, for example, that a location shown on a map might be several steps away from the actual point. While acceptable for everyday use, this level of error is not tolerable in surveying or construction. That is why more precise positioning—namely centimeter-level (half-inch accuracy) high-precision positioning—is required.

What is RTK positioning? The mechanism for achieving centimeter-level (half-inch accuracy)

A representative technology that realizes centimeter-level (half-inch accuracy) positioning is RTK positioning. RTK stands for Real Time Kinematic and refers to a positioning method that applies corrections to GNSS observation data to achieve high precision in real time. RTK uses at least two GNSS receivers: one is a base station installed at a known, precise coordinate (the reference station or base), and the other is a rover that moves and observes at the point to be positioned. Because the base station knows its true position, it can calculate the difference between its measured GPS position and its true position to determine the instantaneous positioning error. The base station then transmits that error amount (correction data) to the rover via radio or the Internet, and the rover applies the correction to its own measured position. This cancels many error sources and dramatically improves positional accuracy. It’s helpful to think of it as “using two receivers instead of one to cancel out errors.”

By using RTK corrections, horizontal positions can be accurate to a few centimeters and vertical positions to a few centimeters to a few tens of centimeters. In practice, when the base and rover are close to each other, planar accuracy of 2〜3 cm (0.8〜1.2 in) and height accuracy under 5 cm (≤2.0 in) have been reported. Furthermore, with network RTK services that utilize government and commercial reference station networks, centimeter-level accuracy (for example, planar accuracy on the order of 3〜5 cm (1.2〜2.0 in)) can sometimes be achieved even when the base stations are tens of km away. In this way, RTK’s major advantage is that it can raise GNSS positioning accuracy from meters down to centimeters.

What is the difference between meter-level and centimeter-level?

What practical differences exist between meter-level accuracy from standalone positioning and centimeter-level accuracy using RTK? First, the magnitude of positional deviation is orders of magnitude different. When errors are several meters, recorded coordinates on-site may be significantly displaced from the intended point. For example, a 5-meter deviation on a small lot could place a recorded boundary outside the property, or a building position could end up in the neighboring parcel. Conversely, if errors are confined to a few centimeters, the target point can be measured almost pinpoint, with only minimal deviation from a mark on the ground—an error range that is practically negligible.

Next, the required equipment and effort differ greatly. Meter-level GPS positioning can be performed immediately with just a receiver (a smartphone or handheld GNSS device). No additional equipment or complex setup is required, making it accessible to anyone. On the other hand, achieving centimeter-level RTK positioning requires the two devices described above: a base station and a rover. If you install your own base station, you need a tripod or mounting equipment, power supply, radios, and other gear. Even when using public or private reference station network services, you must ensure a communication environment to receive correction data over the Internet. In short, attaining centimeter-level positioning has traditionally involved higher barriers in both equipment and operation compared to standalone positioning.

The difference in cost is also significant. Using GPS on a typical smartphone involves no extra cost, but high-precision surveying instruments and GNSS receivers are expensive, and RTK operation has traditionally required substantial budgets. RTK surveying has often required two or more personnel (for example, one person handling the rover and another managing the base station). For these reasons, centimeter-level positioning has historically been a specialized method performed by professional surveyors with costly equipment.

Why high-precision positioning is required in surveying and construction

Why is centimeter-level accuracy required on surveying and construction sites? One reason is the need for accuracy in work. In civil engineering, structures must be positioned according to design drawings and land elevations must be adjusted precisely; meter-level deviations can cause serious errors. For instance, if the foundation location of a building is off by even one meter, construction defects may result, affecting safety and quality. Centimeter-level positioning allows construction positions to be set almost exactly relative to design reference points, ensuring accuracy.

There is also the aspect of operational efficiency. With high-precision GNSS positioning, tasks that were previously done manually—such as setting out reference lines or checking as-built shapes—can be automated or streamlined. ICT civil engineering technologies such as machine guidance and machine control equip construction machines with GNSS for excavation and grading, where centimeter-level positioning is indispensable. High-precision location data also benefits infrastructure inspection: if you record crack locations or equipment positions with centimeter-level accuracy, you can precisely identify the same spot in subsequent inspections. High-precision positioning data play an important role in tracking changes over time.

As described above, in civil engineering, construction, and infrastructure management, meter-level accuracy is often insufficient and centimeter-level accuracy is required. However, as previously noted, high-precision positioning has traditionally been difficult to use casually. The next section introduces LRTK, a solution that overcomes many RTK challenges and enables simple on-site operation.

Challenges of conventional RTK positioning

Although RTK positioning achieves high precision, its practical operation has involved several challenges. Here are the main hurdles pointed out in conventional RTK operations:

• Equipment is bulky and difficult to transport to sites: In addition to high-performance GNSS receivers and specialized antennas, tripods, external batteries, radios, and communication modems must be prepared and transported.

• Securing a reference station is necessary: If you install your own base station, you need an accurate known point (such as a public reference station or an existing survey mark) and the effort to set up equipment there. Even when using public or commercial reference station services (e.g., the Geospatial Information Authority of Japan’s reference station network or private correction services), agreements and configuration are required.

• Dependence on communication environments: For a rover to receive correction information, stable radio or Internet connectivity is required. In mountainous areas or places out of coverage, it may be impossible to obtain real-time correction data, preventing RTK positioning.

• Range limitations: RTK accuracy depends on the distance between the base and rover. Generally, when they are within a few km of each other, many error sources are common and high accuracy is achieved, but accuracy degrades as distance increases. Covering wide areas therefore requires multiple base stations, mobile bases, or utilization of network RTK.

• Cost and operational burden: High-precision surveying equipment and receivers are costly, requiring significant investment. Transporting and installing equipment and the need for two or more operators have made RTK challenging for small sites or frequent measurements.

Because of these factors, RTK-based high-precision positioning was long seen as something that required well-equipped teams, sufficient budgets, and experts to execute. Recently, however, new technologies have emerged to eliminate these challenges and enable anyone to use centimeter-level positioning easily. This solution is called LRTK.

High-precision positioning realized by LRTK

LRTK is a modern GNSS solution developed to maintain RTK accuracy while greatly reducing equipment and operational burdens. In short, it is a “simplified RTK positioning system usable with a smartphone,” enabling centimeter-level (half-inch accuracy) positioning without specialized surveying instruments. The major difference from conventional systems is that required equipment is extremely compact and simple. The basic configuration of an LRTK system is a pocket-sized high-precision GNSS receiver (LRTK device) and a dedicated smartphone app. Heavy tripods, mounting gear, and large batteries are unnecessary: you can start high-precision positioning simply by taking a small receiver and your smartphone to the site.

Main features of LRTK include:

• Positioning with just a smartphone: No dedicated controller terminals or bulky base station apparatus are required—centimeter-level (half-inch accuracy) positioning can be started on site with only a smartphone and an LRTK device.

• Compact, lightweight, and highly portable: The receiver is pocket-sized, weighs only several hundred grams, and runs continuously on its internal battery for about 12 hours, so it is not a burden to carry all day.

• Easy setup with wireless connection: The device connects to the smartphone via Bluetooth or Wi‑Fi, eliminating cable wiring. Turn on the power and start the app to begin positioning immediately.

• Intuitive app operation: The smartphone app enables one-touch start/stop of positioning and data saving. Measured points are automatically transformed into the specified coordinate system, allowing accurate position handling without specialized knowledge.

• Robust and flexible operation: Dustproof and waterproof specifications allow use in rainy field conditions. If attached to an included pole (monopod), it can be set down for measurements like conventional surveying instruments, enabling flexible operational styles.

LRTK’s usability is matched by advanced GNSS technology inside the device. Its technical features include:

• Multi-GNSS support: It receives signals not only from GPS but also from GLONASS, Galileo, BeiDou, and QZSS (Michibiki), providing abundant satellites and geometries for stable positioning even in urban and mountainous areas.

• Dual-frequency support: By using multiple frequencies such as L1 and L5, frequency-dependent errors like ionospheric delays can be mitigated. This enables faster and more reliable high-precision positioning than single-frequency receivers, particularly helping to maintain vertical accuracy.

• Support for satellite augmentation signals (CLAS): It can receive CLAS, the centimeter-class augmentation service broadcast by Japan’s quasi-zenith satellite Michibiki. Even in areas without cellular coverage, correction information can be obtained directly from satellites to continue centimeter-level (half-inch accuracy) positioning.

• Use of high-precision correction data: It can ingest precise correction information provided in real time from networks such as the Geospatial Information Authority of Japan’s reference station network.

By combining these technologies, LRTK’s strength is the ability to maintain centimeter-level (half-inch accuracy) positioning stably anywhere in Japan.

Overall, LRTK realizes “centimeter-level (half-inch accuracy) positioning that anyone can use anywhere easily.” High-precision positioning that previously required contracting specialists can now be performed by on-site personnel themselves, reducing work costs and time. The following section provides examples of what can be done on-site with LRTK.

What is simplified surveying with LRTK?

By leveraging LRTK, surveying tasks that previously required heavy equipment and specialist skills can be performed simply. For example, a local government adopted LRTK for disaster recovery sites so that a single staff member could quickly perform surveying of damaged areas. With only a smartphone and a small GNSS receiver, high-precision, geotagged photos and on-site terrain surveys can be completed immediately, speeding up recovery decisions and reporting. In civil construction, LRTK can display design data on a smartphone and visualize stakeout positions with AR (augmented reality) while work proceeds. This can eliminate stages where surveyors used to mark out locations, allowing site workers to directly confirm and construct at the correct positions.

In this way, LRTK-based simplified surveying achieves both improved productivity and maintained accuracy on site. Because it does not require special tools or advanced skills, it is easy for infrastructure inspection and maintenance personnel, as well as small to medium construction firms, to adopt. Making high-precision position information available in everyday operations will make handling surveying data more accessible. LRTK answers the need to make centimeter-level (half-inch accuracy) positioning easier to achieve.

Finally, here are frequently asked questions and answers about RTK and LRTK.

FAQ (Frequently Asked Questions)

Q: What is the difference between RTK and regular GPS positioning? A: Regular GPS positioning (standalone) computes position using only satellite signals and therefore produces errors of several meters. RTK positioning uses correction information from a base station to cancel errors, enabling extremely high accuracy on the order of a few centimeters.

Q: How should the terms GNSS and GPS be distinguished? A: GNSS is a general term that includes GPS as well as other satellite positioning systems. GPS is the US satellite positioning system; in Japan people often call satellite positioning “GPS” because it is familiar, but strictly speaking GPS is one type of GNSS alongside GLONASS and Galileo, among others.

Q: When you say centimeter-level (half-inch accuracy), how large are the actual errors? A: Under favorable conditions, RTK can provide planar errors of 2〜3 cm (0.8〜1.2 in) and vertical errors under 5 cm (≤2.0 in). Accuracy varies with site conditions, but it is at least far smaller than meter-level deviations.

Q: What equipment and environment are needed to use RTK? A: Basically you need high-precision GNSS receivers and a reference station (or a reference station service) that provides correction information. If you operate it yourself, prepare both base and rover equipment. However, solutions like LRTK enable RTK positioning with just a smartphone and a small receiver. In locations without communication coverage, one option is to use Michibiki (QZSS) satellite augmentation signals.

Q: What benefits come from introducing high-precision GNSS on-site? A: Surveying and construction management efficiency improves dramatically. Tasks like setting out reference lines and marking can be shortened and personnel reduced. As‑built verification can be performed instantly and accurately, preventing rework and mistakes. Accumulated high-precision data are also useful for future maintenance planning and verification. Improved accuracy directly translates to improved quality and productivity.