Revolutionizing GNSS Positioning with Network RTK: Centimeter-Level Accuracy (half-inch accuracy) Anywhere Nationwide Using Correction Services

GNSS (Global Navigation Satellite System) positioning is an indispensable technology in our daily lives. The ability of car navigation systems and smartphone map apps to show your location in near real time is thanks to GNSS satellites such as GPS. However, the conventional wisdom has been that standalone GNSS positioning yields accuracy on the order of several meters, which is insufficient for the "centimeter-level accuracy (half-inch accuracy)" required in construction sites and civil surveying. Traditionally, achieving centimeter-level precision required long static observations or RTK surveying that involved installing base stations (reference points) on site—procedures that were time-consuming and labor-intensive.

In recent years, however, the emergence of network RTK technology has dramatically overturned this conventional wisdom. By utilizing correction information services (GNSS correction services) delivered from nationwide continuous GNSS reference networks such as electronic reference stations, it has become possible for a rover (mobile receiver) alone to perform real-time centimeter-level positioning without setting up a dedicated base station. In an era when stable, high-precision positioning is required nationwide, the spread of network RTK brings immeasurable benefits to surveying and construction sites. This article begins with the basics of GNSS positioning and the limitations of conventional technologies, then explains the differences between RTK and network RTK, the background that enables nationwide centimeter-level accuracy (half-inch accuracy), the advantages of not needing a base station, and practical cases of field deployment. Finally, it introduces future developments such as simple RTK positioning using smartphones and integration with AR technologies.

How GNSS Positioning Works and the Limits of Conventional Techniques

First, let’s briefly review how GNSS-based positioning works. GNSS satellites, represented by GPS, broadcast their orbit positions and time information via radio signals to receivers on the ground. A receiver (positioning device) obtains signals from multiple satellites and calculates the distance to each satellite to determine its current position. This principle is based on trilateration, and in theory, if signals from four or more satellites are received, a position on Earth can be determined.

However, satellite positioning involves various sources of error. For example, signal delays through the ionosphere and troposphere, slight errors in satellite clocks and orbit information, and multipath (signal reflections) near the receiver accumulate and cause standalone GNSS positioning to have errors on the order of several meters. In urban areas and mountainous regions, signal blockage by buildings and terrain further degrades positioning accuracy and stability. Therefore, it has been conventional practice that, for precision-demanding surveying, raw standalone GNSS results are difficult to use as-is, and differential positioning using known points and careful observations were indispensable.

Classic methods for achieving high precision include static surveying (observing from a stationary receiver for tens of minutes to hours and removing errors through post-processing) and RTK-GPS surveying, which installs known-coordinate reference points on site and sends real-time correction information. In real-time kinematic (RTK) surveying, a reference receiver (base) is placed on a known point and measurement data of satellite signals are exchanged with a rover via communication to cancel errors and achieve relative high-precision positioning. This enables centimeter-level positioning in real time within a few km to more than ten kilometers from the base. However, conventional RTK surveying also had several constraints.

One such constraint is the baseline distance. In single-base RTK, the further the distance between the base and rover, the larger the error due to differences in ionospheric and tropospheric effects, reducing accuracy. Practically, it is difficult to maintain centimeter-level accuracy unless the base is within about 10 km, and covering wide areas required repeatedly relocating the base or establishing new known points. The effort of installing and dismantling a base station for each site was also a major burden. Preparing high-precision GNSS equipment, power supplies, and communications for the base, and tying the base location rigorously to known coordinates (coordinate determination) were necessary. Typically, surveying teams required at least two people—one to manage the base and another to operate the rover—incurring personnel and time costs. Moreover, although GNSS surveying does not require direct line-of-sight like optical surveying (total stations, etc.), positioning can be difficult in places with extremely poor satellite signal reception such as directly under dense canopy or in canyons, in which case alternative methods had to be used.

Differences and Mechanisms of RTK and Network RTK

So what distinguishes conventional RTK from network RTK? The basic positioning principle—using carrier-phase differential techniques of GNSS to improve precision—is the same, but the decisive difference is that the reference station providing correction information is not a single station but a "network."

In network RTK, observation data from numerous reference stations deployed nationwide, including electronic reference stations maintained by the Geospatial Information Authority of Japan, are integrated to generate local error information in real time. The user (rover) sends an approximate position via a communication link, and the network calculates and returns information for a Virtual Reference Station (VRS) near the user. In other words, users receive correction data equivalent to having a reference station right next to them, eliminating the accuracy degradation due to distance from a base in conventional setups.

The mechanism of network RTK can be summarized as follows:

• Multiple reference stations for wide-area error correction: The reference station network models atmospheric errors and satellite orbit errors over a wide area and generates surface-like correction information. Errors that a single station could not fully correct at long distances can be covered by the network.

• Generation of a Virtual Reference Station (VRS): The network computes correction values near the user’s position in real time and distributes correction data that make it appear as if a reference station exists at that location. The rover receiver simply treats this data as ordinary RTK base data to obtain high-precision solutions.

• Use of communication infrastructure: Traditionally, base-to-rover connections used radio communications (low-power radio or UHF, etc.), but network RTK mainly relies on internet-based data distribution (Ntrip protocol, etc.). With the development of mobile networks, connecting from the field to the correction service is sufficient for positioning, eliminating the need for dedicated radio setup.

As described above, network RTK is a concept of "sharing an extensive preexisting reference station network instead of placing your own base." Consequently, high-precision positioning can be completed with a single GNSS receiver, bringing significant operational advantages over traditional methods.

Background That Enables Centimeter-Level Accuracy (half-inch accuracy) Nationwide

The reason network RTK can achieve centimeter-level accuracy (half-inch accuracy) "anywhere nationwide" lies in Japan’s extensive reference point infrastructure and the correction information services that leverage it. The Geospatial Information Authority of Japan operates approximately 1,300 electronic reference stations nationwide, roughly at 20 km intervals, and this dense observation network makes high-precision positioning coverage available across the country. Electronic reference stations themselves are national reference points, equipped with high-sensitivity antennas mounted on about 5 m (16.4 ft) pillars that collect satellite data 24 hours a day. Observational data from this network (commonly called "GEONET") are distributed in real time via the government GPS correction information system and private GNSS correction service providers, forming the basis for network RTK positioning.

Correction information services, which are key to network RTK, employ a variety of methods beyond the VRS approach mentioned earlier. Techniques such as the FKP method (generating spatial correction information from multiple reference station data) and the MAC method (distributing a grid model between reference stations) are used by service providers to supply wide-area corrections optimized for their systems. The common idea is to minimize the amount of data required by the user terminal while embedding wide-area error correction effects into the delivered data. From the user’s perspective, regardless of the underlying method, connecting to the specified correction service yields data from a virtual reference station near them and enables immediate high-precision positioning.

In Japan, the ubiquitous development of mobile communication infrastructure is another crucial factor supporting "anywhere nationwide." Because correction data can be received over mobile networks such as 3G/LTE/5G, network RTK can be used not only in urban areas but also at mountainous construction sites and on remote islands—as long as the site is within communication coverage (electronic reference stations have indeed been installed on several major remote islands). Conversely, in areas outside communication coverage, network RTK is not usable—just as conventional RTK radio cannot reach—but solutions to this problem are emerging. For example, the Quasi-Zenith Satellite System (QZSS, "Michibiki") provides the Centimeter-Level Augmentation Service (CLAS), which allows users to receive correction information directly from satellites without relying on communication, enabling high-precision positioning even in deep mountain areas. Although not a form of network RTK, such satellite augmentation combined with network RTK makes truly location-agnostic centimeter positioning more realistic.

Advantages of No Base Station and Contribution to Immediate Positioning and Efficiency

The greatest advantage that network RTK brings to the field is, above all, the simplicity of "no required base station." Let’s outline the concrete benefits this brings.

• One-person operation surveying: Conventional RTK surveying required at least two people—one to manage the base and another to operate the rover—but with network RTK, a single person carrying a GNSS receiver (rover) can complete the survey. In an age of severe labor shortages, the significance of single-person surveying is substantial and directly contributes to workforce reduction at worksites.

• Drastically reduced setup time: Because no base needs to be established, on-site equipment setup time is nearly zero. Turn on the receiver, connect to a correction service, and after tens of seconds to several minutes of initial convergence, surveying can begin. Observation per point can be completed in on the order of a few seconds, enabling rapid measurement of a large number of points.

• Support for long-distance and wide-area surveying: As noted earlier, network RTK is nearly free from concerns about baseline-length-induced accuracy degradation. Therefore, for large sites or long linear surveys, high-precision continuous positioning is possible simply by moving while receiving correction data. Line-of-sight between measurement points is unnecessary, so points across a valley or behind forest cover can be measured as long as GNSS signals are receivable.

• Stable accuracy and consistency in the geodetic system: Correction information is provided based on the national coordinate system, so obtained coordinates always have absolute accuracy consistent with the Japanese Geodetic Datum (JGD). Unlike methods that require frequently installing base stations, measured data are always obtained in a common coordinate system, reducing the need for consistency checks and coordinate transformations in subsequent work. This also reduces daily variability due to reference point errors over multiple surveying days, making stable precision management possible.

• Reduced equipment and operational costs: Eliminating the need for base receivers and high-performance radios reduces initial investment and equipment management costs. It also reduces risk factors for equipment failure and lessens on-site management burdens (while subscription fees for correction services are needed, the overall cost-effectiveness often favors network RTK).

Thus, network RTK has brought a revolutionary improvement in efficiency and labor saving. It is easy to handle even by non-experts, and because positioning results are available in real time on site, the PDCA cycle from surveying to design and construction can be accelerated. Tasks that were cumbersome with traditional methods—such as as-built management and verification—benefit from immediate coordinate confirmation on site, helping to prevent rework and ensure quality.

Field Deployment Examples in Mountainous and Rural Areas: Practicality Anywhere

High-precision positioning with network RTK demonstrates its strengths not only in urban areas but also at mountain and rural sites. For example, at dam construction sites in mountainous terrain, surveying in valleys used to be a challenge. Total station surveys required securing line-of-sight over ridgelines or sending survey staff down to the valley floor for round trips. However, with network RTK, as long as the sky is open even on the valley floor, positions can be obtained directly from satellites overhead. Even in complex terrain, you can simply carry the rover to the point you want to measure and determine coordinates on the spot without worrying about line-of-sight.

Network RTK is also valuable in rural roadworks and farmland improvement projects. In depopulated areas, there are often few established survey control points nearby, but network RTK can deliver centimeter-level accuracy (half-inch accuracy) even from electronic reference stations tens of kilometers away, eliminating the need to establish new control points. Operations such as a single worker carrying the surveying instrument across dispersed sites and efficiently obtaining coordinates become practical. A surveying company reported substantial reductions in work time for mountain forest road route surveying by leveraging the advantages of "no line-of-sight required and one-person operation."

Network RTK use is not limited to ground surveying. Recently, RTK-equipped drones have been used in aerial surveying to improve geolocation accuracy of aerial imagery and omit ground control points (GCPs). For instance, using network RTK-capable drones to rapidly create accurate terrain models from the air at landslide sites in mountainous areas is becoming common. Furthermore, high-precision position information from network RTK is being used for machine guidance and machine control of construction equipment, supporting automated construction in rural sites that lack skilled operators.

In this way, network RTK’s advantage of "high precision regardless of location" is being realized in practical applications across the country. As long as communication coverage exists, almost the same operations can be conducted in mountains and on remote islands, enabling consistent surveying quality across regions. Even when mobile signals are unavailable and network RTK cannot be used, sites have adapted by temporarily switching to static surveying or utilizing satellite augmentation (CLAS) as noted above, allowing them to continue reaping the benefits of GNSS surveying. Creative on-site solutions maximize the advantages of network RTK.

The Future: RTK Positioning on Smartphones and AR Integration

Lowering the barrier to GNSS positioning via network RTK has opened up new application possibilities, such as simple RTK positioning with smartphones and integration with AR (augmented reality). Recently, solutions that attach compact RTK-capable antennas to smartphones to enable centimeter-level positioning—such as systems known as LRTK—have appeared. These devices can also receive QZSS Michibiki’s CLAS signals, allowing a smartphone alone to obtain correction information and achieve high-precision positioning. It is becoming realistic to tag photos taken on site with accurate coordinates automatically or perform point cloud scans while holding a smartphone.

Another noteworthy possibility is combining RTK’s high-precision position information with AR technology. For example, you could overlay a 3D model of a future structure onto the real landscape via a smartphone screen, or visualize buried pipelines through the ground. Traditional AR has struggled with alignment precision, but using precise coordinates from RTK allows digital information and the real world to align nearly perfectly. This enables intuitive design verification and as-built inspection on surveying sites, facilitating consensus building and error prevention.

If the convenient pairing of smartphones and RTK becomes widespread, the use cases for surveying and location information will expand further. Centimeter-level positioning, which once required specialized equipment, could become a tool available to anyone, accelerating on-site digital transformation (DX). The changed assumptions of GNSS positioning brought by network RTK are now permeating our everyday smart devices as the next stage. Civil surveyors and construction engineers should continue to watch the evolution of high-precision GNSS technologies. With network RTK as the new standard, an era is approaching in which anyone, anywhere nationwide can ensure positioning accuracy.