The required “positional accuracy” in construction sites and surveying work directly affects project quality and safety. However, conventional GPS (GNSS) positioning can have errors of several meters (several ft), making it inadequate for tasks that require precise alignment. For example, setting out structures in civil engineering or detecting minute displacements in infrastructure inspections demand accuracy not of several meters but of a few centimeters or less (a few in or less). Ensuring and managing that level of accuracy has traditionally required significant effort and expertise. On site, it was necessary to re-measure reference points repeatedly to check errors, and on small sites it was sometimes unavoidable to rely on specialist surveyors.

In recent years, a technology attracting attention for solving this problem is real-time high-precision positioning using network RTK. RTK (Real Time Kinematic) is a method that uses two GNSS receivers—one mobile and one reference—to cancel out errors and dramatically improve positioning accuracy in real time. In particular, network RTK lets users receive correction information from a network of reference stations in the area, making it possible to achieve centimeter-level accuracy (half-inch accuracy) without deploying a local base station. This article explains how network RTK works and its effects, and explores how real-time corrections make accuracy management much easier.

Why Centimeter-Level Accuracy Is Necessary

There are many situations beyond map apps where meter-level errors become a problem. In construction, for example, strict control of positioning and elevation is required to build structures according to design drawings. Large surveying errors in road or bridge construction can result in finished structures being misaligned, leading to reduced quality or safety issues. In infrastructure maintenance, monitoring ground subsidence or measuring displacements of bridge piers sometimes requires detecting differences of a few centimeters. In sites that require this centimeter-level accuracy (half-inch accuracy), ordinary single-receiver positioning (one GNSS receiver alone) is inadequate, and high-precision positioning methods are indispensable.

Traditionally, achieving precise positioning required combining optical survey instruments like total stations and leveling surveys for elevation measurements. These methods demand on-site equipment setup and manpower, and are inefficient for covering wide areas. Recently, enhancements from the Quasi-Zenith Satellite “Michibiki”—sub-meter and decimeter class correction signals (SBAS/PPP)—have improved smartphone GPS accuracy, but errors remain on the order of several tens of centimeters. For applications such as structure positioning and displacement detection, a positioning technology that can still provide real-time accuracy on the order of a few centimeters (half-inch accuracy) has continued to be required.

High-Precision Positioning Achieved by RTK Real-Time Corrections

RTK GNSS positioning has emerged to meet this need. In RTK positioning, a reference station (a receiver with a known accurate coordinate) and a rover (the receiver at the point to be measured) are operated simultaneously; the difference between the satellite signals received by the two allows real-time calculation of the error components. The reference station continuously computes the difference between its known accurate position and the satellite measurements and transmits that positioning error information to the rover. The rover uses the received correction information to correct its own measurements, reducing errors that were several meters with standalone positioning down to about a few centimeters.

A major feature of RTK is that this real-time error correction maintains high accuracy even while the rover is moving. For example, horizontal positioning accuracy can be on the order of 3-5 cm (1.2-2.0 in), and vertical errors can be around 5-10 cm (2.0-3.9 in) depending on environmental conditions and satellite geometry. Because positioning results are refined on the spot, there is no need for post-processing, and accurate position coordinates are available immediately in the field. Also, the closer the reference station is to the rover, the more similar their error sources are, so higher accuracy is maintained. Network RTK generates correction information by selecting appropriate surrounding reference points, enabling efficient centimeter-level positioning (half-inch accuracy).

Advantages of Network RTK – No Need to Deploy a Base Station

In conventional RTK operations, users needed to provide their own reference station and set its position to a known point. This was a major burden, and when surveying over wide areas accuracy degraded as distance from the base station increased. However, using network RTK greatly reduces these burdens.

Network RTK involves a pre-established network of multiple reference stations (such as electronic reference points) that provide correction data to users. Specifically, based on data from reference stations near the user’s current location, a virtual reference station (VRS) is generated and real-time error correction information for that point is delivered. The user (rover) simply receives this correction information via the Internet, enabling centimeter-level positioning (half-inch accuracy) anywhere on site without installing their own base station. Eliminating the need to set up a base station simplifies equipment and improves mobility—major benefits of network RTK. As long as you are within cellular coverage, you can perform mobile surveying while maintaining consistent accuracy over a wide area, so you do not need to return to reference points to ensure accuracy. For example, where it was once necessary to set reference points in the morning and begin observations in the afternoon, with network RTK you can start measuring as soon as you arrive on site.

In Japan, the Geospatial Information Authority has installed about 1,300 electronic reference points nationwide, and public and private correction services using this network are available. By using services provided by mobile carriers and surveying equipment manufacturers, centimeter-level position information (half-inch accuracy) can be obtained across a region. With this infrastructure in place, RTK positioning is becoming accessible not only to specialists but also to general civil engineers and surveying personnel.

Why Positioning Accuracy Management Becomes Easier

Introducing network RTK makes on-site positioning accuracy management markedly easier. One reason is that you can verify accuracy in real time. In RTK, when a “FIX solution” is obtained, centimeter-level accuracy (half-inch accuracy) is guaranteed, and network RTK receivers or dedicated apps always display the solution status (FIX or FLOAT) and current accuracy metrics. This allows operators to proceed while judging on-site whether the required accuracy is met. Discovering after returning from the field that survey data lacks sufficient accuracy and must be redone wastes time and can lead to human error, but network RTK eliminates that concern.

Another important benefit is the ease of sharing accuracy and unifying quality among multiple personnel. With network RTK, everyone on site can perform positioning based on the same correction reference. Previously, when different survey teams used different reference points or equipment, coordinate offsets could occur between datasets, requiring later adjustments. With network RTK, everyone surveys in a unified coordinate system, maintaining data consistency and simplifying quality control. Comparisons with design values and inspections can be performed accurately without offsets, reducing rework downstream and improving overall project efficiency.

Moreover, network RTK simplifies the surveying procedure itself. Eliminating the time needed to set up and dismantle a base station and to tie to known points greatly shortens surveying time. Reduced work time lowers the risk of human error and has safety benefits. For example, where a two-step process of measuring known points in the morning and surveying new points in the afternoon was once necessary, network RTK allows immediate measurement at required points. Constraints due to weather and terrain are also minimized when measurements can be completed quickly. In this way, network RTK, which automatically provides high-precision positioning, reduces many burdens associated with accuracy management.

Effects on the Field and Use Cases

With a constant centimeter-level positioning environment (half-inch accuracy) provided by network RTK, field workflows are changing significantly. In construction management, for example, layout tasks such as batter boards and pile positioning can be done accurately in one pass, enabling high-quality work without rework. In as-built management, measuring completed structures and comparing them with plans becomes faster. If high-precision coordinates can be obtained on site and saved to the cloud immediately, there is no need to return to the office for record整理 or re-computation, and inspection reports can be compiled right away.

Network RTK also has major effects in infrastructure maintenance. In periodic inspections of bridges and tunnels, being able to accurately record the locations of damage in photos or precisely locate sensors for anomaly detection is where the cm level accuracy (half-inch accuracy) of network RTK shines. Tasks that once required on-site matching or drawing checks can now be completed simply by holding up a GNSS receiver. This not only streamlines inspections but also shortens time spent in hazardous areas, contributing to improved on-site safety. In post-disaster damage surveys where rapid, accurate data are needed, network RTK enables short-time, wide-area surveying and is highly useful.

Going forward, network RTK–compatible equipment is expected to become smaller and simpler, spreading as tools that any field staff can use. Recently, solutions combining a smartphone with an external small RTK receiver have emerged, enabling easy centimeter-level positioning. RTK equipment that used to be expensive and aimed at specialists is now available at more affordable price points, lowering the barrier to adoption. Dedicated apps enable coordinate transformations and automatic measurement data recording, making systems intuitive for anyone to use.

Summary

By leveraging real-time corrections via network RTK, the previously difficult task of managing positioning accuracy becomes dramatically easier. The assurance of always knowing positions to centimeter-level accuracy (half-inch accuracy) will raise work quality and safety across a wide range of fieldwork from construction and surveying to infrastructure inspection. In an industry facing severe labor shortages, RTK technology that enables high-precision work with fewer people is a trump card for productivity improvement. GNSS-based ICT construction and as-built management are emphasized in the Ministry of Land, Infrastructure, Transport and Tourism’s i-Construction initiative, and the importance of introducing high-precision positioning technologies is expected to grow.

Today, new technologies such as simple surveying with LRTK using a smartphone have also appeared. By adopting such tools, the barrier to managing positioning accuracy is further lowered, accelerating digital transformation (DX) on site. Use network RTK to take the step toward smart construction where positioning accuracy management is easy and reliable.

Network RTK Makes Safety Inspections Smarter: High-Precision Positioning Shortens Time Spent in Hazardous Areas

Safety inspections and surveying work at social infrastructure and construction sites are always accompanied by danger. Bridge and tunnel inspections require personnel to enter high or confined spaces, and work on railways and roads involves attention to passing trains and vehicles. Inspections and measurements in these hazardous areas should be completed as quickly as possible to ensure worker safety, yet inspection accuracy must not be compromised. Acquiring high-accuracy data within limited time using traditional labor-intensive methods has limits, so technological smartification is needed.

Recently, high-precision positioning using network RTK has attracted attention as a solution. RTK (Real Time Kinematic) refers to a method that corrects GNSS positioning errors between a reference station and a rover to achieve centimeter-level positioning accuracy (half-inch accuracy) in real time. With network RTK, correction information can be obtained over the Internet from a network of reference stations in the area, enabling centimeter-level positioning without deploying a base station on site. This makes it possible to obtain always-accurate position information immediately even in hazardous locations, improving both the efficiency and safety of inspection work.

Challenges of Hazardous Inspections

Traditional infrastructure inspection and surveying often require workers to remain on site for long periods and perform careful manual measurements and recordings. For example, close visual inspections of bridges use elevated work platforms or scaffolding for personnel to access bridge undersides or piers, exposing them to the risk of falls or high-elevation accidents throughout the task. Measurements inside tunnels require road closures and extensive safety measures, incurring high costs. Railway surveys require personnel to set up equipment beside tracks and wait for train passages, where a momentary lapse can lead to serious accidents.

In addition, many structures built during Japan’s high-growth period are now reaching the age for deterioration and will increasingly require inspection and repair. As aging infrastructure increases the number of inspection targets, the shortage of field technicians is also becoming more severe. Relying on experienced technicians leads to person-dependence and reduced efficiency, and the industry faces the common challenge of shortening work time while ensuring safety and measurement accuracy. Against this backdrop, the need for “smart inspections” using digital technology is rising.

Real-Time High-Precision Positioning Enabled by Network RTK

RTK reduces GNSS errors that were several meters with standalone positioning to a few centimeters, and does so by using two receivers to cancel errors. The reference station (with known accurate coordinates) and the rover (used at the inspection site) simultaneously receive the same satellite signals; the reference station computes error information and sends it to the rover, which applies corrections to achieve instantaneous high-precision positioning. A notable feature is that real-time correction maintains accuracy even when moving. Put simply, “two receivers cancel errors better than one,” and RTK delivers a vastly improved level of positioning accuracy.

Network RTK obtains RTK correction information not from a user-deployed base station but from a wide-area network of reference stations. The user carries a rover receiver and connects to a correction data distribution service via cellular or similar communications. Because correction information optimized to the user’s position (a virtual reference station) is provided based on data from several nearby reference stations, homogeneous centimeter-level accuracy (half-inch accuracy) can be achieved over a wide area. For example, combining the nationwide network of electronic reference points (the Geospatial Information Authority’s high-precision GNSS observation network) with communication networks enables centimeter positioning even in mountainous or rural sites. Modern receivers support multi-GNSS (GPS, GLONASS, Galileo, and Michibiki (QZSS)), and with more satellites available, FIX solutions are obtained more quickly and stably than in the past. As long as you have a receiver that supports network RTK, high-precision positioning is becoming available to anyone, anywhere.

Currently, private services that provide correction information via cellular networks (such as VRS methods integrating multiple GNSS reference stations) are in operation across regions, allowing easy adoption of network RTK.

Generally, horizontal accuracy improves to about 3-5 cm (1.2-2.0 in), and vertical accuracy to around 5-10 cm (2.0-3.9 in). To obtain a high-precision solution in RTK, it is necessary to resolve integer ambiguities in satellite signals to achieve a FIX solution, and network RTK benefits from dense reference station networks that shorten initialization times.

Safety and Efficiency Benefits of RTK High-Precision Positioning

Centimeter-level position information (half-inch accuracy) from network RTK delivers various benefits to safety inspection sites. The biggest advantage is that it shortens time spent in hazardous areas. With RTK positioning, you can obtain coordinates for required inspection points instantly, minimizing on-site work time. For example, surveying along railway lines or highways can be done quickly with network RTK, greatly reducing exposure time to trains and vehicles. One construction company reported that introducing RTK into surveying under extreme heat reduced on-site time and was greatly appreciated for lowering workload in harsh conditions. Shorter surveying time also reduces the burden on lookouts and other monitoring personnel.

Another advantage is being able to work with fewer people and non-contact methods, which enhances safety. High-precision GNSS equipment allows a single person to perform layout or inspection surveying, reducing the number of people needed in hazardous locations and decreasing the number of monitoring staff required, thereby reducing the risk of occupational accidents. Non-contact data acquisition means that operators do not need to touch or approach measured objects closely, helping prevent falls, electrocution, and other accidents.

Further, the reassurance of obtaining high-quality data in real time should not be overlooked. Being able to confirm on-site that measurements are reliable prevents situations where “data was inaccurate and re-inspection is needed” later. Getting accurate results correctly the first time eliminates the need to re-enter hazardous areas. If coordinates and distances can be calculated immediately on site, decisions and reporting are faster, shortening road closure times related to inspections and enabling earlier start of restoration work. Also, site personnel can complete measurements and inspections without waiting for specialist survey teams, eliminating downtime and improving efficiency.

Summarizing the main benefits of network RTK for balancing efficiency and safety:

• Shortened work time in hazardous areas reduces workers’ exposure to risk

• Fewer personnel and non-contact operation reduce the number of people entering dangerous locations

• Reliable on-site data acquisition eliminates re-measurement and additional inspections

• Improved inspection efficiency can reduce costs for scaffolding and labor

Introducing network RTK makes it possible to achieve both safety assurance and productivity gains that were previously difficult to reconcile.

Examples of Network RTK Use Cases for Smart Inspections

High-precision positioning from network RTK is being used in various ways in smart inspections that leverage digital technology. Representative use cases include:

• Bridge and high-elevation equipment remote inspections: The use of drones for inspecting high structures like bridges and towers is increasing. When an RTK-equipped drone captures images, accurate position coordinates can be linked to the images, allowing pinpoint identification of damage. This avoids sending personnel to dangerous heights and dramatically improves safety and inspection efficiency.

• Railway infrastructure displacement measurement: RTK is effective for periodically measuring settlement and displacement of tracks and catenary poles. Tasks that previously took a long time with leveling surveys or total stations can now be completed by walking along the track with a smartphone plus an RTK receiver. Shorter measurement times reduce the impact on train operations and lower personnel wait times on the tracks. After earthquakes, quick, wide-area measurement enables faster safety confirmation of track alignment.

• Road patrols and disaster surveys: Rapidity and accuracy are required in routine road patrols and post-earthquake or heavy-rain damage surveys. Using network RTK-enabled tablets or surveying instruments, collapsed structures or cracked sections can be mapped immediately. This minimizes the time roads need to be closed while maintaining high-precision records.

• Locating and marking buried utilities: Accurately identifying the positions of buried gas pipes and cables before excavation makes pre-digging surveys safer and smoother. Pre-marking with RTK positioning enables heavy equipment operators to avoid hazardous zones, directly preventing accidents such as gas pipe ruptures.

• Plant and factory equipment inspections: GNSS positioning is increasingly used in facilities handling hazardous materials, such as chemical plants and power stations. Tagging equipment across large sites with high-precision location information reduces the need to enter dangerous areas during inspections. Immediate identification of anomaly locations speeds emergency response.

• Real-time safety management on construction sites: Equipping heavy machinery and workers with GNSS devices to monitor relative positions in real time can help prevent collisions. Leveraging network RTK accuracy enables virtual fences (geofences) around hazardous zones that automatically stop machinery or trigger alarms if approached, enabling advanced safety management.

In one municipality, trial use of an RTK-equipped drone for periodic inspection of an aging bridge reduced a three-day high-elevation inspection to half a day. Workers no longer needed to climb onto bridge girders, greatly improving safety and efficiency. The collected data were used to create a 3D model for detailed deterioration analysis, enhancing maintenance planning. Such feedback from the field indicates that network RTK significantly improves safety and productivity.

Network RTK is thus enabling diverse smartification of inspection and surveying work. Especially when combined with portable devices and drones, tasks that were once hazardous can now be performed remotely from safe locations. Integration with 5G communications and AI-based image analysis is expected to further enhance precise and labor-saving infrastructure management.

Supporting Technologies for Adoption and Future Prospects

Maximizing the benefits of network RTK requires user-friendly equipment and systems. Smartphone-compatible RTK receivers that have appeared in recent years are a prime example. Whereas expensive, stationary equipment was once necessary, now attaching a small module to a smartphone can provide centimeter-level positioning (half-inch accuracy) to anyone. Dedicated apps focusing on field usability have been developed, offering navigation to inspection points on maps and automatic coordinate tagging of photos, with UI designs tailored to field operators. Bluetooth and Wi-Fi wireless connectivity eliminate complicated wiring between a phone and the receiver, improving field usability. Built-in batteries supporting long continuous positioning sessions provide the reliability needed to cover a day’s inspections.

Augmented reality (AR) integration on-site is also advancing, with trials overlaying inspection points on smartphone or smart-glass displays to guide workers. Such new inspection methods are made possible by RTK’s high precision.

For example, when inspection points are hard to find on maps or drawings, workers can rely on high-precision coordinates shown on a smartphone to reach the exact location without getting lost. Measured point information can be saved directly to the cloud and shared with office PCs for report preparation. Accumulated high-precision data are useful for tracking equipment condition changes over time. In the future, combining these datasets with AI analysis could enable anomaly prediction and preventive maintenance.

Of course, GNSS positioning cannot be used inside tunnels or indoors where signals do not reach, and drone inspections face challenges such as strong winds, rain, safety assurance, and flight permission procedures. These issues are being addressed through technological development and regulatory improvements.

The Ministry of Land, Infrastructure, Transport and Tourism is promoting ICT and robot technology adoption for bridge and tunnel inspections, and on-site smartification is expected to accelerate. Network RTK is anticipated to be a core technology contributing to both safety management and efficiency.

Summary

Incorporating network RTK into hazardous inspection work is making it possible to collect data “quickly, safely, and accurately.” The ability to obtain high-precision information in a short time with limited personnel will be a significant asset for infrastructure maintenance and construction sites. As aging infrastructure increases, the importance of smart inspections that do not rely solely on manpower will only grow. Network RTK can be seen as a foundational technology supporting next-generation infrastructure management.

Today, solutions such as simple surveying with LRTK using a smartphone have emerged, enabling anyone to perform measurements easily. By adopting these latest technologies, you might consider bringing the wave of smartification to your company’s inspection operations. Network RTK will surely further enhance on-site safety and efficiency. We can look forward to broader use of network RTK to support safe and efficient infrastructure maintenance.