The “accuracy of position” required on construction sites and in surveying directly affects project quality and safety. However, conventional GPS (GNSS) positioning can produce errors of several meters, making it insufficient for tasks that need precise alignment. For example, setting out structures in civil engineering or detecting minute displacements in infrastructure inspection requires not just meter-level but sub-centimeter accuracy. Ensuring and managing that level of accuracy has traditionally been a labor-intensive challenge requiring specialized knowledge. On site, repeated measurements against control points were necessary to check errors, and on small sites it was often unavoidable to rely on dedicated survey technicians.

In recent years, one technology attracting attention for solving this problem is real-time high-precision positioning using network RTK. RTK (Real Time Kinematic) is a method that dramatically improves real-time positioning accuracy by using two GNSS receivers—a rover and a base station—to cancel out errors. Especially with network-based RTK, receiving correction information from a network of multiple reference stations installed regionally enables centimeter-level accuracy without deploying your own base station on site. This article explains how network RTK works and its effects, and explores how real-time corrections make accuracy management easier.

Why centimeter-level accuracy is necessary

There are many situations beyond map apps where meter-level errors become problematic. In construction, for instance, strict control of positioning and elevation is required to build structures according to design. Large surveying errors in road or bridge construction can shift the finished structure, leading to reduced quality or safety issues. In infrastructure maintenance, monitoring ground subsidence or measuring pier displacements often requires detecting differences of just a few centimeters. In these environments that require centimeter-level accuracy, standalone positioning (a single GNSS receiver) is insufficient, and high-precision positioning methods are essential.

Traditionally, achieving precise positioning required combining optical surveying instruments like total stations with leveling surveys for elevation measurements. These methods require equipment setup and manpower on site and are inefficient for covering wide areas. Recently, sub-meter and decimeter-level augmentation signals (SBAS/PPP) from the quasi-zenith satellite "Michibiki" have improved smartphone GPS accuracy, but errors still remain on the order of tens of centimeters. For tasks like determining structure locations or detecting displacements, a positioning technology that can provide real-time centimeter-level accuracy is still necessary.

High-precision positioning achieved by RTK real-time corrections

RTK is a GNSS positioning technique developed for this purpose. In RTK, two receivers operate simultaneously: a base station at a known, precise coordinate and a rover at the point to be measured. By comparing the satellite signals received by both, error components are calculated in real time. The base station continuously computes the difference between its true position and the satellite measurements and sequentially sends that positioning error information to the rover. Using the received corrections, the rover adjusts its measurements, reducing errors that were several meters in standalone positioning to around a few centimeters.

A major feature of RTK is that this real-time error correction maintains high accuracy even when the rover is moving. For example, horizontal accuracy can be on the order of 3–5 cm, and vertical errors typically fall around 5–10 cm (depending on environmental conditions and satellite geometry). Because positioning results are refined on the spot, post-processing is unnecessary and precise coordinates are available immediately at the site. Accuracy is also higher when the base and rover are close because their error sources are more similar. Network RTK generates correction information by selecting appropriate nearby reference points, enabling efficient centimeter-level positioning for that reason as well.

Advantages of network RTK – no need to set up a base station

In conventional RTK you had to set up your own base station at a known control point, which was a significant hassle and limited accuracy as you moved farther from the base. However, with network RTK, that burden is greatly reduced.

Network RTK provides users with correction data from a pre-established network of multiple reference stations (such as continuously operating reference stations). Specifically, the network generates a virtual reference station (VRS) based on data from reference stations around the user’s current location and streams error correction information for that virtual point in real time. The user (the rover) only needs to receive these corrections via the Internet to achieve centimeter-level positioning no matter where on site they are. There is no need to install your own base station, simplifying equipment and improving mobility—major benefits of network RTK. As long as you are within mobile coverage, you can perform mobile surveying across broad areas while maintaining consistent accuracy, eliminating the need to return to control points for recalibration. For example, where you once had to set base points in the morning and start observations in the afternoon, with network RTK you can begin measurements immediately upon arriving at the site.

In Japan, the Geospatial Information Authority of Japan (GSI) has installed about 1,300 continuously operating reference stations nationwide, and public and private correction services using this network are available. Using services provided by mobile carriers or surveying equipment manufacturers, you can obtain centimeter-level position data 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 staff.

Why managing positioning accuracy becomes easier

Adopting network RTK makes on-site management of positioning accuracy markedly simpler. One reason is that you can verify accuracy in real time. In RTK, centimeter-level accuracy is guaranteed while a "FIX" solution is attained, and network RTK receivers or dedicated apps constantly display the solution status (FIX or FLOAT) and current accuracy indicators. This allows you to proceed with work while confirming on the spot whether the required accuracy is being met. Discovering after returning to the office that accuracy was insufficient leads to wasted time and potential human error, but network RTK eliminates this worry.

Also important is the ease of sharing accuracy and unifying quality among multiple personnel. With network RTK, everyone on site measures based on the same correction standard. Previously, if different survey teams used separate control points or equipment, coordinate shifts between datasets could occur, requiring later adjustments. Network RTK ensures everyone measures in a unified coordinate system, maintaining data consistency and simplifying quality control. Comparisons with design values and checks can be done accurately without misalignment, reducing rework downstream and improving overall project efficiency.

Additionally, network RTK simplifies the surveying workflow itself. Because there is no need to set up or tear down a base station or perform steps to validate known points, surveying time is greatly shortened. Reduced working time lowers the risk of human error and has safety benefits. For example, where you previously needed a two-step process—measure known points in the morning and survey new points in the afternoon—you can now measure immediately at required points with network RTK. Minimizing measurement time also reduces the impact of weather and terrain constraints. In these ways, network RTK, which automatically delivers high-precision positioning, reduces various burdens associated with accuracy management.

Effects on the field and use cases

With a constant centimeter-level positioning environment provided by network RTK, workflows on site are changing considerably. In construction management, layout tasks like batter boards and pile positioning can be done accurately in one pass, enabling high-quality construction without rework. In as-built verification, measuring completed structures and comparing them to drawings speeds up. If high-precision coordinates are acquired on site and saved to the cloud immediately, there is no need for record整理 or post-processing in the office, enabling inspection reports to be compiled right away.

Network RTK also produces great effects in infrastructure maintenance. During routine inspections of bridges or tunnels, accurately recording the positions of damage in photos or precisely locating anomaly sensors benefits greatly from centimeter accuracy. Tasks that once required on-site adjustments or drawing comparisons can now be completed simply by holding up a GNSS receiver. This not only streamlines inspections but also shortens time spent in hazardous areas, improving site safety. After disasters, where rapid collection of accurate data is needed, network RTK enables quick surveying over wide areas, proving highly useful.

Going forward, network RTK-compatible devices are expected to become smaller and simpler, spreading as tools that any site staff can use. Recently, solutions combining smartphones with small external RTK receivers allow easy centimeter-level positioning. RTK equipment that used to be costly and specialist-oriented is now available in more affordable products and services, lowering the barrier to adoption. Dedicated apps that support coordinate transformations and automatic measurement logging make these tools intuitive for anyone to use.

Summary

Utilizing real-time corrections from network RTK makes what was once difficult—managing positioning accuracy—drastically easier. The reassurance of always knowing positions at the centimeter level will raise work quality and safety across construction, surveying, and infrastructure inspection. In the construction industry, where labor shortages are becoming more serious, RTK technology that enables high-precision work with fewer personnel is a trump card for productivity improvement. Under initiatives like the Ministry of Land, Infrastructure, Transport and Tourism’s i-Construction, ICT-based construction and as-built management using GNSS are emphasized, and the importance of adopting high-precision positioning technologies will continue to grow.

Today, new technologies such as simplified surveying using LRTK on smartphones have also appeared. By adopting such tools, the hurdle for managing positioning accuracy will fall further, accelerating DX (digital transformation) at worksites. Consider using network RTK to step into smart construction where positioning accuracy management is easy and reliable.

Smartening Safety Inspections with Network RTK: Reducing Work Time in Hazardous Areas with High-Precision Positioning

Safety inspections and surveying at social infrastructure and construction sites are always accompanied by hazards. Bridge and tunnel inspections often require personnel to enter high or confined spaces, and work on railways and roads requires vigilance for passing trains or vehicles. Inspections and measurements in such hazardous areas should be completed as quickly as possible to protect workers, while inspection accuracy must not be compromised. Obtaining high-precision data within limited time using traditional labor-intensive methods has limitations, so technological smartification is necessary.

Recently, high-precision positioning using network RTK has attracted attention as a solution. RTK (Real Time Kinematic) refers to a method of obtaining centimeter-level position accuracy in real time by correcting GNSS positioning errors using a base station and a rover. With network RTK, correction information can be obtained over the Internet from a regional network of reference stations, making centimeter-level positioning possible without installing a base station at the site. This enables always obtaining accurate position information immediately, which is expected to simultaneously improve inspection efficiency and safety in hazardous environments.

Challenges of inspections that involve risk

Conventional infrastructure inspection and surveying often required personnel to remain on site for long periods, performing careful manual measurements and recordings. For example, close-up visual inspection of bridges often uses elevated work platforms or scaffolding to allow inspectors to climb under bridge decks or onto piers, exposing them to fall and slip risks throughout the task. In-tunnel measurements also require dealing with confined spaces and costs and safety measures associated with traffic closures. Railway surveying requires standing near tracks with equipment while waiting for train passages, where a momentary lapse could lead to a serious accident.

Additionally, many structures built during Japan’s rapid economic growth era are now reaching aging phases, and inspection and repair demand is expected to increase. As infrastructure ages, the number of inspection targets rises while skilled personnel remain scarce. Inspections dependent on experienced technicians lead to knowledge siloing and decreased efficiency, making it a common industry challenge to shorten work time while maintaining both safety and measurement accuracy. Against this backdrop, the need for “smart inspections” that leverage digital technology is growing.

Real-time high-precision positioning enabled by network RTK

RTK positioning can reduce GNSS errors that were several meters in standalone mode down to a few centimeters. The reason is that two receivers measure to cancel errors: a base station (with a known accurate coordinate) and a rover (the device used for inspection) simultaneously receive the same satellite signals. The base station computes error information and sends it to the rover, which corrects its measurements to achieve instantaneous high-precision positioning. A key advantage is that corrections are applied in real time, so accuracy can be maintained even while moving. Put simply, "two receivers cancel errors more effectively than one," and RTK provides a dramatically improved positioning solution.

In network RTK, RTK correction information is sourced not from the user’s own base station but from a wide-area network of reference stations. The user simply carries a rover receiver and connects to a correction data distribution service via mobile communications. Because the correction information is optimized—often using a virtual reference station generated from several nearby reference stations—uniform centimeter-level accuracy is achievable over wide areas. For example, combining Japan’s nationwide network of continuously operating reference stations (the GSI high-precision GNSS observation network) with communications networks allows centimeter-level positioning even in mountainous or rural sites. Modern receivers support multi-GNSS (GPS, GLONASS, Galileo, QZSS/Michibiki, etc.), increasing satellite visibility and enabling faster, more stable attainment of FIX solutions than before. As long as you have a network RTK-capable receiver, high-precision positioning is becoming available to anyone, anywhere.

Private services that deliver correction data via mobile networks (e.g., VRS methods that integrate multiple GNSS reference stations) are already operated in many areas, making network RTK easy to introduce.

Generally, horizontal accuracy improves to about 3–5 cm, and vertical accuracy to around 5–10 cm. Obtaining a high-precision RTK solution requires resolving integer ambiguities to get a "FIX" solution, and a dense reference station network in network RTK shortens initialization time.

Safety and efficiency benefits from RTK high-precision positioning

Centimeter-accurate position information from network RTK brings many benefits to safety inspection sites. The greatest advantage is the ability to shorten work time in hazardous areas. Using RTK, coordinates for required inspection points can be obtained immediately, allowing on-site tasks to be completed in minimal time. For example, in surveying along railways or beside expressways, network RTK lets you quickly measure needed points, significantly reducing the time workers are exposed to danger from trains or vehicles. One construction company reported that after adopting RTK for surveying in extreme heat, on-site time was reduced and staff appreciated the decreased workload in harsh conditions. Reducing surveying time also lessens the burden on lookout personnel and other monitoring staff.

Second, the ability to operate with fewer personnel and no-contact increases safety. High-precision GNSS equipment enables one person to perform layout or inspection measurements, reducing tasks that previously required multiple staff. Minimizing the number of people entering hazardous areas and cutting down on watchers lowers the risk of occupational accidents. Non-contact data acquisition means inspectors do not need to touch or approach targets closely, preventing falls, electric shocks, and other accidents.

Moreover, there is the reassuring benefit of obtaining high-quality data in real time. Because measurements can be trusted on the spot, scenarios like "inaccurate data requiring re-inspection" are less likely. Reliable results in a single pass mean no need to re-enter hazardous areas for retakes. If coordinates and distances are computed immediately on site, decisions and reports can be made quickly, shortening road closures for inspections and enabling faster recovery work. Site personnel can complete measurements and inspections themselves without waiting for specialist survey teams, reducing downtime and improving efficiency.

The main benefits of network RTK for balancing efficiency and safety are:

• Reducing workers' exposure time in hazardous areas by shortening inspection durations

• Enabling fewer-person or no-contact operations, reducing the number of people who need to enter danger zones

• Obtaining reliable on-the-spot data, eliminating the need for re-measurements or additional inspections

• Improving efficiency and reducing costs such as scaffolding setup and labor expenses

By adopting network RTK, the long-standing trade-off between safety and productivity can be overcome.

Examples of network RTK use for smart inspections

Smart inspections using digital technologies leverage high-precision positioning from network RTK in various ways. Typical use cases include:

• Remote inspection of bridges and high-altitude structures: Drone inspections of bridges and towers are increasing. Drones equipped with RTK can geotag images with precise coordinates, enabling pinpoint identification of damage. This avoids sending people to dangerous heights and dramatically improves both safety and inspection efficiency.

• Displacement measurement for railway infrastructure: RTK is effective for routinely measuring settlement or displacement of tracks and catenary poles. Tasks that once required long hours using leveling or total stations can now be completed by walking along tracks with a smartphone plus an RTK receiver. Shorter measurement times reduce impacts on train operations and limit the time workers spend on the tracks. After an earthquake, quick wide-area measurements are possible, speeding up safety checks.

• Road patrols and disaster surveys: Road patrols and post-earthquake or heavy-rain disaster surveys require speed and accuracy. Tablets or surveying devices compatible with network RTK allow immediate mapping of collapsed structures or cracked sections with high precision while minimizing road closure durations.

• Locating and marking buried utilities: Precisely mapping the positions of underground utilities like gas pipes and cables enables safe, smooth excavation planning. Pre-marking with RTK helps machine operators avoid hazardous zones, reducing the likelihood of accidents such as gas pipeline ruptures.

• Factory and plant equipment inspections: In facilities handling hazardous materials, GNSS positioning is advancing. Tagging equipment across large campuses with high-precision location data reduces the need to enter dangerous areas during inspections. Immediate localization of anomalies speeds emergency response.

• Real-time safety management on construction sites: Equipping heavy machinery and personnel with GNSS devices and monitoring relative positions in real time can prevent collisions. Leveraging network RTK accuracy, virtual fences (geofences) can be set to trigger automatic stops or alarms when machinery approaches restricted zones, enabling advanced safety management.

In one municipality, a trial using an RTK-equipped drone for bridge inspections cut a three-day high-altitude inspection down to half a day. Inspectors no longer needed to climb girders, greatly improving safety and efficiency. The collected data enabled creation of 3D models for detailed deterioration analysis, contributing to more advanced maintenance planning. Such feedback from the field shows network RTK significantly improves safety and productivity.

Network RTK supports a wide range of smart inspection use cases. Especially when combined with portable devices and drones, tasks that were once hazardous can be performed safely from secure locations. Going forward, integration with 5G and AI image analysis will further enable precise and labor-saving infrastructure management.

Latest supporting technologies and future outlook

To fully leverage network RTK, user-friendly devices and systems are essential. Smartphone-compatible RTK receivers that have appeared recently are a prime example. Where expensive, stationary equipment was once required, now simply attaching a small module to a smartphone enables centimeter-level positioning for anyone. Dedicated apps focused on site usability have been developed, including navigation to inspection points on a map and automatic coordinate tagging of photos, all tailored to field operators. Wireless connections via Bluetooth or Wi-Fi eliminate complex cabling between smartphones and receivers, improving on-site usability. Built-in batteries offering long continuous operation mean a full day’s inspections can be covered reliably.

On-site AR (augmented reality) applications are also advancing, with trials overlaying inspection points on smartphone or smart glasses displays to guide workers. These inspection methods are made possible by RTK’s high accuracy.

For instance, when periodic inspection points are hard to find on maps or drawings, users can rely on high-precision coordinates displayed on a smartphone to reach the exact spot without getting lost. Measured location data can be saved to the cloud and shared with office PCs for report preparation. Accumulated high-precision time-series data also helps track equipment condition changes. In the future, combining RTK data with AI analysis could enable anomaly prediction and preventive maintenance.

Of course, GNSS positioning has limitations—signals do not reach inside tunnels or indoors—and drone inspections face challenges such as strong winds, rain, flight safety, and permit procedures. These issues are being improved through technological development and regulatory measures.

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

Summary

Incorporating network RTK into hazardous inspections makes it increasingly possible to collect data "fast, safely, and accurately." The ability to obtain high-precision information quickly with limited personnel is a major advantage for infrastructure maintenance and construction. As aging infrastructure grows, the importance of smart, less labor-intensive inspections will only increase. Network RTK can be considered a foundational technology supporting next-generation infrastructure management.

Today, solutions such as simplified surveying using LRTK with a smartphone have emerged, enabling anyone to perform surveying easily. By adopting such cutting-edge technologies, consider bringing smart workflows into your inspection operations. Network RTK is likely to further enhance safety and efficiency on site. Let us期待 the wider spread of network RTK to support safe and efficient infrastructure maintenance.