Innovating Infrastructure Inspections with Network RTK: Improved Efficiency and Reduced Risk

As infrastructure ages, routine inspections of roads, sewers, and other assets are indispensable for maintaining a safe and secure society. However, traditional inspection methods have long faced many challenges. Much of the inspection work has relied on manual labor, with measurements based on maps and drawings and records kept on paper, leading to the following inefficiencies:

• Heavy labor and time burden: Detailed visual inspections require many technicians and sometimes necessitate traffic control, which drives up operational costs.

• Cumbersome data management: Managing inspection results on paper ledgers or drawings makes searching and sharing information time-consuming and makes it difficult to analyze degradation trends using past inspection histories.

• Limits to accuracy and objectivity: Conventional methods often cannot record the precise coordinates of deterioration locations, relying instead on experience and intuition. This leads to a high dependence on veteran staff and makes skill transfer a challenge.

A promising solution to these problems is high-precision positioning using GNSS (Global Navigation Satellite Systems) through network RTK. By incorporating network RTK into infrastructure inspections, it is expected that inspection efficiency can be improved and risks reduced, fundamentally transforming infrastructure maintenance and management. This article outlines the principles and benefits of GNSS positioning and network RTK, describes use cases and effects in sewer and slope inspections, and introduces prospects for workflow improvements through integration with digital ledgers and GIS as well as future inspection support using smartphone-based simplified surveying (LRTK) and AR technologies.

Principles and Benefits of GNSS Positioning and Network RTK

GNSS positioning identifies a location by receiving signals from multiple satellites such as GPS, GLONASS, and Michibiki (QZSS). Ordinary standalone GNSS positioning (such as a smartphone’s GPS) typically has errors of several meters to tens of meters, but accuracy can be dramatically improved using a method called RTK (Real-Time Kinematic). RTK uses two receivers: a base station installed at a known precise location and a rover that measures while moving. By simultaneously receiving satellite data at both receivers, RTK corrects errors in real time. As a result, positioning errors can be reduced to a few centimeters, enabling centimeter-level location accuracy.

Among RTK methods, network RTK receives correction information (differential data) over the internet from a network of multiple reference stations installed across a region, enabling stable, high-precision positioning over wide areas. Users access regional reference station data via cellular communications, eliminating the need to deploy their own base stations. In Japan, the Geospatial Information Authority of Japan’s network of permanent GNSS reference stations and private VRS services have been developed as network RTK infrastructures, and environments where cm-level positioning is stably available—even in urban areas—are becoming established. Even in areas with dense buildings, the spread of high-performance GNSS equipment capable of receiving not only GPS but also GLONASS and QZSS has made high-accuracy positioning feasible.

Advantages of network RTK: Because it provides centimeter-level accurate position information in real time, surveying tasks that were previously difficult can be performed efficiently. For example, large-area terrain surveys can be completed as rapid 3D measurements using network RTK. Immediate access to high-accuracy coordinates on site allows measurement results to be checked and additional surveys to be made on the spot. Above all, the ability to record and share data digitally in real time eliminates the need for paper transcription and post-processing, greatly improving the accuracy of inspection records and overall operational efficiency.

Minimizing Entry into Hazardous Areas via High-Precision Positioning

Using network RTK also contributes to improved safety during infrastructure inspections because it enables necessary data collection while minimizing entry into hazardous areas. For instance, when inspecting slopes at risk of landslides or aging tunnel interiors, technicians traditionally needed to approach dangerous spots to take measurements. With high-precision GNSS equipment, however, positions and displacements can be measured from a safe distance. In slope movement monitoring, installing GNSS sensors on hillsides and continuously observing them with RTK positioning allows detection of subtle ground movements without personnel entering the site. In cases of road collapse caused by sewer pipe subsidence, an RTK-equipped surveying instrument has enabled a single inspector to measure the shape and size of the collapse area in a short time, completing data collection while ensuring safety. Network RTK, which enables precise position confirmation, shortens work time in hazardous locations and greatly contributes to securing inspector safety and reducing risk.

Applying Network RTK to Sewer Inspections: Record Management and Efficiency Gains

Network RTK is also powerful in managing aging sewer networks. Some local governments have re-surveyed manhole coordinates across entire municipalities using network RTK to revise the positions recorded in traditional sewer ledgers. Previous surveys often relied on paper topographic maps or aerial photos, yielding positional errors of about ±20–30 cm, which was inadequate for GIS use. By obtaining latitude, longitude, and elevation for all manholes with centimeter accuracy via network RTK, the data were immediately registered in electronic ledger systems, greatly reducing later drawing corrections and manual data entry. Overall, some reports indicate that surveying and recording labor and time were reduced to a fraction of conventional methods.

The increased accuracy of position data helps precisely represent pipe and facility conditions in sewer GIS. With correct alignment between manholes and pipelines, identifying inspection points becomes easier. Also, by linking past inspection and repair histories to map locations, one can quickly reference where and what types of defects have occurred. This enables data-driven sewer management, such as extracting severely degraded sections and prioritizing repair planning.

Network RTK is also useful in emergency response. In suspected sewer pipe failures that cause road collapses, RTK positioning allows immediate on-site measurement of the exact location and extent of the sinkhole, and the data can be shared with relevant departments via the cloud. Unified position information among stakeholders speeds up recovery planning and clarifies the affected area, helping to prevent further damage.

Use in Slope Inspections: Displacement Management and 3D Records for Preventive Maintenance

Network RTK is effective for inspecting and monitoring slopes and embankments. For slopes at risk of landslides, quantitative displacement measurement in addition to routine patrols is important. RTK’s high-precision positioning enables periodic measurement of the height and position of multiple points on a slope and captures changes at centimeter resolution. For example, alongside expressways, RTK surveys conducted several times a year record subsidence or heave, and even small movements can be analyzed for trends through accumulated data. Because network RTK allows wide-area measurements using a consistent coordinate reference, subtle deformations can be detected across surfaces, enabling early identification of signs such as “gradual subsidence in a specific area.” This makes it possible to preemptively identify high-risk slopes and accelerate reinforcement work or resident evacuation preparations, strengthening preventive maintenance.

Traditionally, slope inspections involved technicians approaching cliffs to measure crack widths with crack gauges and visually recording deformations. By combining network RTK with photogrammetry or 3D scanning, detailed 3D records can be obtained from a distance while assigning precise coordinates to every point. For example, using an RTK-capable drone for photogrammetry yields point clouds and orthophotos accurately aligned to map coordinates, allowing cracks and collapse zones to be pinpointed on maps. Additionally, mobile mapping—mounting an RTK-GNSS receiver and 360-degree camera on a service vehicle to record imagery and position data while driving—is possible. Inspectors can then identify the exact positions of anomalies from the office on the recorded footage, reducing the need for prolonged on-site manual note-taking on hazardous slopes and enabling rapid, wide-area digital recording and analysis.

Introducing high-precision position data via network RTK thus brings major changes to preventive maintenance and recording methods for slope inspections. The combination of 3D data and accurate coordinate information makes building digital twins—virtual replicas of real-world infrastructure—feasible, enabling visualization of changes over time and realistic forecasting of future risks.

Workflow Efficiency through Integration with Digital Ledgers and GIS

The precise position data obtained with network RTK also integrate smoothly with electronic ledger systems and GIS, which is another significant advantage. Traditionally, transferring inspection results from paper to a computer or reflecting survey data onto drawings required time and effort. If high-accuracy positioning data are acquired digitally from the outset, they can be uploaded directly from the field to cloud databases or GIS.

In the earlier-mentioned sewer inspections, location data measured with network RTK were registered in an electronic sewer ledger on site, greatly reducing office work after returning. In road-collapse investigations, sharing RTK survey data in real time via the cloud enables all stakeholders to understand the situation on the same map while discussing countermeasures. By integrating with digital ledgers and GIS, centralized information management and instant sharing become possible, shortening the time lag from inspection to reporting and decision-making.

Visualizing accumulated data on GIS also makes it easier to analyze degradation distributions and long-term changes of infrastructure. For example, overlaying past repair histories and inspection evaluations on a map helps identify areas prone to frequent issues or structural weaknesses. This enables more effective planning of future maintenance and helps prioritize the allocation of limited budgets and personnel. The fusion of accurate network RTK data with digital tools is accelerating DX (digital transformation) across infrastructure maintenance operations.

The Future of Inspection Support with Smartphone RTK and AR: A New Era Opened by LRTK

Network RTK technology continues to advance, and more accessible solutions are emerging. One noteworthy development is smartphone RTK, which turns a smartphone into a high-precision positioning device. A representative example is the initiative called LRTK, where attaching a small RTK-capable GNSS receiver to a smartphone can reduce typical smartphone GPS errors of several meters down to a few centimeters. The lightweight device, weighing around 100 grams and attaching to the back of a phone, makes every smartphone a “portable surveying instrument,” enabling anyone on site to perform high-precision positioning and recording.

With LRTK, field technicians can complete surveying and data recording themselves without specialized surveying equipment or bulky devices. For example, an app that links to the smartphone camera can scan the surroundings to generate 3D point cloud data on the spot, and each captured point is tagged in real time with accurate coordinates. The intuitive operation requires no surveying expertise, and because positioning information is saved during capture, there is no need for time-consuming post-processing to reconcile photo locations after returning to the office. AR (augmented reality) functionality can overlay buried pipes or past inspection data onto the real world through the smartphone screen. For instance, if the positions of sewers and cables have been previously measured and recorded with LRTK, AR display during inspection allows workers to know underground structure locations without excavation. In bridge and tunnel inspections, AR can overlay previously recorded cracks or displacement data in the field to immediately compare changes since the last inspection.

As smartphone RTK becomes widespread, the style of infrastructure inspections is likely to change dramatically. When each technician carries a means of high-precision positioning, inspections become faster and safer. Real-time completion of data collection, analysis, and sharing will make results more visible, improving on-site decision accuracy and speeding up decision-making. From a cost perspective, compact and versatile smartphone-based solutions lower the introduction barrier compared with dedicated equipment, making it easier for many municipalities and small and medium-sized enterprises to adopt advanced technologies.

Conclusion: Network RTK Pioneering Innovation in Infrastructure Inspections

GNSS-based network RTK positioning is a driving force that can dramatically improve the efficiency and accuracy of infrastructure inspections and maintenance. Leveraging centimeter-level position information replaces ambiguous, labor-intensive field work with digital records, reducing workload and enabling objective, data-driven decisions. Combining high-precision positioning with digital ledgers, AR, and other modern tools also significantly contributes to risk reduction during inspections and to more advanced preventive maintenance. The field is now entering an era of transformation. With ongoing advances in satellite positioning and digital sensors, inspection methods will continue to mature. Actively adopting digital innovation centered on network RTK is essential to building safer and more efficient infrastructure management systems. Let’s maximize the benefits of high-precision positioning for improved efficiency and risk reduction, and connect them to sustainable, safe infrastructure management.