Revolutionizing Infrastructure Inspections with Network RTK: Improving Inspection Efficiency and Reducing Risk

As infrastructure ages, regular inspections of roads, sewers, and other facilities are indispensable for maintaining a safe and secure society. However, conventional inspection methods have many challenges. Much of the inspection work relies on manual labor, with measurements taken by hand based on maps and drawings and records kept on paper, which tend to cause inefficiencies such as the following.

• High manpower and time burden: Detailed visual inspections require a large number of technicians and, in some cases, traffic controls, which increases operational costs.

• Complex data management: Managing inspection results in 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 cannot record the precise coordinates of degraded locations and tend to rely on experience and intuition. As a result, dependence on veteran staff is strong, and transferring technical skills has also been a challenge.

To address these challenges, attention has turned to high-precision positioning technology using GNSS (Global Navigation Satellite System) through Network RTK. By integrating Network RTK into infrastructure inspections, it is expected to streamline inspection operations, reduce risks, and revolutionize the way infrastructure maintenance is managed. This article outlines the principles and advantages of GNSS positioning and Network RTK, and explains use cases and effects in sewer inspections and slope (embankment) inspections. It also introduces efficiency improvements achieved by linking with digital ledgers and GIS, and prospects for future inspection support using smartphone-based simplified surveying (LRTK) and AR technology.

Principles and Advantages of GNSS Positioning and Network RTK

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

Among them, Network RTK is a method that receives correction information (differential data) via the Internet from a network of multiple reference stations installed across various locations, enabling stable, high‑precision positioning over wide areas. Because users access the regional reference station data through mobile communications, there is no need to install their own base station as before. In Japan, network‑type RTK infrastructures such as the Geospatial Information Authority of Japan’s Continuously Operating Reference Stations and private VRS services are being established, creating an environment in which centimeter‑level positioning can be obtained stably even in urban areas. Even in areas lined with buildings, high‑precision positioning has become possible thanks to the spread of high‑performance GNSS receivers that can receive satellites such as GLONASS and QZSS in addition to GPS.

Advantages of network RTK: Because it enables real-time acquisition of centimeter-level accurate position information, surveying can be performed efficiently even in situations that were previously difficult. For example, large-area terrain surveys can be completed as 3D measurements in a short time using network RTK. In addition, because high-precision coordinates can be obtained immediately on site, measurement results can be checked on the spot and reflected in additional investigations, allowing for flexible responses. Above all, the ability to record and share the obtained data digitally and instantly is significant; eliminating the need for transcribing to paper and post-processing leads to a major improvement in the accuracy of inspection records and overall work efficiency.

Minimizing Entry into Hazardous Areas Through High-Precision Position Confirmation

Using network RTK also contributes to improved safety during infrastructure inspections. This is because it allows necessary data to be acquired while minimizing entry into hazardous areas. For example, inspections of slopes at risk of landslides or aging tunnel interiors traditionally required technicians to approach dangerous spots to take measurements. However, by using high-precision GNSS equipment, the position and displacement of targets can be measured from a safe distance. In practice, initiatives for slope movement monitoring are progressing: by continuously observing GNSS sensors installed on hillsides with RTK positioning, subtle ground movements can be detected without anyone entering the area. Likewise, at sites where road collapse has occurred due to sewer pipe sinkholes, using RTK-equipped surveying instruments enables a single operator to quickly measure the shape and size of the collapsed area and complete data collection while ensuring safety. Network RTK, which enables highly accurate position verification, significantly contributes to shortening work time in hazardous areas and to ensuring inspector safety and reducing risk.

Utilizing Network RTK for Sewer Inspections: Inspection History Management and Improved Efficiency

Network RTK is proving highly effective even in the maintenance and management of aging sewer pipeline networks. Some municipalities, in order to review the location information of manholes and pipelines recorded in conventional sewer registers, have re-surveyed the coordinates of all manholes across the city using network RTK. Until then, surveys mainly relied on estimates from paper topographic maps and aerial photographs, resulting in position errors of about ±20–30 cm, which was insufficient for use in GIS. By obtaining latitude, longitude, and elevation for every manhole with centimeter-level accuracy using network RTK, the data were immediately registered in electronic ledger systems, greatly reducing the need for post-survey drawing corrections and manual data entry. Overall, there are reports that, compared with traditional methods, labor costs and time for surveying and recording work were cut to a fraction.

Accurate location data obtained through improved precision helps to reliably capture the condition of pipelines and facilities in sewer GIS (geographic information systems). Since the connections and routes between manholes and pipes can be displayed without misalignment, identifying inspection points has become easier. In addition, past inspection and repair records can be linked and managed on the map, allowing quick reference to where and what types of defects have occurred. This enables data-driven sewer management, such as extracting severely deteriorated sections and prioritizing them for rehabilitation planning.

Furthermore, network RTK is also useful for emergency accident response. In cases where damage to sewer pipes is suspected, such as road collapses, the exact location and extent of the sinkhole can be measured on-site immediately using RTK positioning, and that data can be shared with relevant departments via the cloud. Because location information is unified among personnel, planning of restoration work and assessing the extent of impact on surrounding areas can be done more quickly, helping to prevent further damage.

Application to Slope Inspection: Preventive Maintenance through Displacement Management and 3D Recording

Network RTK is also proving useful for the inspection and monitoring of slopes and embankments. On slopes at risk of landslides, quantitative displacement measurement is important in addition to routine patrols. With high-precision positioning using RTK, the heights and positions of multiple points on a slope can be measured periodically, allowing changes to be captured to the centimeter level. For example, along highway slopes, RTK surveys are conducted several times a year to record ground subsidence and heave, and efforts are being made to analyze trends from accumulated data even for very small movements. Because Network RTK can measure wide areas using a single coordinate reference, it can detect slight deformations across a surface, enabling early detection of signs such as gradual subsidence in a specific area. This strengthens preventive maintenance measures, allowing for the early identification of high-risk slopes and the prompt implementation of reinforcement work and evacuation preparations for residents.

In traditional slope inspections, inspectors used to approach cliffs to measure crack widths with crack gauges or visually record deformations. By combining network RTK with photogrammetry and 3D scanning technologies, it is possible to obtain detailed 3D records from a distance while assigning accurate coordinates to every point. For example, when performing photogrammetry of a slope with a drone, using an RTK-enabled drone means the resulting point cloud data and orthoimages are accurately aligned to the map coordinate system, allowing crack locations and collapse sites to be pinpointed on drawings. Furthermore, mobile mapping is possible by mounting an RTK-GNSS receiver and a 360-degree camera on a work vehicle to record surrounding imagery and position information while driving. Because you can later identify the exact locations of observed anomalies on the footage from the office, the need for inspectors to spend long periods on hazardous slopes making handwritten records is reduced, and wide areas can be digitally recorded and analyzed in a short time.

The introduction of high-precision positioning data using network RTK is thus bringing major changes to preventive maintenance and recording methods in slope inspections. By combining 3D data with precise coordinate information, it enables the construction of a digital twin (a virtual replica of the real world) of infrastructure structures, and advanced maintenance practices—such as visualizing changes from the past to the present and predicting future risks—are becoming a realistic possibility.

Operational Efficiency through Integration of Digital Ledgers and GIS

Precise position data obtained with network RTK also offers the significant advantage of seamless integration with digital ledger systems and GIS. Traditionally, transferring inspection results from paper documents to a computer or reflecting survey data on drawings required considerable time and effort. If high-precision positioning data are captured in digital form from the outset, they can be uploaded directly from the field to cloud-based databases and geographic information systems.

Indeed, in the aforementioned sewer inspection, location information measured with network RTK was registered in the electronic sewer ledger on the spot, greatly reducing the amount of work required back at the office. In road sinkhole investigations as well, by sharing RTK survey data to the cloud in real time, all stakeholders can discuss countermeasures while viewing the situation on the same map. In this way, by integrating with digital ledgers and GIS, centralized information management and instant sharing are realized, reducing the time lag from inspection to reporting and decision‑making.

Furthermore, visualizing accumulated data on a GIS makes it easier to analyze the spatial distribution of infrastructure deterioration and changes over time. For example, by cross-referencing past repair histories and inspection assessments on a map, areas where defects frequently occur and structural weaknesses can be identified. This enables more effective planning of future maintenance and management and helps clarify where limited budgets and personnel should be prioritized. The integration of accurate data from network RTK with digital tools is driving the DX (digital transformation) of overall infrastructure maintenance operations.

The Future of Inspection Support with Smartphone RTK and AR: LRTK Opens a New Era

Network RTK technology is advancing daily, and solutions that make its benefits easier to harness are emerging. One approach attracting attention recently is smartphone RTK, which turns a smartphone into a high-precision positioning device. A representative example is the initiative called LRTK: by simply attaching a small RTK-capable GNSS receiver to a smartphone, you can improve the smartphone GPS's accuracy — normally off by several meters — all the way to a few centimeters. With the ease of just attaching a device weighing about 165 grams to the back, the smartphone becomes a one-person “simple surveying instrument”, enabling anyone on site to perform high-precision positioning and recording.

By leveraging LRTK, on-site technicians themselves can complete everything from surveying to data recording with just a smartphone in hand, without using specialized surveying equipment or large-scale devices. For example, scanning the surroundings with an app linked to the smartphone’s camera generates 3D point-cloud data on the spot, and each acquired point is tagged in real time with precise coordinates. Even those without surveying knowledge can operate it intuitively, and because positioning information is saved simultaneously with the capture, there is no need for rework such as organizing the spatial relationships of photos after returning to the office. Furthermore, using AR (augmented reality) functionality makes it possible to project buried pipes or past inspection data into the real world through the smartphone screen. For example, if the locations of buried sewer pipes and cables are measured and recorded in advance with LRTK, displaying them in AR on the smartphone during inspection allows you to identify the positions of underground structures without having to dig up the ground. Also, in bridge and tunnel inspections, information on cracks and displacements recorded previously can be overlaid on site with AR, enabling immediate comparison of changes since the last inspection.

As smartphone RTK becomes widespread, the way infrastructure inspections are carried out will change dramatically. When each technician carries a means of high-precision positioning, inspections can be performed more quickly and more safely. With data collection, analysis, and sharing completed in real time and visualization of inspection results made easier, improvements in on-site judgment accuracy and faster decision-making can be expected. From a cost standpoint as well, using compact, highly versatile smartphones lowers the barrier to adoption compared with dedicated equipment, making it easier for many municipalities and small and medium-sized enterprises to adopt the latest technologies.

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GNSS-based network RTK positioning is a driving force that dramatically improves the efficiency and accuracy of infrastructure inspection and maintenance. By leveraging centimeter-level positioning information, on-site tasks that previously relied on manual methods and ambiguous records are being replaced with digital records, reducing workload and enabling decisions based on objective data. In addition, combining high-precision positioning with cutting-edge tools such as digital ledgers and AR greatly contributes to lowering inspection risks and advancing preventive maintenance. The field is truly entering an era of innovation. As satellite positioning technology and digital sensors continue to evolve, methods for infrastructure inspection will become even more sophisticated. It is important to proactively adopt digital innovation centered on network RTK and build a safer, more efficient infrastructure management system. Let’s maximize the benefits of efficiency gains and risk reduction delivered by high-precision positioning and translate them into sustainable, safe, and secure infrastructure management.