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

As infrastructure ages, regular inspections of roads, sewers, and similar systems are indispensable for maintaining a safe and secure society. However, conventional inspection methods have faced many challenges. Many inspection tasks relied on manual labor, with measurements performed by hand based on maps and drawings and records kept on paper, which tended to result in inefficiencies such as the following.

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

• Data management is cumbersome: Managing inspection results in paper ledgers and drawings makes searching and sharing information time-consuming and makes it difficult to analyze deterioration trends using past inspection histories.

• Limits to accuracy and objectivity: Conventional methods cannot record the locations of deterioration with precise coordinates and tend to rely on experience and intuition. As a result, there is a strong dependence on veteran personnel, and the transfer of skills has posed a challenge.

One promising solution to address these challenges is high-precision positioning technology using GNSS (Global Navigation Satellite System) and network RTK. By incorporating network RTK into infrastructure inspections, it is expected to streamline inspection work, reduce risks, and potentially revolutionize the way infrastructure maintenance and management are conducted. This article outlines the principles and advantages of GNSS positioning and network RTK, and explains use cases and effects in sewer inspections and slope (norimen) inspections. Furthermore, it introduces prospects for operational efficiency through integration with digital ledgers and GIS, and for future inspection support via smartphone-based simple surveying (LRTK) and AR technology.

Principles and Advantages of GNSS Positioning and Network RTK

GNSS positioning is a technology that determines one's position by receiving signals from multiple artificial satellites such as GPS, GLONASS, and Michibiki (QZSS). With ordinary standalone GNSS positioning (such as a smartphone's GPS), errors of several meters (several ft) to a dozen or so meters (a dozen or so ft) occur, but by using a method called RTK (Real-Time Kinematic) the positioning accuracy can be dramatically improved. In RTK, two receivers are prepared: a base station installed at a known precise location and a rover that performs positioning while moving, and the errors in the satellite data received simultaneously by both are corrected in real time. As a result, errors are reduced to on the order of a few centimeters (a few in), enabling centimeter-level positioning (cm level accuracy (half-inch accuracy)).

Among these, Network RTK is a method that receives correction information (differential data) via the Internet from multiple reference station networks installed in various locations, enabling stable high-precision positioning over wide areas. Users access regional reference station data through cellular communications, so there is no need to install their own base stations as in the past. In Japan, network RTK infrastructure such as the Geospatial Information Authority of Japan’s network of Continuously Operating Reference Stations and private VRS services has been developed, and an environment in which cm-level positioning (half-inch-level positioning) can be obtained stably even in urban areas is becoming established. Even in areas with many buildings, coupled with the widespread adoption of high-performance GNSS equipment capable of receiving satellites such as GPS, GLONASS, and QZSS, high-precision positioning has become possible.

Benefits of Network RTK: Because it can obtain centimeter-level accurate positioning information in real time (cm level accuracy, half-inch accuracy), surveying can be carried out efficiently even in situations that were previously difficult. For example, wide-area terrain surveys can be measured in three dimensions in a short time using Network RTK. In addition, since high-precision coordinates can be obtained instantly on site, measurement results can be checked immediately and reflected in additional investigations, enabling flexible responses. Above all, the ability to record and share obtained data immediately in digital form is significant; eliminating the need for manual transcription to paper or post-processing leads to a substantial improvement in the accuracy of inspection records and work efficiency.

Minimize Entry into Hazardous Areas with High-Precision Positioning

The use of network RTK also contributes to improved safety during infrastructure inspections, because it allows necessary data to be obtained while minimizing entry into hazardous areas. For example, inspections of slopes at risk of landslides or the interiors of aging tunnels traditionally required technicians to approach dangerous locations to take measurements. However, by using high-precision GNSS equipment, positions and displacements of targets can be measured from a safe distance. In fact, for slope movement monitoring, initiatives are progressing to detect subtle ground movements without human entry by continuously observing GNSS sensors installed on hillsides with RTK positioning. At sites where a roadway collapsed due to a sewer pipe failure, using RTK-equipped surveying instruments enables a single operator to measure the shape and size of the collapsed area in a short time, completing data collection while ensuring safety. Network RTK, which allows high-precision positioning, shortens the time spent working in hazardous areas and makes a significant contribution to ensuring inspector safety and reducing risk.

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

Network RTK is proving powerful even in the maintenance and management of aging sewer pipelines. Some municipalities have re-surveyed the coordinates of all manholes throughout their cities using network RTK to review the positional information of manholes and pipes registered in conventional sewer ledgers. Until then, surveys mainly relied on estimates using paper topographic maps and aerial photographs, resulting in positional errors of about ±20-30 cm (±7.9-11.8 in), which was insufficient for GIS use. By using network RTK to obtain latitude, longitude, and elevation for all manholes with centimeter accuracy (half-inch accuracy), the data were immediately registered into the electronic ledger system, greatly reducing the subsequent need for drawing corrections and manual data entry. Overall, there are reports that labor costs and time for surveying and recording work were reduced to a fraction of those required by conventional methods.

Accurate location data obtained through improved accuracy help to accurately ascertain the condition of pipelines and facilities on the sewer GIS (geographic information system). Because the connection relationships and routes between manholes and pipes can be displayed without displacement, identifying inspection points has become easier. In addition, because past inspection records and repair histories can be linked and managed on the map, it is possible to quickly reference where and what kinds of defects occurred. This enables data-driven sewer management, such as extracting severely deteriorated sections and prioritizing rehabilitation planning.

Furthermore, network RTK is useful in emergency response to sudden incidents. In cases where damage to sewer pipes is suspected, such as road collapses, the precise location and extent of a 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 standardized among personnel, planning and coordination of recovery work and assessment of the affected area’s extent become faster, helping to prevent further damage.

Application to Slope Inspections: Preventive Maintenance through Displacement Management and 3D Documentation

Network RTK is also proving useful for the inspection and monitoring of slopes and slope faces (nori-men). On slope faces at risk of landslides, quantitative displacement measurements are important in addition to routine patrols. With high-precision positioning using RTK, you can periodically measure the elevations and positions of multiple points on a slope face and determine their changes in centimeters (inches). For example, on slope faces along highways, RTK surveys are carried out several times a year to record ground subsidence and heave, and attempts are made to analyze trends from accumulated data even for minute movements. Because network RTK can measure wide areas on the same coordinate reference frame, it can detect slight deformations across surfaces, enabling early detection of signs such as “a particular area is gradually subsiding.” This strengthens preventive maintenance measures, allowing high-risk slopes to be identified in advance and for reinforcement works or residents’ evacuation preparations to be implemented earlier.

Traditionally, slope inspections involved inspectors approaching slope faces to measure crack widths with crack gauges and visually recording signs of distress. By combining network RTK with photogrammetry and 3D scanning technologies, detailed 3D records can be obtained remotely while assigning accurate coordinates to every point. For example, if photogrammetry of a slope is conducted with an RTK-equipped drone, the resulting point cloud data and orthoimages will be accurately aligned to the map coordinate system, allowing the locations of cracks and collapse points to be pinpointed on drawings. It is also possible to perform mobile mapping by mounting an RTK-GNSS receiver and a 360-degree camera on a work vehicle and recording surrounding imagery and position information while driving. Because inspectors can later identify the precise positions of observed anomalies on the imagery from the office, the need for inspectors to spend long periods on hazardous slopes making handwritten records is reduced, and it becomes possible to digitally record and analyze wide areas in a short time.

Thus, the introduction of high-precision positioning data leveraging network RTK is bringing about a major transformation in preventive maintenance and recording methods for slope inspections. By combining 3D data with accurate coordinate information, it is possible to construct digital twins of infrastructure structures (virtual replicas of the real world), and advanced maintenance management—such as visualizing changes from the past to the present and predicting future risks—has become increasingly realistic.

Improving Operational Efficiency through Integration of Digital Ledgers and GIS

The precise position data obtained by network RTK also has the overlooked advantage of being able to integrate smoothly with digital ledger systems and GIS. Traditionally, transcribing inspection results from paper documents to a computer or reflecting survey data on drawings required considerable time and effort. If high-precision positioning data is acquired in digital format from the start, it can be uploaded directly from the field to cloud-based databases and geographic information systems.

In practice, during the aforementioned sewer inspections, position information measured with network RTK was registered in the electronic sewer ledger on site, greatly reducing the work required after returning to the office. In road collapse surveys, too, by sharing RTK survey data to the cloud in real time, all stakeholders can assess the situation on the same map and discuss countermeasures. By linking with digital ledgers and GIS in this way, centralized information management and instant sharing are realized, shortening the time lag from inspection to reporting and decision-making.

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

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

Network RTK technology is advancing daily, and solutions that make its benefits easier to enjoy are emerging. A recently notable development is smartphone RTK, which turns a smartphone into a high-precision positioning device. A representative example is the initiative called LRTK, where simply attaching a compact RTK-capable GNSS receiver to a smartphone can improve smartphone GPS accuracy, which normally has errors of several meters, all the way to a few centimeters. With the ease of just attaching a device weighing about 165 grams to the back, a smartphone becomes a personal "simple surveying instrument", enabling anyone on site to perform high-precision positioning and recording.

By using LRTK, field technicians themselves can complete everything from surveying to data recording with just a smartphone, without using specialized surveying equipment or large-scale apparatus. For example, if you scan the surroundings with an app linked to the smartphone camera, it will generate 3D point cloud data on the spot, and each acquired point will be tagged with accurate coordinates in real time. It is intuitive enough for people without surveying knowledge to operate, and because positioning information is saved at the time of capture, there is no need for rework such as organizing the positional relationships of photos after returning to the office. Furthermore, using AR (augmented reality) functionality, it is possible to project buried pipes and past inspection data into the real space through the smartphone screen. For example, if you measure and record the buried locations of sewer pipes or cables in advance with LRTK and display them as AR on the smartphone screen during inspection, you can identify the positions of underground structures without digging up the ground. Also, in inspections of bridges and tunnels, you can overlay previously recorded information on cracks and displacements onto the site with AR and immediately compare any developments since the last inspection.

With the proliferation of smartphone RTK, the way infrastructure inspections are conducted will change significantly in the future. By equipping each technician with a means for high-precision positioning, inspection work can be carried out more quickly and safely. Since data collection, analysis, and sharing can be completed in real time and visualization of inspection results will become easier, improvements in the accuracy of on-site judgments and faster decision-making can be expected. In terms of cost, using compact, versatile smartphones has a lower barrier to adoption compared with dedicated equipment, making it easier for many local governments and small and medium-sized enterprises to adopt the latest technologies.

Summary: Innovations in Infrastructure Inspection Pioneered by Network RTK

Network RTK positioning using GNSS has become a driving force that dramatically enhances the efficiency and accuracy of infrastructure inspection and maintenance. By leveraging centimeter-level position information (half-inch-level), field tasks that previously relied on manual labor and ambiguous records have been digitized, reducing workload and enabling decisions based on objective data. In addition, combining high-precision positioning technology with cutting-edge tools such as digital ledgers and AR significantly contributes to reducing inspection risks and advancing preventive maintenance. The field is truly entering an era of innovation. As satellite positioning technologies and digital sensors continue to evolve, methods for infrastructure inspection will become even more sophisticated. It is important to actively embrace digital innovation centered on network RTK and build a safer, more efficient infrastructure management system. Let us make the most of the efficiency gains and risk reductions enabled by high-precision positioning and translate them into sustainable, safe, and secure infrastructure management.