Innovating Infrastructure Inspections with Network RTK: Improved Inspection Efficiency and Risk Reduction

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. Most inspection work relied on manual labor, with measurements based on maps and drawings and records written on paper, leading to the following inefficiencies:

• High labor and time burden: Detailed visual inspections require many technicians and sometimes traffic control, increasing operational costs.

• Complicated data management: Managing inspection results with paper ledgers and drawings makes searching and sharing information time-consuming and makes it difficult to analyze deterioration trends using past inspection histories.

• Limits in accuracy and objectivity: Traditional methods cannot record the exact coordinates of deterioration locations, and assessments tend to rely on experience and intuition. This leads to heavy dependence on veterans and challenges in transferring skills.

To address these issues, high-precision positioning technology using GNSS (Global Navigation Satellite Systems) and network RTK has attracted attention. Adopting network RTK in infrastructure inspections is expected to streamline inspection work, reduce risks, and transform infrastructure asset management. This article outlines the principles and advantages of GNSS positioning and network RTK, explains use cases and effects in sewer inspections and slope inspections, and introduces prospects for workflow improvements linked to digital ledgers and GIS, as well as future smartphone-based simple surveying (LRTK) and AR-assisted inspections.

Principles and advantages of GNSS positioning and network RTK

GNSS positioning is a technology that receives signals from multiple satellites such as GPS, GLONASS, and QZSS (Michibiki) to determine one’s position. General standalone GNSS positioning (such as smartphone GPS) can have errors of several meters to over ten meters (several ft to more than 30 ft), but using a method called RTK (Real-Time Kinematic) can dramatically improve positioning accuracy. RTK uses two receivers: a reference station installed at a known precise location and a rover (mobile receiver) that determines position while moving. By correcting errors in satellite data received simultaneously by both receivers in real time, errors can be reduced to a few centimeters (a few inches), enabling centimeter-level positioning.

Among these, network RTK receives correction information (differential data) via the internet from a network of multiple reference stations installed in various locations, providing stable high-precision positioning over wide areas. Users access regional reference station data via mobile communications, eliminating the need to set up their own base stations as in the past. In Japan, network RTK infrastructure such as the Geospatial Information Authority of Japan’s Continuously Operating Reference Stations and private VRS services is being developed, and environments where cm-level (half-inch accuracy) positioning can be stably obtained even in urban areas are emerging. Even in areas with many buildings, the spread of high-performance GNSS equipment that can receive GLONASS, QZSS, and other satellites in addition to GPS enables high-accuracy positioning.

Advantages of network RTK: Because centimeter-accurate position information can be obtained in real time, surveying can be carried out efficiently even in situations that were previously difficult. For example, wide-area topographic surveys can be completed in a short time with 3D measurements using network RTK. Also, obtaining high-precision coordinates on site allows immediate verification of measurement results and flexible responses such as reflecting findings in additional surveys. Above all, the ability to record and share obtained data digitally immediately—eliminating paper transcription and post-processing—greatly improves the accuracy of inspection records and operational efficiency.

Minimizing entry into hazardous areas through high-precision position verification

Using network RTK also enhances safety during infrastructure inspections because necessary data can be obtained while minimizing entry into dangerous areas. For example, in slope areas at risk of landslides or in inspections inside aging tunnels, technicians traditionally had to approach hazardous spots to take measurements. With high-precision GNSS equipment, positions and displacements of targets can be measured from safe, remote locations. In slope deformation monitoring, for instance, initiatives are progressing to detect subtle ground movements without human entry by continuously observing GNSS sensors installed on slopes with RTK positioning. At sites where roadway collapse occurred due to sewer collapse, a survey instrument equipped with RTK allowed a single inspector to quickly measure the shape and size of the collapse area, completing data collection while ensuring safety. Network RTK’s high-precision position verification shortens time spent in dangerous locations and greatly contributes to ensuring inspector safety and reducing risk.

Applying network RTK to sewer inspections: inspection history management and efficiency gains

Network RTK is powerful in the maintenance management of aging sewer pipelines. Some municipalities have re-surveyed the coordinates of all manholes across their cities using network RTK to review position information recorded in traditional sewer ledgers. Previous surveys relied on estimations using paper topographic maps or aerial photos, resulting in position errors of approximately ±20-30 cm (±7.9-11.8 in), which was insufficient for GIS use. By obtaining latitude, longitude, and elevation of all manholes with centimeter-level accuracy (half-inch accuracy), data were immediately registered into electronic ledger systems, substantially reducing subsequent drawing corrections and manual input. Overall, there are reports that survey and recording labor costs and time were reduced to a fraction of those using traditional methods.

The accurate position data achieved through improved accuracy helps precisely understand the condition of pipelines and facilities on sewer GIS. Connection relationships and routes between manholes and pipes can be displayed without displacement, making it easier to pinpoint inspection locations. Additionally, since past inspection histories and repair records can be linked and managed on maps, one can quickly reference what kinds of defects occurred at which locations. This enables data-driven sewer management, such as extracting heavily deteriorated sections for prioritized repair planning.

Network RTK is also useful in emergency response. In suspected cases of sewer pipe damage causing road collapse, the exact location and scale of the collapse hole can be measured instantly on site with RTK positioning, and that data shared with relevant departments via the cloud. Since all parties use unified position information, recovery work planning and assessment of the affected area proceed more quickly, helping to prevent further damage.

Applying to slope inspections: displacement management and preventive maintenance with 3D records

Network RTK is also active in slope and embankment inspections and monitoring. For slopes at risk of mudslides, quantitative displacement measurement in addition to routine patrols is important. High-precision RTK positioning can measure the heights and positions of multiple points on a slope periodically and capture changes in centimeter units (half-inch units). For example, along expressway slopes, RTK surveys are performed several times a year to record ground subsidence or uplift, and efforts are underway to analyze trends from accumulated data even for minute movements. Because network RTK allows wide areas to be measured against a common coordinate reference, slight deformations can be detected across surfaces, enabling early detection of signs such as “gradual subsidence progressing in a specific area.” This allows pre-identification of high-risk slopes for reinforcement work or earlier evacuation preparations, strengthening preventive maintenance measures.

Traditionally, slope inspections involved technicians approaching cliffs to measure crack widths with crack gauges or visually recording deformations. By combining network RTK with photogrammetry or 3D scanning, detailed 3D records can be obtained remotely while assigning precise coordinates to all points. For example, using an RTK-enabled drone for slope photogrammetry produces point clouds and orthophotos that are accurately georeferenced, allowing crack locations and collapse areas to be pinpointed on drawings. It is also possible to mount an RTK-GNSS receiver and a 360-degree camera on a work vehicle to record surrounding imagery and position information while driving—mobile mapping. From the office later, one can identify the exact positions of abnormal areas on the imagery, reducing the need for inspectors to spend long periods on dangerous slopes making handwritten notes, and enabling rapid digital recording and analysis of wide areas.

Introducing high-precision position data using network RTK is transforming preventive maintenance and recording methods in slope inspections. Combining 3D data and accurate coordinates makes constructing a digital twin (virtual replica of reality) of infrastructure feasible, allowing visualization of changes from the past to the present and making advanced maintenance approaches that predict future risks more realistic.

Workflow efficiency through integration with digital ledgers and GIS

The precise position data obtained with network RTK can be smoothly integrated with digital ledger systems and GIS, which is another key advantage. Previously, transferring inspection results from paper documents to computers or reflecting survey data on drawings was time-consuming. If high-precision positioning data are acquired digitally from the start, they can be uploaded directly from the field to cloud databases and geographic information systems.

In the sewer inspection example mentioned earlier, position information measured with network RTK was registered in the 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 allows all stakeholders to view the situation on the same map and discuss countermeasures. Integration with digital ledgers and GIS achieves centralized information management and instant sharing, shortening the time lag from inspection to reporting and decision-making.

Moreover, visualizing accumulated data on GIS makes it easier to analyze deterioration distribution and aging changes of infrastructure. For example, overlaying past repair histories and inspection evaluations on maps helps identify areas where failures frequently occur or structural weaknesses. This enables more effective future maintenance planning and clarifies where limited budgets and personnel should be prioritized. The fusion of accurate network RTK data and digital tools is driving the DX (digital transformation) of infrastructure maintenance operations.

The future of inspection support with smartphone RTK and AR: a new era opened by LRTK

Network RTK technology is advancing daily, and solutions that make its benefits more accessible are emerging. A notable recent development is smartphone RTK, which turns smartphones into high-precision positioning devices. A representative initiative is LRTK, where attaching a small RTK-capable GNSS receiver to a smartphone can improve smartphone GPS accuracy from several meters to a few centimeters (a few inches). With the convenience of attaching a device weighing about 100 grams to the back, a smartphone becomes a personal “simple surveying device,” enabling anyone on site to perform high-precision positioning and recording.

With LRTK, site technicians can complete surveying and data recording with a smartphone without specialized surveying equipment or large apparatus. For example, scanning the surroundings with a smartphone camera integrated app can generate 3D point cloud data on the spot, and each acquired point is tagged with accurate coordinates in real time. Even those without surveying knowledge can operate intuitively, and since positioning information is saved simultaneously with capture, there is no need for post-return reorganization of photo locations. Using AR (augmented reality) functions, it is possible to project buried pipes or past inspection data onto the real world through the smartphone screen. For example, if buried sewer pipes and cable locations are previously measured and recorded with LRTK, an AR display on the smartphone during inspection lets you know underground structure positions without excavation. In bridge or tunnel inspections, previously recorded cracks or displacement data can be overlaid with AR at the site to instantly compare progress since the last inspection.

As smartphone RTK becomes widespread, the style of infrastructure inspections will likely change significantly. When each technician carries means of high-precision positioning, inspections can be conducted more quickly and safely. Data collection, analysis, and sharing can be completed in real time, making inspection results more visible and improving on-site decision accuracy and speed. From a cost perspective, using small, versatile smartphones lowers the barrier to entry compared with dedicated equipment, making it easier for many municipalities and small and medium-sized enterprises to adopt cutting-edge technologies.

Conclusion: Network RTK pioneering innovation in infrastructure inspections

GNSS-based network RTK positioning is driving a dramatic increase in the efficiency and accuracy of infrastructure inspection and maintenance. By leveraging centimeter-level position information, manual fieldwork and ambiguous records have been replaced by digital processes, reducing workload and enabling objective, data-driven decisions. Combining high-precision positioning with digital ledgers, AR and other modern tools significantly contributes to risk reduction during inspections and to advancing preventive maintenance. The field is entering an era of innovation. As satellite positioning technologies and digital sensors continue to evolve, inspection methods will become increasingly sophisticated. It is important to proactively adopt digital innovations centered on network RTK to build safer, more efficient infrastructure management systems. Let us fully leverage the efficiency gains and risk reductions enabled by high-precision positioning to achieve sustainable, safe, and secure infrastructure management.