The Importance and Challenges of Urban Infrastructure Inspection

Maintaining urban infrastructure—sewers, roads, bridges, and more—is crucial to ensuring a safe and secure society. Planned inspections and repairs are indispensable for preventing failures in aging assets, such as ceiling-panel collapses in tunnels or failures of water-supply bridges. Since 2014, Japan has required periodic inspections—close-up, hands-on checks every five years—for structures like bridges and tunnels, and municipalities as well as road authorities nationwide are working to comply.

Traditional inspection methods, however, face many challenges. Because they rely heavily on manual labor, ground surveys, visual checks, and paper-based records tend to introduce significant inefficiencies.

• High labor and time demands: Detailed visual inspections of roads and bridges require many engineers and often entail traffic restrictions, driving up operational costs.

• Cumbersome data management: When inspection results are stored in paper logbooks or on drawings, searching and sharing information is slow, and analyzing changes over time becomes difficult.

• Limits on precision and objectivity: Conventional methods rarely record deterioration with exact coordinates, so evaluations tend to rely on individual judgment and experience. Expertise remains trapped in veteran inspectors’ heads, making knowledge transfer a persistent challenge.

To address these challenges and streamline infrastructure inspections, the industry is turning to digital technologies—chief among them RTK positioning. By incorporating RTK’s centimetre-level location data, agencies can expect both greater accuracy and higher efficiency in inspection tasks. The next section explains the fundamentals of RTK technology and its usefulness in urban infrastructure management.

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RTK Basics and Its Use in Urban Infrastructure Inspection

RTK (Real Time Kinematic) positioning employs two GNSS receivers—a fixed base station and a mobile rover—to correct satellite-navigation errors in real time, achieving centimetre-level accuracy. Whereas stand-alone GPS/GNSS typically drifts by several to more than ten metres, RTK narrows the error to just a few centimetres. It does so by having the base station transmit its observed satellite-error data to the rover; the rover then combines that information with its own observations to calculate a highly precise relative position.

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Using RTK positioning for urban-infrastructure inspections boosts both positional accuracy and operational efficiency. When manholes or roadside fixtures are recorded in sewer maps or road ledgers at centimetre-level precision, pinpointing inspection targets and drafting maintenance plans become dramatically easier. Because RTK delivers high-accuracy coordinates in real time, data measured in the field can be fed directly into a GIS, eliminating paper transcription and post-processing. The result is faster inspections, quicker data updates, and speedier decision-making.

Why RTK works in built-up areas: Satellite signals in cities are often blocked or distorted by buildings, degrading accuracy. Today, however, high-performance GNSS receivers that track multiple constellations—GPS, GLONASS, QZSS (Michibiki), and others—along with nationwide network-RTK services that use electronic reference stations, now provide stable centimetre-class positioning even in dense urban environments. RTK makes it possible to obtain precise coordinates efficiently in locations that were previously hard to survey, driving digital transformation (DX) in infrastructure inspection.

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Examples of Higher Accuracy and Greater Efficiency

• Large-area surveying: Mapping elevation differences across hundreds of hectares of urban terrain once required time-consuming leveling or manual interpretation of contour maps. In one sewer-planning project, a network-RTK system captured 3-D data for an area of about 1,200 ha in a short period, allowing the work to be completed far more efficiently than before. RTK makes it possible to carry out wide-area infrastructure surveys in a fraction of the usual time.

• Real-time on-site decisions: Because RTK delivers precise coordinates immediately, crews can review data in the field and conduct extra measurements or corrections on the spot. For example, when investigating possible road subsidence, inspectors can use RTK to obtain elevation data instantly, analyze settlement at the scene, judge the hazard level, and initiate emergency measures if necessary.

• More accurate digital records: When inspection results are plotted on a digital map, RTK’s centimetre-level accuracy minimizes positional shift and enables precise comparison with historical data. Cracks or displacements can be pinpointed, allowing maintenance teams to set repair priorities with greater confidence.

In this way, RTK positioning can be a game-changer for urban infrastructure management, sharply boosting survey accuracy and operational efficiency. The next section looks at concrete cases where RTK has been used to carry out infrastructure inspections.

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Case Studies: Successful Uses of RTK in Urban-Infrastructure Inspection
Below are three success stories showing how RTK technology has been deployed in the field. They span different areas—manhole surveying for sewers, roadway-subsidence investigations, and 3-D mapping of infrastructure—illustrating how RTK is applied and the benefits it delivers.

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Case 1: Precise Positioning and Management of Sewer Manholes
To strengthen upkeep of its aging sewer network, one municipality launched a project to improve the positional accuracy of all manholes. Previously, locations were estimated from 1 : 500 base maps and aerial photogrammetry, yielding accuracy of roughly ±25 cm—insufficient for reliable use in the municipal GIS. The city therefore adopted VRS-RTK surveying and re-measured every manhole at centimeter-level precision.

Thanks to RTK, coordinates were recorded digitally on site, cutting post-processing time dramatically. Formerly, crews surveyed in the field and then corrected drawings and keyed data back at the office, incurring significant labor costs. With RTK, positions are captured and exported directly on location, reducing total personnel hours by about two-thirds. The leap in accuracy also lets planners see manholes and pipelines in their true spatial relationship within the new sewer-GIS ledger, raising the quality of maintenance planning.

This case shows that applying RTK to sewer surveying can simultaneously boost measurement accuracy and operational efficiency. Because asset data are now exact, the city can prioritize repairs and replacements far more effectively—a major achievement in infrastructure management.

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Case 2: Using RTK for Road-Subsidence Investigations and Ground-Risk Analysis
In many cities, roadway sinkholes caused by failures in aging sewer lines are a serious concern. One road authority has adopted RTK technology both for rapid response when a collapse occurs and for proactive monitoring of ground-stability risks.

When a sinkhole appears, the first task is to survey the cavity’s position, size, and surrounding topography with high accuracy. Whereas crews once relied on a total station and manual measurements, an inspector can now complete a full 3-D survey in a short time using an RTK-enabled GNSS receiver. The centimetre-level data are uploaded immediately to a cloud-based GIS and shared in real time with all relevant departments, speeding emergency measures and restoration planning.

The authority also uses RTK for preventive maintenance. By periodically measuring subtle settlement or heave along the roadway with RTK and archiving the elevation data, engineers can detect early signs of underground voids. Although RTK height accuracy is on the order of ± 2–3 cm, the method provides a consistent reference across wide areas, making it possible to map even slight surface changes. Decisions such as “this zone is showing subsidence—underground utilities should be investigated” can thus be made on a solid data foundation, reducing future sinkhole risk.

In short, introducing RTK to road inspections supports both emergency response and preventive asset management. High-precision terrain-change data give engineers a scientific basis for assessing subsurface conditions and planning maintenance.

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Case 3: RTK-GNSS in Infrastructure 3-D Mapping
In recent years, 3-D mapping has become widespread in infrastructure inspection through drone imagery, mobile-mapping systems (MMS), and terrestrial LiDAR. Even with these techniques, RTK-GNSS plays a crucial role in achieving precise georeferencing.

For instance, during high-resolution photogrammetric inspections of highway bridges, using a drone equipped with RTK allows every photo to be tagged with centimetre-accurate coordinates. The resulting 3-D products—point-clouds and orthophotos—align perfectly with the map coordinate system, letting engineers pinpoint crack locations and other defects directly on drawings. Tasks that once required ground targets and labor-intensive post-alignment are simplified, and positional accuracy becomes far more consistent.

In another project, a road-maintenance vehicle was outfitted with a 360-degree camera and an RTK-GNSS receiver, creating a mobile-mapping system that captured video of the pavement and nearby structures together with precise position data while driving. Because each video frame was tagged with centimetre-level coordinates via RTK, inspectors back in the office could pinpoint the exact map location of every detected defect. This eliminated the need for inspectors to jot down positions by hand on site and enabled a wide stretch of infrastructure to be digitally archived in a short time.

Thus, cutting-edge 3-D mapping technologies pair naturally with RTK positioning, forming a bridge between the digital and physical worlds. A centimetre-accurate RTK foundation lets data captured by drones and other sensors be merged precisely, making it possible to build a true digital twin of infrastructure for advanced analysis and predictive modeling.

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How to Introduce RTK into Urban-Infrastructure Management
To deploy RTK positioning for inspection and maintenance, you must secure the right equipment and establish an operating framework. The sections below outline the required hardware and costs, ways to use the resulting data, and key points to watch when adopting the system.

●Required equipment and costs:RTK surveying generally needs two GNSS receivers. One serves as the base station, set on a point with known coordinates; the other is the rover, which moves around to measure the targets. You must also provide a communication link to send correction data from the base to the rover. Options include dedicated short-range or UHF radios, or an Internet connection over a mobile network using the Ntrip protocol.

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Approximate equipment setup and costs are as follows:

• GNSS receiver (rover) – A high-precision, RTK-capable unit. Affordable RTK receivers have appeared in recent years, priced from a few hundred thousand yen* each. Supply multiple units if several field crews work simultaneously.

• GNSS receiver (base) – Installed on a control point; the same model used for the rover will suffice. Including a tripod, battery, and communications device, expect another few hundred thousand yen. If you use an existing electronic reference station or a public reference-station service, a dedicated base receiver may not be necessary.

• Communications equipment/service — the data link from the base station to the rover. If you use a radio link, you must cover licensing fees and hardware costs, typically ranging from several tens of thousands to over one hundred thousand yen.If you rely on the cellular network, you’ll need a SIM data plan and a subscription to an RTK correction-data service, usually starting from a few thousand yen per month.

• Field terminal – The controller that the rover operator carries to view and log positioning results. This can be a rugged tablet or laptop, and many modern RTK systems now allow a smartphone to serve as the controller. Be sure to include the cost of any required apps or software.

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●Leveraging Survey Data through GIS Management
High-precision coordinates obtained with RTK should be imported into a GIS or other asset-management platform. In sewer and road maintenance, linking each facility’s attributes to accurate spatial data creates a map-based ledger that streamlines inspection and repair planning.

Because RTK positions are stored in a common reference frame—such as Japan’s Geodetic Datum 2000/2011—they can be overlaid easily with other map layers. For example, registering RTK-measured manhole locations in a GIS and linking them to pipe-deterioration or pavement-damage records lets managers visualize exactly “where” and “how severely” defects occur. With a cloud-based GIS, field data entered on site become instantly available across the organization, accelerating decision-making.

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●Precautions when introducing RTK: There are several key considerations to keep in mind during implementation.

• Securing a reliable positioning environment: In urban settings, buildings and trees can block GNSS signals. Place the antenna where it has the clearest sky view; if necessary, mount it on an extension pole or supplement reception with zenith satellites such as QZSS (Michibiki).

• Performing accuracy checks: Although RTK’s nominal accuracy is a few centimetres, verify this before full deployment—test on known control points and examine error variations versus baseline length. If needed, tie into existing benchmarks to correct elevations and embed these verifications in your workflow.

• Training operators: Educating field staff is critical. Provide instruction on receiver operation (satellite acquisition, starting a survey, recognising a FIX, handling communication issues) and on managing coordinate data (understanding reference systems, performing transformations).

• Balancing cost and benefit: RTK equipment and services involve upfront and ongoing expenses. Identify exactly which parts of your operation will be streamlined or enhanced, and clarify the cost-effectiveness. Fortunately, lower-priced devices and monthly subscription services are now available, putting RTK within reach even for small and mid-sized civil-engineering firms.

By keeping these considerations in mind and implementing RTK correctly, you can make significant progress toward digital transformation in urban-infrastructure management. The next section introduces LRTK, a compact high-performance RTK device, and explains practical use cases and how to request further information.

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Introducing LRTK

To close, let’s look at LRTK, one of today’s most advanced RTK solutions. Developed by Lefixea Inc., the LRTK series offers compact, lightweight, high-precision RTK-GNSS receivers designed for maximum ease of use in the field. Whereas traditional RTK surveying relied on bulky, tripod-mounted equipment, LRTK brings the same centimetre-level accuracy to a smart, highly portable form factor.

A prime example is the “LRTK Pro2,” a rugged all-in-one unit that integrates antenna, receiver, battery, and radio. It delivers stable centimetre-class positioning even in the harsh conditions typical of construction sites. Thanks to its built-in tilt compensation, you can record the exact tip coordinates of the pole even when it is not perfectly vertical.

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Key Features of LRTK

• Compact and lightweight: A highly portable design makes transport and setup straightforward. The “LRTK Pro2,” for instance, is an antenna-integrated unit roughly 20 cm in diameter; even when mounted on the tip of a survey rod it stays out of the operator’s way.

• High-precision positioning: Supporting multiple GNSS constellations, LRTK handles standard RTK as well as Japan’s Quasi-Zenith Satellite “Michibiki” CLAS centimetre-level augmentation service. Even in remote mountain areas with no internet access, satellite corrections alone can provide centimetre accuracy. Field tests show sub-centimetre precision in static mode and steady centimetre-class accuracy while moving.

• Instant use and seamless integration: Pair the receiver with the dedicated LRTK App on a smartphone via Bluetooth; power up and start surveying within moments. Position data can be pushed to the cloud through the phone or plotted on a map on the spot. Streamlined setup and an intuitive interface let any crew member use the system with minimal training.

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LRTK also comes in unique form factors tailored to different tasks. The “LRTK Phone” is a clip-on RTK attachment for smartphones; it lets every photo you take carry a centimetre-accurate geotag, dramatically enhancing the reliability of inspection records such as crack images. The “LRTK Helmet” mounts an ultra-thin antenna on a hard hat, enabling hands-free surveying while you walk. Because positioning happens above your head, you can measure as you inspect—and the lighter load reduces fatigue during long patrols.

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The “LRTK Phone” clips onto an ordinary smartphone, instantly enabling RTK positioning. Every photo taken with the phone is automatically linked to centimetre-level coordinates and saved to the cloud—an invaluable tool for documenting disaster scenes or recording cracks and other defects in structures.

Field deployment on construction sites: The LRTK series is already in use across construction and civil-engineering projects. On one paving site, the LRTK Pro2 was used for as-built checks; finish-surface measurements were completed in less than half the time required by conventional methods. In inspection work, a road-bridge team adopted LRTK Phone so that every damage photograph taken by staff is automatically stamped with coordinates, streamlining report preparation and boosting accuracy. The helmet-mounted version has been introduced for patrol inspections at a large industrial plant, precisely logging workers’ movement histories to prevent missed checkpoints and improve safety—an example of the new applications emerging for LRTK.