High-precision Positioning and AR Changing Kilopost Inspections: The New Normal of Smart Maintenance

The "kilopost" that indicates location on railways and roads is now at the center of a major shift in maintenance inspections thanks to the introduction of high-precision positioning technology (GNSS) and AR (augmented reality). This article starts with the basics of what a kilopost is, explains the challenges of conventional methods and the latest technologies that solve them, and details the benefits for both field crews and management. At the end, we introduce a first step anyone can take toward smart maintenance using the high-precision positioning system "LRTK."

What is a kilopost? The cornerstone of position management for railways and roads

A kilopost is a sign that indicates distance along a line, such as on railways or highways. In many cases, the cumulative distance from the line’s origin is displayed in kilometers (and, where needed, in 100 m (328.1 ft) units), and in Japanese railways it is also called a "distance marker." For example, a sign reading "KP 12.5" means that the location is 12.5 km from the origin.

On railways, kiloposts are important landmarks used by drivers to determine their current position, by track maintenance crews to specify target sections, and by asset managers to organize the placement of signals, level crossings, and stations. On roads, kiloposts installed on the shoulder of highways serve as distance markers and as a clue for drivers to accurately report their location in the event of an accident or breakdown. In this way, a kilopost can be thought of as the "address" on a track or road, serving as the positional reference for infrastructure management. Kiloposts are essential baseline information for daily patrols and repair planning, forming the basic way to express locations in maintenance tasks, such as "an anomaly occurred near km ◯◯ on line ◯◯."

Problems with conventional kilopost inspection and recording methods

For many years, inspections of linear infrastructure have relied on kiloposts to locate sites, with verification by visual inspection or simple measurements and records written on paper. However, these conventional inspection and recording methods have many inefficiencies and risks. Much depends on the experience of field technicians, and managers often struggle to utilize the information. Major issues include the following:

• Signs are hard to see and positions are easily misidentified: Kilopost signs themselves can be obscured by dirt or the surrounding scenery and overlooked. Visual confirmation is difficult during night work or along overgrown linesides, which often leads to mistaking the actual location and incurring losses from re-searching or redoing work.

• Measuring and verifying distances is time-consuming: Even if you know a point is "X km Y m from the origin," pinpointing that point in the field requires measuring with a tape or surveying instruments, often needing multiple people and back-and-forth checks. It also takes time to cross-reference your position on paper drawings.

• Cross-checking with ledgers and drawings is inefficient: Matching field information to existing asset ledgers or paper plans is a cumbersome process. For example, even if you are told "the drainage facility near km X," it takes time in the office to open the ledger and find the relevant spot, often spreading paper drawings out to verify. This analog cross-checking is also a breeding ground for mistakes.

• Linking photos to location information is tedious: Organizing photos taken during inspections later and recording which kilopost area they were taken near is cumbersome. Standard cameras or smartphone photos often have positional errors of several meters to several tens of meters, leading to manual annotation of photos or jotting positions into ledgers. This places a heavy burden on later report creation and data organization.

• Digital utilization lags and information sharing is difficult: Because many inspection results remain on paper or in oral reports, collected information cannot be fully shared or utilized internally. Vague positional records prevent registration in GIS (geographic information systems), blocking advanced asset management such as analyzing past data to detect deterioration trends. In an emergency, receiving a report of "damage near km X" may still take time to accurately locate, becoming an obstacle to future DX (digital transformation).

Eliminating positional ambiguity through coordinateization with high-precision GNSS

A trump card for eliminating such "positional ambiguity" is coordinateization using high-precision GNSS positioning. GNSS (Global Navigation Satellite Systems) calculates ground positions from multiple satellite signals. Conventional GPS typically has errors of several meters, but recent RTK (Real-Time Kinematic) methods dramatically reduce positioning errors. RTK uses real-time correction information from a base station to achieve centimeter-level positioning, and combinations of smartphones and compact receivers can now realize centimeter-level accuracy, not just specialized equipment.

With high-precision GNSS, you can record the positions of kiloposts themselves as exact coordinates (latitude and longitude) and measure inspection points’ coordinates on site. For instance, typical GPS errors of ±5–10 m (±16.4–32.8 ft) can be reduced to ±a few centimeters by using network RTK services. This enables absolute positioning such as "latitude/longitude on the World Geodetic System is XX," rather than merely saying "near which kilopost." If you pre-acquire coordinates for all kiloposts as reference points, you can immediately determine from your current latitude and longitude which kilometer and meter point you correspond to, eliminating the risk of mistaking locations even if a sign is missing. With position information accurate to a few centimeters, matching to assets on ledgers can be automated more easily, forming the basis for cloud and AR utilization described below.

Smartphone × AR for on-site "visible" inspections and position identification

Once high-precision position data is available, AR (augmented reality) technology becomes useful as an intuitive way to use it on site. AR overlays digital information onto the camera view of a smartphone or tablet and is effective for kilopost inspections. For example, when looking at track or road scenery through a phone screen, virtual signs or arrows could indicate the direction and distance to the next kilopost. This makes it immediately clear "the next X km post is Y meters ahead," reducing the risk of missing it in low light or bad weather.

AR also lets you visualize information from drawings and ledgers directly at the site. For bridge or tunnel inspections, past crack locations and repair histories can be displayed as AR markers on the actual structure. This allows you to see on one screen "where and what kind of damage existed before" while visually inspecting the object, helping prevent missed deterioration and making condition comparisons easy. The locations of buried cables and pipes can be projected onto the ground with AR for pre-excavation checks. AR can project 3D models on-site too, enabling overlay of as-built or design models onto the real landscape to share construction expectations.

In such a smartphone × AR "visualized" site, even less-experienced personnel can follow on-screen guidance to be led to the correct spots and confirm key points without omission. Easier image sharing among workers smooths team communication, improving both the quality and efficiency of inspections.

Integrated records of photos, point clouds, and drawings: from the field to the cloud

High-precision positioning and AR also greatly advance the digitization and cloudification of field records. Previously, photos taken with a digital camera required handwritten kilometer notes, later imported to a PC and cross-checked with ledgers. Modern smartphone apps can automatically add precise position coordinates and orientation data (camera heading) to photos at the moment of capture and save them directly to the cloud. For example, using an app like LRTK, the moment you photograph a crack on a bridge pier, metadata such as "captured at latitude XX, longitude XX, height XX m, heading XX°" is recorded, avoiding manual notes. These photos can be managed on the cloud in conjunction with maps, so you can accurately trace "which point the photo was taken at" even later.

Smartphone 3D scanning (point cloud measurement) has also become realistic. Using LiDAR sensors on devices like the iPhone or photogrammetry from camera images, the shape of structures or roadbeds can be recorded as a dense set of points (a point cloud). Whereas dedicated 3D laser scanners once cost hundreds of thousands of dollars, a combination of a smartphone and high-precision GNSS can acquire point cloud data in a matter of minutes. The acquired point cloud is stored in the cloud as three-dimensional data with absolute coordinates, enabling advanced uses such as measuring dimensions from the office or overlaying with design drawings to analyze displacement.

Digitally recording photos, point clouds, notes, and drawings on-site and sending them directly to the cloud is the essence of "smart maintenance." When data is uploaded to the cloud, office managers and other teams can share information in real time. Eliminating transcription to paper or retyping into Excel reduces recording errors and greatly streamlines report creation. As data accumulates from inspections, the company’s digital assets grow, creating a virtuous cycle.

Becoming the core of asset management through ledger integration, GIS linkage, and CIM

High-precision positional data, images, and point clouds collected at the site show their true value when integrated with existing asset ledgers and GIS systems. For example, asset information for bridges and tunnels previously managed with paper drawings or Excel can gain tremendous visibility when plotted on a GIS map with precise coordinates. If kiloposts are used as keys to link equipment information and past inspection histories, clicking a point on the map can instantly display related photos and records. Field staff and managers can reference a common database, meaning "what was found in the field" is immediately shared as a management resource. In disasters, affected coordinates can be shared promptly among stakeholders to identify locations on a map and quickly discuss response measures.

In the future, these integrated data sets can be used to promote CIM (Construction/Infrastructure Information Modeling). CIM is the civil infrastructure counterpart of BIM (Building Information Modeling), aiming to centralize structure geometry, attributes, and history on a 3D model. Aggregating point clouds and design data tied to kiloposts makes it possible to build a digital twin of long linear assets like railways and roads. If a 3D model covering the entire line can visualize equipment information and deterioration linked to each kilopost, asset management—once planar and fragmented—evolves into a three-dimensional, bird’s-eye view. Maintenance data becomes corporate knowledge, serving as a core management resource for future repair planning and budgeting.

Smart strategy for linear asset modernization centered on kiloposts

Improving the precision and digitization of position information centered on kiloposts naturally leads to a smartization strategy for the entire linear asset. Because line-type infrastructure like railways and roads are long and composed of numerous elements, partial digitization can still leave gaps in overall understanding. By using kiloposts installed at regular intervals along the line as data integration hubs, you can achieve vertically and horizontally connected infrastructure management.

For example, in railways, first survey all kiloposts with high-precision GNSS and register each as a reference point with absolute coordinates. Then link data for level crossings, bridges, signals, grade markers, and other equipment located between those posts to build a digital map of the line. Organizing data along kilopost distances allows systematic management of "what equipment is at what kilometer point and when it was inspected or repaired." The keys to progressing DX for linear assets are establishing a unified standard across the whole (coordinates and kilometrage) and phased data preparation. Kiloposts are a familiar on-site standard that can serve as the core for clear digitalization understandable by both field staff and executives.

Once a kilopost-based data foundation is in place, advanced technologies like IoT sensor monitoring and AI-powered predictive maintenance can be smoothly integrated. Smartization technologies for infrastructure ultimately rely on accurate field data and positional information to be effective. Building digital data assets centered on kiloposts now is a forward investment for future technology adoption.

Effects of introducing kilopost coordinateization and AR inspection with LRTK

What specific tools can realize the high-precision positioning and AR in the field described above? One answer is LRTK. LRTK is an all-in-one solution that implements RTK-GNSS positioning, 3D scanning, and AR display using a smartphone. A dedicated compact high-precision GNSS receiver (weighing about 165 g) is attached to an iPhone or similar device to perform real-time centimeter-level positioning while automatically syncing acquired coordinates, photos, and point-cloud data to the cloud. The operation is simple, and the positioning status is displayed on-screen as "accuracy XX cm," making it usable even by non-specialist surveyors.

With LRTK, kilopost coordinateization becomes astonishingly simple. For example, tapping the positioning button in the smartphone app while standing next to a kilopost sign records that point’s precise latitude, longitude, and altitude in one touch. If you enter a note such as "Line XX km XX m post" in the memo field, it is registered on the cloud map and can later be searched and viewed in the database. If kilopost coordinates are already registered, confirming your current position on site becomes easy: your position and the kilopost’s position are shown simultaneously on the phone screen, eliminating the need for rough guesswork. The ability for newcomers to reach designated points without getting lost is a major advantage.

The LRTK app also includes a "coordinate navigation" function that guides users to specified coordinates and an AR function that overlays arbitrary 3D model data on site. For example, if you set the coordinates for the next work point, holding up your phone will display arrows to guide your way. If you load design data or buried object locations in advance, virtual models or markers appear in your view to enable inspection of otherwise invisible targets. The fact that all of this can be achieved with a single smartphone and cloud linkage is a core strength of LRTK.

So what benefits can be expected from introducing LRTK? Incorporating high-precision positioning and AR into field inspections produces a wide range of advantages from field operations to information management:

• Major efficiency gains in inspection work: Tasks that previously required 2–3 people and half a day for surveying and position identification can be completed by one person in tens of minutes using LRTK. Reduced travel and re-measuring saves time and shortens patrol inspection durations.

• Reduction of human error: Mistakes such as misjudging locations or incorrect records are nearly eliminated. Working from always-accurate coordinate data prevents wasted investigations at the wrong locations.

• Streamlined reporting and ledger creation: Photos and survey point data are automatically organized and saved to the cloud, making office report creation significantly easier. Transcription errors are avoided and data organization workload is reduced.

• Improved safety: As more tasks can be completed by a single person, inspections can be carried out with a minimum crew, lowering risks during night work or on high-traffic sites. Faster measurements reduce the time workers spend on tracks or roads, contributing to worker safety.

• Accumulation and utilization of data assets: High-precision data collected with LRTK is stored in the cloud, so the company’s digital assets grow with use. This enables long-term deterioration trend analysis and more advanced preventive maintenance planning, facilitating data-driven asset management.

Trials of LRTK by local governments and railway operators are already underway domestically, with feedback such as "the ease of doing positioning and recording at the same time is revolutionary" and "inspection productivity has dramatically improved." The combination of high-precision GNSS and AR is expected to inject a fresh breeze into an infrastructure maintenance world that has been analog-centered, raising both field capability and management capability.

Start with a single point: Recommended first step toward high-precision, labor-saving inspections with LRTK

The benefits of smart maintenance using high-precision positioning and AR are clear, but switching everything at once is not realistic. What we propose is to start small with "just one point." For example, pick a single important kilopost on a route where management faces challenges and try simple surveying and AR inspection there using LRTK.

For a simple LRTK survey, the required equipment is minimal—just a smartphone and a compact GNSS receiver—and no complex preparation is necessary. Performing positioning and recording at one point will make the near-zero effort required to identify locations apparent, and you will experience the comfort of data being automatically organized and shared. You may be surprised that "all the recording was completed with just this little work!"

Accumulating those small successes reduces field staff resistance and makes it easier to gradually expand the introduction. Begin at one point, then expand to a portion of the line, and eventually to the entire line in stages to promote digitalization without undue strain. Please consider adopting high-precision positioning + AR, which is becoming the new normal of smart maintenance, in your infrastructure management. The small step you take now should lead to significant future efficiency gains and increased asset value.