Using LRTK for Kilometerage Surveying in Roadworks – Streamlining Construction Management with Centimeter-Level (cm level accuracy (half-inch accuracy)) Precision

In roadworks, measuring and managing kilometerage (kilotei) is essential for locating worksites and ensuring quality control. Traditionally, obtaining kilometerage on site required manual distance measurements or positioning using surveying instruments, which was time-consuming and labor-intensive. However, with the recent emergence of LRTK—RTK-GNSS technology combined with a smartphone—anyone on site can now obtain kilometerage instantly with centimeter-level precision. This article first explains what kilometerage is and why it matters, then reviews the challenges of traditional surveying methods. Next, it describes the advantages of real-time positioning using RTK-GNSS with a smartphone, the on-site surveying and recording workflow using LRTK, and prospects for sharing position information via point-cloud measurement, AR, and cloud integration. Finally, it summarizes the benefits of adopting these technologies.

What is kilometerage? The importance of position management in roadworks

An example of a kilometerage marker (kilopost) installed on a road. The “175.1” on the sign indicates the point 175.1 km (574,475.1 ft) from the starting point. In the road and railway sectors, the display of distance from the starting point—known as kilometerage—is widely used. Roads are equipped with distance markers called “kiloposts” every 100 m (328.1 ft) or 1 km (3,280.8 ft); for example, a display of “12.5” indicates the point 12.5 km (41,010.5 ft) from the road’s starting point. Kilometerage is often called the “address of the road” [distance from the road’s starting point = address], serving as a common reference to indicate specific points on a road. Kilometerage management is critically important at construction sites. Design drawings denote the start and end points of structures such as interchanges, intersections, bridges, and tunnels using kilometerage—for example, “The ○○ Bridge is located from 15.2 km (49,868.8 ft) to 15.8 km (51,837.3 ft) from the starting point.” During construction, all events and structures are managed and reported by kilometerage—for example, “The ○○ intersection is installed at kilometerage 12.500 km (41,010.499 ft)” or “The drainage structure is installed at kilometerage 5.250 km (17,224.409 ft).” Even in post-construction as-built inspections (checking quantities and forms), it is necessary to verify “whether things fall within the designed kilometerage” and “whether construction in each prescribed segment was performed at the correct location.” Thus, kilometerage is the axis of position reference in roadworks and indispensable for sharing accurate location information among stakeholders.

However, accurately determining kilometerage along long roadworks sites is not easy. When station intervals are long, distance markers or survey stakes may be missing on site, and workers can struggle to estimate their location or the kilometerage of a construction point. For example, on expressway renovation sites workers rely on kiloposts at the shoulder to identify their current location, but on ordinary roadworks there may be no kiloposts at all. Therefore, technology that can measure kilometerage quickly and accurately is a crucial factor directly linked to on-site efficiency and quality assurance.

Traditional kilometerage surveying methods and their challenges

Traditionally, kilometerage on road sites was measured mainly by manual distance measurement or with dedicated surveying equipment. Typical methods included measuring distance from a reference starting point or known point using a tape measure or survey chain, or rolling a wheel-type distance meter along the road surface. For long sections, survey stakes were driven every 50 m (164.0 ft) or 100 m (328.1 ft), with kilometerage markings recorded on the stakes to help roughly locate positions on site. However, these tasks require a lot of manpower, and cumulative measurement errors become significant as distances increase. On curved or sloped sections in particular, differences between planimetric distance and surface distance and slope corrections must be considered, and leveling (horizontal setup) and corrections on inclined ground add further work.

Using surveying instruments such as total stations (electro-optical distance meters) or levels is another option. For example, a surveyor sets up a total station and calculates the coordinates of survey points from distances and angles to known points, then converts those coordinates to kilometerage on the drawings. But bringing high-precision equipment to site involves large, heavy instruments and tripods, and leveling and setup alone consume time. Typically a crew of two or more is required—one to operate the instrument and another to hold the staff (prism) at the survey point—resulting in significant personnel costs. In addition, these specialized instruments are expensive and precise, requiring regular calibration and maintenance, and arranging and preparing equipment for each survey can be time-consuming.

Manual surveys centered on labor also tend to prolong working hours, and adverse weather or site conditions can prevent planned progress. For example, tape measurements are difficult in rain, and poor visibility reduces the observational accuracy of surveying equipment. Moreover, processes that involve manually copying measured values into notebooks and later re-entering them into spreadsheets are prone to recording or transcription errors. In short, traditional kilometerage measurement faces challenges such as “high labor requirements,” “complex procedures,” “time consumption,” and “risk of errors and mistakes.”

Real-time kilometerage measurement using RTK-GNSS and smartphone integration

To address these surveying challenges, a new technology combining RTK-GNSS (real-time kinematic GNSS) with smartphones has emerged. RTK-GNSS is a method that dramatically improves positioning accuracy in satellite-based positioning systems (GPS, GLONASS, QZSS, etc.) by using correction information from a base station. While a smartphone’s built-in GPS typically has errors of several meters, RTK can improve accuracy to the order of several centimeters (cm level accuracy (half-inch accuracy)). Specifically, a base station (fixed station) at a known position and a rover (the surveyor’s receiver) simultaneously receive satellite signals, and the phase difference between their signals is used to compute high-precision relative positions. Performing this processing in real time enables the rover to obtain its precise coordinates instantly.

By using RTK-GNSS, centimeter-level position coordinates (cm level accuracy (half-inch accuracy)) can be obtained immediately even on roadworks sites. Applied to kilometerage management, it becomes possible to directly calculate the distance from the starting point. For example, if the starting point coordinates and route alignment data are known from the road design, the current position’s coordinates measured by GNSS can be used to compute the distance from the starting point, allowing the system to display in real time “this point is X km Y m from the starting point.” Tasks that previously required calculating distances on drawings or confirming with chain tapes on site can now be computed instantly from GNSS coordinates, greatly improving the speed and accuracy of measurement.

Making RTK positioning easy to use on site is achieved by integrating it with smartphones. A smartphone is a ubiquitous communication device and an intuitive platform for various apps. By linking a compact RTK-GNSS receiver to a smartphone, an era has arrived in which “a smartphone itself becomes a high-precision surveying instrument.” If the smartphone uses mobile communications to receive base station correction data over the Internet, high-precision positioning can be achieved without large dedicated equipment. In Japan, the QZSS (“Michibiki”) provides a centimeter-level positioning augmentation service (CLAS) (cm level accuracy (half-inch accuracy)), and with a compatible receiver it is possible to obtain correction information directly from satellites even without cellular coverage. This enables RTK positioning to continue in mountainous areas where the Internet is unavailable, allowing high-accuracy kilometerage measurement anywhere.

A smartphone-integrated RTK-GNSS system is revolutionary not only for acquiring position information but also for real-time data processing and sharing. Positioning results are displayed on the smartphone screen as numerical values or map points, making one’s location immediately visible. For example, if the system provides “current location: longitude XXX°, latitude YYY°, ellipsoidal height ZZZ m (geoid height △△ m), plane rectangular coordinates (X=..., Y=..., H=...),” the app can automatically calculate and display the kilometerage (distance from the starting point) based on those coordinates, and the data can be sent to the cloud for immediate sharing with office staff. As a handheld, high-accuracy positioning tool available to anyone on site, the smartphone + RTK combination is transforming surveying practices in roadworks.

On-site surveying and recording workflow using LRTK

How does the on-site workflow change when using LRTK, the smartphone-connected RTK-GNSS device? LRTK is a pocket-sized receiver that attaches to a smartphone. To prepare, install the dedicated app on the smartphone, power on the LRTK device, and connect via Bluetooth or similar—no complicated wiring is required, and there is no long initialization time like with conventional equipment. Tapping a button in the app instantly configures RTK positioning, starts receiving satellite signals, and acquires correction information. Within several tens of seconds the “fixed solution (Fix)” is obtained, and once positioning stabilizes to centimeter precision (cm level accuracy (half-inch accuracy)), you are ready to measure.

An LRTK Phone device attached to a monopod. By touching the tip to the ground and pressing a button on the smartphone screen, the coordinates of a survey point can be recorded. Because LRTK is lightweight it can be used handheld, but attaching it to a commercially available monopod as shown provides stable measurements. Using a dedicated attachment to fix the smartphone and receiver to the pole, simply touch the pole tip to the point to be measured (ground or on a structure) and operate the button to obtain the precise coordinates of that point. If the height offset (distance from the ground to the device) is pre-set in the app, the correction is applied automatically, so simply holding the pole vertically yields a 3D coordinate that includes height. Because you move to each measurement location and press a button, one person can continuously measure many points.

Positioning results can be confirmed in real time on the smartphone screen. For example, the display may show “current location: longitude XXX°, latitude YYY°, ellipsoidal height ZZZ m (geoid height △△ m), plane rectangular coordinates (X=..., Y=..., H=...)” and indicate whether the RTK solution is fixed and how many satellites are being tracked. Each survey point is automatically assigned a sequential number and timestamp, and users can add titles or notes such as “intersection start point” or “pier installation location.” Instead of writing notes in a field book, you can manage them digitally on the smartphone. Recorded data can be saved in the app and uploaded to the cloud with a single button. Uploaded data can be viewed from an office PC via a web browser, eliminating the need to hand over USB drives or paper between the field and the office.

Using LRTK simplifies the overall arrangement of surveying tasks. In the past, a specialist surveying team had to be called in to set up equipment, but with LRTK construction managers or workers can quickly take the device from their pocket and measure as needed, enabling “measure whenever you want.” For example, if a discrepancy with the design is suspected during construction, the exact position can be confirmed on the spot with high accuracy. This allows reporting materials for clients or supervisors to be prepared with accurate on-site measurements, avoiding the need to later spread out drawings and recalculate kilometerage. Of course, LRTK can also be used for stakeout, as-built measurements, and general surveying. If design coordinates (reference points, structure locations, etc.) are registered in the app, the screen can navigate the user toward the target point by displaying direction and distance, and notify them when they reach the prescribed coordinates. This makes it possible to accurately place signs or structures at specified kilometerage without guesswork.

Sharing and utilizing position information via point-cloud measurement, AR, and cloud integration

LRTK does more than measure single points: features such as continuous positioning, AR (augmented reality), and cloud integration allow on-site conditions to be recorded and used in a three-dimensional, easily shareable form. For example, using the LRTK app’s continuous positioning function, users can automatically acquire coordinates at a high frequency of up to 10 points per second while moving. Walking along the road centerline with this function enabled produces trajectory data that can be used to obtain measured point clouds of the road alignment. The resulting large set of points can be plotted on a cloud-based map and examined as 3D point-cloud data. Viewed in plan, the data form a surveyed alignment on a plan view; viewed vertically, the data can be used to understand cross-sections. For instance, for slopes or stepped structures you can draw cross-sectional shapes from continuous positioning data and immediately compare them with design sections on site. Tasks that formerly required expensive 3D laser scanners or drone photogrammetry can increasingly be completed simply by walking with an LRTK and a smartphone.

Smartphone-specific features such as photo capture and AR visualization are also useful. When taking a photo with the LRTK app, the high-precision position coordinates of the photo location and the camera orientation (azimuth) are automatically tagged to the image. This records precisely “from which point and in which direction the photo was taken,” and clicking the photo icon on the cloud map reveals the site condition. Even in locations where GNSS signals do not reach directly, such as under a bridge, you can first identify your location at the entrance and switch to an indoor positioning mode; photos taken inside can still be tagged with accurate location information, allowing inspection results from dark bridge interiors or tunnels to be linked to the map.

Using AR, design data or target objects can be overlaid as virtual objects on the smartphone camera view. For example, you can project a line indicating the buried position of a sewer pipe or a model of a completed structure onto the road, making intuitive on-site position confirmation and stakeholder explanations easy. Because LRTK provides high-precision positioning, AR models are less likely to be misaligned and can be displayed to match the real world closely. This is extremely useful for pre-construction planning and as-built checks. Being able to view the completed form at full scale on site prevents mistakes and helps stakeholders share a common understanding, rather than relying on drawings or 2D photos.

Cloud integration enables these on-site data to be shared instantly among all stakeholders. Positioning data, photos, and point clouds uploaded to the LRTK cloud can be shared with clients and subcontractors via a URL. Without special software, users can open the link in a browser to view points and photos plotted on a map, eliminating the need to create report materials and send them by email. Data can be downloaded as CSV or PDF as needed for import into CAD drawings or for transfer to as-built management forms. Centralized cloud management of data makes it easy to track “which survey information is the latest” and “who measured where and when,” minimizing information loss between the field, office, and clients.

Thus, by using LRTK you can digitize and share not only single-point kilometerage measurements but the entire state of the site. This technology aligns with the construction industry’s DX (digital transformation) initiatives and the Ministry of Land, Infrastructure, Transport and Tourism’s i-Construction efforts, and is becoming a future standard for construction management. Even amid concerns about labor shortages, LRTK’s labor-saving and visualization capabilities promise safer and more efficient infrastructure management.

Conclusion: Benefits of adopting LRTK as a simple surveying tool

We have reviewed the importance of kilometerage surveying in roadworks, the challenges of traditional methods, and solutions provided by the latest LRTK technology. The benefits of introducing LRTK can be summarized as follows:

• Efficiency and labor savings: One person can easily perform surveys without assembling a surveying team or transporting and setting up heavy equipment. Freed-up personnel can be assigned to other tasks, improving overall productivity.

• High accuracy: RTK-GNSS enables consistent centimeter-level positioning (cm level accuracy (half-inch accuracy)), minimizing kilometerage offsets and measurement errors. From a quality-control perspective, reliable positioning and as-built checks reduce rework and help ensure successful inspection outcomes.

• Immediacy and real-time sharing: Measured data are digitized on the spot and can be shared with the office or clients via the cloud. Time lags waiting for reports or instructions are reduced, enabling faster decision-making and corrective actions. Eliminating paper-based processes also reduces human errors.

• Multifunctionality: In addition to obtaining kilometerage and coordinates, LRTK can record 3D terrain and structures via point-cloud scanning, provide intuitive AR visualization, and combine photos and notes for survey records. One device can replace multiple measurement instruments, reducing equipment costs.

• Ease of operation: Familiar smartphone operations make the system accessible to non-specialists, enabling on-site personnel to actively perform measurements and checks. New engineers can use it intuitively, aiding skill transfer.

Introducing LRTK to the field significantly advances surveying and construction management methods in roadworks. Making the basic information of distance from the starting point—kilometerage—more accurate and easier to use than ever dramatically improves site visibility and communication. Freed from heavy traditional tasks, and with an environment in which you can “measure anytime, anywhere,” necessary measurements are less likely to be postponed, ultimately improving quality and safety. LRTK, which is useful for a wide range of applications beyond kilometerage surveying, can be called the new standard for simple surveying tools on future infrastructure sites. Try it on site and experience its efficiency and accuracy improvements for yourself.