The New Standard for On-site Layout Marking: Dramatic Improvements in Accuracy and Work Efficiency with LRTK

Layout marking (sumidashi), an indispensable task on construction sites, is the important work of accurately translating information from design drawings to the actual site. However, traditional layout marking has required considerable effort and manpower and has been prone to mistakes. In this context, a new technology called LRTK that has appeared in recent years is bringing a revolutionary change to layout marking. By combining smartphones with ultra-high-precision positioning technology, LRTK can dramatically improve the accuracy and work efficiency of layout marking and greatly reduce on-site burdens. This article reviews traditional layout marking methods and their challenges, explains the new workflow and technical features enabled by LRTK, and introduces concrete examples of the accuracy improvements, efficiency gains, and labor reduction achievable through its adoption, showing use cases across building and civil engineering sites. Finally, we consider the new norms that simple surveying enabled by LRTK may bring to the field.

Traditional Layout Marking Work and Its Challenges

In both building and civil engineering, on-site layout marking has traditionally been performed by experienced surveyors using tape measures, transits (optical surveying instruments), laser layout tools, and so on. Based on the reference dimensions on drawings, positions on site are determined and lines or marks are made on floors or ground with chalk or ink, or markers such as wooden stakes or screws are installed to indicate construction references. These tasks require multiple people and time, and when a building has a complex shape or many measurement points, layout marking alone can sometimes take half a day.

Several issues have been pointed out with traditional methods. First is the problem of time and labor. Layout marking requires careful, step-by-step processes from establishing reference points to extending measurement lines and confirming them, making it difficult to improve efficiency. On some sites, layout marking by survey teams took more than half a day, whereas with the latest technologies it was completed in about an hour. Experimental comparisons also showed that traditional optical surveying for layout marking took about six times longer than the new technology (GNSS×AR utilization). In other words, with conventional methods the layout marking phase could become a schedule bottleneck and a factor impeding productivity.

Second is the risk of human error. When surveyors and workers are different people, miscommunication of instructions can lead to marks being placed in the wrong locations or reference lines being slightly off. Stakes used as markers can be displaced by some impact, making it difficult to determine the correct position. Human errors such as misreading layout drawings or dimensions can lead to construction mistakes in subsequent processes, resulting in rework.

There are also constraints imposed by the working environment. In locations that are difficult to mark physically—such as at height, on slopes, or by water—traditional layout marking can be inherently challenging. Ceiling layout marking in narrow interiors or measurements in areas with many obstacles can make it difficult to set up surveying instruments or maintain line-of-sight. In such environments, awkward postures or two-person fine-tuning are required, leaving safety and efficiency issues unresolved.

In recent years, machine guidance systems that equip heavy machinery with GNSS receivers to guide operators have begun to be introduced in some large-scale infrastructure projects. However, these advanced systems require costly dedicated equipment and software, and have not yet become widespread in small- to medium-scale sites. As a result, many sites still rely on manual layout marking, and variability in accuracy and heavy human burdens remain persistent problems.

Workflow and Technical Features of Layout Marking Using LRTK

The key to solving the above challenges is the utilization of RTK positioning technology. RTK (Real Time Kinematic) is a technology that corrects satellite positioning (GPS/GNSS) errors in real time using correction data from a base station, enabling position determination with errors on the order of centimeters. In simple terms, it is an “ultra-high-precision GPS usable on site,” and applying it to layout marking makes it possible to match design coordinates and actual site positions exactly. For example, if the coordinates of target points where you want to place marks—such as stake locations or equipment installation points—are set into an RTK-compatible device, the device can navigate to those points and directly indicate the target positions, omitting intermediate dimensioning or line drawing steps.

In recent years, a method of “smartphone surveying” that makes RTK positioning easier to use has emerged and is bringing major changes to construction sites. By attaching a small RTK-GNSS receiver to a smartphone, centimeter-level positioning that formerly required expensive dedicated equipment is now accessible to anyone. A representative system is LRTK. LRTK was developed by a startup originating from Tokyo Institute of Technology; it is used by attaching a thin, lightweight (about 100–200 grams) receiver device to an iPhone or Android smartphone. Despite its smartphone size, it delivers positioning accuracy comparable to conventional optical surveying instruments: horizontal ±1–2 cm (±0.4–0.8 in) and vertical ±3 cm (±1.2 in) approximately. Correction information can be obtained from the Geospatial Information Authority of Japan’s electronic reference point network (GNSS reference network) and the QZSS (Quasi-Zenith Satellite System) “Michibiki” CLAS signal, so high-precision positioning is possible anywhere in the country within communication coverage without installing a dedicated base station on site (positioning can continue in locations where communication is difficult as long as the “Michibiki” satellites are visible above).

Now let us look at the concrete procedure for layout marking using LRTK. Compared with traditional methods it is remarkably simple and can be operated intuitively by a single person.

• Design data preparation: Import the coordinate data of the points to be marked (for example, foundation center points or column locations) into the cloud or the smartphone in advance. Creating a coordinate list from CAD drawings or BIM data makes the process smooth.

• Equipment setup: Attach the LRTK receiver to the smartphone and launch the dedicated app. Correction information reception is handled automatically, and centimeter-level positioning (cm level accuracy (half-inch accuracy)) begins in a few seconds. There is no need to carry heavy tripods or surveying instruments; with pocket-sized equipment you can walk around the site.

• Selection of target coordinates: Select the target coordinates you want to mark in the app and start navigation. The screen displays the current position and the direction and distance to the target in real time, with arrows or a compass indicating the target direction.

• On-site guidance: The worker simply follows the indicated direction while checking the smartphone screen. As you approach the target point, the display switches to a more precise mode, and with crosshair targets or distance readouts you can make fine adjustments of “a few centimeters.” Scenes that used to require a surveying staff member peering through a transit and telling another worker “a little to the right” or “move forward by X cm” can now be achieved by one person with a smartphone.

• Marking: Once you reach the specified position, make a mark there. On floors or ground this could be a chalk mark or staking; on walls it could be a pencil or marker. In addition to physical marking, you can overlay virtual marks through the smartphone camera using AR and share them with stakeholders.

• Measuring the next point: Select the next target coordinate and repeat the guidance and marking. When measuring multiple points in sequence, you can switch efficiently within the app without referring back to paper drawings or re-extending tape measures.

As shown above, using LRTK greatly simplifies the workflow of layout marking. The smartphone app’s display is very easy to understand, enabling intuitive operation even by workers without specialized knowledge. Because positioning, guidance, and recording are digitized end-to-end, calculation errors and misreads are less likely to occur. The AR function that overlays drawing lines or models on camera images allows you to align positions as if “checking the drawing to scale on site.” For example, even where obstacles prevent physical marking, you can display virtual stakes or columns in AR—such as “a column here”—and proceed with construction without shifting the position later. LRTK is truly a next-generation smart construction tool that enables anyone to perform accurate layout marking alone.

Accuracy Improvement, Efficiency Gains, and Labor Reduction from LRTK Adoption

By digitalizing and smartening layout marking with LRTK, various benefits emerge on site. Let us look at the main effects.

• Improved construction accuracy: High-precision positioning that consistently stays within a few centimeters reduces deviations in marking positions to a minimum. With a smaller gap between design coordinates and actual marked positions, subsequent construction accuracy improves dramatically. Especially when many positions such as columns or piles need to be located, suppressing cumulative errors for each point contributes to the overall quality and safety of structures. Fine position adjustments that used to rely on craftsmen’s intuition or experience can be reproduced with high reproducibility by digital coordinate-based guidance, enabling anyone to achieve the same accuracy. Reducing mistakes like “making a wrong measurement and re-marking” or “misaligned positions requiring rework” lowers the risk of defects and rework.

• Dramatic improvement in work efficiency: RTK navigation and AR guidance significantly shorten the time required for layout marking. As noted above, new technologies can reduce surveying time to about one-sixth of conventional methods in some cases—an astonishing efficiency gain. Because site workers can perform positioning themselves without waiting for a survey team, waiting times in other processes are reduced. One person can consecutively measure many points, and the app’s direction and distance guidance eliminates wasted movement and fine-tuning. Time spent by multiple people discussing positioning is cut, dramatically improving productivity. In addition, positioning data and marked locations are automatically recorded digitally, streamlining post-work reporting and as-built inspections.

• Labor reduction and skill leveling for improved labor conditions: The ability to complete layout marking alone offers major labor advantages. With LRTK, heavy surveying equipment and large surveying teams are not necessary; on-site workers can handle positioning tasks single-handedly. This allows valuable human resources to be allocated to other tasks in an industry facing severe labor shortages. The smartphone’s intuitive interface means that even non-experts can operate it, reducing quality variation due to skill differences. New hires or temporary staff can achieve the same marking accuracy as veterans simply by following the device, enabling consistent construction management independent of the individual. Reducing physical strain—less time on heavy equipment at height or surveying under harsh sun—also lessens on-site staff fatigue and stress.

• Cost reduction and ease of introduction: Smartphone surveying equipment like LRTK is offered at a much lower cost compared to conventional high-precision GNSS surveying systems (hundreds of thousands to millions of yen class). Because they are affordable, provisioning one device per person becomes realistic, making adoption feasible for small and medium-sized firms and small projects. The system leverages existing smartphones, so little additional training on dedicated terminals is required. Familiar smartphone interfaces promote on-site penetration. With lower initial investment and easily appreciable effects, the solution is cost-effective.

• Versatility and contribution to digitalization: Smartphone surveying systems are useful not only for layout marking but also for topographic surveys, as-built management after construction, and maintenance management. For example, the same device can be used to 3D-scan marked positions after layout for as-built inspections, or automatically upload geotagged construction photos to the cloud, contributing to overall site DX (digital transformation). Data obtained from a single layout task can be used for subsequent inspections and records and accumulated in maintenance databases. Introducing LRTK is not just about improving layout efficiency; it is a step toward centralized digital data management of site workflows, improving productivity and quality holistically.

Use Cases of Layout Marking on Building Sites

Simple surveying with LRTK is expected to be useful at every stage of building construction. For example, in reinforced concrete buildings there is an important layout process called “establishing setting-out lines” after foundation casting, where positions for columns and walls are established on site. Traditionally, axis lines were established and intersection points were found with tape measures and marked with chalk, but with LRTK you can call up the coordinate of the intersection from the design drawing and mark the point accurately alone. Even on a large floor, you can reach a column location simply by following arrows on the smartphone screen, dramatically reducing the time required for positioning.

LRTK also excels in interior work. For marking partition wall locations or ceiling equipment installation points on office floors, it is usually necessary to transfer positions using laser layout tools or plumb lines. If GNSS signals reach the interior area from outside, LRTK can also reference coordinates easily. For example, in a large renovation project, if you preload the coordinates of finish elements from drawings into the smartphone, the device can navigate to each point. Locations for floor or ceiling openings, lighting fixtures, or pipe sleeves can be indicated accurately on site without referring to drawings, helping prevent construction mistakes.

Furthermore, LRTK can be applied to high-rise building construction management. Traditionally, when transferring layout marks to upper floors, vertical transfer from lower-floor reference marks using spirit levels or lasers could accumulate small errors with each floor. With LRTK, each floor can reference absolute coordinates via satellite positioning (operations require moving the reference using a rooftop or balcony where the sky is visible for positioning), enabling layout marking based on unified reference coordinates for the entire building. This almost eliminates misalignment of setting-out lines to the top floor, reducing finishing-stage adjustment work.

Thus, LRTK can streamline and enhance layout marking tasks from structural work to equipment and finishing. In practice, one construction company used LRTK for rebar inspection of concrete walls by AR-displaying on-site the locations of holes (such as post-installed anchors) corresponding to the drawings, achieving both reduced inspection time and prevention of oversights. Amid calls for DX promotion on construction sites, smartphone layout marking with LRTK is attracting attention as a trump card for improving productivity and reducing human error.

Use Cases of Layout Marking in Civil Engineering

In civil engineering sites as well, high-precision position guidance with LRTK is producing significant results. A representative example is positioning for foundation piles. In bridge pier foundation works, multiple piles must be driven at precise locations; traditionally, surveyors set reference points on site and used tape measures and transits to determine each pile location and mark them with chalk or wooden stakes. On one site where LRTK was introduced for pile layout, the procedure was dramatically simplified: design coordinates for pile locations registered in the cloud were called up on a smartphone app, and workers simply moved to the indicated spots and marked them. What used to take half a day for pile position layout was reported to be completed in about one hour. Experimental comparisons also showed that the latest GNSS＋AR pile layout took about one-sixth the time of the most time-consuming traditional optical method, demonstrating a dramatic productivity improvement.

Use in sites with challenging terrain is also noteworthy. For example, on steep slope reinforcement works where it was once difficult even to install survey stakes, LRTK’s AR function allows virtual marking of target locations from a safe place. In one slope construction case, virtual stakes were displayed on a smartphone from a distant safe location, and excavation and pile driving were carried out directly beneath those virtual indicators, achieving both safety and accuracy. Because information such as “there is a target here” can be visualized even where physical markers cannot be placed, construction accuracy can be maintained while reducing the need for personnel to enter hazardous areas.

LRTK is also useful in roadworks and land development. For marking design heights and lines on vast development sites, survey teams traditionally had to set and check many points repeatedly. With LRTK, machine operators or site supervisors can carry the device themselves and be guided to design coordinates for on-the-spot confirmation. For example, curve positions, control stakes for width, or boundaries between fill and cut can be displayed on site if the design data is prepared in advance. For as-built management, LRTK contributes to faster quality inspection by projecting the design model onto the finished road surface in AR to check finish conditions or by measuring surface irregularities and elevation differences on site.

Moreover, LRTK’s mobility is valued in disaster recovery sites. Even where communications infrastructure is disrupted, small smartphone RTK receivers can be quickly transported by helicopter or vehicle to affected areas. In fact, during the 2023 Noto Peninsula earthquake, LRTK devices were useful in environments where base stations were down. By directly receiving centimeter-level correction information (CLAS) distributed from the QZSS Michibiki satellites, high-precision positioning was achieved, enabling rapid measurement and sharing of height changes of subsided utility poles and locations of ground cracks caused by liquefaction. Thus, LRTK demonstrates its accuracy and mobility not only in normal construction but also in emergency surveying and investigations.

In civil engineering, LRTK-based layout marking and positioning are steadily penetrating sites. Within the Ministry of Land, Infrastructure, Transport and Tourism’s push for ICT construction and i-Construction, improving construction accuracy using GNSS is an important theme. Solutions like LRTK align with industry-wide DX promotion and have the potential to become the “new standard” across a wide range of sites from large projects to local small-scale works.

Conclusion: The New Norm of “Simple Surveying” Enabled by LRTK

The traditional layout marking challenges of accuracy, time, and manpower are being greatly improved by a new approach—simple surveying using smartphones such as LRTK. We are approaching an era where site workers no longer need to rely on specialized survey teams; each worker can master high-precision positioning technology and complete layout marking themselves. In advanced sites, operations using “one smartphone surveying device per person” are already starting, simultaneously achieving accuracy and productivity improvements.

Of course, challenges remain, such as limitations due to satellite reception conditions and the need to train workers unfamiliar with digital devices. Even taking these into account, RTK positioning combined with smartphones is highly likely to become a standard in future construction sites. As advanced technology becomes accessible on everyday smartphones, the routine but important work of layout marking will be dramatically simplified and enhanced, and an era in which “anyone can quickly and accurately perform layout marking without mistakes” is drawing near. The simple surveying enabled by LRTK can rightly be called the new standard for on-site layout marking. It is expected that this technology will spread further and that more construction sites will benefit from it.