The New Normal for On-site Layouts: LRTK Dramatically Improves Accuracy and Work Efficiency

On construction sites, the indispensable task of layout marking (sumidashi) is critical for accurately translating design drawings into the actual site. However, traditional layout marking has required substantial time and manpower and has been prone to errors. In recent years, a new technology called LRTK has brought a revolutionary change to this process. By combining a smartphone with ultra-high-precision positioning technology, LRTK can dramatically increase both the accuracy and work efficiency of layout marking, significantly reducing on-site burdens. This article reviews conventional layout marking methods and their challenges, explains the new workflow and technical features enabled by LRTK, and presents concrete examples of accuracy improvements, efficiency gains, and labor savings. Finally, we consider the new norms that simplified surveying enabled by LRTK may bring to construction sites.

Conventional Layout Marking and Its Challenges

In both building and civil engineering, traditional on-site layout marking has been carried out by experienced surveyors using tape measures (scales), transits (optical surveying instruments), laser layout devices, and the like. Based on reference dimensions on drawings, they determine positions on site and mark lines or points on floors or ground with chalk or ink, or place wooden stakes or screws as markers to indicate construction references. These tasks often require multiple workers and considerable time; when a building is complex or there are many measurement points, layout marking alone can take half a day or more.

Several issues have been pointed out with conventional methods. First is the problem of time and effort. Layout marking requires careful step-by-step work from setting reference points to drawing and verifying lines, making it difficult to improve efficiency. At one site, layout marking that previously took the surveying team more than half a day was completed in about an hour using the latest technology. In experimental comparisons, layout marking using conventional optical surveying took about six times longer than new technology using GNSS×AR. In other words, the traditional approach can make layout marking a bottleneck in the overall schedule and hinder productivity.

Second is the risk of human error. When surveyors and workers are separate, miscommunication can lead to marking the wrong location or slight shifts in the reference lines. If a stake used as a marker is displaced by some impact, the accurate position may be lost. Misreading layout drawings or dimensions can cascade into construction mistakes in subsequent processes, causing rework and backtracking.

There are also environmental constraints. In places where marking is physically difficult—high locations, slopes, or near water—traditional layout methods can be impractical. Tight indoor ceilings or areas with many obstacles can make it hard to set up surveying equipment or secure lines of sight. Such environments often require awkward postures or close two-person adjustments, creating safety and efficiency issues.

Recently, machine guidance systems that equip heavy machinery with GNSS receivers to guide operators have begun to appear on large infrastructure projects. However, these advanced systems have high costs for specialized hardware and software and have not yet spread to medium and small sites. As a result, many sites still rely on manual layout marking, leaving issues of accuracy variation and heavy labor unresolved.

Workflow and Technical Features of Layout Marking Using LRTK

A key to solving the above challenges is the use of RTK positioning technology. RTK (Real Time Kinematic) is a technique that corrects errors in satellite positioning (GPS/GNSS) in real time using correction data from a base station, enabling position fixes to within a few centimeters. Simply put, it is "ultra-high-precision GPS usable on site." Applied to layout marking, RTK makes it possible to align the coordinates on design drawings precisely with actual on-site positions. For example, if the coordinates of target points—such as stake positions or equipment installation points—are set in an RTK-capable device, the device can navigate to those points and directly indicate the target position, eliminating intermediate measuring or line drawing.

Recently, smartphone-based surveying methods that make RTK easier to use have emerged and are changing construction sites. By attaching a small RTK-GNSS receiver to a smartphone, centimeter-level positioning that once required expensive specialized equipment is now available to anyone. A representative system is LRTK. LRTK was developed by a startup originating from Tokyo Institute of Technology and uses a slim, lightweight (around a few hundred grams) receiver attached to an iPhone or Android device. Despite the smartphone-scale hardware, it achieves positioning accuracy comparable to conventional optical surveying instruments—approximately ±1–2 cm horizontally and ±3 cm vertically. Correction information can be obtained from the Geospatial Information Authority of Japan’s Continuously Operating Reference Stations network and the Quasi-Zenith Satellite System "Michibiki" CLAS signal, so high-precision positioning is available nationwide within communication coverage without installing a dedicated base station on site (in areas where communication is difficult, positioning can continue as long as Michibiki is visible overhead).

Now let’s look at the specific steps for layout marking using LRTK. Compared to traditional methods, the workflow is surprisingly simple and can be operated intuitively by one person.

• Prepare design data: Import coordinate data for the layout target points (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.

• Set up equipment: Attach the LRTK receiver to the smartphone and launch the dedicated app. Correction data reception is automatic, and centimeter-level positioning begins within seconds. There is no need to carry heavy tripods or surveying instruments; you can walk the site with a pocket-sized device.

• Select the target coordinate: Choose the target coordinate to be laid out 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 directions on the smartphone screen. As they approach the target, the display switches to a more precise mode, allowing "within a few centimeters" fine adjustment with a crosshair target and distance readout. Tasks that used to require a surveyor peering through a transit while another worker was told "a bit to the right" or "forward X cm" can now be accomplished solo with just a smartphone.

• Marking: Upon reaching the specified location, mark the point. On floors or ground this may be chalk marks or stakes; on walls, pencil or marker marks. In addition to physical marking, AR overlays can show virtual markers through the smartphone camera for sharing with stakeholders.

• Measure the next point: Select the next target coordinate and repeat the guidance and marking. When measuring multiple points in sequence, there is no need to recheck paper drawings or re-extend tape measures; the app allows efficient switching and continuous work.

As described, LRTK greatly simplifies the layout marking workflow. The smartphone app’s display is very easy to understand and can be operated intuitively even by non-experts. Because positioning, guidance, and recording are digitized end-to-end, intermediate calculation errors and misreads are much less likely. The AR feature that overlays design lines or models on camera imagery also allows position alignment as if "checking the drawing at full scale on site." For example, where obstacles prevent physical marking, AR can display a virtual stake or column labeled "column here," enabling accurate placement later without shifting positions. LRTK is truly a next-generation smart construction tool that enables anyone to perform accurate layout marking alone.

Effects of LRTK Adoption: Improved Accuracy, Efficiency, and Labor Savings

Digitizing and smartening layout marking with LRTK brings many benefits to job sites. The main effects are as follows.

• Improved construction accuracy: High-precision positioning that consistently stays within a few centimeters minimizes placement errors. Reducing the gap between design coordinates and actual layout positions significantly boosts downstream construction accuracy. This is especially important when many column or pile positions must be set; keeping cumulative errors low improves overall structural quality and safety. Fine alignments that previously depended on craftsmen’s intuition can now be reproduced with high repeatability through digital coordinate guidance. Reducing mistakes such as "re-marking due to dimension errors" or "rework because positions don't match" lowers the risk of quality defects and rework.

• Dramatic improvement in work efficiency: RTK navigation and AR guidance substantially shorten layout marking time. As mentioned above, new technologies have been shown in some cases to reduce surveying time to about 1/6 of conventional methods—an impressive efficiency gain. Workers can perform layout marking themselves without waiting for a surveying team, reducing idle time in other processes. One person can sequentially measure multiple points, and the app’s direction and distance cues minimize wasted movement and adjustments. The time spent debating positions among several people is cut, greatly boosting productivity. Since positioning data and marking locations are automatically recorded digitally, post-work reporting and as-built inspections are also more efficient.

• Labor savings and skill leveling: The ability to complete layout marking solo offers significant labor benefits. With LRTK, heavy surveying equipment and large survey teams are not necessary; on-site workers can perform position setting alone. This allows scarce personnel in the construction industry to be redeployed to other tasks. The intuitive smartphone interface means that even non-experts can operate the system, reducing quality variability caused by different skill levels. New hires or temporary staff can achieve veteran-level layout accuracy simply by following the device’s instructions, enabling stable construction management independent of the individual. Reducing the physical burden—less time on equipment at heights or in the heat—also lowers staff fatigue and stress.

• Cost reduction and ease of adoption: Smartphone surveying devices like LRTK are offered at much lower cost than traditional high-precision GNSS surveying equipment (hundreds of thousands of dollars class), making one-device-per-person deployment realistic and accessible to small and medium-sized contractors. Because the system leverages existing smartphones, little training on new dedicated terminals is required. Familiar smartphone interfaces help accelerate on-site adoption. With lower initial investment and tangible benefits, LRTK is a cost-effective solution.

• Versatility and contribution to digitalization: Smartphone surveying systems can be used for far more than layout marking: topographic surveys, as-built quality control after construction, and maintenance management are all potential applications. For example, the same device can be used to 3D-scan marked positions for as-built inspection, or automatically upload geotagged progress photos to the cloud, contributing to site-wide DX (digital transformation). Data obtained from a single layout task can be used in subsequent inspection and record-keeping processes and stored in a future maintenance database. Adopting LRTK can thus be not only an efficiency gain for layout marking but also a step toward centralized digital management of construction workflows that enhances overall productivity and quality.

On-site Use Cases for Building Construction

Simplified surveying with LRTK is expected to be useful at virtually every stage of building construction. For example, in reinforced concrete buildings, a critical layout process after foundation casting is "gridline layout" to establish column and wall center positions. Traditionally this involved defining reference axes, using tape measures to find intersections, and marking them with chalk. With LRTK, you can call up the coordinate of the intersection from the design drawing and mark the point accurately by a single person. On large floors, simply following the smartphone arrow will take you to column locations, greatly reducing positioning time.

LRTK is also effective in interior finishing work. For interior layouts such as partition walls and ceiling equipment, laser layout devices or plumb bobs are typically used to transfer positions. If satellite signals reach the indoors, LRTK can reference coordinates easily. On large renovation sites, loading finish-element coordinates into a smartphone in advance allows the app to navigate to each point for marking without referring back to drawings. This permits accurate on-the-spot marking for floor or ceiling openings, lighting fixtures, and pipe sleeve positions, preventing installation errors.

Furthermore, LRTK can be applied to high-rise construction management. Traditionally, transferring marks to upper floors involves vertically projecting from lower-floor reference marks with plumb lines or lasers, which can accumulate small errors floor by floor. With LRTK, each floor can reference absolute satellite coordinates (operations such as relocating a reference from a rooftop or balcony with a clear sky view may be required), enabling layout marking based on a unified coordinate system across the building. This reduces vertical misalignment through to the top floor and minimizes final-stage adjustments.

In this way, LRTK streamlines and enhances layout tasks from structural work to equipment and finishing. One construction company, for example, used LRTK to AR-display positions of holes (for post-installed anchors, etc.) on drawings during rebar inspection of concrete walls, reducing inspection time and preventing oversights. As construction sites push for DX, smartphone-based LRTK layout marking is gaining attention as a key measure for boosting productivity and reducing human error.

On-site Use Cases for Civil Engineering

High-precision position guidance with LRTK is also producing significant results in civil engineering. A representative example is pile position layout for foundations. In bridge pier foundation works, multiple piles must be driven at exact positions. Traditionally, surveyors needed to place reference points and use tape measures and transits to determine each pile location for marking. At one site that introduced LRTK for pile layout, the workflow was dramatically simplified: design coordinates for pile positions registered in the cloud were called up from a smartphone app on site, and operators were guided to each position and marked it. What used to take half a day was reportedly completed in about one hour. Experimental comparisons have also shown that the latest GNSS+AR pile layout takes roughly 1/6 the time of the slowest conventional optical method, demonstrating a substantial productivity increase.

LRTK’s use in challenging terrain is also notable. For steep slope reinforcement, it was once difficult even to drive survey stakes, but AR features in LRTK allow virtual marking of target points from safe locations. In one slope project, workers displayed a virtual stake on the smartphone from a remote position and excavated directly under that virtual marker to drive piles, achieving both safety and accuracy. When physical marking is impossible, visualizing "the target is here" maintains positioning accuracy while reducing the risk of personnel entering hazardous areas.

LRTK is useful in roadworks and land development as well. For setting design heights and lines across large sites, survey teams repeatedly had to set and verify points. With LRTK, machine operators or site supervisors carry the device and are guided to required coordinates to verify them on the spot. Positions for road curves, offset stakes, and fill/cut boundary lines can be displayed instantly if design data is preloaded. For as-built quality control, projecting the design model via AR onto the finished road surface to check conformity or measuring unevenness and elevation differences on site are examples of how LRTK accelerates quality inspections.

Moreover, LRTK’s mobility is valued in disaster recovery. Even in disaster areas where communication infrastructure is down, small smartphone RTK receivers can be rapidly transported by helicopter or vehicle. For instance, after the 2023 Noto Peninsula earthquake, LRTK devices proved useful in an environment where base stations were down. They directly received centimeter-level correction information (CLAS) broadcast from the Michibiki satellites and achieved high-precision positioning, enabling rapid measurement and sharing of submerged utility pole height changes and ground fissure locations. Thus, LRTK demonstrates accuracy and mobility not only for routine construction but also for emergency surveying and investigations.

In civil engineering, LRTK-based layout and positioning are steadily penetrating job sites. As the Ministry of Land, Infrastructure, Transport and Tourism promotes ICT construction and i-Construction, GNSS-based improvements in construction accuracy remain a key theme. Solutions like LRTK align with the industry-wide drive toward DX and have the potential to become the "new normal" across a wide range of projects from large-scale to local small works.

Conclusion: The New Normal of "Simplified Surveying" Enabled by LRTK

The traditional layout marking challenges—accuracy, time, and manpower—are being greatly improved by the new approach of smartphone-based simplified surveying such as LRTK. A time is approaching when site workers need not rely on specialized surveying teams; each worker will be able to master high-precision positioning and complete layout marking independently. In advanced sites, operations using "one smartphone surveying device per person" are already underway, delivering both higher accuracy and increased productivity.

Of course, constraints related to satellite signal reception and the need to train workers unfamiliar with digital devices remain. Even so, RTK positioning × smartphones are highly likely to become a standard on future construction sites. As advanced technologies become integrated into everyday smartphones, the essential task of layout marking will be dramatically streamlined and elevated, making it commonplace for anyone to "perform fast, accurate layout marking without errors." Simplified surveying enabled by LRTK is, indeed, the new normal for on-site layout marking. Wider adoption of such technologies is expected to bring benefits to an increasing number of construction sites.