LRTK That Changes the Common Sense of Layout Marking: Smartphone Integration Makes Solo Work Safe and Secure

“Layout marking” performed on construction sites is a critical task to accurately indicate the positions and elevations of buildings and structures. However, conventional layout marking work has required multiple workers, consumed significant time and labor, and involved risks of human error and safety issues. A new technology that overturns these assumptions is LRTK, which integrates with smartphones. By attaching a pocket-sized device to a smartphone, a single worker can perform layout marking quickly and with high accuracy, dramatically improving the safety and security of the work. This article reviews conventional layout marking methods and their challenges, explains the innovative mechanisms and effects brought by smartphone-integrated LRTK, and details use cases in building and civil engineering sites.

Conventional Layout Marking Work and Its Challenges

Layout marking refers to the work of drawing reference lines and marks on site based on design drawings for foundation work, formwork, and other tasks. For example, lines are drawn on concrete foundations or floors with chalk or a chalk line, and columns, walls, or equipment are installed along those lines. Because the accuracy of layout marking directly affects the quality of structures, it is extremely important, but conventional methods have several issues.

First is the need for manpower. Layout marking used to be carried out by two or more people as a matter of course. One person would hold a tape measure to measure distances while another would mark the indicated points, or two people would hold a long chalk line at both ends to snap a straight line—cooperating with multiple people was necessary to establish reference lines. When setting building squareness, one person would look through a measuring instrument at a reference point while another held a stake or rod; such role division was required.

Another major issue was the time and effort required. Layout marking requires setting up and aligning instruments each time a measurement or marking is made, and workers often had to go back and forth on site while making fine adjustments. Traditionally, accuracy was improved using dedicated instruments such as transits (theodolites), levels, and later laser layout tools, but position setting still demanded considerable effort and expertise. On complex terrain or at heights and in confined spaces, even the preparatory steps before starting layout marking could take substantial time.

Moreover, the risk of human error is unavoidable. Mistakes such as misreading a tape measure, calculation errors, or slight offsets in chalk lines can occur whenever work relies on people’s hands. Even with repeated measurements and checks, small deviations can accumulate and be noticed only later in subsequent processes as “positions don’t match.” Inexperienced workers who struggle to read drawings may mark incorrect reference positions, leading to major rework.

In addition, safety issues cannot be overlooked. Layout marking often involves workers going to heights to make marks, or installing stakes and batter boards near areas where heavy machinery is operating. Working at height carries the risk of falls, and staking on slopes or unstable surfaces always carries the risk of slips and injuries. If surveying is carried out in positions outside the operator’s view, there is even a risk of collision accidents. In this way, conventional layout marking faced the challenges of “requiring manpower,” “being labor-intensive,” “being prone to mistakes,” and “having safety risks.”

Innovation in Layout Marking with Smartphone-Integrated LRTK

A new solution that addresses the above challenges is LRTK, which can be used in conjunction with a smartphone. LRTK consists of a small high-precision GNSS receiver (GPS receiver) and a dedicated app; simply attach the device to a smartphone and power it on to correct positioning information from quasi-zenith satellites and GPS, achieving centimeter-level positioning accuracy (cm level accuracy (half-inch accuracy)). It is revolutionary that the accuracy once obtainable only with surveying equipment costing millions of yen can now be handled easily by anyone using a palm-sized device plus a smartphone.

The basic configuration of an LRTK system is simple. A lightweight device attached to the back of the smartphone acquires high-precision position information and communicates wirelessly with the smartphone app. Error correction data received via the Internet (RTK correction information from reference stations) refines the smartphone’s position in real time. As a result, GPS positioning, which normally has errors of several meters, is improved to almost centimeter-level accuracy (a few inches), enabling the precise positioning required for on-site layout marking.

Using high-precision positioning via smartphone integration dramatically changes the workflow for layout marking. Below is a general flow when performing layout marking alone using LRTK.

• Preparing the Device and Drawing Data: First, attach the LRTK receiver to the smartphone and launch the dedicated app. Sync the coordinate data and reference point information of the design drawings previously uploaded to the cloud with the app, and set the points to be guided on site (you can also manually input coordinates).

• Guidance to Points: Select the layout point you want to guide to in the app, and the smartphone screen will display the direction and distance to that point in real time. The worker simply walks following the on-screen compass or arrow and is smoothly guided to the specified coordinates. The effort of measuring “X meters from Y” is no longer necessary, and intuitive navigation leads you straight to the target point.

• Marking the Point: When you arrive at the target position, the screen switches to a mode that indicates deviations from the target coordinates in centimeter units. For example, instructions such as “+2 cm east-west, -1 cm north-south” are displayed so you can make fine positional adjustments while looking at the smartphone. Once the error is minimized, you mark the ground or structure. This completes the marking of the reference point.

• Line and Elevation Marking: As needed, draw layout lines based on multiple marked points. For a straight line, mark the start and end points and snap a chalk line; for horizontal level marking, you can use the height coordinates obtained by LRTK and confirm with the app’s level function or AR display without a laser level. Tasks that previously required coordinated shouts or hand signals among survey staff can now be completed by one worker looking at the smartphone.

With LRTK, you can indicate target positions accurately with a smartphone in hand without complicated equipment operation or long tape measurements. It also supports AR (augmented reality) features, allowing design positions and lines to be overlaid on the smartphone camera image. For example, in places where physical stakes cannot be driven into the ground, virtual stakes or lines can be displayed through the phone to share positions visually. This enables intuitive on-site communication such as “the center of the column is here” or “this is the finish line at this height.”

Benefits That Enable Solo Work: Improved Safety and Efficiency

The benefits of smartphone-integrated LRTK go beyond changing procedures. The greatest advantage is that even non-experts can complete layout marking alone. This reduces on-site labor burden and allows efficient deployment of scarce personnel in the construction industry. Key benefits include:

• Labor reduction and flexible staffing: Tasks that previously required 2–3 people can be done by one, freeing personnel for other work. Even without experienced surveyors, newcomers can achieve a certain level of positioning accuracy by following LRTK navigation. As generational change among skilled workers proceeds, standardizing skills through technology can help absorb skill gaps.

• Dramatic improvements in work efficiency: One person can move efficiently, eliminating waiting times and communication losses within survey teams. The time-consuming repeated setup and removal of heavy equipment is reduced, allowing many points to be measured and marked in a short time. In some cases, layout marking that took two people half a day can be completed by one person in a matter of hours, achieving dramatic time savings.

• Improved accuracy and fewer mistakes: Digital guidance greatly reduces room for human error. Measurement mistakes and calculation errors are eliminated, and because design data in the cloud is directly compared with the site, layouts can be reproduced with high consistency. Marker positions are saved to the cloud immediately, making post-work verification and sharing easy. As a result, rework and redo rates are reduced, enhancing quality control.

• Improved safety: Enabling safe solo layout marking is a major benefit. Shorter work times reduce the time spent in hazardous areas, and operations can be conducted while checking the status of heavy machinery on a smartphone (operations that link to other machinery’s operational data via the cloud are also being considered). For work at height, tasks that previously required standing on a stepladder to mark can be substituted with AR height checks or photographs, reducing occurrences of awkward postures without safety harnesses. Overall, “slow, safe solo work” raises safety awareness on site and leads to calmer, more reliable construction.

On-Site Use Cases: From Building to Civil Engineering

LRTK-based layout marking is effective across a variety of sites in both building and civil engineering. Below are some specific use cases.

• Foundations and structural work on building sites: Layout marking for column and wall positions requires drawing reference lines on foundation concrete. After introducing LRTK, a single worker can sequentially mark points according to pre-set coordinates, and reference lines can be laid out quickly and accurately. Tasks that were once performed by two experienced craftsmen can now be carried out by a young worker with the same accuracy as the drawings, providing reassurance to construction managers. LRTK is also used for tasks such as checking anchor bolt positions in steel erection and confirming sleeve opening positions in equipment installation.

• Pile driving and batter board installation in civil engineering: In road and land development works, survey crews set batter boards and place survey stakes before heavy equipment work. On one infrastructure project, introducing LRTK allowed surveyors to mark stake positions independently. Heavy equipment operators used not only installed stake markers but also virtual stakes indicated by LRTK (AR stakes) as references for excavation, improving safety and efficiency. In particular, during nighttime work with poor visibility or in development sites involving tree clearing, the need for personnel to standby with surveying instruments for long periods was reduced, allowing surveying to be completed while avoiding dangerous situations.

• Renovation and interior work: LRTK is also useful in renovation projects. For example, scanning and point-clouding the positions of existing columns and underside of beams enables layout marking for new walls. On-site, 3D point cloud data of existing structures acquired by a smartphone can be overlaid with planned positions from the design drawings to immediately identify discrepancies. This allows interference issues that were not noticed during design to be discovered in advance and avoids rework. In confined interiors, there is no need to carry a survey pole or layout tool, allowing agile measurement even in limited space.

In this way, LRTK-based layout marking and surveying produce effective results across a wide range of sites. Feedback from sites that have introduced the technology includes “reduced downtime waiting for surveying” and “layout work can proceed with only younger staff, easing labor allocation,” indicating that LRTK contributes to both productivity and safety on site.

The Potential of Simple Surveying Solutions Expanded by LRTK

While LRTK realizes DX (digital transformation) of layout marking, its range of use is not limited to layout work. LRTK can turn a smartphone into a versatile surveying tool with the potential to meet a wide range of on-site measurement needs. Along the extension of high-precision positioning, the following simple surveying solutions are also expected.

• Application to as-built management and inspection: Point cloud data and coordinate values acquired by LRTK can be immediately compared with drawing data in the cloud, streamlining post-construction as-built checks. Height checks for embankment works and pavement thickness inspections can be compared with design values on site and shared. If tasks that previously required dedicated 3D laser scanners or surveying instruments can be completed with just a smartphone, significant cost savings and rapid feedback can be achieved.

• Use in maintenance and inspection: LRTK is powerful for infrastructure inspection tasks. It can record displacements and crack locations with high accuracy during periodic inspections of bridges and tunnels, and perform layout marking for repair plans on site. The photogrammetry function attaches accurate position information to captured images for storage, making later comparisons and report creation smoother. Combined with a tablet, referencing drawings and past data while making decisions and taking actions on site can improve the efficiency and sophistication of inspection work.

• Future prospects: Smartphone surveying devices like LRTK are expected to become increasingly common on sites. Movements such as i-Construction promoted by the Ministry of Land, Infrastructure, Transport and Tourism encourage the enhancement and labor-saving of construction processes by digital technology. Affordable and easy-to-use LRTK is accessible to small and medium-sized sites and sole proprietors, and an era of “one device per person” may arrive. In fact, construction managers who started using LRTK on site report that “once you use it, you can’t go back to the old ways” and that “the common sense on sites has changed.” This technology that changes the common sense of layout marking is becoming an indispensable tool in the construction industry to improve construction quality and safety.

From work that relied on experience and intuition to smart, data-driven construction—LRTK’s use is steadily transforming construction sites. If your site faces challenges in improving the efficiency and labor-saving of layout marking, why not try this simple surveying solution first? As a new means to balance safety and productivity, LRTK is a choice worth considering.