RTKで誰でもセンチ精度！最新出来形管理ツールの実力

In construction management, "as-built verification"—checking whether completed structures conform to the design—is crucial. However, traditional as-built verification has required significant time and effort, and it has been difficult to measure every point accurately. What is attracting attention now is RTK positioning technology and the latest digital tools. By utilizing RTK (Real-Time Kinematic), anyone can survey with centimeter-level accuracy, and as-built verification workflows are changing dramatically. This article explains the basics of RTK positioning, the challenges of conventional methods, the features of the latest smartphone RTK solution "LRTK", and the benefits on site. Finally, we introduce how to take the first step toward simple surveying using LRTK.

RTK測位とは？施工管理で求められる高精度技術

RTK (Real-Time Kinematic) positioning is a technology that uses GNSS (Global Navigation Satellite Systems) to obtain centimeter-level positioning accuracy in real time. By receiving satellite signals simultaneously at a reference station (base) and a mobile station (rover) and sending correction information from the base to the rover, high-precision positioning is achieved. While ordinary GPS positioning may have errors of several meters, RTK can dramatically reduce errors to a few centimeters. This increased precision enables digital, instantaneous workflows for construction management tasks that require high positional accuracy, such as as-built verification after civil engineering works and machine guidance for mechanized construction. In Japan, the quasi-zenith satellite Michibiki (QZSS) has begun offering the “Centimeter-class Positioning Augmentation Service (CLAS)”, and with compatible receivers, high-precision RTK positioning is possible even at mountain sites where internet connectivity is poor. RTK surveying once required expensive dedicated equipment, radio systems, and skilled technicians, but recent technological advances have made devices smaller and cheaper, making RTK benefits more accessible.

従来の出来形管理と課題

As-built verification is a construction management process that confirms and records whether completed structures or developed land match the design drawings in shape and dimensions. Especially in public works, it is an important task to demonstrate compliance with standards through measurement data based on the "as-built verification standards." Traditionally, as-built verification centered on manual measurements using tape measures and levels. After each construction completion, workers would measure heights, widths, and thicknesses one by one, compare them with the design values, and compile the results into record sheets and as-built drawings.

However, manual as-built measurement required many people and much time, and the number of measurable points was limited, making it difficult to cover the entire site. For example, while main measurement points might meet standards, subtly different areas could be overlooked, resulting in being told at the final inspection "this part differs from the design" and having to rush repairs. Busy sites also risk human error, such as forgetting to photograph buried items and thus leaving no record. Conventional methods therefore had weaknesses like "measuring one point at a time" and "prone to human error," and as structures become larger and more complex, it became harder to understand the whole. As-built verification thus imposed a large burden and stress on site personnel.

3D点群＋スマホRTKが拓く新しい出来形管理

To address these challenges, 3D point cloud–based as-built verification methods have been attracting attention in recent years. Point cloud data records the site shape as a collection of many points (a point cloud) with XYZ coordinates, producing a "3D copy of the site" obtained by scanning the entire space. With the spread of photogrammetry using drones and 3D laser scanners, high-density point cloud measurement has become practical. Backed by the Ministry of Land, Infrastructure, Transport and Tourism’s promotion of *i-Construction*, using point clouds for as-built verification is becoming the new norm.

Point cloud data records the site surface exhaustively as countless points, enabling detection of differences from the design down to millimeter-scale irregularities. It can cover areas easily overlooked by manual spot measurements, dramatically improving the accuracy and comprehensiveness of as-built verification. This leads to early detection and correction of construction errors and improved quality, reducing the chance of later regretting, “We forgot to measure that spot…”

Moreover, combining point clouds with volume calculations is powerful for earthwork management and quantity estimation. For example, in earthworks, comparing the design model with the as-built point cloud can immediately calculate required fill and excavation volumes. The Ministry has introduced a "surface management" method that evaluates the as-built condition of entire surfaces using 3D measurement data, enabling comprehensive verification compared to traditional spot inspections. In paving work, which traditionally measured thickness at points, point clouds allow assessment of the entire finished surface for unevenness and insufficient thickness, advancing quality control. Some analysis software can automatically compute differences from the design and perform pass/fail judging from point clouds, making semi-automated as-built inspection feasible. Integrating measurement and analysis digitally, 3D point clouds plus volume calculation are key to dramatically improving the efficiency and reliability of as-built verification. According to a ministry survey, sites that introduced ICT construction (3D surveying, machine guidance, etc.) reduced total working hours by about 30% on average, greatly decreasing the effort for drawing creation and manual calculations. As-built verification, which used to rely on experienced intuition and labor, is becoming something anyone can perform accurately and quickly through data utilization.

The latest 3D point cloud measurement technology can now be easily implemented with a smartphone and an app. By attaching a small RTK-capable GNSS antenna to a smartphone and walking the site with a dedicated app, high-precision point cloud data with absolute coordinates can be acquired. Because each image taken by the smartphone camera is assigned accurate position coordinates corrected by RTK, the resulting point cloud is produced already aligned to the survey coordinate system. This smartphone RTK + app approach has made as-built measurement much easier and faster. For example, surveying that used to take several people a full day can be completed in actual work time of minutes with smartphone point cloud scanning. Analysis of results can be performed immediately in the cloud, enabling on-the-spot calculation of necessary dimensions and volumes. Furthermore, measurement can be completed by a single site staff member without forming a specialized survey team, and remote safe scanning allows measurement of hazardous areas without putting personnel at risk.

LRTKの特長：センチ精度・点群・AR・帳票・クラウド共有

The latest smartphone RTK tool called LRTK has features that transform as-built verification:

• センチメートル級の測位精度: RTK-GNSS technology provides high positioning accuracy within a few centimeters for both planimetric position and elevation. Under appropriate measurement conditions, it easily meets the tolerance requirements demanded by the Ministry of Land, Infrastructure, Transport and Tourism for as-built verification, comparable to conventional surveying equipment. In fact, the LRTK app includes a function to average static positioning data, and verification showed that a single-point positioning error of about 12 mm (0.47 in) improved to about 8 mm (0.31 in) after averaging 60 observations. Even during mobile point cloud scanning, an accuracy of about 1-2 cm (0.4-0.8 in) can be maintained, which is sufficient for typical civil engineering as-built measurements. In a case of scanning a bridge with a smartphone, the obtained point cloud, including areas such as the underside of girders where GNSS reception is not possible directly, showed almost no difference compared to existing control survey measurements. With LRTK’s ability to stably deliver such high precision, rigorous quality control across entire structures can be confidently performed.

• 高密度な点群データ取得: You can obtain high-density 3D point cloud data simply by walking around the site with a smartphone. By attaching an ultra-compact RTK-GNSS antenna to the phone and continuously photographing with the camera, you can generate a point cloud with absolute coordinates in a short time. Because the entire site can be recorded as countless points, differences in details that were previously unmeasurable can be detected. For example, even in areas where GNSS signals do not reach, like under bridge girders, coordinates for those parts can be indirectly computed from point clouds obtained around them, enabling high-accuracy as-built verification across the whole structure.

• ARによる現場可視化: LRTK also provides AR (augmented reality) display of acquired 3D data and design models on the smartphone. By overlaying as-built point clouds and design drawings on the phone screen at the site, you can intuitively see at a glance whether the finish conforms to the design. For instance, if buried pipelines are scanned with LRTK and saved to the cloud, during subsequent excavation work the smartphone can project the positions of existing pipes in AR, visualizing underground obstacles in advance. This helps avoid accidentally damaging unseen buried utilities and supports safer construction. Also, if the client and contractor view the same AR screen while discussing on site, it becomes easier to share judgments about as-built conformity and design intent, facilitating smoother communication.

• 帳票作成の効率化: Point cloud data acquired with LRTK can be directly used to create as-built drawings and quantity reports. Having digital point cloud data allows you to freely generate cross-sections or plans later, removing the worry of omissions due to “forgotten measurements” on site. Using point clouds together with design data also enables automated creation of as-built drawings and management tables, and simplification of photo logs. In practice, trials of as-built inspection using 3D point clouds reported a significant reduction in the burden of creating as-built drawings and photographs. The LRTK system supports the deliverable formats specified in the Ministry’s "3D As-built Management Guidelines (draft)," and volumes and section data calculated from point clouds can be output in LandXML or CSV formats for electronic deliverables. As-built reporting, which used to rely on veteran experience and manual work, can be greatly streamlined by automated calculations and report generation based on data.

• クラウド共有: Data acquired and processed with LRTK is stored in the cloud and can be shared with stakeholders in real time. For example, on the LRTK cloud you can overlay the design model and point cloud to create an "as-built heat map" (a color-coded map of differences from the design) and allow all stakeholders to check as-built conditions. Sharing data with the client permits remote as-built inspections as needed. Because on-site data, inspection, and approval workflows are linked in the cloud, confirmation and discussion can be completed online without mailing or bringing paper drawings and photos. Cloud-based information sharing smooths communication between site representatives, construction management engineers, and clients, speeding up and improving the efficiency of inspection procedures.

実務上のメリット（検査合格率・安全性・省人化・誰でも使える）

• 検査合格率の向上: By using comprehensive measurement data from 3D point clouds, you can reduce the risk of failing as-built inspections. Thorough pre-checks of the as-built condition and correction of any deviations from the design reduce the chance of being caught out at final inspection. Solid measurement data provides reliable evidence, making explanations to clients and preparation of inspection documents smoother. Achieving the required standards at first pass and clearing inspections without delay is a major advantage.

• 安全性の向上: Non-contact, wide-area measurement significantly reduces the need to enter hazardous areas for surveying. For example, steep slopes and busy roadways can be measured safely from a distance. Lightweight surveying by a small team reduces the frequency of personnel entering areas with heavy machinery, lowering the risk of contact accidents. LRTK-based as-built management not only increases efficiency but also contributes to site safety.

• 省人化と効率化: With LRTK, as-built measurements that previously required a surveying team and a full day can be completed quickly by one site staff member. In an environment of labor shortages, the ability to handle surveying with in-house staff without experienced surveyors is a major strength. Time and personnel previously devoted to surveying can be reallocated to other tasks, shortening schedules and reducing costs. Frequent point cloud scans for continuous monitoring of as-built conditions and progress help prevent rework and overconstruction, contributing to overall productivity improvements.

• 誰でも使える簡易さ: Because the system uses a smartphone and an app, the operation is intuitive and can be handled without special expertise. Complex settings or difficult procedures are unnecessary, and site staff can start using it after a short briefing. Even new staff can perform high-precision surveying, making adoption easier for companies struggling with a shortage of veteran technicians. There is no burden of each individual acquiring surveying skills, and everyone on site can benefit from digital measurement. In practice, using LRTK gives the impression, "We can handle this ourselves," due to its ease of use.

まとめ：LRTKで誰でも簡易測量を始めよう

As-built management using 3D point cloud data enables more accurate, faster, safer, and more labor-efficient construction management. The advent of LRTK has made high-precision surveying—previously reliant on specialists and expensive equipment—accessible to anyone. Improved as-built verification accuracy ensures quality, and labor savings and shortened schedules from efficiency gains boost productivity. This new method, which prevents human error while preserving reliable evidence, offers significantly greater benefits to sites than traditional approaches.

Today, such on-site DX (digital transformation) is spreading rapidly across the industry from large firms to small and medium enterprises. The government, promoting ICT construction, is expanding support measures for SMEs and encouraging the adoption of user-friendly technologies on site. Affordable, easy-to-start solutions like LRTK epitomize "easy-to-begin DX." With just a smartphone and LRTK, anyone can start simple, centimeter-accurate surveying on site as early as tomorrow. Once you try it, you will be amazed at its efficiency and usefulness.

If you have not yet adopted the latest RTK technology and 3D point cloud–based as-built management, please consider doing so now. It is an opportunity to move away from paper-based and labor-centered construction management toward data-driven smart construction management. Gain centimeter accuracy with simple surveying using LRTK that anyone can use, and evolve your site to the next stage.