The Cutting Edge of Surveying DX by i-Construction: Toward an Era of Smartphone Surveying

The construction and civil engineering industries face chronic labor shortages and the major challenge of improving productivity. To break this situation, the Ministry of Land, Infrastructure, Transport and Tourism has been promoting i-Construction (Ai-Construction) since around 2016 as a productivity revolution for construction sites. i-Construction is a national project that leverages cutting-edge ICT technologies to digitize and streamline the entire construction process—from surveying to design, construction, inspection, and maintenance. Among its initiatives, the most notable is the surveying DX (digital transformation). Surveying work that traditionally relied on manpower and experience is being dramatically transformed by new technologies such as drones, 3D scanners, and smartphones. The era in which surveying can be done with just a smartphone is now emerging, and this has become a front-line topic when discussing DX on construction sites.

Aims and Background of i-Construction

i-Construction aims to dramatically improve productivity on construction sites through the full-scale introduction of ICT. The Ministry of Land, Infrastructure, Transport and Tourism (MLIT) has set the bold goal of "increasing construction site productivity by 50% compared with conventional levels" and is working to realize attractive construction sites while addressing labor shortages. The key is an initiative to transform the old 3K workplaces—traditionally "tough, dirty, and dangerous"—into new 3K workplaces where pay, vacation, and hope are satisfied. As a concrete measure, 3D data and automation technologies are utilized across all processes, from surveying and design to construction and inspection, to improve efficiency and achieve labor savings. Hazardous tasks are being replaced by remote operation and automation, pursuing improved safety with the goal of zero fatalities. On the quality side, by conducting accurate, real-time measurements and inspections with ICT devices instead of relying on craftsmen's experience, rework is prevented and the aim is to standardize construction quality.

Thus, i-Construction is a national project that seeks to solve the structural challenges of the construction industry through digital technologies. In particular, the introduction of 3D surveying technology is a core element of i-Construction, and the government is actively promoting the adoption and spread of drone surveying and ICT civil engineering. In the next chapter, we will focus on smartphone-based surveying, which has been rapidly gaining ground among such digital surveying methods in recent years, and explain its mechanisms and benefits.

What is smartphone surveying?

Recently, a technology attracting attention as a driver of on-site surveying DX is smartphone surveying. Smartphone surveying, as the name suggests, refers to a method that utilizes the functions of smartphones and tablets to perform on-site surveying and 3D measurement. For example, the latest iPhones and iPads are equipped with high-performance cameras and LiDAR sensors, and by using dedicated apps you can scan the surrounding terrain and structures to acquire point cloud data. From the acquired 3D data, it's also possible to perform analyses on the spot, such as measuring required distances and areas or automatically generating cross-sectional drawings. The fact that tasks that previously required 3D laser scanners or drones costing several million yen can be completed with a single palm-sized smartphone is revolutionary.

The rise of smartphone surveying stems not only from the aforementioned labor shortages and measures in response to work-style reform, but also from expectations for digital tools that are easy to use even for younger generations (expectations for digital tools). With the number of veteran survey technicians declining, smartphone surveying—which allows a single person to perform measurements in a short time—is expected to help alleviate labor shortages. In addition, intuitive smartphone apps are easy for digital-native young employees to adopt, making them effective for promoting on-site DX and for passing on technical skills.

Another tailwind is national policy. The Ministry of Land, Infrastructure, Transport and Tourism has been actively promoting the use of 3D data at construction sites, and in 2022 revised the Draft As-Built Management Manual to formally include the use of point-cloud surveying apps using smartphones and tablets in its guidelines. As a result, smartphone apps that perform high‑precision 3D surveying on iPhone and iPad are now available for practical use, and surveying with smartphones has become a realistic option for as‑built management of public works. With this policy push, at worksites, in addition to conventional total stations and manual surveying, smartphone‑based surveying has begun to spread rapidly.

Smartphone surveying enables site conditions that could not be fully grasped from paper drawings or photos alone to be recorded and shared through complete 3D digitization. Because anyone can easily obtain data that combines the accuracy of drawings with the visual clarity of photographs, the quality and efficiency of construction management improve dramatically. Furthermore, because measurements can be taken without people approaching hazardous areas and by non-contact means, the safety benefits are very large. It is truly a next-generation surveying method that supports on-site digital transformation.

RTK Technology Supporting High-Precision Positioning

To fully utilize smartphone surveying in professional work, high-precision positioning information is indispensable. The built-in GPS in ordinary smartphones typically has errors on the order of several meters (several ft), making it insufficient for accurate surveying. This is where the positioning technology called RTK (real-time kinematic) comes in. RTK exchanges GNSS satellite observation data in real time between a base station (reference point) and a rover (the surveying side), and by canceling error factors it achieves centimeter-level accuracy (half-inch accuracy). As a result, GPS errors that were typically 5–10 m (16.4–32.8 ft) are reduced at once to within a few centimeters (within a few in), yielding position coordinates with accuracy suitable for surveying.

In recent years, high-precision positioning using RTK has evolved to the stage of being easily usable on smartphones. The key is the utilization of CLAS (Centimeter-Level Augmentation Service) provided by Japan's Quasi-Zenith Satellite System "Michibiki". By using a CLAS-compatible GNSS receiver, you can receive correction information directly from satellites overhead without installing a dedicated base station. As a result, even in mountainous areas where mobile signals do not reach, real-time centimeter-level positioning is possible as long as you can receive Michibiki's signals. As introduced in public materials from the Cabinet Office, this technology is gradually being adopted in local government field operations and elsewhere.

Smartphones themselves are becoming more powerful year by year, and models that support multi-GNSS and L1+L5 dual-frequency reception have appeared. However, there are limits to positioning accuracy with a smartphone alone, so to obtain cm level accuracy (half-inch accuracy) in practical work, using an external RTK receiver that can link to the smartphone is realistic. By using a compact RTK-GNSS device that connects via the smartphone’s Lightning port or Bluetooth, a handheld smartphone can instantly turn into an ad-hoc surveying instrument. For example, if you attach a pocket-sized receiver to your smartphone, it’s not a dream for a single person holding the phone to complete everything from control point surveying to point cloud scanning. In fact, there have been case reports of positioning with an average error of about 8 mm (0.31 in) by combining the latest compact RTK device with a smartphone, and we are increasingly entering an era where relying on expensive stationary GNSS units is no longer necessary for practical use.

Thus, the combination of smartphone × RTK has revolutionized surveying styles by combining ease of use and practical accuracy. Because the smartphone screen constantly displays the current position with cm level accuracy (half-inch accuracy), it becomes possible to confirm on-site construction deviations and to navigate stakeout positions, enabling real-time construction management. Since positioning can be done using the Michibiki CLAS signal even in offline environments, surveys can continue even in situations where communications infrastructure has been cut off, such as immediately after disasters. Also, because there is no need to equip expensive dedicated surveying instruments, there are significant cost advantages. It is easy for small and medium-sized enterprises and local governments to adopt, and equipment can be tried on a rental basis as needed.

Benefits of Smartphone Surveying

Introducing the combination of a smartphone, RTK, and point cloud measurement on-site provides various advantages not found in conventional methods. The main benefits are as follows:

• High-precision 3D data acquisition: With RTK centimeter-level positioning (half-inch accuracy) and point cloud technology, the site’s geometry can be digitally recorded with millimeter- to centimeter-level precision (millimeter to centimeter levels; centimeter-level = half-inch accuracy). Even minute deviations that were overlooked by visual inspection or isolated point measurements can be detected, improving the quality of as-built management.

• Efficiency and labor savings: Large areas can be non-contact measured at once in a short time, and a single scan can acquire a large volume of data. Survey work that previously required multiple people and several days can sometimes be completed by one person in a short time. Volume calculations and drawing creation can also be automated, substantially shortening overall work time.

• Improved safety: Because measurements can be taken remotely in hazardous areas where personnel cannot enter, worker safety can be ensured. Surveys at height or on slopes can be completed with a smartphone in hand, in some cases eliminating the need for aerial work platforms or fall-protection equipment.

• Quality control through data: If the entire site is captured as 3D data, as-built inspections by comparison with the design model can be made more efficient. By continuously collecting survey data during construction and checking differences, rework and redo can be reduced, leading to improved quality. Recording objective digital data instead of paper forms also increases the reliability of inspections and reporting.

• Easy to master: Those familiar with smartphone operation can use it intuitively without special surveying knowledge. Training costs can be kept low, allowing younger personnel to contribute to on-site DX immediately. Even veterans who are uncomfortable with IT are likely to be more receptive if the tool is a smartphone.

• Low-cost introduction: Compared with purchasing specialized surveying instruments or large equipment, a configuration of smartphone + small device + app allows relatively inexpensive startup. Because many sites already issue smartphones, additional investment is small, making it easy for small and medium-sized enterprises to introduce — a major advantage.

Main use cases of smartphone surveying

Smartphone surveying enables a wide range of capabilities. Here are several use cases that are particularly useful on-site.

• Digitization of as-built records: In as-built management, which records the shapes of structures and ground at project completion, smartphone surveying is highly effective. Traditionally, it was common to measure some dimensions with a tape measure or total station and take photos for reporting. Using smartphone point-cloud scans, the entire completed structure can be preserved as high-precision 3D data. For concrete placement surfaces, even surface irregularities can be measured, so subtle differences from the design data are not missed. Since as-built reports can include not only numerical values but also 3D models, inspection efficiency and persuasiveness are dramatically improved.

• Improving efficiency of pile-driving and layout marking: Smartphone surveying can also be applied to essential pile-driving and layout marking (positioning) tasks in building and civil engineering works. Normally, setting piles or marks at coordinates on drawings required multiple people with surveying expertise. By attaching an RTK receiver to a smartphone and using an app that guides you to specified coordinates, you can reach the target position simply by following arrows on the screen. A single person can perform pile position layout, greatly reducing personnel and time.

• Streamlining earthwork volume calculations: Smartphone surveying can also streamline volume calculations for embankment and excavation in earthworks. Previously, ground heights were measured at fixed points before and after construction, cross-sections were created, and volumes were calculated. If you scan the ground surface before and after with a smartphone, software can automatically calculate embankment and excavation volumes from the difference between the two point clouds. Scanning the whole site in a short time allows accurate volume calculation including small surface undulations, greatly improving accuracy and efficiency compared to conventional methods.

• Infrastructure maintenance and monitoring: Smartphone surveying is also useful for maintenance management of completed structures and terrain. For example, when performing regular inspections of tunnel walls or bridge bearings, scanning the target with a smartphone allows you to grasp long-term changes by comparing with past point-cloud data. If slopes are measured as point clouds annually, visualization of settlement amounts and deformation locations becomes possible and can be used to prioritize repairs. Such 3D data–based monitoring provides quantitative and objective decision-making materials compared to conventional visual inspections.

• Supporting consensus building through AR: A unique application of smartphone surveying is visualizing design data using AR (augmented reality) technology. By displaying a design-stage 3D model (BIM/CIM data, etc.) on a smartphone or tablet and overlaying it on the real landscape, stakeholders can intuitively share the image of the completed project. For example, displaying the planned structure model in AR on a site before development makes explanations to clients and nearby residents much easier. With an RTK-capable smartphone app, the model can be displayed without positional offset from the site, making it highly useful for consensus building as an accurate projected completion view.

Precautions When Introducing Smartphone Surveying

Smartphone surveying is convenient, but there are several points to be mindful of when implementing and operating it. Here we summarize the main precautions together with the current technological limitations.

• LiDARの有効範囲と環境条件: スマホ内蔵LiDARの測定範囲は半径5 m (16.4 ft)程度と限られており、広大な現場を一度にスキャンするのは得意ではありません。大規模な現場ではエリアを分割して複数回計測し、点群データを後で結合する必要があります。また直射日光下では赤外線センサーにノイズが乗りやすく、ガラスや水面など反射・透過のある素材は点群取得が困難です。雨天時も精度低下や機器故障のリスクが高まるため、基本的に避けるべきでしょう。

• 精度確保と習熟: スマホを用いた点群計測には、ある程度のコツと慣れが必要です。端末の動かし方が速すぎるとデータに抜けや歪みが生じてしまうため、安定した計測のためにはゆっくり丁寧なスキャン（slow, careful scanning）を心がける必要があります。またスマホ単体のGPS精度は数 m (several ft)と粗いため、厳密な測位にはRTKによる補強が不可欠です。言い換えれば、RTK無しのスマホ測量だけで出来形検査に使うのは難しく、用途に応じて適切な機器構成を揃える必要があります。

• データ容量と処理環境: 高密度な点群データはファイルサイズが非常に大きく、スマホ本体のストレージ容量や処理性能を圧迫しがちです。長時間のスキャンや高詳細モードでは数百万点に及ぶデータとなり、古い端末ではアプリが落ちてしまうケースもあります。取得後のデータ管理やバックアップにも注意が必要で、点群編集には高性能なPCやクラウドサービスの活用も検討すべきでしょう。

• バッテリー・機器管理: スマホや受信機は連続使用でバッテリー消費が激しくなります。長時間の測量ではモバイルバッテリーなど予備電源を用意し、適宜充電休憩を挟むことが大切です。またスマートフォンは精密機器のため、高温多湿や衝撃への耐久性にも留意する必要があります。現場で使う際は防水ケースや落下防止ストラップを活用し、雨天での使用は避けるなど機器トラブルを防ぐ工夫も重要です。

Future Prospects for Smartphone Surveying

The technologies surrounding smartphone surveying are expected to evolve further. LiDAR sensors built into smartphones will likely see improvements in range (distance) and accuracy, making wider-area scanning and the capture of fine details easier. In the GNSS field, the performance of smartphone‑embedded chips is also advancing, and with multi‑band support and the use of satellite augmentation signals, it may become possible to achieve higher‑precision positioning with a smartphone alone. Eventually, an era may come when surveying can be completed with a single smartphone at centimeter‑level accuracy (half-inch accuracy).

At the same time, the spread of digital surveying across the industry is expected to accelerate. National standards and procedures will also be developed, and construction management methods based on smartphone surveying will become standardized. On-site, the use of three-dimensional data will become commonplace, and a culture of communicating based not only on drawings and photos but also on point clouds and 3D models is expected to take root. For younger generations of engineers, an era may arrive where surveying with smartphone apps is more common than using total stations.

As an ideal form of on-site DX, an environment in which each worker carries one smartphone surveying device and anyone can instantly conduct surveys whenever needed can be envisaged. In recent years, initiatives have emerged that link ultra-compact GNSS receivers and wearable devices with smartphones, enabling all workers to carry out construction while knowing their own positions in real time. Looking ahead, there is also the possibility of combining AR-enabled smart glasses with high-precision positioning to enable hands-free measurement and design verification.

Smartphone surveying will increasingly advance and become more widespread. The fact that high-precision RTK positioning can now be easily handled on smartphones is itself a major paradigm shift, and its impact on contributing to the on-site productivity revolution (DX) is extremely significant. The era of "anytime, anywhere, anyone can survey" is becoming a reality, and smartphone surveying will become indispensable to the construction industry going forward.

Conclusion: Easily start on-site digital transformation with simplified surveying using LRTK

Finally, as an easy-to-practice solution for smartphone surveying, we introduce LRTK. LRTK is a compact RTK-GNSS receiver that can be attached to smartphones, a device that turns an iPhone or iPad into a versatile surveying instrument supporting centimeter-accuracy positioning. Despite its compact body weighing just 165 grams and about 1 cm (0.4 in) thick, it receives augmentation signals from multi-frequency GPS/GLONASS and Japan’s Michibiki satellites and can provide positioning with approximately horizontal ±1–2 cm (±0.4–0.8 in) and vertical ±3 cm (±1.2 in) accuracy.

Furthermore, it comes with a dedicated smartphone app and cloud service, offering an all-in-one suite of a wide range of features useful for on-site DX such as point cloud scanning, as-built measurement, volume calculation, and AR overlay of design data. For example, if you scan a structure with the smartphone camera + LiDAR, combining that with LRTK’s high-precision position information will generate an on-site 3D point cloud model with absolute coordinates. Acquired point cloud data and survey points can be uploaded to the cloud with one click, enabling analysis in a browser such as comparing with drawing data or measuring distances and areas.

There is also a function to display the design model in AR on the smartphone screen and overlay it on site, allowing sharing of an accurate, offset-free finished image without the need for alignment. Because all these rich functions are completed with only a smartphone and the LRTK device, no additional expensive equipment or complex software is required. It can truly be called an “all-in-one” on-site DX tool that is easy for small and medium-sized businesses and local governments to adopt.

For those interested in LRTK, please visit the official website to view detailed information and case studies. A comprehensive support system is in place so it can be operated without specialized surveying knowledge, and consultations regarding implementation are also available. By combining a smartphone with LRTK, high-precision surveying can be achieved anytime, anywhere, by anyone. Why not take this opportunity to leverage the latest tools and take a step forward in your company's on-site DX? We at LRTK are fully committed to supporting a future in which your worksites are safer and more efficient.