Smartphone Surveying with LRTK: A New Norm in the i-Construction Era

In recent years, the construction industry has been rapidly digitizing to improve productivity. One approach gaining attention is "smartphone surveying," which combines smartphones with RTK (Real-Time Kinematic) technology. This method, which could be called a new norm in the i-Construction era, is revolutionary in that it allows anyone to perform high-precision surveying easily. This article explains in detail the benefits and functions of smartphone surveying, the DX effects it brings to job sites, and how to introduce it using LRTK.

What is i-Construction (from a surveying perspective)

i-Construction is a productivity-revolution project for the construction industry proposed by the Ministry of Land, Infrastructure, Transport and Tourism in 2016. Its objective is to introduce ICT (information and communication technology) across the entire construction process—surveying, design, construction, inspection, and maintenance—to dramatically increase on-site productivity. The initiative responds to issues such as labor shortages of construction technicians due to Japan’s declining birthrate and aging population, and the challenging working conditions at sites often described as "kitsui, kitanai, kiken (3Ks)"—hard, dirty, and dangerous. The government aims to improve productivity at construction sites by 20% by fiscal 2025 through promoting ICT use and standardizing rules, among other measures.

One major change i-Construction has brought to surveying is the spread of three-dimensional surveying technologies. Site surveys that used to take many days by manual work can now measure large areas at high density in a short time via drone photogrammetry and ground-based laser scanners. For example, flying a drone over a site to take photographs and then generating point cloud data (3D survey data) with software enables detailed understanding of terrain and structures. In the i-Construction era, surveying tasks themselves are becoming digitized and automated, dramatically improving both efficiency and accuracy.

The emergence of smartphone surveying and the challenges on site

As ICT use advances, a new approach called "smartphone surveying" has emerged. As the name suggests, smartphone surveying leverages smartphones as surveying instruments, combining dedicated apps and small sensors to perform position measurements and terrain scanning. Smartphones are equipped with high-performance cameras, sensors, and communication functions, making them like compact computers. The movement to utilize these familiar devices for surveying is spreading among on-site practitioners.

Traditional surveying required expensive, specialized equipment such as total stations and GNSS receivers and demanded skilled operators. Work typically required two people and involved time-consuming tasks such as compiling survey results into drawings or Excel. Many sites also face shortages of surveying specialists, leaving construction supervisors worried: "We don’t have enough people to ask for surveys," or "It’s inefficient to call a specialist for small measurements." Smartphone surveying, which allows immediate measurement with a phone in hand, is expected to be a major help to these field problems as a new technology.

However, standalone smartphone GPS accuracy was coarse—on the order of several meters—and insufficient for professional civil engineering surveying. The emergence of a technology that solves this problem has brought smartphone surveying into practical use: integrating RTK high-precision positioning into smartphones.

High-precision surveying achieved by RTK positioning integrated with smartphones

RTK (Real Time Kinematic) is a method that uses GNSS (Global Navigation Satellite Systems) with real-time error correction to achieve centimeter-level positioning accuracy. Standard GPS positioning has errors of several meters, but RTK greatly reduces these errors by using correction information from a base station. Until recently, RTK required RTK-capable surveying equipment and dedicated antennas, but recently small RTK receiver modules have been developed that can be used in conjunction with smartphones.

By attaching an external RTK-GNSS receiver to a smartphone and receiving correction data from a reference station over the internet (using methods like Ntrip), a smartphone can immediately obtain highly accurate position information. In other words, a smartphone can achieve accuracy comparable to professional surveying instruments. This enables establishing control points and performing fine surveying work with a smartphone, allowing it to be used in situations that previously required specialized equipment. The combination of RTK positioning and smartphones has dispelled concerns about accuracy and turned smartphone surveying into a solution fit for serious field work.

Main functions achievable with smartphone surveying

Smartphone surveying enables various functions comparable to conventional surveying instruments. Here are the main functions and use cases.

• High-precision coordinate measurement: Using a smartphone with RTK, you can measure the latitude, longitude, and elevation of any point with centimeter-level accuracy. Simply placing the device on the ground or on a structure and pressing a button records the 3D coordinates of the survey point. Measured points are automatically transformed into the survey coordinate system (such as plane rectangular coordinates), reducing the time spent on creating record books.

• 3D point cloud scanning: By leveraging built-in LiDAR scanners or cameras in smartphones, you can capture the surrounding environment as 3D point cloud data. Scanning while correcting positions with RTK assigns global coordinates to all captured points. This makes it possible, for example, to scan an excavation area with a smartphone and calculate earthwork volumes on the spot. The ability to capture high-precision coordinate-tagged point clouds with only a small, lightweight smartphone is a major advantage for field work.

• AR-based layout and design verification: AR (augmented reality) features can overlay design data or drawing positions onto the real world through the smartphone screen. With a smartphone that has high-precision coordinates, you can accurately project design models into physical space, visualize installation positions of structures, and check for interferences with existing structures in advance. This reduces the time previously spent on batter-boards and layout marking and helps prevent work errors.

• Photogrammetry and report generation: Photos taken by the smartphone camera can automatically be tagged with position information and saved as photogrammetric data. Taking photos of required locations for quality control, for example, becomes data with position and timestamp, reducing the effort to organize them on drawings later. Measurement results and photo data can be automatically compiled into forms, improving the efficiency of report creation and record keeping.

• Cloud sharing and data utilization: Coordinate and point cloud data obtained via smartphone surveying can be shared in real time through the cloud. Uploading measurements from the field to the cloud allows remote offices to immediately check results and share data with stakeholders. Advanced uses, such as viewing current 3D data in a cloud point cloud viewer and checking differences with design models, are also possible. The ability to link data between field and office is a unique strength of smartphone surveying.

*LRTK, a small RTK-GNSS receiver mounted on a smartphone. It can turn an iPhone into a pocket-sized high-precision surveying instrument.*

Benefits for surveyors, site supervisors, and municipal staff

Introducing smartphone surveying brings significant benefits to people in various roles on site.

• For surveyors: Smartphone surveying reduces the workload for surveyors. For simple site checks and quality inspections, site staff can perform measurements themselves using smartphone surveying. This allows surveyors to focus on highly specialized tasks such as advanced survey planning and data analysis. One-person surveying becomes easier, enabling efficient coverage of many sites even amid labor shortages.

• For site supervisors and construction managers: Supervisors at construction sites can "measure whenever they need to" using smartphone surveying. For instance, they can check foundation excavation depth or embankment heights on the spot and immediately reflect that information in construction. Eliminating the need to wait for a specialist team directly shortens schedules and prevents rework. Using AR, supervisors can compare design models with actual site conditions to check construction accuracy and reduce variability in finished quality. When supervisors themselves can measure and verify data, site management becomes significantly more autonomous and accurate.

• For municipal staff: Smartphone surveying is powerful for municipal tasks like road and park maintenance or disaster damage surveys. Even without specialized surveying equipment, staff can quantify site conditions quickly using a smartphone and a simple surveying device. For example, staff can measure and photograph a disaster site with their phones and instantly share it via the cloud, allowing the main office to grasp the situation in real time and plan responses. As an owner, a municipality can also review and verify 3D data submitted by contractors in the cloud, facilitating smoother digital consensus-building.

DX effects at sites enabled by adopting smartphone surveying

Introducing smartphone surveying on site not only streamlines surveying work but also serves as a driving force for digital transformation (DX) at construction sites. The main effects are as follows.

• Productivity gains through labor savings: Smartphone surveying directly leads to labor and effort reductions. Surveys that previously required two or more people can be completed by one person, and surveying time can be greatly reduced. Conducting surveys in parallel across many sites dramatically increases productivity. The burden of transporting heavy equipment is also reduced, cutting time spent on setup and teardown.

• Reduced rework and improved quality: Regularly acquiring and using high-precision survey data makes it easier to detect and correct construction errors or deviations early. For example, using smartphone surveying during construction to check finishes prevents rework due to dimensional mismatches after completion. Making decisions based on accurate current data helps standardize and improve construction quality.

• Improved safety: Smartphone surveying can reduce risks associated with surveying in hazardous areas. Using drones or poles to measure from a distance and completing surveys quickly minimizes on-site work time in high places, slopes, or busy roads. Reducing the need to carry heavy surveying equipment also lessens physical strain on workers, offering safety management benefits.

*An image shows a smartphone and LRTK mounted on a dedicated pole (monopod) for surveying. One person can easily perform measurements, improving safety.*

Workflow for introducing smartphone surveying using LRTK

When starting smartphone surveying, introducing a solution like LRTK enables smooth deployment. Below is an overview of the flow for introducing LRTK.

• Prepare devices and apps: Prepare the smartphone(s) to be used for surveying (iPhone, iPad, etc.) and the LRTK device. LRTK is a small RTK-GNSS receiver attached to a smartphone, and compatible dedicated cases or mounts are available. First, attach LRTK to the smartphone and install the dedicated app from the App Store.

• Initial setup and connection: Launch the app and configure the connection to the LRTK device. Configure settings to receive network RTK correction information (Ntrip method). By connecting to the nationwide network of GNSS reference stations (geodetic control points), you can obtain correction data in real time anywhere. Once connected correctly, the smartphone screen will display a stable centimeter-level current position.

• Conduct surveying: When ready, perform surveying on site. Take the smartphone (with LRTK attached) to the point you want to measure and tap the app’s button to record a high-precision coordinate. Use a dedicated pole for accurate ground point measurement, or walk while scanning to capture 3D point cloud data. The app instantly displays coordinates and elevations of captured points so you can add many survey points quickly. The intuitive interface makes it easy to operate even for users without surveying expertise.

• Data utilization and sharing: After surveying, use the acquired data. Data in the app can be exported as CSV or drawing formats, and necessary reports can be auto-generated. Furthermore, uploading from the LRTK app to the cloud allows office PCs to view point clouds and coordinate lists via a web browser immediately. Comparing data with design drawings or historical data in the cloud is also straightforward. In this way, survey data acquired on a smartphone can be shared among stakeholders immediately and used to inform real-time decisions on site.

Use smartphone surveying as the first step to promote DX on site

Smartphone surveying is an ideal first step for promoting DX at construction sites in the i-Construction era. The LRTK-based approach, in particular, offers a low entry barrier and delivers immediate improvements. Because you don’t need to buy expensive dedicated equipment, you can start simply by attaching a small device to a smartphone you already own, which is cost-effective. The idea of "one survey device per person"—everyone carrying a pocket-sized smartphone surveying tool and measuring when needed—is becoming the new norm.

Using LRTK makes surveying dramatically simpler and speeds up data utilization. Replacing parts of work that relied on paper drawings and personal experience with digital data helps eliminate dependence on individuals and increases transparency. Starting DX from smartphone surveying can improve overall site productivity, quality, and safety, and ultimately contribute to work-style reforms across the construction industry. Adopt smartphone surveying, which has become a new norm in the i-Construction era, and take the next step at your site.