One-handed centimeter-level positioning! Accelerating on-site DX with high-precision smartphone positioning

In recent years, new technologies that enable centimeter-level high-precision positioning and 3D measurement using only a smartphone have attracted major attention in the construction and civil engineering industries. Against a backdrop of worsening labor shortages, an aging workforce of technicians, and tighter restrictions on overtime under the 2024 work-style reform laws, the need to improve on-site efficiency and digitalize operations (on-site DX) is rapidly increasing. With the tailwind of the Ministry of Land, Infrastructure, Transport and Tourism’s i-Construction initiatives, construction sites that were traditionally managed with paper drawings and photos are shifting toward digital management using 3D point cloud data acquired by smartphones. It is now an era in which a palm-sized smartphone can handle everything from precise surveying and as-built management to overlaying design data via AR (augmented reality).

This article explains in detail the overview of high-precision positioning using smartphones (smartphone surveying), the core RTK (Real-Time Kinematic) technology, the benefits and use cases of smartphone surveying, precautions for adoption, and future prospects. Finally, we introduce LRTK, a solution that enables anyone to easily achieve centimeter-class positioning.

What is smartphone surveying

Smartphone surveying refers to methods of conducting surveying and 3D measurements on site using smartphones or tablet devices. Using the latest smartphones equipped with high-performance cameras and LiDAR sensors, you can scan surrounding structures and terrain to obtain point cloud data (a collection of numerous 3D coordinate points). With dedicated surveying apps, you can measure distances and areas on the spot from the acquired point cloud data or generate cross-sections of the terrain. It is revolutionary that tasks that previously required expensive 3D laser scanners or drones can now be completed with a single smartphone.

The attention on smartphone surveying stems not only from the aforementioned labor shortages and the need to improve productivity, but also from government promotion of 3D data utilization. In 2022, the Ministry of Land, Infrastructure, Transport and Tourism revised the as-built management guidelines (draft), explicitly including the use of point-cloud surveying apps for smartphones and tablets in the guidance. As a result, high-precision 3D surveying apps running on iPhone and iPad can now be used seriously on site, and the style of “surveying with a smartphone” is rapidly spreading alongside total stations and laser scanners.

By adopting smartphone surveying, site conditions that could not be fully captured by paper drawings or photos can be recorded and shared in 3D without omission. Because you can easily obtain data that combines the precision of drawings with the intuitive visual nature of photographs, the quality and efficiency of construction management improve dramatically. In addition, because surveying can be done non-contact even in hazardous areas where personnel cannot enter, there are significant safety benefits. It is truly a next-generation surveying method that supports on-site DX.

RTK technology indispensable for high-precision smartphone positioning

To achieve centimeter-level high-precision positioning with a smartphone, the positioning technology called RTK (Real-Time Kinematic) is indispensable. RTK is a method that adds real-time correction information to satellite positioning like GPS to determine the current position with surveying-level accuracy within a few centimeters. The GPS built into general smartphones can have position errors of several meters, but RTK cancels out such error sources using correction data sent from a reference station, achieving dramatically higher accuracy.

In smartphone surveying, this high-precision GNSS positioning provided by RTK is combined with the smartphone. Specifically, a small RTK-GNSS receiver (antenna) that attaches externally to the smartphone is prepared and linked with the smartphone surveying app, enabling continuous centimeter-level positioning. Point cloud data and measured points acquired by the smartphone can then be tagged on the spot with absolute coordinates such as latitude, longitude, and height in a global geodetic system. Traditionally, post-processing such as transforming point cloud data to fit reference points after laser scanning was necessary, but with smartphone × RTK you can obtain 3D data based on the design coordinate system immediately on site.

Thus, combining a smartphone with RTK is essential not only for ease of use but also for ensuring accuracy that can withstand practical use. To fully utilize smartphones for surveying work, high-precision positioning technology via RTK is indispensable.

Benefits of high-precision smartphone positioning

• High-precision measurement: By combining RTK corrections with point cloud measurement, you can record site shapes with millimeter-to-centimeter accuracy. Small deviations that would be overlooked by visual checks or spot measurements can be detected, contributing to improved quality of as-built management.

• Efficiency and labor saving: Large areas can be measured non-contact in a short time, and a single scan can acquire vast amounts of data. Surveying work that previously required several people and days can sometimes be completed by one person in a short time. Earthwork volume calculations and drawing generation from acquired data are also automated, greatly reducing work time.

• Data sharing and reuse: Measurement data can be stored and shared in the cloud, enabling real-time site status checks from the office. Once point cloud data is acquired, you can review it from arbitrary viewpoints or create cross-sections later, reducing the need for re-measurement. If you retain data at project completion, it can be directly used for maintenance and future renovations. Unlike paper documents, digital data does not degrade and can be preserved long-term.

• Improved safety: Remote measurement is possible at heights, steep slopes, or dangerous locations immediately after a disaster where people cannot enter. Measurements that previously involved risk can be done non-contact, making it easier to ensure worker safety. In disaster investigations, you can assess conditions without approaching affected areas, reducing the risk of secondary disasters.

• Low cost: Initial investment can be lower than purchasing dedicated surveying equipment. High-performance 3D laser scanners can cost several million yen or more, but smartphone-based measurement solutions allow you to start with a significantly smaller investment. Because you can use a smartphone you already have, unnecessary capital expenditure can be reduced.

Use cases of smartphone surveying

Digitizing as-built records

Smartphone surveying is also powerful for digitizing as-built records that document the shape of structures and the ground at project completion. Traditionally, it was common to measure some dimensions with a tape measure or total station and record/report them with photos and drawings. But with smartphone point cloud scans, you can save the entire completed structure as 3D data. For example, concrete structures can have surface micro-unevenness recorded, and you can later check dimensions on arbitrary cross-sections. As-built records can be kept as digital data that is more reliable than drawings or photos, making inspections easier to explain. Also, for elements like buried piping or foundations that cannot be directly checked after backfilling, quickly capturing 3D records before backfilling helps prevent construction errors and oversights.

Layout work that one person can perform

High-precision smartphone positioning can be applied to layout tasks (staking out) essential on construction sites. Usually, staking out a specified position on drawings by driving stakes or marking requires surveying expertise and multiple people. However, if you attach an RTK-compatible positioning device to a smartphone and use an app that loads design coordinate data, you can arrive at the target location simply by following arrow guidance displayed on the screen. When approaching a specified point, the smartphone notifies you or shows AR cues, allowing one person to accurately drive stakes or mark locations on the spot. There is no need to set up cumbersome surveying equipment, and even non-experts can perform intuitive layout work, which is revolutionary. This greatly streamlines the establishment of reference points that previously required manpower and time.

Efficient earthwork volume calculations

Smartphone surveying is useful for calculating earthwork volumes (excavation and fill). Traditionally, it was necessary to measure ground heights at regular intervals, create cross-sections, and calculate volumes using the average cross-section method, which required considerable effort. By scanning the ground surface before and after construction with a smartphone, you can automatically calculate the fill or excavation volume from the difference between two point clouds. Because you can obtain accurate quantities that include fine ground undulations in a short time, you can understand as-built quantities immediately on site. There are reported cases where earth volume measurement work that previously took several dozen person-days was reduced to several person-days by using drones and point-cloud technology. With smartphone surveying, preparation is easy even for small sites, so you can casually perform 3D measurements for minor excavations and determine accurate volumes on the spot.

Infrastructure maintenance and monitoring

Smartphone surveying is also effective for maintenance and monitoring of completed structures and infrastructure. If you scan tunnel walls or slopes with a smartphone during regular inspections and record them, you can compare past point clouds with newly acquired data to numerically detect signs of deformation or deterioration over time. For example, by performing annual slope point cloud measurements and accumulating the data, you can visualize settlement amounts and deformation trends, allowing detection of small changes that would be missed by visual inspection. Monitoring with such 3D data improves the accuracy of infrastructure inspections and strengthens preventive maintenance.

Visualizing design data with AR

A unique application of smartphone surveying is visualizing design data using AR (augmented reality). By displaying a 3D design model (BIM/CIM data, etc.) on the smartphone or tablet screen and overlaying it on the real scene, you can intuitively compare pre- and post-construction states or use it for as-built inspection. With smartphone apps that support high-precision RTK positioning, the digital model and real structure align without positional drift, enabling accurate AR-based inspections and verifications. Spatial discrepancies that were hard to understand from drawings or renderings can be visually grasped on site, which is a major advantage.

Precautions when adopting

Although smartphone surveying is convenient, there are precautions and current technical limitations to consider when introducing and operating it. The main points to note are as follows.

• Measurement range and environmental conditions: The effective range of smartphone-built-in LiDAR is limited to about 5 m (16.4 ft), so scanning an entire large site at once is difficult. In wide areas, you need to scan multiple zones and merge the data. Also, under direct sunlight the smartphone’s infrared sensor can pick up noise, and reflective or transmissive materials such as glass or water surfaces are difficult to capture as point clouds. Rain also risks reduced accuracy and equipment failure, so it is generally best to avoid use in such conditions.

• Ensuring accuracy and gaining proficiency: Point cloud measurement with a smartphone requires some technique and practice. If you move the device too quickly, gaps or distortions can occur in the data, so stable measurement requires experience. Furthermore, the standalone GPS accuracy of a smartphone is on the order of several meters (several ft), so external RTK augmentation is essential for precise positioning. In other words, achieving as-built inspection-level accuracy with a smartphone alone and without RTK is difficult, and you need to equip appropriate hardware depending on the application.

• Data volume and processing environment: High-density point cloud data tend to result in very large file sizes, which can strain a smartphone’s storage capacity and processing performance. Long scans or high-detail modes can produce data on the order of millions of points, and older devices may cause the app to crash. Post-acquisition data management and backup are also important, and handling large point clouds may require high-performance PCs or cloud services.

• Battery and device management: Long surveying sessions consume smartphone and GNSS receiver batteries quickly. Prepare spare mobile batteries and take periodic charging breaks. Since smartphones are precision devices, pay attention to their tolerance for high temperature, humidity, and shocks. When using them on site, use waterproof cases or drop-prevention straps to help prevent equipment trouble.

Future prospects

Gradual improvements in sensor performance and app refinement will likely overcome the aforementioned challenges. For example, the range and accuracy of smartphone-built-in LiDAR sensors are expected to increase, making broader area scans and capturing finer details easier. GNSS chip functionality is also advancing, and with multi-band GNSS reception and direct use of satellite-based augmentation signals (e.g., the Quasi-Zenith Satellite System’s CLAS), it may become possible in the future for smartphones alone to achieve even higher positioning accuracy.

Meanwhile, the adoption of digital surveying across the industry is expected to accelerate. As national standards and guidelines are developed, construction management methods premised on smartphone surveying may become standardized. On site, 3D data utilization will become commonplace, and communication will be based not only on drawings and photos but also on point clouds and models. For young engineers, surveying with smartphone apps may become more common than using total stations.

As on-site DX progresses, the ideal future is that each person carries a smartphone surveying device and anyone can instantly perform surveying when needed. In practice, attempts are emerging to link ultra-compact GNSS receivers or wearable devices with smartphones so that all workers can know their own positions in real time while working. Also, combining AR-capable smart glasses with high-precision positioning could enable hands-free on-site measurement and design verification in the not-too-distant future.

In this way, high-precision positioning using smartphones is expected to continue advancing and spreading. The fact that anyone can now easily handle centimeter-level positioning by combining smartphones with RTK itself is becoming a new “common sense” and will greatly contribute to a productivity revolution in construction sites.

Easily start high-precision smartphone positioning with LRTK

Finally, we introduce LRTK as a solution that enables anyone to easily realize high-precision positioning with a smartphone. LRTK consists of a small RTK-GNSS receiver that can be attached to a smartphone, together with dedicated apps and cloud services that work with it, and its key feature is that it upgrades a smartphone to support high-precision positioning without complicated setup. The basic steps to start centimeter-level positioning on site are as follows.

• Preparing equipment and the app: Prepare a smart device such as an iPhone or iPad equipped with a LiDAR sensor. Attach the LRTK receiver using a dedicated case or attachment and install the dedicated surveying app provided on the App Store. The receiver body is lightweight and compact with a built-in battery, so it does not add bulk when attached to the smartphone and can be easily taken to the site.

• Positioning setup: Connect the smartphone and receiver via Bluetooth or the like and configure the reception of RTK correction information in the app. Where mobile communications are available, correction data can be obtained via the Internet from a regional reference station network (Ntrip services, etc.). Even when out of mobile coverage, in Japan you can directly receive centimeter-level positioning augmentation provided by the Quasi-Zenith Satellite System’s CLAS and use it for corrections. Once correction data is applied, the app screen displays the estimated position error (e.g., ± a few cm (± a few in)), and high-precision positioning is ready.

• Start surveying on site: Then just follow the app’s instructions to measure. In point cloud scan mode, simply hold up the smartphone and walk while the surrounding 3D point cloud data accumulates in real time. The acquired point cloud is displayed on the spot as a 3D model, and measurements of distance and volume can be done with one touch. If you load design data, you can overlay the model on site in AR mode, and using the layout function you can easily drive stakes at specified coordinates. Measurement data is automatically synchronized to the cloud, so office PCs can immediately check results.

By using the LRTK series, anyone can dramatically improve on-site surveying accuracy and work efficiency using a smartphone. As a next-generation surveying solution compatible with the Ministry of Land, Infrastructure, Transport and Tourism’s i-Construction, it will strongly support DX in the construction industry. If you are considering performing high-precision positioning with a smartphone only, we invite you to experience the ease and accuracy of LRTK.