Speed support for civil surveying during disasters! What is the surprising performance of smartphone high-precision LRTK

Immediately after a disaster strikes, rapid situational awareness and accurate surveying are required. Roads severed by landslides, collapsed slopes, inundated urban areas—civil surveying plays an extremely important role at such disaster sites. Initial surveys capture the full extent of damage and form the basis for recovery planning, which is key to subsequent response. However, conventional methods are limited by manpower and time, and it is not easy to obtain sufficient data quickly in hazardous environments. Amid this, high-precision RTK surveying technology using smartphones and small devices called “LRTK” has attracted attention. What exactly is the surprising capability of smartphone high-precision LRTK? This article organizes the importance of surveying in disasters and the challenges of conventional methods, explains the possibilities brought by the latest smartphone RTK surveying and the features of LRTK, and details examples of municipal use and future prospects.

The important role surveying plays at disaster sites

When disasters such as earthquakes or heavy rain occur, roads are severed, terrain is deformed, and structures are damaged throughout the affected area. To carry out recovery work smoothly, it is essential to accurately measure and record the damage. For example, on a slope where a landslide has occurred, if the volume of collapsed soil is not calculated, it is impossible to determine the necessary amount of soil or the construction methods for recovery. Similarly, when bridges or roads are damaged, measuring on-site dimensions and terrain helps with emergency measures and planning temporary routes.

Obtaining rapid and precise survey data in the initial response phase is extremely important from the perspectives of safe recovery and prevention of secondary disasters. Accurate on-site condition data of damaged locations allows verification of recovery plans and later evaluation of how much has been restored by comparing with design drawings. Survey data is also indispensable for creating damage reports and recovery plans to submit to national and local governments. In large-scale disasters, reports and assessment materials must often be submitted within weeks of occurrence, making it a race against time. Civil surveying during disasters functions as the “eyes” that lay out a path to early recovery and is therefore a critical mission.

Challenges in conventional disaster surveying

However, there were many challenges in applying conventional surveying methods to disaster sites. First is the constraint of manpower and time. When using optical surveying instruments such as total stations or levels, setup and operation are labor-intensive and usually require a survey team of two or more people (one person operating the instrument, another holding the rod at the target point, etc.). When the affected area is extensive, the number of observation points becomes enormous, and conventional methods require vast amounts of time to measure each point carefully. When multiple damaged sites are scattered, limited personnel may not be able to visit all sites, risking delayed investigations.

Safety issues cannot be ignored either. Conducting surveys near loosened slopes or collapsing structures poses significant danger to survey staff. Carrying heavy equipment onto unstable collapse sites is burdensome, and in areas affected by landslides immediately after heavy rain, aftershocks or additional collapses pose constant risk of secondary disasters. In particular, conventional RTK-GNSS surveying equipment requires time for tripod setup and initial configuration and demands specialized knowledge, so not everyone can use it immediately in emergencies. Additionally, converting collected survey data into drawings or compiling it into reports takes time and effort, hindering rapid recovery planning.

Furthermore, there was a trade-off between accuracy and effort. To quickly grasp the overall situation, one had to rely on simplified methods that tended to be less accurate. Conversely, prioritizing accuracy required increasing the number of survey points and measuring meticulously, sacrificing speed in initial responses. Depending on the scale of the disaster, reference survey monuments could be washed away or destroyed, forcing re-surveying. Dependence on communication infrastructure is another concern. In major disasters, power outages and communication failures can occur, and network-type RTK surveying may be unable to connect to base stations or mobile networks, making high-precision positioning difficult. In this way, the traditional disaster surveying methods characterized by “taking time,” “requiring personnel,” and “involving danger” needed a fundamental solution provided by new technologies.

New possibilities opened by smartphone RTK surveying

As a solution to these challenges, high-precision RTK surveying using smartphones has emerged. Among them, the technology called “LRTK” has attracted attention. LRTK is a small RTK-GNSS receiver that attaches to a smartphone, transforming a general smartphone into a full-fledged surveying instrument capable of centimeter-level positioning. For example, when a dedicated case-type receiver is attached to a smartphone and powered on, the antenna on the back of the phone begins receiving signals from satellites. Simply launching the app triggers automatic GNSS satellite acquisition and initialization, and in about 30 seconds an RTK “Fix” solution (establishment of high-precision positioning) can be obtained. No specialized settings are required, and the ability to start surveying immediately upon arrival at the site is a major advantage in disaster response, where time is of the essence.

The positioning accuracy achievable with LRTK is about horizontal ±1–2 cm (±0.4–0.8 in) and vertical ±3 cm (±1.2 in), comparable to conventional expensive surveying equipment. Yet the device itself is lightweight and compact at several hundred grams (depending on the model, around 150 g), and combined with a smartphone it is easily portable with one hand. The built-in battery operates for 5–6 hours, and it can be charged from a mobile battery for extended continuous operation. Large GNSS receivers that previously had cumbersome setup needs have become smartphone-integrated devices that fit in a pocket, dramatically improving surveyors’ mobility. Even on sites where you must traverse debris piles or steep slopes, a lightweight smartphone surveying device allows quick access to required points.

Additionally, LRTK enables autonomous positioning that does not rely on communication infrastructure. It supports the centimeter-level augmentation service (CLAS) provided by Japan’s quasi-zenith satellite system Michibiki (QZSS), allowing reception of correction information directly from satellites and continued centimeter-level positioning in real time even in mountainous areas without mobile phone signals or in situations where communication networks are down after a major disaster. In other words, high-precision positioning is possible independently without base stations or internet connections, allowing reliable self-positioning even in the chaotic conditions immediately following a disaster. This builds a robust positioning system that is not affected by power outages or communication failures.

For example, at a site where a mountainside has collapsed due to heavy rain, walking along the slope while performing a LiDAR scan with a smartphone equipped with LRTK can acquire a precise 3D point cloud model of a wide area in just a few minutes. Because volume calculations of the collapsed soil can be performed on the spot, the amount of soil to be removed can be estimated immediately. Tasks that previously required survey teams to perform dozens of observations from both above and below the dangerous slope and then produce drawings and quantity calculations in the office can now be completed by a single person operating a smartphone. Likewise, the cross-sectional shape and extent of damage to severed roads can be accurately derived from point cloud data, immediately assisting planning of temporary routes and consideration of recovery methods.

Main features of LRTK smartphone surveying

The main benefits and functions offered by the LRTK RTK-GNSS device for smartphones can be summarized as follows.

• Centimeter-level high-precision positioning: Using RTK, position coordinates can be measured within an error range of a few centimeters. It ensures accuracy comparable to conventional equipment and provides reliable data as survey results.

• Portability operable with one hand: The receiver and smartphone together weigh only a few hundred grams. They require no tripod or heavy equipment and can be carried while walking with one hand. This enables agile movement on debris-strewn or sloped disaster sites and allows survey of required points quickly and sequentially.

• Safety and labor savings through single-person operation: With LRTK, multiple people do not need to be deployed for surveying. One person can handle height measurements and stake-out, minimizing the number of people exposed to hazardous locations. A remote measurement function using the smartphone camera is also provided to obtain coordinates of distant objects, enabling measurement of points that cannot be approached safely from a safe position.

• High-precision 3D point cloud scanning: Combined with a smartphone camera or LiDAR sensor, surrounding terrain and structures can be scanned to acquire three-dimensional point cloud data. It can measure up to tens of meters and generate detailed 3D models of wide areas in a short time. The acquired point cloud is tagged with accurate position coordinates in real time, so the resulting 3D model aligns with real-world coordinate systems. Soil volumes, distances, and areas can also be calculated on site, and the results can be used as outputs compliant with the Ministry of Land, Infrastructure, Transport and Tourism’s as-built management guidelines.

• Michibiki CLAS support—no communication required: LRTK can receive the high-precision augmentation signal (CLAS) of Japan’s satellite positioning system QZSS (Michibiki). Thus, even in deep mountains or out-of-coverage areas, the smartphone alone can maintain high-precision positioning. Even if mobile networks are down during disasters, as long as satellites are visible, positioning accuracy does not degrade, dramatically improving reliability in affected areas.

• Cloud integration and data sharing: Measured coordinates, captured photos, and generated point cloud data can be uploaded to the cloud with one tap from the smartphone app. Through a shared cloud link, office members far away can instantly view 3D models and photos. Even without being on site, stakeholders can grasp the damage situation through immersive 3D information, accelerating discussions and decision-making on recovery policies. If the site is out of network range, data are stored on the device and can be uploaded later from a location with connectivity.

• AR (augmented reality) support functions: By utilizing high-precision position information, design drawings and buried utility information can be overlaid on site imagery. For example, displaying a design model for recovery work in AR on site allows intuitive sharing of the finished image. Projecting pre-scanned underground utility locations in AR makes it easier to avoid pipes during excavation. In construction scenes, the smartphone screen can guide the exact positions for staking or installing structures, enabling anyone to perform accurate work without confusion.

LRTK adoption by municipalities: Fukui City’s initiatives

The usefulness of LRTK smartphone surveying has already been demonstrated in advanced municipalities. Fukui City in Fukui Prefecture was an early adopter of LRTK Phone for disaster recovery sites and succeeded in speeding up recovery work and reducing costs compared to conventional methods. At a landslide site caused by heavy rain, point cloud data of a hazardous slope were acquired from a safe, distant position in a short time, enabling rapid comprehensive understanding of damage that would have been difficult with manpower alone. This achievement was also confirmed in other cases such as recovery surveying after the 2023 Noto Peninsula earthquake, and high-precision surveying using smartphones is attracting attention as a new trump card for disaster response.

In Fukui City’s case, the obtained 3D point cloud data and high-precision survey photos were immediately shared within the city hall, enabling prompt discussion of recovery policies among the responsible departments. Processes that previously took several days—surveying, drawing creation, and quantity calculation—were dramatically shortened, leading to earlier commencement of recovery construction. When this initiative was reported, other municipalities also showed interest, and the Ministry of Internal Affairs and Communications and the Ministry of Land, Infrastructure, Transport and Tourism began to take note of LRTK’s effectiveness as an ICT-based disaster response case. In fact, movements have emerged to include the establishment of smartphone surveying systems using high-precision GNSS in national disaster reduction plans and local DX promotion plans. The introduction of such smartphone surveying technologies also aligns with the Ministry of Land, Infrastructure, Transport and Tourism’s i-Construction initiative (productivity improvement measures through ICT use on construction sites), and further diffusion is expected to accelerate.

LRTK has also started to be used in the construction sector. Major construction and surveying companies have adopted smartphone surveying for as-built management and land surveying, praising it as “helpful for resolving labor shortages because one person can even perform staking” and “easy for novice operators to use immediately.” Not only for disaster response, but also for everyday civil construction management, the smartphone + RTK combination is becoming a new field standard.

The future and prospects of disaster surveying opened by LRTK

The emergence of LRTK, which combines smartphones and high-precision GNSS, is set to greatly change how surveying and information collection are conducted during disasters. Because high-quality surveying can be performed with limited personnel, it will be a reassuring tool for municipalities and companies struggling with labor shortages. The long-standing challenge of balancing labor savings and speed with accuracy is becoming a reality with LRTK. The idea of each field staff carrying a smartphone surveying device and surveying whenever needed is becoming increasingly realistic.

Looking further ahead, big data acquired by LRTK could be analyzed by AI to propose damage predictions and emergency measures, or integrated with other technologies (drone aerial imagery and satellite images) for real-time monitoring of damage. As on-site DX (digital transformation) advances, recovery decisions that used to rely on human experience and intuition can become data-driven, enabling more objective and efficient disaster response. Smartphone high-precision surveying technologies like LRTK are key technologies supporting that transformation.

Going forward, it is expected that LRTK will be used at an increasing number of sites, and rapid damage assessment and accurate recovery planning will become commonplace. In Japan, a country prone to disasters, the spread of such advanced technologies is profoundly meaningful as it directly contributes to damage reduction and early recovery. If disaster managers train with tools like LRTK during peacetime and non-specialist staff become proficient in their operation, emergency responsiveness will be further enhanced.

Why not introduce next-generation simple surveying using smartphones at your site as well? Embracing the surprising capability of LRTK that overturns conventional wisdom can enable faster and higher-quality operations—from initial disaster response to routine construction management—than ever before.