Surveying with Only a Smartphone! The Impact of Centimeter‑Level LRTK

In recent years, astonishment has been spreading across civil engineering surveying sites. Centimeter‑level (centi‑level) precision surveying, which traditionally required expensive surveying instruments and specialized skills, can now be done with just a single smartphone. This revolutionary system is called “LRTK.” With only one smartphone, tasks that once demanded experienced surveyors and dedicated equipment—high‑precision positioning, 3D measurement, and even AR (augmented reality)–based construction support—can be handled, attracting attention from a wide range of civil surveying professionals, from construction site managers and municipal infrastructure administrators to surveying office technicians. The arrival of LRTK, which enables high‑precision positioning and point cloud scanning with a smartphone, is truly a disruptive event for the industry.

This article explores the innovation behind LRTK that makes smartphone surveying possible. We comprehensively introduce the changes LRTK brings to civil surveying, from how it achieves centimeter‑level accuracy in GNSS surveying using a smartphone, to smartphone‑based 3D point cloud scanning, new surveying methods using AR, applications in pile driving, and examples of use at disaster sites. At the end we touch on the benefits of adopting this innovative smartphone surveying technology on site and offer tips for using LRTK as a tool for simple surveying.

Differences between traditional civil surveying and smartphone surveying

First, let’s clarify the differences between traditional civil surveying and the new surveying methods using smartphones. In civil surveying, it has been common to use expensive instruments such as total stations, dedicated GNSS receivers (so‑called surveying GPS), and levels, typically operated by a team of people. To obtain precise positioning, processes that take time and effort—like mounting instruments on tripods and performing coordinate calculations based on control points—are necessary. The equipment itself is heavy and costly, and handling it requires specialized knowledge and experience. These factors have been a significant burden in terms of cost and personnel for small to mid‑sized contractors and local governments, becoming an obstacle to advancing DX (digital transformation) in the field.

On the other hand, the recently introduced smartphone surveying is a groundbreaking idea that uses the smartphone everyone has as a surveying instrument. Conventional built‑in smartphone GPS has long been considered unsuitable for surveying because it typically has errors on the order of several meters, but advances in satellite positioning accuracy technology are changing that situation. A notable approach is incorporating RTK (real‑time kinematic) GNSS positioning into smartphones. RTK‑GNSS dramatically improves positioning accuracy by using correction data from base stations, reducing errors that were normally meters to just a few centimeters. LRTK is essentially the miniaturization of this RTK technology so that it can be used with a smartphone.

What is LRTK? Turning a smartphone into a universal centimeter‑level surveying device

So what exactly is LRTK? LRTK is a surveying device composed of an ultra‑compact RTK‑GNSS receiver that is attached to a smartphone and a dedicated app. Developed by a startup originating from Tokyo Institute of Technology, this device—called the “LRTK Phone”—is pocket‑sized at only about 125 g and approximately 13 mm thick, and is used mounted in a dedicated smartphone case. The appeal is the ease: attach this receiver to a single smartphone and it instantly transforms into a versatile surveying instrument ready for field use.

The biggest feature LRTK achieves is enabling centimeter‑level positioning with only a smartphone. Conventional smartphone GPS had errors of about 5–10 m, but LRTK dramatically reduces that error using the RTK method. It supports network‑based RTK (Ntrip) over cellular lines and is also compatible with Japan’s Quasi‑Zenith Satellite System “Michibiki” centimeter‑level augmentation service ([CLAS](https://qzss.go.jp/overview/services/sv06_clas.html)), allowing high‑precision positioning to be maintained even in communications‑outage environments such as mountainous areas or disaster sites. Experiments have shown that when LRTK is set up stationary, single measurements yield horizontal errors of about 12 mm, and averaging 60 measurements reduces the error to about 8 mm (under 1 cm). Achieving accuracy comparable to stationary surveying instruments with a palm‑sized smartphone—that is the innovation of LRTK.

Furthermore, LRTK is designed with the idea of “one device per person.” Because it is small, lightweight, and has a built‑in battery, workers can carry it in a pocket and take it out quickly to perform measurements as needed. The price is also set very affordably compared to traditional surveying equipment, making it realistic for every field worker to have their own high‑precision surveying device. In the next sections, we will look at the concrete benefits and use cases that this small LRTK brings to the field.

Point cloud scanning and 3D modeling: a smartphone becomes a high‑precision 3D scanner

With LRTK, a smartphone itself functions as a 3D point cloud scanner. Recent high‑end smartphones are equipped with LiDAR sensors and high‑performance cameras, allowing them to scan surrounding structures and terrain to obtain point cloud data (a collection of many measured points). However, ordinary smartphone point cloud scans typically do not include absolute coordinates (positions in a geodetic reference), so later it can be unclear where on a map the data corresponds to, and errors can accumulate as the user walks, causing the terrain model to distort.

The strength of LRTK is that it solves these problems at once. By linking the smartphone with the LRTK receiver, the smartphone’s own position can be known to centimeter‑level accuracy during scanning. As a result, global coordinates (latitude, longitude, altitude) are assigned to every point in the acquired 3D point cloud, eliminating the need to align multiple point cloud datasets afterward. Also, because the device can track its position with high accuracy, long continuous scans do not cause the point cloud data to warp, and wide‑area measurements maintain faithful shape recording. It is truly an era when high‑precision 3D surveying can be done easily with a single smartphone.

On site, this point cloud scanning capability proves powerful in many uses. For example, scanning current site topography allows immediate calculation of cut and fill volumes, measurement of distances or elevation differences between any two points, and more. LRTK enables uploading acquired point cloud data to the cloud and viewing and sharing it via a dedicated web app. Point clouds scanned on site can be reviewed on office PCs for earthwork calculations or imported into CAD software for comparison with design data, smoothing workflows. The ability to digitize site 3D data via smartphone surveying and use it effectively without specialized expensive equipment or software is a major advantage.

LRTK also includes photogrammetry (photo‑based surveying) functionality that reconstructs detailed 3D models from multiple photos taken with the smartphone camera. Images can be processed in the cloud to generate high‑resolution 3D models, and because these models include accurate position coordinates from the start, cracks and deterioration on structures like bridges and retaining walls can be recorded and shared with spatially referenced locations. The combination of point cloud data and precise 3D models greatly aids maintenance management of civil structures and improves efficiency in as‑built (post‑construction) inspections.

AR guidance for pile driving and visualization of design data

Another innovative point of LRTK is AR (augmented reality)–based surveying and construction support. Because design targets and alignments can be overlaid on the real‑time view on the smartphone screen, surveying and pile driving operations can be performed intuitively and efficiently. Traditionally, layout work for building foundations or placement of structures—known as marking out—required transferring coordinates from drawings to the field using surveying equipment in a process called “reverse staking,” which involved surveyors calculating coordinates and physically setting batter boards or chalk marks. With LRTK, these staking and layout tasks can be guided with just a smartphone.

Specifically, target point coordinate data (e.g., positions where piles should be driven) calculated from construction drawings are pre‑registered in the LRTK app. On site, using the navigation feature, the smartphone screen displays the direction and distance to the target point in real time, and when approaching the designated position it switches to AR mode. A virtual pile (AR pile) appears on the smartphone’s camera view so the worker can use that AR pile as a reference to position the physical pile accurately. AR piles can indicate positions in steep or otherwise inaccessible areas, or on asphalt or concrete surfaces where driving piles is difficult, allowing safe and reliable positioning. This reduces the need for people to enter unstable slopes, contributing to improved worksite safety.

AR functionality also excels at visualizing 3D design data beyond pile driving. If construction models (BIM/CIM data, etc.) are uploaded to the LRTK cloud in advance, they can be overlaid with the actual site point cloud and displayed on site to confirm the finished appearance. For example, in slope reinforcement work for an embankment, you can easily overlay the designed fill model on the current terrain point cloud and display it in AR for simulation. A key strength of LRTK is that the AR overlay exhibits very small positional drift. Ordinary smartphone AR can suffer from displayed 3D models shifting due to GPS limitations and sensor errors, but LRTK performs AR rendering while continuously correcting the user’s position to centimeter accuracy, so the overlaid model rarely floats or sinks as the user moves. Even if workers change viewpoints and walk around, the virtual model remains firmly fixed to the real object.

Such an AR surveying approach is also highly useful for communication with clients and site staff. Sharing a projected completion view on the smartphone while discussing on site makes it possible to review whether construction can proceed as designed or whether there are clashes with surrounding structures, helping prevent construction errors and resolve misunderstandings. Experiencing the completed form overlaid on the actual scene—something difficult to grasp from paper drawings or 2D CAD—facilitates consensus building and speeds up on‑site decision making.

Powerful in disaster sites: rapid field response by a compact surveying system

Smartphone surveying with LRTK is also highly effective in disaster response situations. After major disasters such as earthquakes or landslides, surveying is indispensable for quickly assessing damage and planning recovery. However, immediately after an event, road disruptions and secondary hazard risks can make it difficult to bring in large surveying equipment. Power outages or base station failures may also render communication networks unusable. In such harsh conditions, a pocketable LRTK alone enables immediate surveying and recording of disaster sites.

In fact, LRTK was used for field surveying in the 2023 Noto Peninsula offshore earthquake disaster. Even when communication infrastructure was down and mobile phones were out of range, LRTK continued to provide standalone centimeter‑level positioning by receiving augmentation signals from satellites (Michibiki’s CLAS). When photos of damage are taken with a smartphone, high‑precision position coordinates and shooting orientation are automatically recorded, allowing detailed documentation and instant sharing of “what happened at which location.” Previously, damage assessment site surveys required taking digital photos, noting locations on paper maps, and later reconciling photos with maps—a time‑consuming process. With LRTK, positioning and documentation on site are completed in one workflow. The compact, lightweight smartphone surveying device proves its worth as a rapid investigation tool in emergencies.

Cloud integration and data sharing for seamless field‑to‑office workflows

Another major strength of LRTK is easy data management and sharing through cloud service integration. Traditional surveying required bringing collected coordinate data and photos back on USB drives or handwritten notes, then importing and organizing them on office PCs for analysis. Any delay in data handover slowed reporting and decision making, and manual processes carried a risk of errors.

With LRTK, data synchronization to the cloud is possible from the smartphone app with the push of a button. All information collected on site—control point coordinates, point cloud scan results, and geotagged photos—is automatically saved to the project in the cloud. Office staff can access the cloud via a web browser to instantly view the latest field data. Without installing special software, they can view locations and notes for each survey point on a map, rotate and zoom point cloud data in a 3D viewer to inspect details, and more.

Cloud data sharing features are also robust. When you want to explain the situation to subcontractors or the client, LRTK Cloud can generate a viewing URL for the target data that can be emailed so the recipient can view the data without logging in (passwords and expiration settings can be applied if needed). Because freshly captured site data can be sent out immediately and all stakeholders can discuss using the same dataset, the speed and accuracy of information transfer improve dramatically. This is the very essence of the seamless field‑to‑office collaboration enabled by smartphone surveying.

Conclusion: a new normal in civil surveying opened by smartphone surveying

LRTK, which enables high‑precision civil surveying using only a smartphone, has the potential to dramatically improve on‑site productivity and efficiency. When centimeter‑level position information becomes accessible to anyone, surveying tasks that once had to be entrusted to specialized teams will become routine tasks that anyone on site can perform. Construction managers will be able to quickly measure conditions as needed, municipal staff can conduct simple surveys during maintenance duties, and depending on how smartphone surveying is used, site DX will accelerate further.

LRTK’s focus on achieving cost reduction for a one‑device‑per‑person rollout makes it especially attractive for small and medium‑sized construction companies and local governments. Tasks that relied on veteran surveyors’ intuition and experience will become manageable by anyone through intuitive smartphone apps, helping address industry issues such as the decline of experienced personnel and labor shortages. Moreover, LRTK’s accuracy and usability have already been proven in many field applications; one civil engineer’s blog highly praised that it achieved stable high‑precision positioning “even deep in dense forests where GPS signals are usually weak.” On social media, favorable comments such as “Using the LRTK delivered to the site immediately improved surveying efficiency dramatically” are spreading, reflecting high expectations for smartphone surveying.

The world of civil surveying is now undergoing major transformation. With the rise of smartphone surveying technologies like LRTK, surveying work will become more familiar and faster, and field data utilization will advance even further. By proactively adopting new tools rather than clinging to conventional practices, you can improve operational efficiency and safety. The era when civil surveying can be done with only a smartphone is here—experience its impact yourself and consider using LRTK for simple on‑site surveying.