A Must for Surveyors! A Centimeter-Level Positioning Revolution Realized with a Smartphone: One Device That Will Change Field Practices

Surveyors and construction management engineers working on site, aren't you encountering these kinds of issues in your daily surveying tasks? "I want to increase work efficiency but don't have enough personnel", "It's hard to carry heavy surveying equipment", "I have to be very careful to drive stakes exactly according to the plans"... In the construction industry, the aging of skilled surveyors and the shortage of younger workers are becoming serious, and with work-style reforms introducing overtime restrictions, methods that can survey quickly and with high accuracy even with a small number of people are in strong demand. In this context, a new technology "LRTK" has appeared that achieves centimeter-level positioning accuracy (half-inch accuracy) using a smartphone and a small device. This single unit, which could truly be called a "surveying revolution you can do with a smartphone", is set to dramatically change common practice on site.

On-site Challenges for Surveyors: The Dilemma of Efficiency and Accuracy Improvement

In the field of surveying, practitioners are constantly wrestling with the balance between efficiency and precision. For example, optical surveying instruments such as total stations and levels are highly accurate, but they require setup and multiple people to operate, making them labor-intensive. On the other hand, simple surveying using drones and smartphones, which has become widespread in recent years, is convenient but has limitations in accuracy and applicability. In particular, the positioning error of typical smartphone-built-in GPS is said to be about 5-10 m (16.4-32.8 ft), and while that may suffice for navigation, it cannot be used for surveys that require centimeter-level accuracy (half-inch accuracy) for tasks such as staking out positions and as-built management. In the end, for crucial operations such as staking out and setting control points, experienced surveyors had to rely on traditional equipment, creating a dilemma between "convenience" and "accuracy."

Furthermore, the field is being hit by a wave of labor shortages. While surveyors and other specialized technicians are aging, new personnel are in short supply. The more dangerous and burdensome tasks—such as surveying in mountainous areas or at sites immediately after disasters—are the ones that inevitably require manpower, and there are limits to what a small team can handle. Recording and sharing survey results is also a challenge. Analog tasks like jotting down coordinates measured on site and transcribing them into drawings at the office carry the risk of human error. "If only surveying could be easier and more accurate, and data management simpler..."──a solution that answers those voices from the field was being sought.

Why centimeter-level positioning accuracy is necessary

There are many situations in construction and civil engineering surveying where centimeter-level accuracy (half-inch accuracy) is required. For example, when laying out a building's position, even slight errors can lead to encroachment on neighboring properties or surface irregularities in structures. In as-built management, early detection of deviations of a few centimeters from the design values directly links to quality assurance and the prevention of rework. In disaster-site topographic surveys and infrastructure inspections as well, it is necessary to accurately capture differences of a few centimeters, such as changes over time in crack widths and slope displacements.

However, achieving high-precision positioning has until now required specialized GNSS receivers, reference points, and time-consuming observations. As noted above, standalone GPS positioning generally has large errors, and the hassle and inefficiency of repeatedly switching to total stations and the like is problematic. Conventional technologies have not sufficiently met the on-site demand of "we just need something simple, but with better accuracy." Although the importance of centimeter-level positioning has been recognized, balancing that accuracy with ease of use has long been a challenge.

What Is "LRTK": the Centimeter-Level Positioning Revolution Realized on Smartphones?

Into this context came "LRTK", developed by Refixia, a startup originating from Tokyo Institute of Technology. LRTK consists of an ultra-compact RTK-GNSS receiver device that attaches to a smartphone (currently mainly iPhone/iPad) and a dedicated app, and is a product aimed at being a pocket-sized, all-purpose surveying instrument usable one-per-person. RTK is a technique that corrects satellite positioning errors to achieve high accuracy, and LRTK is designed to make this easily available on a smartphone.

By one-touch attaching the receiver, which weighs only about 150 g and is approximately 13 mm (0.51 in) thick, to the back of a smartphone with a dedicated cover, your existing smartphone is instantly transformed into a surveying instrument that supports centimeter-level accuracy (cm level accuracy, half-inch accuracy).

This LRTK device has a built-in antenna and battery and operates by communicating with a smartphone via Bluetooth, etc. It also supports the domestic satellite system "Michibiki"'s centimeter-level positioning augmentation service (CLAS) (cm level accuracy (half-inch accuracy)), allowing it to receive correction information directly from the satellites and perform positioning even in mountainous areas outside communications coverage. By using the dedicated app "LRTK App", users can intuitively operate everything from acquiring and recording positioning data to various calculations and even AR display. It is truly gaining quiet popularity among field practitioners as "a surveying tool that lets you do anything with just your smartphone".

Main Functions and Features of LRTK

◎ High-precision surveying for solo work The biggest feature of LRTK is that a single person can easily perform centimeter-level surveying (cm level accuracy, half-inch accuracy). Height surveys and traverse surveys, which used to be carried out by teams of two, can be done with LRTK simply by placing the device on the survey point and pressing a button. Because the app automatically processes correction information calculations and coordinate transformations, accurate positioning is possible even without specialized knowledge. For example, when recording coordinate values, you just place the device at the measurement point and tap the shutter button on the smartphone screen, and the location information—including latitude, longitude, and elevation down to the millimeter (mm) level (0.04 in)—is saved instantly. Measurement date/time and the number of satellites captured are also recorded automatically, and you can add notes. Instead of scribbling in a paper field notebook, your smartphone itself becomes a digital field notebook.

◎ Intuitive operation through iPhone integration The excellent usability unique to smartphone apps is also an appeal of LRTK. You can perform surveying intuitively on the familiar touch screens of your iPhone/iPad while viewing maps and camera images. For example, if you place the attached device on any point on the ground and start positioning, your current location is displayed on the map as a point on the screen and can be saved with a single tap. The app also automatically calculates coordinates in the Japan Plane Rectangular Coordinate System, so surveyors do not need to perform coordinate conversions afterward. It also includes a continuous measurement mode, allowing you to hold down a button to continuously acquire data at regular intervals. Even when you want to continuously record over a wide area, such as during point cloud scanning, you don’t need to repeat operations each time, which makes the process smooth. The smartphone’s high-resolution display and responsive performance greatly improve usability as a surveying instrument.

◎ On-site projection of stake setting and design data with AR features What makes LRTK innovative is that it incorporates AR (augmented reality) technology into surveying. The dedicated app can overlay survey data and design information in real time onto the live camera view of the site. For example, the "coordinate navigation" feature, which guides users to pre-set coordinates, lets you select previously recorded control points or boundary points, and displays arrows and distances on the smartphone screen to guide the user to that location. As you approach the destination, the display switches to an enlarged mode, assisting alignment to within a few centimeters (a few inches).

AR is also highly effective for staking and layout marking tasks. With a function that acquires the coordinates of the point you want to measure and places an "AR stake" on the spot, you can display a virtual stake marker on the smartphone screen. Even on rocky ground where physical stakes cannot be installed or on dangerous slopes, you can place a virtual stake to mark the position at the measured point. This allows surveying and giving instructions from a safe location without going directly to the spot, even when you want to mark a distant point. In addition, by importing BIM/CIM data from the design phase and past inspection photos, you can also overlay 3D models and information onto the real-world scenery. For example, you can overlay a planned embankment model onto the actual site terrain and share the completion image with the client. Because LRTK enables high-precision self-positioning, there is no worry that AR-displayed models will shift as the user moves. "AR projection without positional drift" is a feature unique to LRTK, strongly supporting on-site consensus building and review work.

◎ Smartphone LiDAR and point cloud measurement The LiDAR scanners built into the latest smartphones also demonstrate their full value when combined with LRTK. While 3D scanning with a standalone smartphone is convenient, it has faced issues such as the acquired point cloud data not being assigned absolute coordinates and the shape becoming distorted when scanning while walking (particularly the ground shifting as if undulating). With LRTK, precise position information from survey-grade GNSS is linked with the smartphone’s LiDAR measurements, allowing geographic coordinates to be assigned to all point clouds in real time. Because the device’s position is continuously and highly accurately corrected even during scanning, the relative positions between point clouds do not drift even when covering large areas on foot. For example, if you scan the complex shapes of retaining walls or slopes with an LRTK-equipped smartphone, the point cloud obtained on site already contains geodetic coordinates. After that, any distance between two points, cross-sectional shapes, or volume calculations for fills and excavations can be performed instantly in the app. Without carrying heavy tripods, tripod-mounted laser scanners, or a laptop, high-precision point cloud measurement and analysis can be completed with just a single smartphone in your pocket.

◎ Cloud synchronization and real-time sharing LRTK provides a cloud service that enables immediate uploading and sharing of collected data. Coordinate points measured on site, point cloud data, and photos can be synchronized to the dedicated LRTK cloud with a single button in the app. Colleagues in the office or design staff can check the latest survey results simply by accessing the cloud through a web browser. They can check survey point locations and values on the map or grasp the on-site 3D situation with a point cloud viewer, so information sharing between the field and the office becomes dramatically smoother. The need to bring data back on paper drawings or USB drives is reduced, and real-time progress management becomes possible.

On the cloud, it is also easy to make use of accumulated data. You can, for example, compare inspection photos in chronological order or display boundary point coordinate data imported from other systems (CSV or GeoJSON format) on a map for on-site reference. For instance, in infrastructure inspections, advanced uses—such as viewing photos from the previous inspection and those taken this time side-by-side on the app screen to check the progression of deterioration—can be achieved with a single tap. The information accumulated in the cloud is truly "the site's electronic medical record". The introduction of LRTK will rapidly advance the DX (digital transformation) of survey data management and maintenance records.

Main Use Cases: Transform the Worksite with This Single Unit

LRTK leverages its versatile features to broadly support the tasks of surveyors and field engineers. Here are a few representative examples of the situations in which it proves particularly effective.

• Pile driving and setting-out tasks: For positioning buildings and structures, you can drive piles while displaying them on-site with AR stakes and AR markings based on high-precision coordinates obtained with LRTK. If you pre-register the planned points from the drawings to the cloud, it will navigate you to those points on-site, enabling accurate layout marking even by non-experts. Tasks that previously required surveyors to set up batter boards and were time-consuming are dramatically streamlined.

• As-built management and quality checks: LRTK is also useful for as-built measurements after concrete placement and upon completion of earthworks. You can quickly scan the finished terrain as a point cloud and, by comparing it with the design data, confirm on-site any excesses or shortages of fill and even slight differences in finished elevations. You can also record key dimensions using the measurement-point function and share them via the cloud, enabling inspections to be carried out immediately from a remote office. Same-day inspections and corrective instructions are also possible, accelerating the quality management cycle.

• Disaster response and surveying hazardous locations: At disaster sites such as landslides and floods, rapid situational assessment and documentation are required. With an LRTK-equipped smartphone, you can scan affected terrain from a safe position without venturing into dangerous areas and obtain precise three-dimensional data. You can instantly calculate the volume of a collapsed slope to help estimate the amount of debris to be removed, and it is also easy to record the locations of cracks with photos and coordinates to help prevent secondary disasters. In time-critical disaster response, a portable surveying device that needs no preparation and can be deployed immediately is a reassuring ally.

• Infrastructure inspection and maintenance: LRTK is highly effective for routine inspections of tunnels, bridges, and slopes. For example, in tunnel crack surveys, even outside GPS coverage where measurements are difficult, the inertial navigation technology stored in the LRTK device maintains position while an AR guide enables photos to be taken from the same location and angle as the previous time. By comparing photos in the cloud in chronological order, you won't miss the progression of cracks. Large numbers of inspection photos are also organized with coordinates, so you won't later wonder "which part was that?" As an infrastructure electronic ledger, it also contributes to improving the reliability of maintenance and management data.

• Confirmation and staking of land boundaries: LRTK is also useful for site surveying and locating boundary stakes. If known boundary point coordinates are pre-registered in the cloud, AR navigation will guide you toward those points on site. Boundary stakes buried in vegetation and not visible can be located pinpointed using the smartphone screen's arrows and distance display. When installing new boundary markers, their positions can be surveyed and immediately recorded and shared. This eliminates the need for surveyors to recalculate coordinates later, improving efficiency.

As you can see, with a single LRTK you can meet a wide range of needs from surveying and measurement to construction management and maintenance management. It has the potential to solve "things that couldn't be done before" and "things that were cumbersome" in various on-site situations, and to completely transform workflows.

Differences from traditional surveying methods

Although LRTK is innovative, what exactly distinguishes it from conventional methods? Let's briefly summarize that here.

• Comparison with optical surveying instruments: Optical instruments such as total stations, theodolites, and levels, while highly accurate, assume line-of-sight and multi-person operation. Because LRTK uses GNSS, you can measure or stake out distant points alone without worrying about straight-line distance or obstructed sightlines. Also, these optical instruments take time to set up and level, but with LRTK you can take out your smartphone and start measuring immediately. It demonstrates mobility even on confined sites and in urban surveys with poor visibility, and the ease of "go and measure immediately" is a major difference.

• Comparison with conventional GNSS surveying: Conventional RTK-GNSS receivers exist as dedicated surveying equipment, but they were mainly used mounted on poles roughly the height of a person. They are heavy and inconvenient to carry, and some are operated with dedicated controllers that have unfamiliar user interfaces. LRTK's revolutionary point is that it condenses this into pocket-size and enables operation via a smartphone app. Instead of sharing expensive large devices among a team, having an affordable unit that each person carries ensures you can measure whenever needed. Furthermore, the integration of cloud services is a strength not found in conventional devices, making post-measurement data utilization seamless.

• Comparison with drone photogrammetry: Drone-based photogrammetry and 3D modeling have attracted attention in recent years, but there are hurdles such as aviation law restrictions, weather impacts, and initial costs. Moreover, overhead data has limitations when it comes to checking dimensions of fine details. LRTK has the strength of can measure details anywhere a person can enter, and is suited to local surveys and real-time verification of survey results that are difficult with drones. By using drones and LRTK selectively as needed, and having wide-area and detailed surveys complement each other, it is possible to further improve the overall efficiency and accuracy of surveying.

• Comparison with smartphone-only use: There are simple surveying apps that use only a smartphone or tablet, but as mentioned above, there are limitations of positioning accuracy. LRTK may at first seem to add extra steps compared with those (because a device must be mounted), but the reliability of positioning is drastically improved. As a result, the need to re-measure later or to perform corrective calculations is reduced, leading to significant overall efficiency gains. It solves the dilemma "Smartphone surveying is convenient, but the accuracy...", and its unique advantage is that it provides data that is immediately useful on site.

Benefits of Adoption: The Value LRTK Delivers

As described above, LRTK has the potential to fundamentally change the way surveying is performed. Let’s once again summarize the benefits of adopting it.

• Labor-saving measures and addressing workforce shortages: Because it can be operated by a single person, it directly contributes to reduced labor costs and alleviating staffing shortages. There is no burden of transporting and installing heavy equipment, and because it is easy to handle without requiring elderly veteran surveyors, it can broaden the pool of operators. As construction management personnel can obtain the necessary data themselves without waiting for a surveying team at each site, it also helps eliminate reliance on specific individuals in operations.

• Responsiveness and Mobility: Because it's a pocket-sized device, it can be carried at all times, and you can take measurements as soon as you think of it, resulting in nimble footwork. It can respond immediately to sudden surveying needs (responding to design changes or additional work, on-site checks during disasters, etc.). Even in cases that previously took several days to arrange surveying, you can obtain data on the spot and make immediate decisions, so the overall project can be expected to speed up.

• Improved Data Accuracy and Reliability: Data accuracy attained through GNSS + RTK corrections rivals that of optical instruments and high-end GNSS equipment. High-precision positioning is possible, with horizontal positions within approximately ±2 cm (±0.8 in) and vertical positions within approximately ±3–5 cm (±1.2–2.0 in). By using repeated measurements and averaging functions, accuracy better than 1 cm (better than 0.4 in) can be achieved. This reduces rework caused by surveying errors, helping to prevent quality problems before they occur. Also, data whose history is managed in the cloud is less susceptible to tampering or loss, and because accurate information is accessible at any time, reliability is enhanced.

• Operational Efficiency and Cost Performance: The introduction cost of LRTK is very low compared to conventional surveying instruments, and considering that it can achieve accuracy comparable to dedicated equipment, it excels in cost performance. Furthermore, secondary cost-reduction effects can be expected, such as reduced paper drawings and paperwork, shorter surveying durations, and suppressed outsourcing costs. Because it can handle everything consistently from surveying and measurement to data organization and sharing, it also shortens travel time and time spent transcribing data. Overall, a major advantage is "high performance can be achieved with inexpensive equipment".

• Improved safety and working conditions: Reducing surveying work in hazardous locations is also an important advantage. With LRTK, many measurements can be taken from a remote safe zone, reducing the need for work at height or surveys that require traffic control. Its high portability also makes movement on site easier, lessening workers' physical burden. Situations where equipment had to be held for long periods in extreme heat or cold are alleviated, enabling safe and comfortable surveying.

Future Possibilities and Outlook

LRTK, which enables centimeter-level positioning on smartphones, will continue to evolve and become a key technology for construction DX. In the future, it may be linked with smart glasses (AR glasses) so that virtual on-site objects can be viewed hands-free. By having all workers carry LRTK devices and share each other’s location information, the realization of smart construction—such as preventing collisions with heavy machinery and automatically monitoring construction progress—is also expected. The expansion of positioning satellite systems themselves is also progressing, and Japan’s Quasi-Zenith Satellite System Michibiki is planned to move to a 7-satellite configuration to improve service. With an increase in the number of satellites and the introduction of new augmentation signals, positioning will become increasingly accurate even in urban and mountainous areas.

Also, looking at the construction industry as a whole, within the trends of i-Construction and digital twins, the digitalization of construction sites is unavoidable. In that context, easy-to-use, high-precision surveying tools like LRTK can become foundational technologies that contribute to efficiency improvements across all processes. Going forward, data integration with other measurement devices and software will advance, enabling consistent data utilization from design through construction to maintenance management. The wave of "smartphone surveying" pioneered by LRTK may change not only the work of surveyors but also the way on-site collaboration is conducted.

Summary: The centimeter-level positioning revolution is changing common practices on worksites

LRTK, which enables centimeter-level positioning on smartphones and small devices, is a groundbreaking solution that overturns conventional wisdom. It achieves the long-standing challenge for surveyors of combining "ease of use" and "accuracy", greatly streamlining on-site surveying and measurement processes. Its effects extend across many areas, such as alleviating labor shortages, immediate sharing of high-precision data, and improved safety. It is truly a "must-see for surveyors" technology.

Not being bound by conventional methods and proactively adopting new tools is the key to strengthening on-site capabilities going forward. LRTK can be introduced without difficult operations or extensive equipment investment, so it can be used widely by individuals and companies. If you feel even a little inconvenience or limitation in your current surveying work, why not take a step into the centimeter-level positioning revolution that starts with a smartphone? This single device will surely change the conventional wisdom on your site. Please experience simple surveying with LRTK that opens up the future of your field.