Complete with a Single Smartphone! RTK Surveying Delivering Centimeter-Level Accuracy and Cloud Integration

Table of Contents

• What is RTK surveying?

• How smartphone RTK surveying works

• Benefits of smartphone RTK surveying

• Use cases enabled by centimeter-level accuracy

• Efficiency through cloud integration

• Simple surveying with LRTK

• FAQ

In recent years, a new surveying method using smartphones called "smartphone RTK surveying" has been attracting attention. Traditionally, achieving precise positioning on the order of a few centimeters required expensive dedicated equipment and specialized surveyors. But now, an era is approaching in which a single smartphone can achieve centimeter-level positioning accuracy (cm level accuracy (half-inch accuracy)) and that data can be shared to the cloud in real time. This article explains what RTK surveying is, how it works and its benefits, and how smartphones and the cloud enable efficient field operations. Finally, we introduce the solution LRTK, which allows anyone to start high-precision surveying easily.

What is RTK surveying?

First, let’s cover the basics of RTK surveying. RTK (Real Time Kinematic) is a technique that corrects GNSS (Global Navigation Satellite System) positioning errors—such as those from GPS—in real time using correction data sent from a reference station, enabling position determination with centimeter-level accuracy (cm level accuracy (half-inch accuracy)). In other words, it can be considered an “extremely high-precision GPS usable in the field.” Traditionally, achieving high-precision RTK positioning required dedicated GNSS receivers or base station equipment costing several million yen per unit, limiting its use to specialized surveyors. However, the RTK technique itself can be realized as long as the underlying principle of canceling error sources is applied, even without expensive equipment.

With standalone positioning (such as a smartphone’s built-in GPS), accuracy is at best about 5–10 m (16.4–32.8 ft), and vertical accuracy is even worse and often impractical. In contrast, RTK surveying compares signals received by a rover (the receiver used for measurement) and a reference station (a receiver with known, accurate coordinates) from the same satellites to cancel effects like the ionosphere and clock errors. As a result, three-dimensional positioning becomes possible with extremely high accuracy—horizontal positions within ±1–2 cm (±0.4–0.8 in) and vertical positions within ± a few cm (± a few in). Because absolute coordinates including elevation can be obtained in real time, measurement points in the field can be matched to design coordinates with errors of only a few centimeters (a few inches).

Such high-precision RTK positioning is indispensable in civil surveying and construction sites. It is widely used in situations that require centimeter-level accuracy, such as establishing control points, as-built (post-construction) management, and land surveys.

How smartphone RTK surveying works

Smartphone RTK surveying was born to make RTK positioning more accessible. Specifically, by using a small RTK-GNSS receiver that can be attached to a smartphone and a dedicated app, and by using Internet-based correction services (or augmentation signals from satellites), a smartphone itself becomes a surveying device capable of centimeter-class positioning accuracy (cm level accuracy (half-inch accuracy)). For example, by attaching an ultra-compact GNSS antenna to a smartphone and launching an app, centimeter-level positioning that previously required large stationary equipment can be achieved with pocket-sized gear.

Recent smartphones (supported models) increasingly support multi-frequency GNSS reception, and when combined with high-quality correction data, they can achieve accuracies comparable to professional surveying equipment. Also, attaching an RTK receiver to a smartphone and using an app makes obtaining correction information simple. You can receive Internet-distributed correction data from reference stations (Ntrip method) while positioning, and in Japan you can directly receive the Quasi-Zenith Satellite System Michibiki’s centimeter-class augmentation service (CLAS) (cm level accuracy (half-inch accuracy)) to maintain high accuracy even outside mobile network coverage. In practice, CLAS-capable smartphone RTK receivers are powerful in mountain areas and other sites without mobile connectivity.

Furthermore, smartphones equipped with LiDAR scanners (for example, certain iPhone Pro models) can capture surrounding terrain and structures as point clouds simply by walking, and each point can be assigned absolute coordinates (latitude, longitude, elevation) obtained by RTK. In this way, high-precision 3D measurement that used to require a team of veteran surveyors is becoming possible for anyone to perform solo with only a smartphone and a GNSS receiver. In addition, smartphone×RTK surveying is expected to be a solution that achieves both labor savings and higher sophistication within construction DX initiatives promoted by the Ministry of Land, Infrastructure, Transport and Tourism, such as i-Construction.

Benefits of smartphone RTK surveying

Combining a smartphone with RTK brings three major advantages to field surveying operations that greatly surpass traditional methods.

• Centimeter-level high accuracy (cm level accuracy (half-inch accuracy)): Because positioning accuracy is always within ± a few centimeters (± a few inches), even slight height differences or dimensional errors in structures can be detected. Point clouds and coordinate point sets obtained cover the entire site, eliminating “missed measurements” and “blind spots,” and enabling reliable verification of as-built conditions. Small deviations that might be pointed out later in quality inspections can be identified and corrected in advance thanks to the achievable accuracy.

• Ease of use and labor savings: Smartphones are everyday tools that users are familiar with, and they require none of the complex operations of dedicated equipment. Attach a small RTK receiver to an iPhone and launch the dedicated app to start positioning intuitively by following on-screen prompts. Survey tasks that used to require two to three people can now be completed by one person, greatly reducing the burden of staffing. There is no need to carry heavy survey equipment—the convenience of fitting everything in a pocket is a major benefit for field workers.

• Speed and immediacy: With smartphone RTK surveying, you can measure large areas of as-built conditions in a short time and complete data processing and sharing on the same day. Using point-cloud scanning, the entire site can be digitally recorded in a few minutes, and the workflow of “survey → drafting → quantity calculation → feedback,” which used to take several days, can be completed within the day. Real-time access to as-built data allows on-the-spot judgment of construction quality and rapid adjustments to construction plans for the next day. This leads to zero rework and shorter schedules, enabling faster overall construction progress management.

Use cases enabled by centimeter-level accuracy

The combination of smartphone RTK and the cloud generates new value on site beyond simply measuring point coordinates by integrating with 3D data and AR technology. Below are representative use cases made possible specifically by high-precision positioning.

• AR overlay of 3D design models: Through a smartphone screen, 3D design models can be displayed on site via AR (augmented reality). With smartphone RTK’s centimeter-level accuracy (cm level accuracy (half-inch accuracy)), digital design models can be overlaid in the real world at the correct position and scale. For example, loading BIM/CIM models of planned structures or roads into a smartphone and compositing them with the actual scenery at the site ensures that plans and site conditions align. This makes it easy to share the completion image that was previously only visible on drawings, facilitating consensus building with clients and construction teams.

• As-built inspection and quality control: Using a smartphone’s built-in LiDAR scanner or photogrammetry features, completed structures or terrain can be captured as point clouds and compared to design data. Point clouds corrected by RTK are assigned precise absolute coordinates, enabling efficient checks on whether as-built conditions match design. For example, you can scan excavated ground or embankments to calculate volumes, or closely verify pavement elevations using point clouds—tasks that can be easily performed with a smartphone and cloud-based analysis. Photos taken with a smartphone RTK app automatically record high-precision location information and camera orientation (bearing), simplifying photographic records of inspection points. By comparing photos taken previously at the same location within the app, you can one-touch monitor aging changes such as crack progression, dramatically improving the accuracy and efficiency of quality management.

• Visualization of buried utilities: Another notable use case is visualizing the positions of buried pipes, cables, and other underground utilities on a smartphone screen. If you preload location data of buried infrastructure (as-built drawings or GIS data) into the smartphone via the cloud, you can display the subsurface pipe routes on the ground as AR simply by pointing the smartphone at the site. This enables workers to detect “invisible hazards” before excavation, directly contributing to safety measures. Thanks to high-precision smartphone positioning, virtual pipe locations are displayed with minimal offset, allowing excavation to proceed on site with confidence.

Efficiency through cloud integration

With smartphone RTK surveying, field-collected survey data can be uploaded to the cloud on the spot and shared immediately with remote teams. This eliminates the need to carry data back on USB drives or send files by email, creating various efficiency gains. Key advantages include:

• Real-time sharing: Because coordinates, photos, point clouds, and other measured data can be synchronized to the cloud immediately, team members in the office or at remote locations can view the latest data right away. For example, a point measured on site can be checked by headquarters technicians in real time, who can immediately instruct additional measurements. Timely information sharing reduces the risk of rework or oversight.

• Time-series management: As data accumulates in the cloud, survey data can be managed systematically with timestamps. Each survey point and photo is time-stamped, making it easy to track changes and progress over time. For example, you can place previous survey results or before-and-after construction photos side by side in the cloud to smoothly check aging changes or as-built progress. Organized historical data also makes it easy to reference what was measured previously, helping to prevent duplicate measurements.

• Internal collaboration: Cloud sharing allows related departments and team members within a company to reference the same latest data. Survey teams, design staff, and construction management can collaborate smoothly based on centralized data. Because data on the cloud is always updated to the latest version, discrepancies such as “the field is using the new drawing but the office is viewing an old version” are less likely to occur. You can issue access URLs to cloud data as needed and share them with external contractors or clients protected by passwords. With browser-based viewing and downloading, external information transfer becomes fast and reliable.

Real-time data linkage between the field and the office enables both to function as a unified team. Previously, field data had to be processed and shared in the office after being brought back, causing time lags; cloud integration makes field activity visible in the office instantly and removes most physical distance barriers.

This unification leads to significant labor savings. For example, as soon as a field worker finishes measurements, the office can immediately check the results and proceed to the next decision or instruction without waiting. Superiors and stakeholders can review the data on the same day and request additional measurements on the spot if necessary, reducing the waste of dispatching personnel later for rework. Eliminating manual data entry and file handovers also greatly reduces office workload (such as entering numbers into Excel or plotting in CAD). If coordinate transformations and drafting can be automated in the cloud, some tasks traditionally done by surveyors in the office may no longer be necessary.

Moreover, on-site verification efficiency is expected to improve. Many items that required construction managers or designers to visit the site for visual confirmation can now be understood by viewing detailed cloud data. As a result, unnecessary site visits and travel time are reduced, saving personnel and time. Direct data links between the field and office greatly speed up information transfer and decision-making, increasing overall operational productivity.

Simple surveying with LRTK

So far, we have looked at the benefits of smartphone RTK surveying and cloud utilization. You can appreciate how centimeter-level positioning accuracy and real-time data sharing drive efficiency and labor savings, breaking down the barriers between field and office and advancing construction site DX. However, some may feel that adopting this technology in-house could be difficult.

This is where the smartphone RTK solution LRTK is noteworthy. LRTK is a system designed to let anyone easily start centimeter-level surveying by attaching an ultra-compact RTK-GNSS receiver to a smartphone (iPhone or some Android models) and using a dedicated app and cloud service. With only a small receiver weighing a few hundred grams and a smartphone, high-precision positioning is possible without setting up a special base station, and collected data is saved to the cloud and shared in real time. LRTK is developed with ease of initial deployment and intuitive operation in mind, making it easy for field staff without surveying expertise to use—it truly supports “simple surveying.”

By using LRTK, you can immediately experience the benefits of “smartphone RTK × cloud” described in this article. It is an attractive way to start DX on a small scale by leveraging existing smartphones without purchasing expensive dedicated equipment or making large IT investments. Moving field surveying and measurement workflows to a smartphone-centric model is expected to directly improve efficiency, reduce manpower, and enhance safety.

The construction industry is currently demanding productivity innovations through digital technology. The new idea of smartphone RTK surveying with cloud sharing is one of the key initiatives. Consider taking this opportunity to adopt solutions like LRTK to start implementing simple surveying and realize a next-generation workflow that seamlessly connects the field and the office.

FAQ

Q: What equipment and environment are needed to start smartphone RTK surveying? A: Basically, you need a “supported smartphone,” an RTK-capable small GNSS receiver, and a communication environment to receive correction information. For example, with LRTK you attach a dedicated ultra-compact GNSS receiver to an iPhone or Android device and perform positioning with a smartphone app. Correction information can be provided via Internet-distributed reference station data, and in Japan you can also directly receive the Quasi-Zenith Satellite Michibiki’s centimeter-class augmentation service (CLAS) (cm level accuracy (half-inch accuracy)) so positioning is possible even outside mobile network coverage. In short, if you are outdoors with a clear view of the sky, you can start high-precision positioning with just a smartphone and a receiver.

Q: Can smartphone RTK surveying really achieve centimeter-level accuracy? Is it reliable? A: Yes—when operated properly, smartphone RTK can achieve horizontal accuracy of about ±1–2 cm (±0.4–0.8 in). In practice, smartphone RTK systems (for example, LRTK) have reported test results showing accuracy comparable to specialized first-class GNSS survey equipment. However, because satellite positioning depends on sky visibility, accuracy can degrade in locations with poor sky view (under overpasses, in dense urban areas, under tree cover, etc.). In open environments, it can be trusted as survey equipment. Modern smartphone receivers support multiple satellites and multiple frequencies, enabling more stable positioning than before. Vertical accuracy also typically falls within a few centimeters (a few inches), making it practically adequate for many civil surveying and as-built management tasks.

Q: Can it be used in mountain areas or disaster sites where Internet connectivity is unavailable? A: Yes—smartphone RTK can be used in sites with poor network connectivity. In Japan, the Quasi-Zenith Satellite “Michibiki” provides a nationwide high-precision correction service (CLAS), and compatible receivers can receive correction information directly from satellites to achieve centimeter-level positioning even without mobile signals. In fact, smartphone RTK systems (LRTK devices) have been used effectively in disaster sites where communications were cut, enabling high-precision surveying and recording without the Internet. Even when Internet connectivity is available, you can also set up a simple standalone base station as a backup if connection to a correction server is unstable. In any case, smartphone RTK can be operated flexibly according to the environment, making it useful across mountain areas, remote islands, and diverse fields.

Q: Is specialized knowledge required for installation and operation? I’m worried about whether field staff can handle it. A: Smartphone RTK solutions are designed with user-friendliness in mind so non-experts can use them. The app visually displays current position and target points on maps or in AR, and positioning and recording can be done by following prompts and pressing buttons. Basic surveying knowledge (concepts like reference points and coordinate systems) helps deepen understanding but is not mandatory. For example, LRTK automates coordinate transformations and geoid height corrections within the app, so users do not need to perform complex calculations. Manuals and support systems for the cloud service are available, and once initial setup is complete, daily operation is intuitive. Even teams with limited IT literacy can learn to use it within a relatively short training period.

Q: How can measurement data be used? Can it integrate with other software or systems? A: Data obtained with smartphone RTK is stored in the cloud and can be exported and used in various formats. Coordinate point data can be downloaded as CSV, DXF, or the Geospatial Information Authority of Japan’s standard SIMA format, making it easy to import into your CAD drawings or as-built management software. Point clouds can be exported in LAS or PLY formats for analysis with advanced point-cloud processing software. Some cloud services also offer built-in tools to measure distances and areas or create cross-sections directly, enabling analysis in a browser without specialized software. Platforms that exchange data with other site management systems or BIM models via APIs are also emerging. High-precision data from smartphone RTK can be flexibly combined with various internal and external systems.

Q: What is LRTK? It was mentioned in the article—can you explain it specifically? A: LRTK is the solution (product name) introduced in this article that makes smartphone RTK surveying easy to implement. Developed by a startup originating from Tokyo Institute of Technology, the system consists of an ultra-compact RTK-GNSS receiver, a smartphone app, and a web-based cloud service. By attaching the dedicated receiver to an iPhone or Android smartphone, you can perform centimeter-level positioning, point-cloud scanning, AR functions, and a variety of surveying tasks with a single device—essentially a “universal surveying instrument.” Collected data is immediately uploaded to the LRTK cloud, where it can be visualized on maps, measured for distance and area, and easily shared. In short, by adopting LRTK you can complete surveying and data sharing with just one smartphone, without specialized equipment. Note that “LRTK” is a brand name rather than an abbreviation, but it is positioned to mean a high-precision positioning system that completes tasks locally (“Local RTK”). For organizations considering starting smartphone RTK, LRTK is a strong option.