Smartphones Rapidly Transform into High-Precision Positioning Devices! Easy On-Site Surveying with RTK Devices

Table of Contents

• Why centimeter-level accuracy is required for on-site surveying

• How RTK devices make smartphones high-precision

• Benefits of smartphone RTK surveying

• Use cases for RTK devices

• Points to consider when choosing an RTK device

• Easy on-site surveying with LRTK

• FAQ

Why centimeter-level accuracy is required for on-site surveying

In construction and civil engineering sites, position measurement accuracy on the order of centimeters is required to construct structures precisely and to detect minute displacements in infrastructure equipment. Typically, the positional information obtained from smartphones or handheld GPS units is said to have an error of about 5–10 m (16.4–32.8 ft), which is acceptable for checking your location on a map app. However, when performing stakeout or as-built surveying on an actual construction site, an error of several meters can be critical.

This is where high-precision positioning technology called RTK (Real Time Kinematic) comes in. RTK reduces satellite positioning errors in real time, shrinking errors that would be several meters when used alone to the order of several centimeters. In practice, when leveraging RTK under favorable conditions, it is possible to reduce positioning error to about 1–3 cm (0.4–1.2 in) horizontally and about 3–6 cm (1.2–2.4 in) vertically.

Traditionally, achieving centimeter-level positioning required dedicated surveying equipment such as total stations or high-performance GNSS receivers. These devices were large and expensive, and their setup and operation required skilled technicians and multiple personnel. Total stations, in particular, boast millimeter-level accuracy but are inefficient for wide-area surveys because they require repositioning and line-of-sight for each measurement. GNSS-based RTK surveying equipment often required investments on the order of several million yen, making it impractical for every technician to carry such equipment daily. As a result, even though the demand for high-precision surveying existed amid a shortage of surveying specialists, it was not an environment where everyone on site could easily use the technology. Recently, however, driven by the Ministry of Land, Infrastructure, Transport and Tourism’s promotion of construction DX (i-Construction), adoption of RTK technology has been rapidly expanding from major general contractors to small and medium-sized construction and surveying companies and infrastructure maintenance personnel. As solutions that can achieve centimeter-level positioning more easily are sought, a new approach combining smartphones with compact RTK devices has attracted attention.

How RTK devices make smartphones high-precision

So how can combining a smartphone with an RTK device achieve centimeter-level positioning? The key is the use of “correction data” and a “dedicated receiver.” RTK positioning operates two GNSS receivers simultaneously: a base station with a known precise position (reference station) and a rover placed at the point to be measured. The base station calculates error components in real time from the satellite signals it receives (such as satellite clock errors and ionospheric delays) and transmits that correction data to the rover. The rover applies the received corrections to its own satellite positioning, reducing errors that would otherwise be several meters down to several centimeters.

With a smartphone + RTK device setup, the smartphone connects via the Internet to regional continuously operating reference station networks or commercial correction data services (so-called network RTK) to obtain real-time correction data. Meanwhile, a small RTK-GNSS receiver (RTK device) attached to the smartphone receives signals from multiple satellite constellations such as GPS, GLONASS, Galileo, and QZSS (Michibiki), and high-precision position calculations are performed within the smartphone app. The latest RTK devices support multiple frequencies (L1/L2/L5, etc.), enabling noise reduction and faster initialization (integer ambiguity resolution) of satellite signals to provide stable centimeter-level positioning. Products that can directly receive the centimeter-class augmentation service (CLAS) signals provided by Japan’s quasi-zenith satellite “Michibiki” have also emerged, allowing high-precision positioning to be maintained using satellite-based corrections alone in areas without cellular coverage, such as mountainous regions or disaster sites.

In this way, the smartphone serves as a communications and processing unit while the compact device functions as a high-performance antenna, enabling RTK surveying without the need to deploy a fixed base station or set up dedicated low-power radio links on site. Dedicated equipment sometimes required lengthy setup or radio licenses, but smartphone RTK eliminates the need to deal with complex equipment settings. Simply attach a pocket-sized RTK device to a smartphone and launch the app, and anyone can start high-precision positioning on the spot—this simplicity is a major attraction. In short, a smartphone can instantly become a high-precision surveying instrument.

Benefits of smartphone RTK surveying

Surveying using a smartphone and a portable RTK device offers many advantages not found in traditional methods. The main benefits are summarized below.

• Cloud-based instant sharing: Positioning results and observation data can be saved to the cloud on site and shared in real time with office staff and other team members. Since surveyed data can be used immediately for drawing creation and reporting, information flow between the field and the office is dramatically improved.

• Automated surveying processing via app: Dedicated surveying apps on the smartphone automatically handle coordinate calculations, drafting, and point naming management. Distance and elevation difference calculations between measured points and conversion to planar coordinate systems can be completed with a single tap, eliminating manual calculations or PC-based post-processing.

• Improved efficiency for single-person operations: Tasks that previously required two or more surveyors can be completed by one person with smartphone RTK. There is no need to transport and set up heavy equipment, and shortened preparation time allows more points to be measured in less time. Intuitive operation means even non-experts can use the tools, helping to alleviate labor shortages.

• Significant reduction in introduction costs: Smartphone-compatible RTK-GNSS receivers are inexpensive compared to total stations or high-end GNSS equipment, and they can leverage existing smartphones to greatly reduce initial investment. It becomes realistic for each worker to carry their own surveying device rather than procuring expensive equipment for multiple staff.

• Immediate use of data: Because survey data is stored digitally as it is collected, it can be used on the spot for terrain analysis or as-built management, and geotagging photos with precise position information is easy. There is no need to take notes in a paper field book and return to the office; the entire workflow from field records to drawing creation and reporting is streamlined.

As described above, surveying with a smartphone + RTK device secures accuracy while providing groundbreaking improvements in operational efficiency and cost. In open-sky environments, positioning is possible virtually anywhere, and the lack of complicated setup is a major strength for wide-area surveying. Unlike specialized equipment, smartphone apps are simple to operate, reducing training costs. For these reasons, smartphone RTK is expected to be a powerful solution driving digital transformation (DX) in the construction industry.

Use cases for RTK devices

With easy access to high-precision position information, many surveying and measurement scenarios on site can change dramatically. Here are the main use cases enabled by smartphone + RTK devices.

• Boundary and as-built surveys: You can accurately measure land boundary points and terrain elevation differences. While survey teams traditionally performed boundary stake positioning and pre-construction terrain surveys, smartphone RTK allows one person to acquire coordinates for multiple points in a short time. It is powerful for land acquisition surveys and assessing ground conditions before and after earthworks.

• As-built management and construction control: RTK provides high-precision measured values useful for confirming that roads and structures match design drawings. You can measure the height and position of arbitrary points during construction and check differences from design values on site, improving quality control and streamlining as-built drawing creation.

• Stakeout and layout work: Smartphone RTK is effective for stakeout work to mark foundations and structural placements. With centimeter-level positioning based on design coordinates, you can mark or install stakes at accurate positions without positional drift. Steps that previously relied on batter boards and measuring tapes are simplified, improving construction precision and speed.

• Infrastructure inspection and maintenance: For regular inspections of bridges and tunnels, accurately recording the locations of damage is important. By measuring photo locations and displacement with smartphone RTK, inspection records can include precise positional information. This aids in comparing changes over time and planning repairs, promoting DX in infrastructure maintenance.

• Support for drone photogrammetry: RTK devices are useful in drone-based photogrammetry (3D model creation from aerial photos). If ground control points or check points are measured in advance with smartphone RTK, the positional accuracy of aerial imagery is improved. Although more drones now incorporate onboard RTK receivers, having a handheld smartphone RTK makes it easy to confirm base point coordinates before flight.

• 3D scan measurement: Combining with LiDAR-equipped smartphones or 360° cameras enables acquisition of high-precision 3D point cloud data. By giving the point cloud from a smartphone LiDAR scanner or a photogrammetry-generated 3D model the global coordinates obtained by RTK, you can accurately determine where the measured object is located in real space. This can be applied to volume calculations and as-built visualization, enabling 3D measurements that used to take much time to be performed easily on site.

• Overlaying design data with AR: By combining AR (augmented reality) technology with high-precision position information, digital design data such as BIM/CIM models can be overlaid on the real object on site. Viewed through a smartphone, virtual structure models are projected in their actual position and dimensions, allowing immediate confirmation that construction conforms to the design. This helps share intuitive completion imagery and prevents incorrect installations.

By introducing smartphone RTK devices, surveying and measurement on site are undergoing major changes. The ability to obtain high-precision position data anywhere improves on-site data utilization, and advancements in construction management and inspection processes are expected.

Points to consider when choosing an RTK device

Various smartphone RTK devices are available from different manufacturers. Here are the key points to consider when selecting one.

• Supported GNSS constellations and frequency bands: The types of satellites and frequency bands a device can receive differ by model. Choose a multi-GNSS model that supports not only GPS but also GLONASS, Galileo, and QZSS (Michibiki) to increase the number of visible satellites and stabilize accuracy. Devices that support multiple frequencies (L1/L2 rather than L1 only) can correct errors more quickly. In challenging environments, higher-performance receivers that support three-frequency reception will deliver the best performance.

• Compatibility with correction data services: Network RTK (receiving corrections via cellular communication) support is essential, and in Japan it’s also important whether the device supports satellite-based CLAS. If you plan to operate in mountainous or communication-dead zones, a device that can directly use Michibiki correction signals provides peace of mind. Also confirm support for overseas GNSS augmentation services and whether the device can be updated for future satellite signals.

• Portability and ease of attachment: Because the device will be carried with your smartphone, compactness and light weight are major advantages. Check whether it fits in a pocket or whether a smartphone case or attachment for easy mounting is included. Heavy units are burdensome to carry for long periods, so lighter is generally better.

• Battery runtime: How many hours the internal battery can power the device is important. Full-time RTK positioning consumes significant power, so devices that can operate continuously for several hours are desirable. A unit that runs for about 6 hours can cover more than half a day of work. Support for USB charging or power via a mobile battery adds reliability for extended fieldwork.

• App usability and data integration: The usability of the smartphone app that pairs with the device is a key factor. Ensure that starting/stopping positioning and recording operations are intuitive, and check the data save formats (CSV, coordinate transformations) and cloud-sharing features. Verify supported OS (iOS/Android) and the potential for future feature expansion (firmware updates), which adds assurance.

Considering these points will help you choose an RTK device that fits your use case and maximize the benefits of smartphone-based high-precision positioning.

Easy on-site surveying with LRTK

Among smartphone-based RTK surveying systems, the LRTK series from Reflexia Inc., a venture originating from Tokyo Institute of Technology, has attracted particular attention. LRTK is an ultra-compact RTK-GNSS receiver designed for use with iPhone and iPad. Despite its pocketable size—approximately 125 g in weight and just 13 mm (0.51 in) thick—it is an all-in-one device with an internal antenna, a high-performance receiving engine, and a battery. It can be attached to a dedicated smartphone case with a one-touch mount and, if necessary, installed on the included pole (monopod) to measure ground points accurately (height offsets can be easily set in the app). With multi-frequency support for high positioning stability and compatibility with the CLAS signals distributed by Japan’s Michibiki, it can maintain accuracy even outside cellular coverage, differentiating it from competing products.

The LRTK series is also priced very affordably, making it easy for everyone on site to adopt. There are reports that “one LRTK Phone per person significantly improved field work productivity,” and it has demonstrated centimeter-level accuracy even in forests where GNSS errors typically increase. Unique features include automatically recording the photo’s capture position (latitude, longitude, and height) and orientation when taking pictures with a smartphone, and a subject positioning function that acquires coordinates of a target at a distance. With potential uses beyond surveying—such as infrastructure inspections and disaster damage surveys—LRTK has attracted attention from industries outside of construction and surveying.

By using LRTK, you can achieve the high-precision positioning and digital field management demanded in the i-Construction era with just the smartphone in your hand. As a new surveying style that overturns conventional wisdom, the LRTK series is expected to greatly contribute to improving on-site work efficiency and accuracy.

Detailed product specifications and case studies are available on the LRTK official website. If you are considering adopting high-precision positioning, feel free to contact them. LRTK is likely to push on-site surveying to the next stage.

FAQ

Q. What kind of device is an RTK device?

A. An RTK device is a small GNSS receiver used in conjunction with a smartphone or tablet. Whereas the smartphone’s built-in GPS alone may have errors of several meters, this external device captures satellite signals at high precision and, when combined with corrections from a base station, enables centimeter-level positioning. Simply put, it’s a peripheral that upgrades a smartphone into a professional surveying instrument.

Q. Can RTK positioning really achieve about 1 cm accuracy?

A. Yes—under the right conditions, you can achieve horizontal positioning accuracy of about 1–3 cm (0.4–1.2 in) and vertical accuracy of about 3–6 cm (1.2–2.4 in). However, this assumes an open-sky environment with stable satellite reception. In urban canyons or dense forests, temporary errors exceeding 10 cm may occur. It’s important to understand that RTK is far more accurate than normal GPS, but some residual error depending on the surrounding environment may remain.

Q. Can RTK positioning be performed without preparing a base station?

A. Yes. Nationwide, the Geospatial Information Authority of Japan’s continuously operating reference stations (CORS) are deployed, and by subscribing to network RTK correction services (such as VRS), you can achieve high-precision positioning without setting up your own base station. Additionally, Japan’s quasi-zenith satellite Michibiki provides the CLAS (centimeter-class augmentation service) signal, which allows direct satellite-based corrections and centimeter-level accuracy even in areas far from terrestrial base stations.

Q. What is the difference between RTK and DGPS (Differential GPS)?

A. Although DGPS also uses corrections from a base station and is similar to RTK in that respect, the accuracy and methods differ. DGPS primarily corrects errors in pseudorange (code) measurements and typically achieves accuracies on the order of several tens of centimeters to about 1 m. RTK, on the other hand, uses carrier phase information to reduce errors to several centimeters. Moreover, DGPS measurements tend to drift over time, while RTK can obtain a stable solution known as a “fixed solution,” maintaining accuracy over extended periods.

Q. Can someone with no surveying experience use smartphone RTK?

A. Yes. Smartphone RTK systems (e.g., LRTK) are designed to minimize specialized操作, and once you connect the device to your smartphone and launch the app, you can start positioning by following the on-screen guide. Simply tap the button at the point you want to measure to record it, and the obtained coordinates will be automatically plotted on the map. There is no need for the complex settings and calculations required by traditional surveying instruments. However, understanding RTK principles and precautions (such as using it where satellites are visible) will help achieve more stable high-precision results.

Q. What advantages does LRTK have compared to conventional high-precision GNSS surveying equipment?

A. The biggest advantages are portability and ease of use. LRTK fits in a pocket, greatly reducing the burden of carrying equipment on site. Its integration with a smartphone allows for cloud sharing and real-time confirmation of positioning results. In terms of accuracy, experiments have confirmed positioning errors in the range of a few millimeters to a few centimeters, comparable to conventional GNSS receivers that cost several million yen. Because it supports reception of Michibiki’s CLAS signal, it can continue positioning even outside cellular coverage and performs well in harsh environments such as mountainous areas. Overall, LRTK realizes a new surveying style of “accuracy comparable to high-end equipment, usability comparable to a smartphone.”

Q. How long does the battery last?

A. It depends on the model and usage, but portable RTK receivers generally allow continuous positioning for several hours to about half a day. For example, the LRTK Phone runs for about 6 hours on its internal battery. Because it supports USB charging and power delivery, using a mobile battery enables a full day of work.