Smart Construction Essential! A Thorough Guide to Using the High-Precision Positioning Device LRTK

Table of Contents

• Positioning technology indispensable for smart construction

• Traditional surveying methods and challenges to high precision

• How RTK achieves high-precision positioning

• How smartphones × high-precision GNSS devices transform the field

• Features of the high-precision positioning device "LRTK"

• Smart construction use cases enabled by LRTK

• Checkpoints for selecting a high-precision positioning device

• Promoting construction DX with simple surveying using LRTK

• FAQ

Positioning technology indispensable for smart construction

On civil engineering and construction sites, achieving positioning accuracy down to the centimeter level is essential for constructing structures according to design drawings and detecting minute displacements in infrastructure. Even deviations of just a few centimeters can become significant errors, so surveying always demands high precision.

However, the positioning accuracy of GNSS (GPS) built into common smartphones and car navigation systems is said to have errors of about 5–10 m (16.4–32.8 ft), which is far from sufficient for accurate onsite positioning. Therefore, conventionally it has been indispensable to use dedicated, expensive surveying instruments such as optical total stations or high-performance GNSS receivers, operated by skilled surveyors. Purchase and maintenance costs for equipment and labor costs for specialist operators piled up, representing a major burden for small and medium construction companies and municipalities.

Against this backdrop, interest in “smart construction,” which aims to improve productivity and reduce manpower, has been growing in the construction industry. As part of the Ministry of Land, Infrastructure, Transport and Tourism’s promotion of construction DX (digital transformation), i-Construction also highlights surveying and construction using ICT as a key pillar. The key to realizing smart construction is managing all onsite work with digital data. In particular, foundational positioning technology is the linchpin of smart construction. With high-precision positioning information, everything from automated control of heavy machinery to as-built management can be accurately digitized, dramatically improving quality and efficiency.

As noted above, achieving centimeter-level high-precision positioning traditionally required substantial cost and effort. Recently, high-precision positioning devices have attracted attention as a new technology that addresses this challenge. Among them, the high-precision GNSS positioning terminal LRTK, which pairs with smartphones so anyone can use it, has been spotlighted as a revolutionary solution that enables centimeter-level positioning on-site with just a smartphone. This article provides an in-depth explanation of the mechanisms and utilization techniques of high-precision positioning centered on LRTK, and introduces use cases and points for introduction that are useful on smart construction sites. Let’s look at the benefits that the latest positioning technology brings to the field.

Traditional surveying methods and challenges to high precision

The main methods traditionally used to obtain high-precision surveying data on site include the following. Each is useful but has challenges in terms of cost, effort, and required expertise.

• Total station surveying: Using an electro-optical distance meter (total station), distances and angles to multiple points are measured toward a reflector prism and coordinates are calculated. It provides extremely high millimeter-level precision and excellent reliability, but each point must be observed carefully one by one, requiring time and effort for wide-area surveys. It is common for skilled surveyors to set up the instrument and carry targets with two or more people, which increases labor costs.

• Photogrammetry (drones, etc.): Aerial photos of the ground are taken from above and 3D shapes are reconstructed through image analysis. Using small unmanned aerial vehicles (drones), terrain can be modeled in a short time even in mountainous areas where people cannot enter, and its use has spread recently. However, drone flights require permits under aviation law and piloting skills, and operations are limited in urban areas or bad weather. Generating point-cloud models from photos takes time, and to improve accuracy ground control points (GCPs) often need to be set and surveyed separately, adding to the effort.

• Terrestrial laser scanner surveying: A ground-based 3D laser scanner is rotated to densely scan surrounding structures and terrain with laser light. Point-cloud data on the order of millions of points can record fine shapes and is effective for as-built management and displacement measurement, but the equipment is large and expensive (millions to tens of millions of yen), and transportation and setup are laborious. Acquired point-cloud data also require post-processing with specialized software for noise removal and merging multiple scans, so it is not a technology anyone can easily use.

• GNSS surveying (RTK method): Positioning by receiving signals from satellites (GNSS) is used to determine coordinates on the Earth. The RTK (Real Time Kinematic) method, in particular, uses two receivers—a base station and a rover—that observe satellites simultaneously and apply real-time error corrections to achieve centimeter-level accuracy. However, conventional RTK surveying equipment was expensive (hundreds of thousands to millions of yen for a set of receivers and communication devices), and some communication devices required radio licenses. Many cases relied on specialist contractors or skilled operators, and the results were typically limited to individual point coordinates, so understanding wide-area 3D shapes required numerous observations or combination with other methods.

As described above, advanced surveying faced multifaceted challenges such as equipment costs, securing personnel, and working time. With the demand for positioning methods that everyone on site can easily use, a new approach that has the potential to change these circumstances significantly has emerged.

How RTK achieves high-precision positioning

So how is centimeter-level positioning achieved using satellites? The key technology is the RTK (Real Time Kinematic) method. RTK positioning operates two GNSS receivers simultaneously: a reference station (fixed station) whose coordinates are already known precisely, and a rover placed at the point to be measured. The reference station computes error factors in real time from the satellite signals it receives (such as satellite clock offsets and ionospheric delays) and sends that correction information to the rover via radio or the internet. The rover applies the received correction information in its positioning computations, reducing errors that would normally be several meters down to a few centimeters.

Using RTK differential positioning, under good conditions positioning errors can be suppressed to about 1–3 cm (0.4–1.2 in) horizontally and 3–6 cm (1.2–2.4 in) vertically. Compared to single-point GNSS positioning, which can have errors greater than 5 m (16.4 ft), the high precision of RTK is obvious. RTK can also obtain a stable solution called a fixed solution that does not drift significantly even with continuous observation, so accuracy can be maintained over long measurement periods.

Traditionally, performing RTK positioning on-site required preparing your own base station or subscribing to a network RTK correction service provided by public or private entities. Fortunately, a nationwide network of reference stations, such as the Geospatial Information Authority of Japan’s continuously operating reference stations, has been established, and by receiving correction data via dedicated communication terminals or Ntrip clients, RTK positioning can be performed without setting up your own base station. Furthermore, in Japan the quasi-zenith satellite system Michibiki also provides a CLAS (Centimeter-Level Augmentation Service) via satellite communication. With a CLAS-compatible receiver, you can receive corrections directly from satellites and maintain centimeter-level positioning even in mountainous areas where cellular communication is unavailable.

Thus, RTK technology enables real-time correction of satellite positioning errors and achieves dramatic improvements in precision. However, conventional RTK surveying equipment was expensive and required specialized operation, so it was not available for everyone on-site to use. The next section looks at the latest devices that make RTK technology astonishingly easy to use.

How smartphones × high-precision GNSS devices transform the field

The new positioning approach that combines smartphones with compact GNSS receivers has made RTK technology more accessible. Traditionally, preparations such as installing a fixed base station or sending and receiving corrections over dedicated radio were necessary, but using a smartphone greatly reduces such effort. The smartphone handles communication and computational processing, while a pocket-sized external GNSS device receives high-precision satellite signals. This makes RTK positioning possible without adding large equipment or a radio license on site. Attach the small device to a smartphone, launch a dedicated app, and you can immediately begin centimeter-level positioning where you stand—an unprecedented convenience. In short, the smartphone effectively becomes a high-precision surveying instrument.

The smartphone × GNSS device high-precision positioning system offers many advantages not found in traditional methods. First, there is no need to transport and set up heavy equipment, and a single person can complete surveying work easily. Correction data can be obtained in real time via the smartphone, and positioning results are displayed and saved on the spot, enabling speedy data utilization such as immediate cloud-based sharing within the company after site confirmation. Dedicated apps automate coordinate calculations and mapping processes, so calculations of distances and elevation differences or coordinate system transformations can be completed with a tap, reducing manual errors and post-processing work. Moreover, GNSS devices themselves can be introduced at relatively low cost and existing smartphones can be used, significantly lowering initial investment. It is becoming realistic for each worker to carry a “one-person-one-device” smartphone surveying system without the need to equip every team member with expensive surveying instruments.

Against this background and with the Ministry of Land, Infrastructure, Transport and Tourism’s push for ICT construction and construction DX, the adoption of smartphone-based RTK positioning technology is rapidly expanding. Not only major general contractors but also small and medium construction companies, surveying firms, and municipal staff increasingly use centimeter-level positioning on site without being surveying specialists. With labor shortages intensifying, enabling anyone to perform high-precision surveying directly leads to improved productivity on-site. The next section examines the features of LRTK, a representative device that actualizes this new positioning style.

Features of the high-precision positioning device "LRTK"

Among smartphone-based RTK surveying devices, the LRTK series developed by Reflexia, a venture company spun out of Tokyo Institute of Technology, has drawn particular attention. LRTK is an ultra-compact RTK-GNSS receiver that attaches to iPhone and iPad devices; despite its pocket size—weighing approximately 125 g and only 13 mm (0.51 in) thick—it is an all-in-one terminal with an internal antenna, a high-performance receiver engine, and even a battery. It attaches to a dedicated smartphone case with a one-touch action and, when necessary, can be mounted on an included pole (monopod) or tripod to accurately observe ground survey points (height offsets can be easily corrected in the app). Although small, it supports multi-GNSS and multi-frequency reception, enabling fast and stable centimeter-level positioning. It can also directly receive the CLAS signals broadcast by Japan’s quasi-zenith satellite Michibiki, so it can maintain high precision via satellite alone even in mountainous or disaster-stricken areas without cellular communication—an important advantage.

The LRTK series is also very reasonably priced, making it easy for anyone on site to introduce. Actual users have reported that “providing one LRTK per person has dramatically improved on-site productivity.” There are reports that it achieved centimeter-level accuracy even in forested areas where errors tend to increase, demonstrating performance that overturns conventional assumptions. In addition to simply measuring coordinates, LRTK has unique functions such as photo-positioning, which automatically records the capture location (latitude, longitude, height) and camera orientation for photos taken with a smartphone, and subject positioning, which can non-contact acquire coordinates of targets at a distance. The system is intuitive enough for non-surveyors to use, yet its accuracy rivals surveying instruments that cost several million yen, making it attractive for fields beyond surveying, such as infrastructure inspection and disaster damage assessment.

By utilizing LRTK, you can realize the high-precision positioning and digital site management required in the i-Construction era with nothing more than a smartphone in the palm of your hand. As a new surveying style that significantly improves on-site efficiency and measurement accuracy, the LRTK series will contribute greatly to smart construction. Detailed product specifications and case studies are available on the official website; those considering introducing high-precision positioning should check them out.

Smart construction use cases enabled by LRTK

By using LRTK, various on-site scenarios for positioning and surveying work can be streamlined, contributing to the realization of smart construction. Here are some concrete use cases.

• Improving pile-driving and layout marking efficiency: In stake-driving work where the installation positions of buildings and structures are marked on site, LRTK is powerful. By importing coordinate data from design drawings into a smartphone map app and moving while confirming your high-precision location with LRTK, you can quickly mark measurement points. Tasks that formerly required multiple people with a total station can now be accomplished accurately by a single person with a smartphone, directly reducing personnel and time.

• Enhancing as-built surveying and quality control: LRTK is useful for as-built management to verify that embankments and structures were constructed to design. For example, measuring pavement elevation after construction with LRTK allows you to calculate and display deviations from design heights on-site. Quality inspections that previously required calling in a specialist surveying team can now be performed by on-site staff in real time, helping prevent rework and improve quality.

• 3D terrain surveying and earthwork volume calculation: Combining LRTK and a smartphone makes small-scale terrain surveys and excavation volume calculations easy. Using a smartphone camera or LiDAR together with LRTK positioning, you can acquire 3D point-cloud data of terrain before and after heavy equipment work and compute volume differences (fill/cut) on the spot. Because you can quickly generate a current 3D model, processes that previously took time—such as earthwork calculations and creation of as-built drawings—are greatly streamlined.

• Application to infrastructure inspection and maintenance: LRTK is also useful for maintenance management of infrastructure such as roads, bridges, and water/sewer pipes. Since photos taken with a smartphone automatically have location and orientation data appended, recording exact inspection locations and plotting them on drawings becomes easy. Combined with AR technology, you can visualize buried pipes or design drawings through the smartphone on site, enabling even less experienced technicians to intuitively grasp site conditions.

• Disaster damage surveys: In large-scale disasters, LRTK’s portability and lower dependence on communication infrastructure make it ideal for damage assessment. Measuring collapsed structures and terrain changes at disaster sites and immediately sharing georeferenced data to the cloud enables rapid information sharing and decision-making among relevant agencies. Because Michibiki-based positioning is available even outside cellular coverage, LRTK serves as an independent surveying tool that enhances disaster response capability during power outages and communication failures.

Checkpoints for selecting a high-precision positioning device

A variety of smartphone-compatible high-precision GNSS positioning devices are offered domestically and internationally. When selecting a model that matches your company’s use, here are the main points to consider.

• Supported GNSS constellations and frequency bands: The stability of positioning depends greatly on which satellite systems the device can receive (not just GPS but also GLONASS, Galileo, Michibiki (QZSS), etc.) and which frequency bands it supports. A multi-GNSS-capable device can pick up signals from more satellites, making correction more stable. Dual-frequency L1/L2 support is superior to L1-only, and higher-end devices with triple-frequency support initialize faster and are more resistant to noise, demonstrating their value even in sites with poor sky visibility.

• Compatibility with correction information services: Support for network RTK (receiving correction data via cellular communication) is essential, but for use in Japan it is also important whether the device can utilize satellite augmentation services such as CLAS from the QZSS. If operation in mountainous or communication-free areas is anticipated, a device that can directly use corrections from Michibiki is reassuring. Also check whether firmware updates will support future new satellites and overseas augmentation services.

• Portability and ease of attachment: Because the device will be carried and used with a smartphone, small size and light weight are major advantages. Check whether it fits in a pocket or comes with a dedicated case or attachment to mount on a smartphone, as well as overall ease of handling on site. A heavy device becomes burdensome to carry for long periods, so as light as possible is ideal.

• Battery operating time: How many hours the built-in battery can operate is also important. RTK positioning consumes significant power in full operation, so a model that can run continuously for at least several hours is desirable. As a guideline, a model that operates for about 6 hours can cover more than half a day’s work. If USB charging/power delivery is supported, combining with a mobile battery can enable all-day use.

• App usability and data integration: The usability of the smartphone app that pairs with the device is a crucial selection factor. Check whether starting/stopping positioning and recording operations are intuitive, whether observation data storage formats (coordinate system conversion and CSV export) and cloud sharing functions are robust, and which OS (iOS/Android) are supported. Also verify support for future feature expansion (firmware updates, etc.).

Taking the above into account and choosing a device that fits your use case will allow you to maximize the benefits of smartphone-based high-precision positioning.

Promoting construction DX with simple surveying using LRTK

With the advent of the high-precision positioning device LRTK, surveying tasks that previously required specialist knowledge and large equipment have been dramatically simplified. The ability for anyone on site to perform simple surveying with their smartphone and obtain accurate position data instantly is a major tailwind for promoting DX (digital transformation) in construction. Tasks that previously had to be entrusted to surveying professionals can now be completed by in-house staff as part of routine operations with LRTK, yielding benefits in both speed and cost.

Smart construction and i-Construction advocated by the Ministry of Land, Infrastructure, Transport and Tourism require high-precision as-built management and ICT earthworks that rely on precise position information. LRTK is an ideal, easy-to-use positioning solution to meet such on-site needs. For example, for small-scale current-condition surveys or preliminary work for construction sites, simple surveying with LRTK can deliver sufficiently accurate results. If heavy equipment operators and construction management engineers use LRTK to take measurements as needed, faster decision-making and reduced operational errors can be expected.

The effects LRTK brings to the field go beyond mere efficiency improvements in surveying tasks. When everyone can visualize the site at centimeter-level accuracy, overall construction productivity and quality improve, which in turn helps alleviate labor shortages. Introducing high-precision positioning is an unavoidable theme for the future of construction. Why not take this opportunity to take the first step toward smart construction using LRTK and evolve your sites to the next stage?

FAQ

Q. What kind of device is an RTK device?

A. It is a small GNSS receiver that connects to smartphones or tablets. While the GPS built into a smartphone can have meter-level errors when used alone, this external device receives satellite signals at high precision and, using correction information from a reference station, enables centimeter-level positioning. Simply put, it is a peripheral that upgrades a smartphone into a professional surveying instrument.

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

A. Yes—under proper conditions, about 1–3 cm horizontally and 3–6 cm vertically can be achieved. However, this assumes an environment with open sky and stable satellite reception. In the canyons between high-rise buildings or inside forests, temporary errors of more than 10 cm may occur. The important point is that RTK is far more precise than ordinary GPS, but some errors remain depending on the surrounding environment.

Q. Can RTK positioning be done without preparing a reference station?

A. Yes. Continuously operating reference stations are installed nationwide by organizations such as the Geospatial Information Authority of Japan, and by subscribing to network RTK correction services (VRS methods, etc.) that use these stations, high-precision positioning is possible without installing your own base station. Additionally, in Japan you can use CLAS signals from the quasi-zenith satellite Michibiki, so even in areas far from base stations you can receive corrections directly from satellites and achieve centimeter-level accuracy.

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

A. DGPS (Differential GPS) also uses correction information from a reference station like RTK, but the accuracy and techniques differ. DGPS corrects mainly pseudorange (code) measurement errors and generally achieves accuracies on the order of tens of centimeters to about 1 m. RTK uses carrier-phase information to reduce errors to a few centimeters. DGPS measurements tend to drift gradually over time, whereas RTK provides a stable solution known as a fixed solution, allowing accuracy to remain stable over long periods.

Q. Can someone without surveying experience use smartphone RTK?

A. Yes. Smartphone RTK systems (for example, LRTK) are designed to minimize specialized operations; attach the device to a smartphone, launch the app, and follow the guide to start positioning. Just tap a button at the point you want to measure to record it, and the acquired coordinates are automatically plotted on a map. Unlike traditional surveying instruments, complex settings and calculations are not required. However, understanding RTK principles and precautions (such as using it where satellites are visible) will help you achieve more stable and 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 smartphone integration allows immediate cloud sharing of data and real-time confirmation of positioning results on the spot. Regarding accuracy, experiments have confirmed positioning with errors on the order of a few millimeters to several centimeters, comparable to GNSS receivers that cost several million yen. LRTK also supports receiving Michibiki’s CLAS signals, enabling continued positioning even in areas without cellular coverage, which is powerful in harsh environments such as mountainous regions. 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 conditions, but portable RTK receivers generally provide continuous positioning from several hours up to half a day. For example, LRTK operates for about 6 hours on its internal battery. Because it supports USB charging and power delivery, using a mobile battery in combination can accommodate all-day work.