RTK Construction Paving the Way: Latest Trends in High-Precision GNSS Technology

Table of Contents

• Introduction

• Evolution of GNSS Technology and RTK High-Precision Positioning

• Solo Surveying Expanded by Smartphone Integration

• Evolution of Data Sharing Through Cloud Utilization

• Major Use Cases at Construction Sites

• Benefits of Implementation and Future Outlook

• Summary: Simplifying High-Precision Surveying and LRTK

• FAQ

Introduction

In construction surveying, digitalization (DX) using ICT technologies has been progressing rapidly in recent years. In addition to traditional total station–centered surveying, the spread of RTK/VRS methods using the Geospatial Information Authority of Japan’s Continuously Operating Reference Station network has greatly advanced construction accuracy and operational efficiency. Against this backdrop, the Ministry of Land, Infrastructure, Transport and Tourism has promoted *i-Construction* and “simplified ICT construction,” aiming to popularize surveying solutions that anyone can use. GNSS receivers that use satellite positioning play an important role in surveying digitalization because they can measure positions directly from satellites and therefore survey wide areas efficiently.

At the same time, the industry faces serious aging of survey technicians and labor shortages, creating demand for methods that allow a small number of people to perform advanced surveying. One approach gaining attention is solo surveying using GNSS receivers. With high-precision GNSS equipment that supports RTK, surveying tasks that previously required two or three people can be performed by one person, achieving both labor savings and accuracy improvements. The latest GNSS trend of “smartphone and cloud integration” is precisely the key technology supporting this kind of solo surveying.

Evolution of GNSS Technology and RTK High-Precision Positioning

GNSS (Global Navigation Satellite System) technology has made dramatic advances in recent years. Today, multi-GNSS—simultaneous use of multiple satellite constellations such as GPS (U.S.), GLONASS (Russia), Galileo (Europe), BeiDou (China), and Japan’s Quasi-Zenith Satellite System (QZSS “Michibiki”)—has become standard, significantly increasing the number of satellites available for positioning. Modern receivers can aggregate signals from well over 100 satellites, enabling stable positioning even in environments such as urban high-rise districts or mountain valleys where satellite visibility is limited. Whereas GPS alone often suffered signal blockages that interrupted positioning, multi-GNSS makes it easier to obtain centimeter-level fixed solutions (Fix) even in the shadows of buildings and trees. The increase in satellites also improves the geometric configuration (DOP values), directly contributing to the stabilization of positioning accuracy and higher success rates for initial fixes.

At the same time, signal multi-frequency (dual-frequency, triple-frequency) has progressed. The latest GNSS receivers can receive not only L1 but also L2 and L5 bands; by combining multiple frequencies, errors such as ionospheric delay can be canceled out, greatly improving positioning accuracy compared with single-frequency operation. The benefits of multi-frequency support are not limited to accuracy. Having more usable signals also helps reduce RTK initialization time. The greater the amount of observation data, the faster integer ambiguity resolution proceeds, shortening the wait time from measurement start to obtaining a Fix solution, so high-precision positioning can be started on site immediately.

The development of multi-GNSS and multi-frequency technologies has thus maximized the potential of RTK (Real Time Kinematic). In the RTK method, error information is exchanged between a base station (reference station) and a rover in real time and corrections are applied to achieve horizontal accuracies on the order of 1-2 cm (0.4-0.8 in). For this reason, RTK has long been used as a representative centimeter-accuracy method for surveying instruments and automated control of construction equipment. However, traditional RTK operations have required setting up a base station, have been constrained to measurement ranges within several tens of kilometers from the base station, and have required ensuring communications—challenges that limited deployment. A next-generation correction technology called PPP-RTK has emerged in recent years. In Japan, PPP-RTK is realized through the centimeter-class augmentation service (CLAS) provided by the QZSS Michibiki satellites, a groundbreaking technology that can deliver RTK-level accuracy in real time without preparing a base station and even outside communication coverage.

Thanks to the multi-frequency, multi-satellite nature of GNSS satellites themselves and the sophistication of correction methods, the barrier to achieving high-precision positioning has fallen dramatically in recent years. With the technical foundation in place, the next stage is application: who will use it and how.

Solo Surveying Expanded by Smartphone Integration

A key to fully leveraging high-precision GNSS is integration with smartphones. RTK positioning, which used to require dedicated handheld computers or large controllers, can now be operated intuitively on smartphones and tablets. Bluetooth connections and ultra-compact GNSS receivers that can be directly attached to a smartphone have appeared, enabling cable-free, low-stress operation. Because the receiver status and positioning results can be monitored in real time on the smartphone screen, operators without specialized knowledge can handle the system intuitively. “Smartphone-mounted” devices weighing several hundred grams have become practical, and integrating them with a smartphone for easy portability significantly lowers the barriers to field surveying.

The advantages of smartphone integration go beyond operability. By combining GNSS positioning with a smartphone’s built-in camera and LiDAR sensor, a single device can perform photogrammetry and 3D scanning to acquire point cloud data. For example, scanning an object with a LiDAR-equipped smartphone can immediately capture detailed three-dimensional shapes, and linking those scans with position coordinates obtained via GNSS can rapidly generate precise 3D point cloud models. Even with a regular smartphone camera, using a dedicated app that pairs with a GNSS receiver allows photos to be tagged with high-precision location data, enabling later plotting of images on a map for recordkeeping. In practice, combinations of small GNSS devices that attach to smartphones and dedicated apps now allow solutions that take a photo and record a position with a single tap, acquiring image data with high-precision coordinates on the spot. This makes it far easier to document site conditions with photos while retaining accurate position information for later drawing or reporting.

Smartphone apps have also simplified the measurement workflow itself. Recording the current location (single-point surveying) can save centimeter-accuracy coordinates with a single tap on the smartphone screen, and continuous positioning modes can automatically log many points while walking. Acquired point clouds and photo data can be visualized immediately within the app, and notes or attribute information can be added as needed. If important survey points are named or commented, information that used to be managed separately in notebooks or drawings can all be centrally managed on the smartphone. By completing the sequence of measure → record → check on a single smartphone, field surveying efficiency has dramatically improved.

Evolution of Data Sharing Through Cloud Utilization

As smartphone and GNSS integration advances, cloud service integration is also transforming surveying workflows. Traditionally, field-collected survey data had to be carried back on USB sticks or SD cards, imported into office PCs, and saved and shared on internal servers—a time-consuming process. Modern smartphone surveying solutions connect the surveying app directly to the cloud, allowing coordinate and point cloud data collected on site to be uploaded to the cloud instantly with a single tap. If point information with photos captured by the GNSS receiver is synchronized to the cloud on the spot, stakeholders can share results without returning to the office. From a cloud-based web platform, uploaded survey data can be visualized on a map or viewed via a 3D viewer for point clouds; functions are also available to automatically generate point lists and photo-inclusive reports. Parties without dedicated software and remote team members can access shared data from a URL in a browser, making reporting to clients and cross-departmental information sharing smooth. This seamless field-to-cloud data linkage significantly streamlines post-survey data organization and drafting work in the office.

Cloud utilization is more than data storage and sharing. It provides the infrastructure for the real-time use of survey data. For example, internet-based RTK correction services (Ntrip distribution) are provided via cloud technology, and advanced network RTK that aggregates corrections from nationwide reference stations and distributes them as virtual reference stations (VRS) has become common. This means that without installing a dedicated base station, a field GNSS receiver can continuously receive the latest correction data via the cloud. Aggregated survey data in the cloud can also be shared immediately with design and construction management departments, making it easy to reflect measured field information in construction plans or use it for as-built management. In practice, for bridge and tunnel periodic inspections, if high-precision coordinate-tagged photos and 3D scan data are recorded and stored in the cloud, it becomes possible to compare past and new data from the office later to analyze displacements and deterioration. Cloud integration is becoming the backbone that supports the entire surveying process, not only collecting data but also enabling subsequent analysis and collaboration.

Cloud-stored survey data also shows its value when integrated with other ICT construction tools. For example, efforts have begun to integrate drone aerial photos and point clouds obtained by mobile LiDAR with GNSS positioning data in the cloud to automatically generate current 3D terrain models or create as-built management documents. In 2022, the Ministry of Land, Infrastructure, Transport and Tourism evaluated the accuracy of “3D measurement technologies using mobile devices” and confirmed they meet the criteria for use in as-built management (within ±50 mm (±1.97 in)), then documented this in guidance. Such guideline development is advancing, and the flow of centrally managing survey data in the cloud and smoothly utilizing it for design, construction, and maintenance is becoming standardized.

Major Use Cases at Construction Sites

The combination of GNSS receivers with smartphone and cloud integration technologies is being put to practical use in a variety of field scenarios. Representative cases include:

• Solo surveying: As noted above, leveraging high-precision GNSS can greatly reduce surveying labor. Tasks that used to require multiple people, such as setting out building positions (layout), can be guided in real time with smartphone GNSS guidance that instructs, for example, “move 5 cm east,” allowing staking to be done accurately by one person. On one civil engineering site, as-built measurements that used to take two people a full day were completed by one person in a few hours after introducing GNSS, achieving about a 70% reduction in work time and labor costs. In a time of severe labor shortages, solo surveying is expected to be a solution that dramatically increases productivity while maintaining safety.

• Disaster response: At sites of large earthquakes or landslides, quickly recording and sharing the damage situation influences the initial phase of recovery work. Using GNSS receivers with smartphones, photos taken in the field can have precise position coordinates recorded on the spot, enabling rapid mapping of damage areas and 3D reconstruction later. For example, during the 2023 Noto Peninsula earthquake, a civil engineering firm that had already adopted a GNSS smartphone surveying system usable even outside mobile coverage was able to record high-precision photo data in mountainous areas where communications were cut off. Photos uploaded to the cloud were shared with local authorities immediately and significantly shortened the lead time for recovery planning. The effectiveness of GNSS solo surveying in disaster response has been demonstrated, and its use in disaster prevention and response is expected to expand further.

• Constrained-site construction: In narrow urban construction sites or locations with poor lines of sight, GNSS receivers are effective as long as the sky above is open. Multi-GNSS–compatible units can capture signals from multiple satellites even in building canyons or under viaducts, maintaining more continuous positioning. In tight sites where bringing in drones or large surveying equipment is difficult, surveying that combines a smartphone’s camera/LiDAR with GNSS can be carried out in a small footprint. In fact, when a local government introduced a smartphone surveying app for small-scale projects they commissioned, it was highly rated as “this one tool does everything.” Even in narrow sites where heavy machinery cannot be brought in, one person using a handheld device can quickly acquire the current point cloud data and check as-built status on the spot. Because surveying can be completed in far less time than traditional methods, traffic restrictions and night work can be shortened, contributing to overall construction efficiency and cost reduction.

• Maintenance and management: High-precision GNSS is also active in infrastructure maintenance and management. For bridge and tunnel inspections, positions were traditionally recorded manually when taking photos, but GNSS-linked cameras now automatically record photos with position information. Accumulating photo data from periodic inspections in the cloud makes it easy to compare with previous data at the next inspection to understand crack progression and displacement amounts. In road and river maintenance, staff are beginning to perform smartphone surveying on site and share the resulting 3D point cloud data via the cloud immediately. This prevents inspection oversights and enables accurate planning of repair work, dramatically improving both the efficiency and accuracy of maintenance operations.

Benefits of Implementation and Future Outlook

There are many advantages to introducing smartphone-and-cloud–integrated high-precision GNSS systems. First, on the cost side, compared with traditional GNSS surveying equipment that used to cost millions of yen, using inexpensive devices combined with a general-purpose smartphone can greatly reduce initial investment and operating costs. In fact, some local governments that introduced affordable smartphone GNSS surveying systems had staff perform surveys in-house instead of outsourcing, resulting in reduced survey costs and internalization of technical skills. For small businesses and local governments, the ability to adopt a low-cost system that delivers immediate results is a major appeal.

Next, the benefits in human resources and training should not be overlooked. GNSS surveying using smartphone apps is intuitive to operate, so even non-experts can become proficient after short training. Less-experienced field engineers can get accustomed to the equipment and methods quickly, and the ease of starting centimeter-precision surveying without specialized knowledge is revolutionary. Preparing surveying tools that anyone can use in anticipation of retiring veterans and labor shortages will also improve organizational resilience. From the perspective of workstyle reform, enabling efficient solo measurement can reduce overtime, lessen physical burden, and improve safety. Shortening time spent on site for surveying reduces heatstroke risk in summer and the risk of accidents during high-altitude work, contributing to better working conditions. There are reports that introducing solo surveying improved both work efficiency and data quality and increased on-site safety.

Looking ahead, smartphone + GNSS surveying methods are expected to become widely established as industry standards. In 2020, the government proposed “simplified ICT utilization construction,” indicating a policy to advance DX by introducing ICT technologies into parts of small-scale projects. Smartphone surveying solutions that can be used by one person are attracting attention as a trump card for on-site DX. As more demonstration cases accumulate nationwide, the reliability of smartphone GNSS surveying is increasing, and voices saying “we should adopt this ourselves” or “this could work in our municipality” are steadily growing. Some municipalities, such as Fukui City, have achieved significant results by introducing smartphone GNSS systems for disaster recovery sites, and as those successes become widely known, adoption by other municipalities and construction firms is expected to expand. Trade publications also predict that one-person surveying using smartphones will spread widely in the construction industry and local governments. Further standardization on both hardware and software sides will enable data compatibility and unified workflows regardless of manufacturer or product, directly contributing to overall industry productivity improvements.

Summary: Simplifying High-Precision Surveying and LRTK

The appearance of ultra-compact GNSS receivers that can be attached to smartphones has turned the smartphone itself into a high-precision surveying instrument. RTK surveying equipment that once weighed several kg can now fit in a pocket, and an era has arrived in which anyone can begin centimeter-level positioning immediately without special expertise. The latest GNSS solution trend of “smartphone and cloud integration” is a major step toward making surveying accessible to everyone as simplified surveying. In practice, the LRTK solo surveying system combines smartphone-mounted RTK devices with cloud services to streamline everything from field surveying to data sharing. Using such solutions makes surveying tasks that used to require specialists surprisingly easy and accurate. Advances in GNSS equipment are creating new norms in the surveying world, and smartphone GNSS systems like LRTK will strongly support future sites as embodiments of the simplification of high-precision surveying.

FAQ

Q: What is RTK? A: RTK (Real Time Kinematic) is a technique in which a reference station (base station) and a rover simultaneously obtain GNSS satellite data at two points, and the difference between them is used to correct error factors in real time for high-precision positioning. Correction information is received from the base station via radio or the Internet, allowing position determination with errors on the order of a few centimeters. It is a centimeter-class positioning method widely used in surveying and construction equipment control.

Q: What is the difference between GNSS and GPS? A: GPS is the name of the U.S. satellite positioning system, while GNSS (Global Navigation Satellite System) refers to global satellite navigation systems including GPS. GNSS includes GPS as well as Russia’s GLONASS, Europe’s Galileo, China’s BeiDou, and Japan’s QZSS (Quasi-Zenith Satellite System), and multi-GNSS–compatible receivers can receive signals from these multiple satellites. Using the whole GNSS constellation increases the number of satellites available for positioning, enabling stable, high-precision positioning even in urban canyons and mountainous areas.

Q: What are the benefits of introducing RTK on construction sites? A: Using RTK on construction sites greatly improves both surveying accuracy and work efficiency. It enables layout and as-built (post-construction) measurements at centimeter-level accuracy, reducing construction errors and rework. RTK-compatible GNSS also allows surveying to be completed by a single person, leading to personnel reductions and safety improvements. Even in sites short of experienced surveyors, high-precision GNSS enables anyone to perform precise position measurements, achieving both quality control and labor savings.

Q: Can smartphones really achieve centimeter-level positioning? A: Yes. By combining a smartphone with a high-precision GNSS receiver, smartphones can achieve centimeter-level positioning. Recent smartphones have high-performance GNSS chips, and attaching an RTK-capable small receiver (for example, an LRTK Phone) can realize accuracies comparable to dedicated equipment. The Ministry of Land, Infrastructure, Transport and Tourism has validated the effectiveness of surveys using smartphones and tablets and confirmed they can meet the criteria for as-built management. Using appropriate correction information (internet-based VRS or satellite-delivered CLAS), smartphones can achieve accuracies comparable to traditional surveying instruments.

Q: Can positioning be done in areas without communication coverage? A: High-precision GNSS positioning is possible even in mountainous or disaster-stricken areas without internet access. In Japan, the QZSS Michibiki provides a satellite augmentation service called CLAS, and compatible receivers can receive correction information directly from satellites even outside communication coverage. For example, LRTK supports CLAS, so as long as the sky above is open, centimeter-level real-time positioning can be performed in sites without mobile service. Because positioning methods that do not rely on communication infrastructure have been established, GNSS surveying can be utilized in offline environments.

Q: What kind of product is LRTK? A: LRTK is a next-generation solution that turns a smartphone into a high-precision GNSS surveying instrument. It consists of an ultra-compact RTK-GNSS receiver (LRTK device) that can be attached to a smartphone, a dedicated app, and cloud services, enabling anyone to easily acquire and share centimeter-level positioning data. Designed in line with the Ministry’s i-Construction initiatives, it is configured so that efficient surveying can be performed by one person without complex operations or specialized knowledge.

Q: Is special technical training required for implementation and operation? A: No. Smartphone GNSS surveying systems, including LRTK, are designed to be intuitive to operate, so they can be used without special technical training. Basic operations are performed with buttons on the smartphone app, so even beginners can start using them in the field after a few hours of instruction or training. Unlike traditional surveying equipment, they do not require complicated setup or specialized knowledge, and people familiar with smartphones can quickly take advantage of high-precision positioning.