Latest Trends in GNSS Receivers ─ Surveying Evolving Through Smartphone and Cloud Integration

Introduction: The Digitization of Surveying and the Role of GNSS Receivers

In the world of construction surveying, ICT-driven digitization (DX) has been advancing rapidly in recent years. In addition to traditional total station-based surveying, the introduction of RTK and VRS methods that utilize electronic reference points has brought significant benefits not only to construction accuracy but also to work efficiency and on-site DX. Against this backdrop, the Ministry of Land, Infrastructure, Transport and Tourism has advocated *i-Construction* and the promotion of "simplified ICT construction," aiming to popularize surveying solutions that are easy for anyone to use. In particular, GNSS receivers play an important role in the digitization of surveying because they measure positions directly from satellites, enabling efficient surveying over wide areas.

On the other hand, industry-wide the aging of surveyors and a shortage of personnel are becoming serious, and methods that allow advanced surveying to be carried out by small teams are being sought. One approach attracting attention is GNSS receiver–based one-person surveying. With high-precision, RTK-capable GNSS, surveying tasks that previously required 2–3 people can be performed by a single person, making it possible to achieve both reduced manpower and improved accuracy. The latest trend in GNSS receivers, "smartphone-cloud integration," can be regarded as a key technology supporting such one-person surveying.

Technical Evolution: Multi-GNSS, Multi-Frequency, RTK, Michibiki, Fix Accuracy, etc

GNSS receiver technology has advanced significantly in recent years. First, support for multi-GNSS, which simultaneously uses multiple satellite positioning systems, has dramatically increased the number of satellites available for positioning. Today, more than 130 satellites from around the world—including GPS (United States), GLONASS (Russia), Galileo (Europe), BeiDou (China), and Japan’s Quasi-Zenith Satellite System (QZSS)—are in operation, and the latest GNSS receivers can receive them all together. As a result, even in environments where satellites are easily blocked—such as city streets lined with buildings or mountain valleys—it is now possible to consistently secure a sufficient number of satellite signals and achieve stable positioning. Whereas conventional GPS-only receivers tended to lose positioning in building shadows or forests, multi-GNSS makes it easier to obtain high-precision solutions (Fix solutions) anywhere. Furthermore, the increased number of satellites improves geometric configuration (DOP values), directly leading to stabilization of positioning accuracy and improved positioning success rates.

At the same time, satellite signals are increasingly becoming multi-frequency (dual and triple-frequency). The latest GNSS receivers can receive signals on multiple bands such as L5 in addition to L1/L2, allowing cancellation of atmospheric delay errors (ionospheric errors), and dramatically improving positioning accuracy compared with single-frequency receivers. An advantage of multi-frequency support is that it leads to shorter initialization times in RTK positioning. The more signals available, the faster integer ambiguity (phase uncertainty) can be resolved, shortening the wait time from the start of positioning to obtaining a fixed solution, so high-precision positioning can be started immediately in the field.

These advances in multi-GNSS and multi-frequency technologies are maximizing the potential of RTK (Real-Time Kinematic) positioning. The RTK method achieves centimeter-level accuracy (half-inch accuracy) by correcting positioning errors in real time between a base station and a rover, and with the latest high-performance receivers, supported by increases in the number of satellites and frequencies, a consistently stable high-precision Fix solution (fixed solution) can be obtained. For example, combining observation information from multiple satellites for error correction increases the reliability of model calculations, and it has been reported that the solution’s accuracy becomes more stable and stays within a few centimeters (within a few inches). In other words, current GNSS receivers are evolving in the direction of “acquiring a fast, accurate Fix and keeping it from being lost.”

Another Japan-specific trend is the use of augmentation signals from the Quasi-Zenith Satellite Michibiki, such as augmentation signals. Michibiki's centimeter-level (half-inch-level) positioning augmentation service (CLAS) can be received by compatible GNSS receivers, allowing them to obtain RTK correction information directly from the satellite even in areas outside mobile network coverage. In practice, by combining Internet-based correction distribution using the Geospatial Information Authority of Japan's Continuously Operating Reference Stations network (Ntrip method) with satellite-based augmentation like Michibiki CLAS, real-time positioning with an accuracy of a few centimeters (a few inches) is possible anywhere in Japan. Because positioning can be continued as long as the sky is unobstructed—even in mountainous areas or disaster sites where communications infrastructure has been cut off—GNSS surveying is proving effective in harsh environments that were previously difficult.

Smartphone Integration: Usability, Imaging, Positioning, and Point Cloud Generation (including photo-based)

A particularly revolutionary recent trend in GNSS receivers is integration with smartphones. High-precision GNSS, which traditionally required dedicated controllers or large display devices, can now be operated intuitively via smartphones and tablets. For example, compact receivers that connect via Bluetooth or can be mounted directly on a smartphone have appeared, enabling cable-free, stress-free operation. Because the receiver status and positioning results can be checked in real time on the smartphone screen, even operators without specialized knowledge can handle them intuitively. Some of the latest GNSS receivers are “smartphone-mounted” devices weighing only a few hundred grams, and their integration with a smartphone greatly lowers the barrier to field surveying by making them easy to carry.

The benefits of smartphone integration go beyond ease of operation. By combining the smartphone’s built-in camera and LiDAR sensor with GNSS positioning, a single device can handle everything from photogrammetry to acquiring point cloud data via 3D scanning. For example, with a LiDAR-equipped smartphone you can obtain detailed three-dimensional shapes simply by scanning an object, and by linking the position coordinates obtained from a GNSS receiver you can generate a high-precision 3D point cloud model in a short time. Even a standard smartphone camera can have high-precision location tags added to photos using a dedicated app connected to a GNSS receiver, allowing the photos to be plotted on a map afterward for recordkeeping. In practice, solutions have emerged that use a small GNSS device attached to the smartphone and a dedicated app to perform capture and positioning simultaneously with a single tap, allowing you to obtain on-site photos with high-precision coordinates. This makes it much easier to create drawings or reports later, since you can record site conditions with photographs while also preserving accurate location information.

Furthermore, innovations in smartphone apps have simplified the positioning process itself. For example, recording your current location (point surveying) can save coordinates with centimeter-level accuracy (cm level accuracy (half-inch accuracy)) simply by pressing a button on the smartphone screen, and using continuous positioning mode makes it possible to automatically log many points while walking. Acquired point cloud data and photo data are instantly visualized within the app, and data previews and metadata edits can be performed on the spot as needed. By attaching text notes to key survey points or entering attribute information, you can centrally manage on the smartphone all the information that was previously kept separately in notebooks or drawings. With smartphone integration, on-site GNSS surveying operations have dramatically streamlined the entire sequence of "measure, record, check".

Cloud Integration: Data Synchronization, Sharing, Office Integration, and Applications to Inspections and As-Built Management

While the integration of smartphones and GNSS receivers is progressing, integration with cloud services is also significantly changing surveying workflows. Traditionally, survey data collected on site had to be brought back on USB or SD cards, imported into a PC, and then saved and shared on an internal server. With the latest solutions, positioning apps are directly linked to the cloud, allowing coordinate and point cloud data collected on site to be uploaded to the cloud instantly with a single tap. For example, if point clouds or surveyed point information with photos obtained by a GNSS receiver are synchronized to the cloud on site, results can be shared with stakeholders without returning to the office. From a web platform on the cloud, uploaded survey data can be visualized on maps or point clouds viewed in a 3D viewer, and it is also possible to output automatic reports that include lists of survey points and photos. Clients who do not have dedicated software and members at remote sites can check the data in their browsers via a shared URL, enabling smooth reporting to owners and information sharing with other departments. Thus, seamless data linkage from the field to the cloud has greatly streamlined office tasks such as post-survey data organization and drawing generation.

Cloud usage goes beyond mere data storage and sharing and enables the real-time use of survey data. For example, internet-based RTK correction services (Ntrip streaming) are provided via cloud architectures, and the latest network RTK, which aggregates correction information from multiple electronic reference stations and distributes it as virtual reference points, has become common. This means that without installing dedicated base stations, field GNSS receivers can always receive the latest correction data via the cloud.

Also, survey data aggregated in the cloud can be shared immediately with design and construction management departments, so it is easy to instantly reflect field measurements in construction planning or use them for as-built management. In fact, in routine inspection work for bridges and tunnels, if high-precision coordinate-tagged photos and 3D scan data are recorded on site and stored in the cloud, it becomes possible to perform advanced uses such as comparing past and new data from the office at a later date to analyze displacements and deterioration.

Thus, cloud integration is not just "collecting data and done" but is becoming a foundation that supports the entire surveying process, including subsequent analysis and collaboration.

Furthermore, surveying data in the cloud also proves powerful for integration with other ICT construction tools. For example, initiatives have begun to integrate external data acquired by drone aerial photographs or mobile LiDAR with GNSS survey data in the cloud, using them to automatically generate current topographic maps and create as-built management reports. In 2022, the Ministry of Land, Infrastructure, Transport and Tourism evaluated the accuracy of “three-dimensional measurement technology using mobile devices” and, after confirming that it meets the criteria for use in as-built management (within ±50 mm (±1.97 in)), explicitly stated this in the guidelines. Such guideline development has progressed, and the process of smoothly applying centrally managed surveying data in the cloud to design, construction, and maintenance management is becoming standardized.

On-site Application Case Studies: Single-Person Surveying, Disaster Response, Narrow-Site Construction, and Maintenance

The integration of GNSS receivers with smartphones and cloud services is being increasingly put into practical use across a variety of on-site scenarios. Here we introduce several representative use cases.

• Single-person surveying: As mentioned above, using high-precision GNSS can reduce labor in surveying tasks. For example, the task of laying out building positions (layout marking) that traditionally required multiple people can be positioned by following real-time guidance from smartphone GNSS such as "move 5 cm (2.0 in) to the east," and even stake driving that used to require several people can be done accurately by one person. At one civil engineering site, a task that used to take two people a full day for as-built measurements was, after introducing a GNSS receiver, completed by one person in a few hours, achieving approximately 70% or more reduction in work time and labor costs. In the context of labor shortages, single-person surveying is expected to be a solution that dramatically increases productivity while maintaining safety.

• Disaster response: At earthquake and landslide sites, quickly recording and sharing the damage situation can determine the initial progress of recovery. By using a GNSS receiver and a smartphone, you can record accurate position coordinates on the spot simply by taking photos in the affected area, enabling speedy mapping of damage extents and 3D reconstruction afterward. For example, during the 2023 Noto Peninsula earthquake, one civil engineering contractor had quickly introduced a GNSS smartphone surveying system that works outside mobile coverage, which allowed them to record damage in mountainous areas where communications were cut off using high-precision photographic data. Site photos uploaded to the cloud were shared immediately with local government offices, and it was reported that this contributed significantly to shortening the lead time for drafting recovery plans. The effectiveness of GNSS single-person surveying in disaster response has been demonstrated in various locations, and its use in the disaster prevention field is expected to expand further.

• Construction in confined sites: Even on narrow urban construction sites or in locations with poor lines of sight, GNSS receivers are effective because they can determine position as long as the sky above is open. Multi-GNSS-capable devices can capture signals from multiple satellites even in building canyons or under elevated structures, maintaining more continuous positioning. Also, on small-scale construction sites where surveying with drones or large equipment is difficult, surveying that combines smartphone-mounted cameras and LiDAR with GNSS enables work in a small footprint. In fact, there are cases in which local governments commissioning small-scale works introduced smartphone surveying apps and received high praise, saying, "This one tool can do everything." Even at constrained sites where heavy machinery cannot be brought in, a single person can quickly acquire current point cloud data with a handheld device and check the as-built condition on the spot, and such uses are beginning to spread. Because surveying can be completed in a dramatically shorter time than conventional methods, it helps shorten traffic restrictions and nighttime work, contributing to improved overall construction efficiency and cost reduction.

• Maintenance and management: High-precision GNSS is also playing an active role in the field of infrastructure maintenance and management. In routine inspections of bridges and tunnels, what used to be recorded manually by inspectors noting photo locations can now be automatically recorded as geotagged photos by GNSS-integrated cameras. If the photo data obtained during each patrol inspection is stored in the cloud, subsequent inspections can easily compare with previous data to understand crack progression and the amount of displacement. In the maintenance of roads and river facilities, initiatives are beginning in which staff perform smartphone surveying on site and immediately share the resulting 3D point cloud data to the cloud. This prevents overlooked inspection results and enables accurate planning of repairs, dramatically improving the efficiency and accuracy of maintenance operations.

Benefits of Adoption and Future Outlook: Cost, No Training Required, Work Style Reform, Standardization

The benefits of introducing smartphone- and cloud-integrated GNSS receivers are wide-ranging. First, in terms of costs, compared with conventional GNSS surveying equipment that used to cost on the order of several million yen, these systems allow the use of inexpensive devices combined with general-purpose smartphones, significantly reducing initial acquisition and operational costs. In fact, in one municipality, the introduction of an inexpensive GNSS smartphone surveying system enabled staff to perform surveys themselves instead of outsourcing, resulting in reduced survey expenses and the internalization of technical capabilities. For small businesses and local governments, the ability to start at low cost and quickly realize benefits is a major attraction.

Next, the benefits in terms of personnel and training should not be overlooked. GNSS surveying using smartphone apps is intuitive to operate, so even those who are not experienced can handle it after a short period of training. Even technicians with little field experience can become proficient with the equipment and methods, and the ease of being able to start surveying with centimeter-level accuracy (half-inch accuracy) immediately without special expertise is revolutionary. Preparing surveying tools that anyone can use in anticipation of veteran retirements and shortages of successors also contributes to improving organizational resilience. From the perspective of work style reform, enabling one person to measure efficiently can be expected to have secondary effects such as reduced overtime, less physical burden, and improved safety. If on-site time required for surveying is shortened, risks of heatstroke in summer and accidents during work at height are also reduced, contributing to improved working conditions. In fact, there are reports that the introduction of one-person surveying has led to operational efficiency and data quality improving, and on-site safety increasing.

Looking ahead, it is expected that these smartphone GNSS surveying methods will become widely established as industry standards. In national policy, the 2020 initiative "simplified ICT-utilization construction" was launched, setting out a policy to promote DX even in small-scale projects by introducing ICT technologies for part of the process. In that context, smartphone surveying solutions that can be used by a single person are attracting attention as a trump card for on-site DX.

Moreover, one-person surveying using "smartphone × GNSS" has been gaining reliability through demonstration cases across regions, and there are steadily increasing voices saying "we should introduce it at our company" and "it seems usable in our municipality." In fact, some municipalities, such as Fukui City, have achieved significant results by introducing smartphone GNSS systems at disaster recovery sites, and as those effects become widely known, adoption will likely spread to other municipalities and construction companies. Trade magazines also predict that one-person surveying using smartphones will become widely adopted across municipalities and the construction industry nationwide.

Furthermore, with continued standardization of both hardware and software, if data compatibility and workflow unification can be achieved regardless of manufacturers or products, it should directly lead to productivity improvements across the industry.

Summary: A natural pathway to simplified surveying with LRTK

With the advent of ultra-compact GNSS receivers that can be attached to smartphones, the smartphone itself has quickly transformed into a high-precision surveying instrument. RTK equipment that used to weigh several kg has shrunk to pocket-sized, and we have entered an era in which centimeter-level positioning can be started immediately without special expertise. The latest trend in GNSS receivers—“smartphone-cloud integration”—can be seen as a major step toward making surveying accessible to everyone as simplified surveying. In practice, the single-person surveying system LRTK combines a smartphone-attached RTK device with cloud services to streamline workflows across the board, from field surveying to data sharing. By leveraging such solutions, surveying tasks that previously required specialists can be handled astonishingly easily and accurately. The evolution of GNSS receivers is establishing a new standard in the world of surveying. Within that trend, smartphone GNSS systems like LRTK will support future fieldwork as embodiments of the simplification of high-precision surveying.