Can your smartphone turn into a surveying instrument!? Centimeter-level positioning realized by the Quasi-Zenith Satellite System

When you think of surveying equipment used in the field, you might imagine bulky tripods and expensive GNSS receivers. But recently, an era is arriving in which a smartphone can quickly transform into a surveying instrument. By leveraging the centimeter-level positioning services provided by Japan’s proprietary Quasi-Zenith Satellite System (QZSS), nicknamed “Michibiki,” a combination of a smartphone and a compact device can achieve the several-centimeter high-precision positioning that previously required equipment costing hundreds of thousands of dollars.

This article centers on the key term “quasi-zenith satellite.” First, it explains what QZSS/Michibiki is and why it has advantages in Japan’s positioning environment. Next, it clarifies the differences from GPS and the institutional background by country, and explains Michibiki’s centimeter-level augmentation service (CLAS) and sub-meter-level augmentation service (SLAS), including how they differ from RTK positioning, in an easy-to-understand way. Furthermore, it introduces how combining a smartphone with Michibiki changes field operations and the benefits that result, with concrete examples in surveying/construction, agriculture, municipal work, disaster response, and infrastructure maintenance. At the end of the article, it also touches on a new-generation surveying system called LRTK, which enables simple surveying with a smartphone, proposing ways to apply these technologies to your work.

The Quasi-Zenith Satellite System “Michibiki”

First, let’s cover the Quasi-Zenith Satellite System (QZSS), nicknamed “Michibiki.” Michibiki is a satellite positioning system developed and operated independently by Japan, sometimes referred to as the “Japanese GPS.” A quasi-zenith satellite uses a special orbit that, as the name implies, stays for long periods near the zenith (directly overhead) of Japan. It is currently operated as a four-satellite constellation (one geostationary satellite + three inclined orbit satellites), and full services began in 2018. This four-satellite configuration ensures that at least one Michibiki satellite is always positioned above Japan. This makes it easier to acquire satellites even in the canyons between high-rise buildings or in mountainous areas, enabling more stable positioning than GPS alone.

Michibiki is compatible with the U.S. GPS and other countries’ satellite positioning systems (Russia’s GLONASS, Europe’s Galileo, China’s BeiDou, etc.), functioning as part of the GNSS (Global Navigation Satellite System). Many commercial GNSS receivers and smartphones are designed to receive signals not only from GPS satellites but also from Michibiki, increasing the apparent number of visible satellites and improving positioning stability. However, while GPS provides global coverage, Michibiki is a regionally limited system whose service area is mainly Asia–Oceania (particularly over Japan). In other words, Michibiki is designed to complement the global GPS, improving positioning accuracy and availability around Japan.

The development and deployment of Michibiki in Japan stem from a national strategy to ensure stable and higher-precision positioning. The QZSS program, advanced under the leadership of the Cabinet Office’s Space Development Strategy Promotion Office, aimed to build a more reliable positioning environment in Japan, a nation prone to natural disasters. Because high-precision positioning is a key enabler in advanced fields promoted by the Ministry of Land, Infrastructure, Transport and Tourism—such as smart construction (e.g., i-Construction), autonomous driving, and precision agriculture—the government strengthened satellite positioning infrastructure. Plans are also underway to increase the number of satellites to seven; by the late 2020s, Michibiki is expected to be able to provide standalone positioning with a seven-satellite constellation. If realized, this would further improve stability and accuracy as a Japan-specific positioning system.

High-precision positioning brought by Michibiki: CLAS and SLAS

A major advantage Michibiki provides is augmentation signals for positioning. Typically, smartphones only receive GPS-compatible “supplementary signals” (such as L1 C/A), which alone yield positioning errors on the order of meters. However, QZSS broadcasts special signals containing augmentation information to dramatically improve GNSS positioning accuracy. The representatives are the Centimeter Level Augmentation Service (CLAS) and the Sub-meter Level Augmentation Service (SLAS).

• CLAS (Centimeter Level Augmentation Service): By receiving QZSS’s CLAS signals, users can reduce positioning errors to the order of several centimeters. Correction information that compensates for satellite orbit and clock errors, ionospheric and tropospheric errors, etc., is transmitted from satellites using reference data obtained from electronic reference stations installed nationwide by the Geospatial Information Authority of Japan. It is, so to speak, “RTK correction information delivered from the sky,” and by ingesting this information on the user side, the errors of traditional standalone positioning can be largely eliminated. CLAS horizontal accuracy reaches several centimeters, dramatically different from conventional standalone positioning (approximately 5–10 m (16.4–32.8 ft)). Although initial convergence takes a little time (about 1 minute), the ability to obtain centimeter accuracy from satellite signals alone anywhere in Japan is globally groundbreaking. However, using CLAS requires a dedicated high-precision GNSS receiver that can receive augmentation signals in the L6 band; smartphone-integrated chips do not support this, so CLAS must be utilized via external devices as discussed later.

• SLAS (Sub-meter Level Augmentation Service): SLAS is a sub-meter-level (error less than 1 m (3.3 ft)) augmentation service provided by satellite. It primarily uses the L1 frequency for single-frequency receivers, sending correction information such as ionospheric delay compensation. Even in areas where GPS alone yields unstable positioning—such as in the shadow of high-rise buildings—applying SLAS can improve accuracy to the order of several meters. Because some time lag occurs, it is not suitable for real-time control, but it is useful for applications that do not require immediacy, such as pedestrian or vehicle navigation, sports measurement, and vessel position logging. SLAS can be received by slightly modifying existing L1-band receivers, making it easy to incorporate into small handheld or in-vehicle devices. Smartphones typically use correction information provided via cellular base stations (A-GPS), but that benefit disappears in areas without coverage. In such places, SLAS-capable devices can provide improved accuracy without communications.

These augmentation services allow Michibiki to offer different levels of accuracy for diverse needs. For example, broad logistics management or guidance of agricultural machinery may be adequately served by “errors within 1 m (3.3 ft),” in which case SLAS is an easy solution. On the other hand, applications such as surveying, construction, and autonomous driving that require centimeter-level accuracy call for CLAS. Moreover, both CLAS and SLAS are open services provided by the government and are free to use (only the necessary receivers must be prepared). This is a significant advantage of QZSS: users can obtain high precision without relying on commercial services.

Differences from RTK positioning

In some respects, the CLAS mechanism can be described as “RTK using satellites.” How do the traditional RTK (Real-Time Kinematic) positioning used in surveying and CLAS/SLAS differ? Let’s compare the main points.

• Required equipment and communications environment: RTK requires two GNSS receivers: a reference station with known coordinates (base station) and a rover receiving positions while moving. The base station computes error information and sends it to the rover via radio or the internet for real-time correction, so a continuous communications environment is required. In contrast, CLAS relies on the role of the reference station network being fulfilled by the nation’s electronic reference stations plus satellite communications, so the user only needs a single receiver. Because correction information is delivered directly from Michibiki above, a major advantage is that positioning is possible even in sites without internet or radio communication.

• Positioning accuracy and initialization time: RTK positioning achieves very high accuracy—on the order of 1–3 cm (0.4–1.2 in)—and has the advantage of short initialization (fix) times of several seconds to a few tens of seconds. CLAS can also provide centimeter-level accuracy similar to RTK, but because it sequentially receives common error parts and grid-by-grid correction information, initial convergence requires about 1 minute. RTK instantly achieves high precision by continuously comparing observation data (the OSR method), while CLAS uses a model correction approach called SSR, which reflects corrections stepwise; therefore, CLAS concedes a bit to RTK in terms of real-time performance during movement. However, if positioning is done while stationary or the user can wait briefly after moving, CLAS can provide accuracy sufficient for surveying purposes.

• Cost and ease of use: Full RTK operation traditionally required two expensive surveying instruments (antenna and receiver sets), and the base station demanded installation work, power supply, and communication contracts. Initial costs could reach the order of millions of yen, making it a high barrier for small businesses. In contrast, CLAS-capable GNSS receivers have become relatively affordable, with some models available for initial investments on the order of several hundred thousand yen. Moreover, if the device can pair with a smartphone, you can significantly reduce introduction costs by utilizing a smartphone you already own. Since no communication charges are required, operating costs are also low. Overall, CLAS lowers the barriers to adoption and operation compared to RTK, opening the door for a wider range of users to take advantage of high-precision positioning.

Of course, RTK and CLAS/SLAS are not strictly “backward- or forward-compatible”; each has its own merits and drawbacks. It is best to use traditional RTK services and Michibiki’s augmentation services depending on the required accuracy and application. For instance, dedicated RTK remains the mainstay for heavy equipment control, where strict real-time centimeter accuracy is required, but for many surveying and recording tasks CLAS/SLAS can be sufficiently practical, and their ease of use is expected to broaden application scenarios.

Your smartphone becomes a surveying instrument! Benefits in field operations

So, what advantages arise in field work when combining a smartphone with Michibiki? Here are the main points.

• Achieve centimeter-level accuracy easily: The positional error that used to be around 5–10 m (16.4–32.8 ft) with smartphone GPS can be improved to several centimeters simply by pairing with an external high-precision GNSS receiver. This allows precision positioning and surveying tasks that were previously difficult without specialized equipment to be carried out easily with a smartphone.

• Significant reduction in equipment cost: By using a smartphone you already own, you do not need to purchase a complete set of large surveying equipment. High-precision GNSS modules have become smaller and more affordable, allowing introduction at costs more than an order of magnitude lower than traditional equipment. The lower initial investment compared to expensive dedicated instruments makes it easier for individuals and small-to-medium sites to adopt high-precision positioning.

• Improved portability and work efficiency: The smartphone plus small receiver combination is extremely lightweight and compact and can be carried and used one-handed. There is no need to carry and set up tripods or lay cables, so setup time on site is greatly reduced. The ability to measure immediately when needed improves work efficiency and safety.

• Stability independent of communications infrastructure: Unlike networked RTK, using Michibiki’s augmentation signals allows positioning even in mountain areas or disaster sites without cellular coverage. As long as satellites are visible overhead, a smartphone can obtain position information even when communications networks are disrupted. In fact, during the major earthquake in 2023, CLAS-capable smartphone positioning was utilized in communication-denied areas, recording high-precision coordinates in photos of the disaster area and contributing to recovery support. Surveying methods that do not rely on communications infrastructure are also superior for ensuring reliability.

• Multifunctional use unique to smartphones: Smartphones are equipped with high-performance cameras, sensors, and app communication functions in addition to positioning. By combining high-precision position data, it becomes easy to tag photos with accurate positions for records, share points on maps, and more. You can also display AR on the smartphone screen for on-site confirmation based on obtained coordinates, or process multiple camera images in the cloud to generate 3D models (point clouds) with real-world coordinates based on photos taken by a smartphone. Smartphone positioning is not limited to mere position measurement; it can become a platform that accelerates on-site digital data utilization.

Expanding use cases across many fields

High-precision smartphone positioning is expected to be useful in a variety of field operations. Here are concrete examples by sector.

• Surveying and construction: Not only surveyors but also on-site technicians themselves can quickly measure control points and check as-built conditions using a smartphone. For example, setting out reference stakes (batter boards) or checking excavation depth—tasks previously done with total stations or heavy-equipment-mounted GPS—can be guided accurately via coordinates on a smartphone screen. You can also photograph structures during construction with a smartphone, convert them to point clouds, and check deviations against design data on-site for quality control. The Ministry of Land, Infrastructure, Transport and Tourism’s i-Construction initiative also highlights smartphone positioning as a productivity-improving tool for construction sites.

• Agriculture: Field parcel surveying and field map creation can be easily done with a smartphone, serving as baseline data for agricultural IoT. For example, accurately measuring field areas to inform fertilization plans, or measuring elevation differences in narrow plots where agricultural machinery cannot enter to improve drainage. In orchards, recording the position of each tree helps with growth monitoring and yield management. High-precision position information can also be applied to path planning for autonomous tractors and drone spraying, becoming one of the technologies supporting smart agriculture.

• Municipal field operations: Smartphone positioning is powerful for road and park maintenance. When inspecting and finding damaged road sections or aging structures, positions can be recorded in centimeter precision, enabling accurate repair scheduling and asset management in GIS. High-precision location information for buried water, sewage, or telecom pipes and cables can reduce the risk of accidental damage during excavation. Coordinates-tagged photos taken during on-site surveys can be uploaded to the municipality’s shared system for immediate information sharing among staff.

• Disaster response: Smartphone high-precision positioning is also useful for understanding disaster damage. By photographing collapsed buildings and inundation areas while patrolling the site and recording their precise positions, you can support recovery planning and determine delivery routes for relief supplies. It is also possible to perform fixed-point observations of landslide or ground fracture locations to track displacement amounts over time in centimeter-level detail. Because CLAS can be used even when communications infrastructure is down, it is a reliable means of information gathering in emergencies.

• Infrastructure inspection and maintenance: High-precision location recording is valuable for routine inspections of infrastructure such as bridges, tunnels, and levees. By pinpointing inspection locations and managing their history, you can accurately compare reoccurrence locations of cracks or deformations. For example, marking a damaged section on a tunnel wall with a smartphone enables easy identification of the same spot on the next inspection, simplifying repair progress management. During rail or road patrols, recording precise coordinates of anomalies and sharing them with headquarters enables rapid response. Introducing smartphone positioning will greatly contribute to improving efficiency and safety in infrastructure maintenance management.

A new era of smartphone surveying starts with LRTK

Finally, as a representative solution for smartphone high-precision positioning, we introduce LRTK. LRTK was developed with the concept of “allowing anyone to use RTK positioning anytime, anywhere.” It requires no complicated操作 or specialized knowledge and is characterized by the ease with which you can start centimeter-level positioning in combination with a smartphone.

LRTK hardware is an ultra-compact GNSS receiver with an integrated antenna and battery, compact enough to handle one-handed even when connected to a smartphone. Durability features such as dust and water resistance are well considered for field use, making it effectively a pocketable high-precision surveying instrument. It also supports Michibiki augmentation services such as CLAS, so it can continue high-precision positioning even in areas outside cellular coverage.

In terms of introduction cost, LRTK is also excellent. The hardware is sold as a one-time purchase at an affordable price, and cloud services for storing/sharing positioning data and generating point clouds are provided on a subscription basis, allowing you to use them only for the periods you need. This enables you to start operating with the minimum initial investment without purchasing expensive equipment outright. Born from the desire to make high-precision positioning more accessible, LRTK lets you perform simple surveying today even without specialized surveying instruments.

As smartphones transform into surveying instruments, LRTK is a true pioneer tool. It has the potential to accelerate on-site DX (digital transformation) and change the conventions of positioning and surveying work. Why not take this opportunity to experience smartphone positioning with LRTK? LRTK is poised to bring a new standard—centimeter-level positioning—to your field.