Table of contents

• Introduction

• Accuracy comparison: smartphone GPS vs. external GNSS receivers

• Technologies that enable high-precision positioning (RTK, Michibiki, etc.)

• Benefits of high-precision surveying using smartphones

• Recommendation: simple surveying with LRTK

• Conclusion

• FAQ

Introduction

Recently, smartphone GPS functions have made it easy to determine your current location. However, the accuracy required on construction and surveying sites is very high, and traditionally expensive surveying equipment and skilled technicians were indispensable. If high-precision surveying could be done using only a smartphone, it would greatly contribute to improving on-site efficiency and reducing costs. To answer that question, this article explores the potential of high-precision positioning using smartphones. We compare the accuracy limits of built-in smartphone GPS and measures to improve it, and examine how much accuracy can be improved when combined with external GNSS receivers. We also explain the latest technologies that support high-precision positioning, such as RTK and Japan’s satellite Michibiki, and discuss the practical benefits of using smartphones for surveying in the field. Finally, we introduce the notable solution "LRTK" that turns a smartphone into a cm-accuracy surveying instrument (cm level accuracy (half-inch accuracy)) and propose simple surveying methods that anyone can start using.

Accuracy comparison: smartphone GPS vs. external GNSS receivers

The GNSS functions included as standard in smartphones typically have errors on the order of several meters. Even outdoors under good conditions, it is not uncommon for the position to be off by about 5–10 m (16.4–32.8 ft). This is acceptable for map apps and car navigation, but built-in smartphone GPS cannot possibly meet tasks that require centimeter-level accuracy, such as establishing control points on construction sites or boundary surveys of land. What compensates for these limitations are specialized positioning devices called external GNSS receivers. These are small GNSS terminals that connect to a smartphone via Bluetooth or cable; they are equipped with multiple satellite frequency bands and high-performance antennas that smartphones cannot receive, and by using advanced correction techniques they dramatically improve positioning accuracy. While built-in smartphone GPS has errors of several meters, using an external GNSS receiver can provide high-precision position information with errors of only a few centimeters. For example, repeatedly measuring a known point with a smartphone yields measurements that vary within a range of several meters, but using a high-precision GNSS receiver can consistently measure within a few centimeters of the actual position. Of course, GNSS-based positioning assumes a clear view of the sky; in forests or among high-rise buildings smartphone GPS errors become even larger. In fact, under trees a smartphone’s position can be off by more than 5 m (16.4 ft). Even dedicated GNSS receivers cannot improve accuracy if satellite signals cannot be received, but smartphone GNSS chips are often designed to prioritize low power and may perform reception processing intermittently (duty cycling), which makes them less accurate for continuous positioning compared with dedicated devices specialized for continuous reception. Multi-GNSS support and dual-frequency reception enable more stable positioning than smartphones. Overall, the positioning accuracy of a standalone smartphone is at best several meters, whereas combining it with an external GNSS receiver can improve accuracy to the level of several centimeters—this is the decisive difference between the two. It should be noted that smartphone GNSS performance has been improving in recent years, and some models can receive multiple satellite systems and L5-band signals in addition to GPS. Accuracy has been improving compared with the past, but the current situation is that dedicated receivers are still needed to reliably achieve centimeter-class accuracy.

Technologies that enable high-precision positioning (RTK, Michibiki, etc.)

To achieve high-precision positioning, raw positioning data from satellites must be subjected to error correction. Sources of GNSS positioning error include atmospheric delays (ionosphere and troposphere), satellite clock errors, orbital errors, receiver noise, and multipath (signal reflections). Historically used correction methods include SBAS (Satellite-Based Augmentation System) and DGPS (Differential GPS). SBAS distributes correction signals from geostationary satellites, and DGPS corrects distance differences relative to nearby reference stations; these methods could reduce standalone positioning errors of several meters down to about 1 m (3.3 ft). The current mainstream method is RTK (Real-Time Kinematic). RTK uses two GNSS receivers simultaneously: a reference station placed at a known position and a rover that performs mobile positioning. The two receivers exchange raw satellite data via communications. By subtracting common error factors (satellite and atmospheric effects) in real time, RTK cancels errors that cannot be corrected by standalone positioning and achieves centimeter-level positioning accuracy. Traditional RTK surveying equipment transmitted correction data from the reference station to the rover by radio, but in recent years network RTK (reference station data distribution services) using the Internet has become more common. For example, it is now common to receive data from public Continuously Operating Reference Station networks or commercial correction services via a smartphone’s mobile data connection. An even more advanced technology is Japan’s quasi-zenith satellite system Michibiki, which provides the centimeter-level positioning augmentation service (CLAS). CLAS delivers RTK-equivalent correction information directly from Michibiki satellites to a receiver, enabling real-time centimeter accuracy without installing your own ground reference stations or setting up communication lines. A GNSS receiver that supports CLAS can perform high-precision positioning autonomously even in mountainous areas without mobile phone coverage. Outside Japan, similar services are emerging—for example, Europe’s Galileo offers a High Accuracy Service (HAS)—and new technologies that deliver augmentation information from satellites (so-called PPP-RTK) are appearing, which will further improve the convenience of high-precision positioning. Note that PPP (Precise Point Positioning) itself has the advantage of not requiring reference stations but historically took a long time to converge to high accuracy; PPP-RTK compensates for that weakness and can converge to centimeter accuracy in a short time.

Benefits of high-precision surveying using smartphones

When centimeter-level positioning becomes possible with a smartphone + external GNSS receiver combination, many benefits arise compared to traditional surveying methods. First, there is a significant reduction in cost and equipment. Achieving centimeter accuracy previously required RTK-GNSS equipment costing hundreds of thousands of dollars or optical total stations, and installation tripods and complex operations often required two or more people. With smartphone surveying, a field worker can start surveying alone simply by attaching a small GNSS receiver to their handheld smartphone. The burden of procuring specialized equipment is reduced, and transportation and staffing costs are lowered. Second, it excels in immediacy and data utilization. With smartphone-linked surveying, coordinate data can be displayed on a map app on-site or shared with the office via the cloud. There is no need to record data in paper field books and carry them back; you can check the as-built immediately on site or overlay it with design drawings. Also, combining a smartphone’s built-in camera or LiDAR scanner enables simultaneous acquisition of not only point coordinates but also site photos and 3D point cloud data. This allows measurements and recording that used to require separate devices to be completed with a single smartphone, accelerating the DX (digital transformation) of surveying operations. Third, ease of learning should not be overlooked. Advanced surveying equipment required specialized knowledge to operate, but smartphone surveying allows positioning and recording via intuitive app operations. For example, registering a survey point can be done by simply tapping a button on the smartphone screen, with complex settings and calculations handled automatically by the app. This allows non-experts to perform layout tasks themselves, helping to alleviate labor shortages. Without relying on veteran surveyors, anyone on site can now benefit from high-precision positioning. Smartphone high-precision surveying is expected to be useful in scenarios such as:

• Civil engineering and construction: Applied to control point surveys and as-built management during construction. Useful for as-built checks during earthwork with heavy machinery and for simple quantity surveys in small- to medium-scale projects.

• Infrastructure inspection: Displacement measurement and 3D recording in periodic inspections of roads, bridges, and tunnels. Contributes to advanced infrastructure maintenance management such as monitoring bridge pier settlement and tracking tunnel deformation.

• Agriculture and forestry: Parcel surveying of fields and forests, boundary confirmation, and support for work planning. Expected to serve as a location information foundation for precision agriculture and forest resource management, such as measuring farmland areas and assessing forest resources.

• Disaster prevention and response: Rapid situation assessment in affected areas and terrain monitoring of hazardous zones. Enables remote acquisition of terrain data in areas difficult for people to enter, speeding up disaster response.

Recommendation: simple surveying with LRTK

As described above, smartphones combined with external GNSS receivers have made high-precision surveying more accessible, and a representative solution is LRTK. LRTK (pronounced "L-R-T-K") is a positioning system composed of an ultra-compact RTK-GNSS receiver that attaches to a smartphone and a dedicated app, instantly turning a handheld smartphone into a cm-accuracy surveying instrument (cm level accuracy (half-inch accuracy)). The LRTK device itself is compact, weighing about 150 g and with a thickness of only about 1 cm (0.4 in). It houses a high-sensitivity GNSS antenna and a battery, and connects wirelessly to the smartphone via Bluetooth, eliminating cumbersome cables. The built-in battery provides about 6 hours of continuous positioning, and it can also be operated while charging via USB. It attaches to the back of a smartphone for carrying, and functions as a device capable of immediate centimeter-class positioning when powered on at the site. It is truly a "surveying instrument that fits in your pocket," useful in a wide range of scenarios from control point surveys to as-built management. The dedicated app is simple to operate: tap "Start positioning" on the screen at the point you want to measure, and high-precision coordinates are obtained on the spot. The errors converge in a few tens of seconds, and latitude, longitude, and height based on the public coordinate system (World Geodetic System) are displayed. Acquired data is automatically saved to the cloud, so there is no need for post-field USB data transfers. Furthermore, LRTK supports Japan’s quasi-zenith satellite system Michibiki and can receive the CLAS augmentation signals mentioned above. Therefore, it can perform high-precision GNSS positioning autonomously even at sites without mobile coverage, such as mountainous areas. Because it does not depend on communication infrastructure for positioning, it is powerful for tasks such as post-disaster surveys and forest surveying. Additionally, the LRTK smartphone app includes AR (augmented reality) features that overlay lines and points based on design drawings onto the real scenery. Using positioning data, it can project stake positions onto the screen or overlay a predicted completion model on the actual site to check discrepancies; intuitive AR displays support construction management. Layout tasks that were previously done by feel can now be carried out accurately while looking at the smartphone screen. In this way, using LRTK allows you to start simple surveying with a low initial investment. Because of its innovativeness, it has also been featured in government satellite positioning service use cases, and adoption at sites is progressing. Some sites that have already introduced it report that "surveys in mountainous areas that used to be done by two people are now completed by one," demonstrating the labor-saving and efficiency effects of LRTK. Since it can be used without special equipment or advanced training as long as you have a smartphone, it is expected to be actively adopted in small construction sites and by local governments for infrastructure inspections—places that previously gave up on high-precision positioning. If you have wondered whether high-precision surveying with a smartphone is possible, consider exploring this new surveying style enabled by LRTK.

Conclusion

High-precision surveying using a smartphone combined with an external GNSS receiver is becoming the standard for future construction sites and surveying work. Centimeter-class accuracy, which could not be achieved with a smartphone alone, has become accessible to anyone thanks to RTK technology and augmentation services like Michibiki. The advantages of quickly and efficiently surveying with on-site personnel without relying on expensive dedicated equipment are immense. By leveraging solutions such as LRTK, smartphones themselves become tools for high-precision positioning, enabling the DX of surveying in many situations where it was previously impractical. The potential of smartphone surveying will continue to expand, and it is expected to be a technology that directly contributes to work-style reform and efficiency improvements in the construction industry. Indeed, the new era of surveying pioneered by smartphones and GNSS is one to watch closely.

FAQ

Q: Can a smartphone alone really achieve centimeter-level surveying? A: Unfortunately, a smartphone’s built-in GPS alone cannot achieve centimeter-class accuracy. As mentioned above, standalone positioning typically has errors of about 5–10 m (16.4–32.8 ft), so high-precision surveying without specialized equipment is difficult. However, combining a smartphone with an external high-precision GNSS receiver can achieve centimeter accuracy. For example, using an RTK-capable receiver like LRTK enables precise positioning based on the public coordinate system even with a smartphone.

Q: Can beginners handle external GNSS receivers? A: Yes. Recent external GNSS receivers and surveying apps have refined user interfaces that allow intuitive operation without specialized knowledge. Starting and stopping positioning and recording points can be done easily with buttons on the smartphone screen. Complex settings and calculations are automated, so even those with limited surveying experience can use them with confidence.

Q: Do high-precision positioning services require network connectivity or paid services? A: Not necessarily. Network RTK requires an Internet connection and possibly a contract with a commercial correction service, but receivers that support Michibiki’s CLAS, such as LRTK, can obtain correction information even outside mobile coverage. In Japan, using CLAS itself does not incur charges, and you can obtain real-time centimeter accuracy without incurring communication fees. Therefore, high-precision positioning is possible in mountainous work sites without worrying about additional costs.

Q: How much accuracy can actually be achieved? A: It depends on conditions, but when using RTK or CLAS, horizontal positioning often falls within 2–3 cm (0.8–1.2 in) of error. Under good conditions with a stationary measurement, accuracy can improve further to the single-centimeter range (around 0.4 in). Vertical errors are somewhat larger but typically remain within a few centimeters to about 5 cm (2.0 in). However, in forests or shadowed by buildings where satellite reception deteriorates, accuracy can fall and errors on the order of several tens of centimeters may occur. To consistently obtain centimeter accuracy, an open-sky environment is ideal.

Q: What preparations and costs are required to introduce smartphone surveying? A: Basically, you need to acquire a compatible GNSS receiver and install the dedicated app on your smartphone. Some receivers attach directly to the smartphone, while others are mounted on poles. Prices vary by model, but they are considerably less expensive than traditional surveying equipment. Also, if you utilize free augmentation services like Michibiki, there may be no monthly usage fees. It is advisable to try it on a small site first to confirm that operations are feasible before full-scale introduction.

Q: How long does a GNSS receiver’s battery last? A: It depends on the model, but LRTK’s built-in battery provides about 6 hours of continuous positioning. This typically covers a normal working period, and for longer surveys you can operate while charging from a mobile battery. This ensures reliable operation even outdoors where power sources are limited. Note, however, that battery performance may degrade in very cold winters or extremely hot summer conditions.

Q: Can it be used in rainy or harsh field environments? A: Many GNSS receivers are ruggedized for outdoor use and some products are waterproof and dustproof. LRTK is designed for use in dusty construction sites and can operate in light rain without problems. However, as with any precision instrument, avoid prolonged use in heavy rain and take appropriate precautions.