Table of Contents

• Can a smartphone become a surveying instrument? A new era of high-precision positioning on-site

• Accuracy comparison: built-in smartphone GPS vs. external GNSS receivers

• Benefits of introducing an external GNSS receiver

• How to choose and compare external GNSS receivers

• Field test results: the real performance of external GNSS receivers

• Expanded use cases with smartphone RTK

• Simple surveying realized by LRTK

• FAQ

Can a smartphone become a surveying instrument? A new era of high-precision positioning on-site

Traditionally, achieving centimeter-level high-precision positioning in surveying and civil engineering required dedicated, expensive surveying equipment. Large GNSS antennas mounted on tripods, base-station receivers, radio modems, batteries, and many other pieces of equipment had to be prepared, and initial investments of several million yen were not uncommon. Operation was assumed to be conducted by surveyors with specialized knowledge and qualifications, making it difficult for ordinary site workers to casually utilize high-precision positioning. However, this situation has been changing dramatically in recent years. Advances in technology and the emergence of new satellite positioning services have brought an era in which anyone on-site can easily achieve centimeter-level positioning with just a smartphone and a small external GNSS receiver. In Japan, the Quasi-Zenith Satellite System “Michibiki” and its centimeter-level augmentation service (CLAS) play a key role. CLAS broadcasts augmentation signals from satellites directly to improve accuracy, and using a compatible GNSS receiver can correct standalone GPS errors—previously on the order of about 5-10 m (16.4-32.8 ft)—down to a few centimeters. Because this service can provide high-precision positioning using satellite signals alone anywhere in Japan, even in mountainous areas outside mobile coverage, high-precision GNSS positioning has become much more accessible. Solutions that combine a smartphone with an external GNSS receiver—often called “smartphone RTK”—are also emerging. RTK (Real Time Kinematic) is a positioning method that cancels errors in real time using two GNSS units, a reference station and a rover, and can reduce errors to a few centimeters. Previously, one had to set up a base station or subscribe to paid correction services, but by leveraging Michibiki’s CLAS you can achieve RTK-equivalent effects without additional infrastructure. Against this background, easy-to-use high-precision positioning systems implemented with a smartphone and a compact receiver are attracting attention, and a new era in which “a smartphone becomes a surveying instrument” is beginning.

Accuracy comparison: built-in smartphone GPS vs. external GNSS receivers

Smartphones come with built-in GNSS receivers including GPS, but their positioning accuracy is generally said to be about 5-10 m (16.4-32.8 ft). You have probably experienced your position being displayed a few meters off in a map app. This is partly because smartphone GPS chips are typically single-frequency and simplified, and their antennas are small, making them highly susceptible to the reception environment. Standalone positioning cannot correct for atmospheric or clock errors in satellite signals, so there are limits to improving accuracy. Vertical positioning errors are also large, making it difficult to determine elevation precisely with smartphone GPS alone. By contrast, connecting an external high-precision GNSS receiver to a smartphone can dramatically improve accuracy. High-precision GNSS receivers generally support multiple frequency bands (multi-band) and multiple satellite systems (not only GPS but also GLONASS, Galileo, Michibiki, etc.), allowing them to reliably capture more satellite signals. Additionally, by using CLAS from Michibiki or correction information from the GNSS reference station network to correct errors in real time, horizontal accuracies of a few centimeters and vertical accuracies from a few centimeters to a dozen or so centimeters can be achieved. For example, performing RTK positioning with a dedicated external receiver can reduce errors that exceeded 5 m (16.4 ft) with a smartphone alone to as little as about 1-2 cm (0.4-0.8 in), enabling position determination approaching the accuracy of surveying instruments. Stability of accuracy is also greatly improved. While a smartphone’s built-in GPS can drift by several meters over time, a high-precision GNSS receiver shows very small variation in repeated measurements at the same point. By removing error factors, measurements become stable and highly reproducible, greatly increasing on-site reliability. Thus, there is an order-of-magnitude difference in accuracy between built-in smartphone GPS and external GNSS receivers, and they should be used according to the application. For situations requiring precise positioning, using an external GNSS receiver is indispensable.

Benefits of introducing an external GNSS receiver

A positioning solution using a smartphone and an external GNSS receiver offers various benefits beyond improved accuracy. First and foremost, it is overwhelmingly smaller and lighter than traditional surveying equipment, making it easy to carry. With a pocket-sized GNSS receiver and a smartphone, you don’t need to transport heavy tripods or large hard cases. A single worker can walk the site and perform surveying, dramatically improving mobility. Second, there are cost advantages. Dedicated surveying equipment has been expensive, and equipping multiple units was not easy. Replacing them with a smartphone plus a small GNSS receiver can greatly reduce initial investment and maintenance costs. In particular, using Michibiki CLAS incurs no additional cost for obtaining correction information, keeping running costs low. Equipment that used to cost millions of yen can now be realized with much cheaper devices, which is a significant advantage. Third, operation is easier and multifunctionality is higher. With dedicated apps running on a smartphone, starting and stopping positioning and saving data can be done intuitively without worrying about complicated settings. Measurement results can be displayed on a map on-site, or high-precision position tags can be attached to photos and saved. You can input notes simultaneously with positioning or compare with past data—functions unique to digital devices are abundant. Cloud integration allows on-site data to be shared with the office immediately. Compared to the conventional method of handwriting notes in a field book and bringing them back, operational efficiency and data utilization expand dramatically. Overall, a smartphone plus an external GNSS receiver is a new surveying style that combines “high accuracy, low cost, and ease of use.” Each field worker can carry their own surveying instrument and measure whenever needed—such a future is becoming a reality.

How to choose and compare external GNSS receivers

When researching external GNSS receivers for smartphones, you will find several types and approaches. Here are the main points to compare when selecting a device.

• Positioning method and supported services: Devices support different positioning methods. Some only support SBAS (satellite-based augmentation systems) and remain limited to around 1 m (3.3 ft) accuracy, while others support RTK and achieve centimeter-level accuracy. If you will use the device in Japan, compatibility with Michibiki’s CLAS is an important point. A CLAS-compatible receiver can provide cm level accuracy (half-inch accuracy) even outside mobile coverage.

• Frequency bands and satellite support: For high precision, multi-band support is desirable. Devices that support multiple frequencies like L1/L2 or L1/L5 are better at removing ionospheric errors and offer more stable positioning than single-frequency L1-only receivers. The more GNSS systems a device supports—GPS plus GLONASS, Galileo, BeiDou, and Michibiki (QZSS)—the more satellites it can use, improving accuracy and availability.

• Connection method and usability: Check how the device connects to your smartphone. Wireless connections like Bluetooth or Wi‑Fi are common and more convenient on-site than wired connections. Confirm whether there is a dedicated app or compatible apps on the smartphone, and whether connection and setup are easy. Also verify whether positioning data can be output in NMEA format or similar for use with your existing apps or systems.

• Battery life: Many external receivers have built-in batteries, so continuous operating time is an important comparison point. For long on-site use, devices that can operate for 5-6 hours or more are reassuring. USB charging or support for mobile battery packs allows you to keep operating with spare power.

• Size, weight, and ruggedness: Because these devices are carried around, smaller and lighter is better. If it fits in a pocket and weighs a few hundred grams or less, portability is good. For construction sites, consider dustproof/waterproof ratings and shock resistance. Durability that withstands some rain or drops gives peace of mind on-site.

• Support and price: Finally, manufacturer support and services matter. If you are new to high-precision positioning, comprehensive manuals and responsive customer support are reassuring. Prices vary widely, and you will choose according to performance and budget. Cheaper models may have limited accuracy or simple features, while high-performance models cost more. Recently, however, surprisingly high-precision products at reasonable prices have appeared, increasing cost-effective options. Based on the above points, choose a GNSS receiver that fits your intended use. Whether you prioritize accuracy or ease of use, you should be able to find an optimal device for your use cases and budget.

Field test results: the real performance of external GNSS receivers

So how much accuracy can you actually get with a smartphone plus an external GNSS receiver? We conducted tests by positioning at known coordinate points using a smartphone and an external GNSS receiver and evaluated the accuracy. First, we connected a high-precision GNSS receiver to a smartphone and performed single-point positioning while receiving Michibiki CLAS augmentation information. The resulting coordinates, when compared to the true values obtained from the Geospatial Information Authority of Japan’s reference station data, showed horizontal errors within 1-2 cm (0.4-0.8 in) and vertical differences of about 3 cm (1.2 in). Compared with values measured by conventional surveying equipment (class-1 GNSS surveying instruments), the difference between the two was less than 5 mm (0.20 in), an astonishing result that confirmed the positioning accuracy of external GNSS receivers can rival traditional professional equipment. We also examined stability by repeating measurements. At a certain point we measured 10 times consecutively; the variation of single-shot measurements (standard deviation of horizontal position) was about 12 mm (0.47 in). However, by using a smartphone app feature to average measurements over 60 seconds, the standard deviation decreased to about 8 mm (0.32 in), showing that a more stable position can be obtained. Achieving sub-1 cm (0.4 in) accuracy with only about one minute of measurement is convenience previously unthinkable. On the other hand, when we attempted the same measurements using the smartphone’s built-in GPS, the reported positions were far from the true values and jumped around moment to moment, making them unsuitable for precise surveying. The conventional smartphone GPS with errors on the order of meters clearly has limits, and the presence or absence of a high-precision receiver produces an overwhelming difference. In our field test we measured in open outdoor conditions with good sky visibility, and under such conditions the external GNSS receiver almost always maintained stable cm level positioning. In locations without tall buildings or trees nearby, positioning converged quickly and high accuracy was demonstrated. Of course, because signals are received directly from satellites, accuracy may degrade or solutions may not be obtained in forests or urban canyons. However, that limitation also applies to conventional surveying instruments; portable GNSS receivers actually offer greater flexibility on-site because you can choose measurement points that avoid obstructions. From these verifications, we found that smartphone plus an external GNSS receiver can achieve professional-level accuracy if used correctly and in appropriate environments. This easy method, which enables immediate measurement and sharing on-site, is practically usable for fieldwork.

Expanded use cases with smartphone RTK

High-precision positioning with a smartphone and an external GNSS receiver greatly expands on-site applications. Tasks that previously required specialized survey teams or were abandoned due to insufficient accuracy can increasingly be handled on the spot with smartphone RTK. Specific applications include:

• Single-point surveying and as-built verification: You can measure required point coordinates on the spot and compare them with design coordinates to check as-built conditions. Conversion to the plane rectangular coordinate system and geoid-based height conversion can be done automatically on the smartphone, allowing immediate confirmation of measurement results on-site.

• Layout work (staking out): High-precision GNSS is useful for staking out positions indicated on design drawings. The smartphone screen can display deviations to the target point in real time or visualize design positions with AR (augmented reality), enabling staking tasks that used to require two or more people and surveying equipment to be efficiently performed by a single person.

• Photo documentation and inspections: Photos taken with a smartphone can be tagged with high-precision position and orientation information. For example, if on-site photos before and after construction include accurate coordinates, they can be easily used for time-series comparisons or as as-built documentation. Recording photos of defects together with coordinates during equipment inspections also streamlines report creation.

• 3D surveying (point cloud acquisition): Combining LiDAR-equipped smartphones, 360° cameras, or drones with high-precision GNSS makes it possible to georeference point cloud data and 3D models accurately. By providing a coordinate reference from positioning, advanced analyses such as 3D as-built verification and earthwork volume calculations become feasible. 3D measurements that once required outsourcing to specialists can now be tried more easily with smartphones and GNSS.

• Other applications: In agriculture, field parcel measurement and guidance for autonomous farm machinery; in disaster response, rapid surveying and map creation of affected areas—applications for smartphone RTK continue to expand. The key is that having high-precision position information in real time enables new on-site solutions that improve productivity and reduce labor. Thus, smartphone RTK is expected not only to streamline surveying but also to accelerate digital transformation (DX) on worksites. If each worker routinely carries a smartphone surveying device, workflows on-site will change significantly, enabling faster and more accurate decision-making.

Simple surveying realized by LRTK

To make high-precision positioning with a smartphone and an external GNSS receiver even easier, we developed LRTK. LRTK is designed as a “pocket-sized versatile surveying instrument” that transforms a smartphone into a centimeter-precision surveying device. A compact GNSS device weighing just about 125 g and with a thickness of about 13 mm (0.51 in) attaches to the back of an iPhone, and by simply launching a dedicated app anyone can immediately start high-precision positioning. If mounted on an optional monopod (pole), it is also possible to take measurement points with the same stable posture as conventional surveying instruments. The standout features of LRTK are its ease of use and accuracy. With an internal battery it operates for about 6 hours, and because it wirelessly links with the smartphone, handling on-site is comfortable. It leverages Michibiki’s CLAS signals and proprietary correction technology to provide positioning in mountainous areas outside mobile coverage with horizontal ±2 cm (±0.8 in) and vertical ±4 cm (±1.6 in) accuracy. That level of accuracy rivals class-1 GNSS surveying instruments defined by the Geospatial Information Authority of Japan, yet operation is completed via a smartphone app without requiring specialized knowledge. Measured data are automatically saved to the cloud, allowing office staff to check on-site surveying results in real time. The LRTK app is packed with useful on-site features such as single-point averaging, coordinate system conversion, and AR-based navigation to measurement points. For example, with a single button you can observe your current position 60 times and record the averaged high-precision coordinate. If you specify the coordinates of the point you want to measure, the app will guide you to the staking position with arrows on the smartphone screen, so even beginners can locate staking points without hesitation. Collected coordinates can be managed with photos and notes, and cloud-based map display, distance/area calculations, and data sharing are readily available. It is truly the definitive “simple surveying” solution that even those with no surveying experience can handle. The impact of LRTK’s simple surveying on worksites is significant, turning the vision of one smartphone surveying device per person into reality. When teams can perform necessary surveys without expensive equipment or skilled specialists, on-site productivity and autonomy increase dramatically. In the coming era, with a smartphone and LRTK, sites may increasingly measure and think for themselves—ushering in a new mainstream style of construction management.

FAQ

Q: Why is smartphone GPS alone so inaccurate? A: Smartphone-built-in GPS (GNSS) receivers are single-frequency and use simplified antennas, so they cannot sufficiently cancel error factors and typically remain accurate only to about 5-10 m (16.4-32.8 ft). In addition to atmospheric and clock errors affecting satellite signals, smartphones are prone to multipath from buildings and terrain, which commonly causes position offsets of several meters. For high-precision positioning, using an external GNSS receiver and augmentation information (RTK or CLAS) that can correct such errors is essential. Q: Can external GNSS receivers really achieve centimeter-level accuracy? A: Yes, with appropriate equipment and environment it is possible. For example, connecting a multi-band high-precision GNSS receiver to a smartphone and using Michibiki’s CLAS or RTK correction information from a reference station can yield horizontal accuracies of a few centimeters and vertical errors within a few to a dozen or so centimeters. In our field tests we obtained positioning results within about 1-2 cm (0.4-0.8 in) horizontally. However, accuracy degrades in environments where satellite signals are distorted, such as locations near tall buildings, so ideal precision cannot be guaranteed under all conditions. Q: Is it difficult to connect and operate a smartphone with an external GNSS receiver? A: It is relatively easy even without special knowledge. Many external GNSS receivers pair to smartphones via Bluetooth or Wi‑Fi and operate through a dedicated app. Once paired, measurement starts by following the app’s prompts and pressing a button, and results are displayed in real time. Settings such as positioning mode and coordinate system conversion are handled automatically by the app, so users do not need to perform complex calculations. Many apps feature intuitive UIs, so even first-time users can begin surveying after a few minutes of use. Q: What is LRTK? A: LRTK is our company’s high-precision positioning solution for smartphones. It consists of a pocket-sized RTK-GNSS receiver (LRTK Phone), a smartphone app, and cloud services, designed so anyone can easily perform centimeter-level surveying. By using Michibiki CLAS and proprietary correction techniques, LRTK achieves cm level accuracy (half-inch accuracy) without a reference station, and positioning data are managed and shared in the cloud. It combines the precision of professional surveying instruments with ease of use and low introduction cost. Q: What precautions should be taken when using high-precision positioning on-site? A: To achieve high-precision positioning, keep a few points in mind. First, choose locations with as clear a sky as possible while measuring, avoiding nearby obstructions that block satellite signals. When buildings or trees are close, satellite visibility is reduced and accuracy may degrade or positioning may become unstable. Also avoid being close to large metal construction machinery or strong sources of radio interference. During measurement, firmly fix the smartphone and receiver and avoid unnecessary movement. Using a monopod or pole for measurements prevents wobble and enables stable positioning. Finally, handle obtained data carefully: back up important measurement results to the cloud and habitually cross-check them against other known points to confirm accuracy. Observing these points will help you get the most benefit from high-precision positioning on-site.