Smartphone GPS vs External GNSS Receiver: Accuracy Comparison | LRTK

Table of Contents

• Introduction

• Accuracy Comparison: Smartphone GPS vs. External GNSS Receivers

• Technologies Enabling High-Precision Positioning (RTK, Michibiki, etc.)

• Benefits of High-Precision Surveying with Smartphones

• Recommendation: Simple Surveying with LRTK

• Conclusion

• FAQ

Introduction

In recent years, smartphone GPS functionality has made it easy to determine your current location. However, the accuracy required on construction and surveying sites is very high, and traditionally expensive surveying instruments and skilled technicians were indispensable. If such high-precision surveying could be achieved with only a smartphone, it would greatly improve onsite efficiency and reduce costs. To answer that question, this article explores the feasibility of high-precision positioning using smartphones.

We compare the inherent accuracy limits of built-in smartphone GPS and ways to improve it, and evaluate how much accuracy can be gained by combining a smartphone with an external GNSS receiver. We also explain the latest technologies that support high-precision positioning, such as RTK and Japan’s Michibiki satellites, and discuss the practical benefits of using smartphone surveying in the field. Finally, we introduce a notable solution, LRTK, that can turn a smartphone into a cm level accuracy (half-inch accuracy) surveying instrument, and suggest simple surveying methods that anyone can start using.

Accuracy Comparison: Smartphone GPS vs. External GNSS Receivers

The GNSS capabilities built into smartphones, such as GPS, typically have errors on the order of several meters. Even under good outdoor conditions, it is not uncommon for the reported position to be off by about 5-10 m (16.4-32.8 ft). This is acceptable for map apps or 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 performing boundary surveys.

To overcome these limitations, specialized positioning devices known as external GNSS receivers are used. These small GNSS terminals connect to a smartphone via Bluetooth or cable and are equipped with multiple satellite frequency bands and high-performance antennas that smartphones cannot receive. By using advanced correction techniques, they dramatically improve positioning accuracy. While smartphone GPS has errors of several meters, using an external GNSS receiver can provide highly accurate position information with errors on the order of a few centimeters. For example, repeatedly measuring a known point with a smartphone may yield values scattered across several meters, but with a high-precision GNSS receiver, measurements will consistently fall within a few centimeters of the true position.

Of course, GNSS positioning assumes an open sky; in forests or dense high-rise areas, smartphone GPS errors become even larger. In practice, 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 power saving and may perform reception processing intermittently (duty cycling), which also makes them less favorable for continuous positioning compared to purpose-built devices. Multi-GNSS support and dual-frequency reception enable more stable positioning than smartphones. Overall, the decisive difference is that smartphone-only positioning accuracy is at best several meters, whereas combining a smartphone with an external GNSS receiver can improve accuracy to the level of a few centimeters.

It should be noted that smartphone GNSS performance has improved in recent years, and some models can receive multiple satellite systems and L5 band signals in addition to GPS. While positioning accuracy has improved compared to the past, dedicated receivers are still required to reliably achieve centimeter-class accuracy.

Technologies Enabling High-Precision Positioning (RTK, Michibiki, etc.)

To achieve high-precision positioning, it is necessary to apply error corrections to the raw positioning data obtained from satellites. GNSS positioning error sources include atmospheric delays (ionosphere and troposphere), satellite clock errors, orbital errors, receiver noise, and multipath (signal reflections). SBAS (Satellite-Based Augmentation System) and DGPS (Differential GPS) have long been used to correct these errors. SBAS broadcasts augmentation signals from geostationary satellites, and DGPS corrects distance errors using nearby reference stations, reducing standalone positioning errors from several meters to around 1 m.

The currently prevalent method is RTK (Real-Time Kinematic). RTK uses two GNSS receivers simultaneously: a base station placed at a known position and a rover that measures while moving. The raw satellite data collected simultaneously by both units is exchanged via communication, and by subtracting common error factors (satellite and atmospheric effects) in real time, RTK cancels errors that standalone positioning cannot correct, achieving positioning accuracy on the order of a few centimeters. Traditional RTK equipment transmitted correction data from the base to the rover via radio, but network RTK services that use the Internet to distribute reference station data are becoming more widespread. For example, it is becoming common to receive correction data via a smartphone’s mobile connection from public Continuously Operating Reference Station networks or private correction services.

A further advancement is Japan’s quasi-zenith satellite system Michibiki, which provides the Centimeter Level Augmentation Service (CLAS). CLAS delivers RTK-equivalent correction information directly from Michibiki satellites to receivers, enabling real-time centimeter accuracy without installing your own ground base station or preparing communication lines. GNSS receivers that support CLAS can achieve high-precision positioning even in mountain areas where mobile signals do not reach. Internationally, services such as Galileo’s High Accuracy Service (HAS) and other satellite-delivered augmentation services (so-called PPP-RTK) are emerging, improving the convenience of high-precision positioning. PPP (Precise Point Positioning) has the advantage of not needing a local reference station but historically required long convergence times to stabilize accuracy; PPP-RTK addresses this weakness and can converge to centimeter accuracy much faster.

Benefits of High-Precision Surveying with Smartphones

Combining a smartphone with an external GNSS receiver to achieve centimeter-level positioning offers many advantages over traditional surveying methods. First, there is a significant reduction in cost and equipment. Historically, obtaining centimeter accuracy required RTK-GNSS equipment costing hundreds of thousands of dollars or optical total stations, which demanded tripods and often two or more personnel for complex operations. With smartphone surveying, a field worker can start surveying alone by simply attaching a small GNSS receiver to their personal smartphone. The burden of acquiring dedicated equipment is reduced, and costs for transporting equipment and arranging personnel are minimized.

Second, smartphone-based surveying excels in immediacy and data utilization. When linked with a smartphone, coordinate data can be displayed on a map app on the spot or shared with the office via the cloud. There is no need to write in field notebooks and bring them back; you can check the measured results and overlay them with design drawings on site. Moreover, by combining the smartphone’s built-in camera or LiDAR scanner, you can simultaneously capture not only point coordinates but also site photos and 3D point cloud data. This enables a single smartphone to complete measurements and records that previously required separate devices, accelerating the digital transformation (DX) of surveying work.

Third, the ease of learning should not be overlooked. Advanced surveying instruments require specialized knowledge to operate, but smartphone surveying allows intuitive app-based operation for positioning and recording. For example, registering a survey point is often as simple as tapping a button on the smartphone screen, with complex settings and calculations automated by the app. This allows non-experts on site to perform layout tasks themselves, helping alleviate labor shortages. The environment is increasingly being set up so that anyone on site can benefit from high-precision positioning without relying solely on veteran surveyors.

Smartphone high-precision surveying is expected to be useful in scenarios such as:

• Civil engineering and construction: control point surveying and as-built management during construction. Useful for checking as-built shapes in earthworks by heavy machinery and for simple volume surveys on small to medium projects.

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

• Agriculture and forestry: field and forest parcel surveys, boundary confirmation, and task planning support. Useful as a positioning information infrastructure for precision agriculture and forest management, such as measuring farmland area and assessing forest resources.

• Disaster prevention and response: rapid situational awareness in disaster-affected areas and topographic monitoring of hazardous zones. Enables acquisition of terrain data remotely in areas difficult or dangerous for people to enter, speeding up disaster response.

Recommendation: Simple Surveying with LRTK

As described above, smartphone plus external GNSS receivers have made high-precision surveying accessible, and a representative solution is LRTK. LRTK is a positioning system consisting of an ultra-compact RTK-GNSS receiver that mounts on a smartphone and a dedicated app, instantly turning your handheld smartphone into a cm level accuracy (half-inch accuracy) surveying instrument.

The LRTK device itself is lightweight at approximately 150 g and compact 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 supports about 6 hours of continuous positioning and can be operated while charging via USB. The device attaches to the back of the smartphone, and by simply powering it on at the site it functions as a terminal capable of centimeter-class positioning. It is truly a "surveying instrument that fits in your pocket" and is useful across a wide range of tasks from control point surveying 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. Errors converge in a matter of tens of seconds, and latitude, longitude, and height based on the public geodetic coordinate system are displayed. Acquired data is automatically saved to the cloud, so there is no need to transfer data by USB after returning to the office. LRTK also supports Japan’s quasi-zenith satellite system Michibiki and can receive the CLAS augmentation signals mentioned earlier. This allows standalone high-precision GNSS positioning even at sites without mobile coverage. Because it does not depend on communication infrastructure, LRTK is effective in post-disaster surveys and forest surveys.

Furthermore, the LRTK smartphone app includes AR (augmented reality) features that overlay design lines and points on the real-world view. Using positioning data, it can project stake-out positions onto the screen or overlay as-built models for discrepancy checks, supporting construction management with intuitive AR displays. Layout tasks that were previously carried out by feel can now be done accurately while looking at the smartphone screen.

By utilizing LRTK, you can start simple surveying with lower initial investment. Its innovation has been featured in government satellite positioning service use cases, and adoption at sites is progressing. Users who have adopted LRTK report that surveying in mountainous areas that previously required two people can now be completed by one person, demonstrating labor-saving and efficiency gains. Since it can be used with just a smartphone and without special equipment or extensive training, LRTK is expected to be actively used in small construction sites and local government infrastructure inspections where high-precision positioning was previously impractical. If you have wondered whether high-precision surveying with a smartphone is possible, consider the new surveying style enabled by LRTK.

Conclusion

High-precision surveying using a combination of smartphones and external GNSS receivers is becoming the standard for future construction sites and surveying operations. Centimeter-level accuracy that was unattainable with a smartphone alone is now within reach for anyone thanks to RTK technology and Michibiki’s augmentation services. The advantages of rapid, efficient surveying by on-site personnel without relying on expensive dedicated equipment are immense. By leveraging solutions like LRTK, smartphones become tools for high-precision positioning, enabling the DX of surveying in situations that were previously out of reach. The potential for smartphone surveying will continue to expand and is expected to contribute directly to labor reforms and efficiency improvements in the construction industry. Truly, this is a new era of surveying opened up by smartphones and GNSS.

FAQ

Q: Can a smartphone alone really achieve centimeter-level surveying? A: Unfortunately, the GPS built into smartphones alone cannot achieve centimeter-level accuracy. As noted above, standalone positioning typically produces 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 allows precise positioning based on public coordinate systems even with a smartphone.

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

Q: Do you need a communications environment or paid services for high-precision positioning? A: Not necessarily. Network RTK requires Internet connectivity or a subscription to private correction services, but receivers that support Michibiki’s CLAS can obtain correction information even outside mobile coverage. In Japan, using CLAS itself does not incur a fee, and you can obtain real-time centimeter accuracy in environments without communication charges. Therefore, high-precision positioning is possible in mountainous work sites without worrying about additional costs.

Q: What level of accuracy can actually be achieved? A: Depending on conditions, using RTK or CLAS typically yields horizontal position errors of about 2-3 cm (0.8-1.2 in). Under favorable conditions with a stationary measurement, accuracy can improve to the 1 cm range. Vertical errors are somewhat larger but are generally on the order of a few centimeters to about 5 cm (2.0 in). However, in forests or shadowed areas near buildings, satellite signal reception degrades and accuracy can drop, resulting in errors of several tens of centimeters. An open sky environment is ideal for consistently obtaining centimeter-level accuracy.

Q: What preparation and costs are required to introduce smartphone surveying? A: Essentially, you need a compatible GNSS receiver and to install the dedicated app on your smartphone to get started. Receivers may be designed to attach directly to a smartphone or be mounted on a pole. Prices vary by model, but they are significantly more affordable than traditional surveying instruments. Also, free augmentation services like Michibiki can be used without monthly fees. It is recommended to trial the system on a small site to confirm it meets your operational needs before full deployment.

Q: How long does the GNSS receiver’s battery last? A: It depends on the model, but LRTK provides about 6 hours of continuous positioning on its built-in battery. This typically covers a normal workday, and for longer surveys you can operate while charging from a mobile battery. It is suitable for outdoor use where power is limited. Note, however, that battery performance can decline in very cold or very hot environments.

Q: Can it be used in rain or harsh site conditions? A: Many GNSS receivers are ruggedly designed for outdoor use and have waterproof and dustproof features. LRTK is constructed with on-site use in dusty construction environments in mind and can operate normally in light rain. However, as with all precision instruments, avoid prolonged use in heavy rain and take appropriate precautions.