Civil Surveying Is Changing! Centimeter-Level High-Precision Positioning Technology Achievable with a Smartphone

Table of Contents

• Challenges of field surveying

• Importance of centimeter-level high-precision positioning

• RTK positioning technology and the evolution of smartphones

• LRTK: turning a smartphone into a surveying instrument

• Innovations in surveying work brought by smartphone integration

• Simple surveying with LRTK

• FAQ

On construction and civil engineering sites, surveyors measure terrain and the heights and positions of structures with precision to support construction quality. However, until now, achieving centimeter-level positioning required specialized surveying equipment such as total stations or high-performance GNSS receivers. It has long been common knowledge that “smartphone GPS has too much error to be used for surveying.” Even though smartphones are now widely used on sites, surveying has still relied on expensive equipment and skilled personnel.

But that conventional wisdom is changing dramatically. Thanks to new technologies developed in recent years, anyone can now achieve centimeter-level high-precision positioning using a smartphone. By attaching a pocket-sized GNSS receiver to a phone and using a dedicated app, it is possible to achieve on-site accuracy comparable to conventional optical surveying instruments and stationary GNSS systems. As smartphones become high-precision surveying tools, the way civil surveying is done is undergoing a transformation. This article explains in detail the challenges of field surveying, the importance of high-precision positioning technology, the technological evolution of smartphone GNSS and how to use it, and new surveying styles and simple surveying solutions.

Challenges of field surveying

Surveyors and technicians at civil engineering sites face various issues daily. The first is a problem of workforce shortage and skill transfer. While experienced surveyors are aging, younger personnel are in short supply, and more situations require a small number of people to handle many surveying tasks. Traditional surveying often required two people to set up equipment and take measurements, so a lack of personnel directly reduced work efficiency.

The second issue is the burden of equipment. High-precision surveying requires transporting and installing tripod-mounted total stations or large GNSS receivers, which is a heavy burden in confined or rugged areas. For example, surveying in mountainous regions may involve carrying heavy equipment over long distances or setting it up at heights while maintaining balance, resulting in physical strain. In forests or downtown areas with tall buildings, satellite signals can be blocked and GNSS positioning accuracy can drop sharply. In such environments, surveying can take longer or require additional manual work, creating productivity and safety problems.

Another challenge is the lag in data utilization and sharing. Traditionally, survey results obtained on site were recorded in handwritten field notebooks and then taken back to the office for drafting and organization. It was difficult to share data with other departments on the spot or use it immediately for analysis, so there was a time lag before field survey results were reflected in design changes or as-built management. Recently, the Ministry of Land, Infrastructure, Transport and Tourism has been promoting *i-Construction*, which advances three-dimensional as-built management using point cloud data and the like. However, obtaining high-density 3D survey results with traditional methods requires advanced equipment and specialized skills, and aside from some large-scale sites, adoption has been slow.

Importance of centimeter-level high-precision positioning

On construction sites, centimeter-level positioning accuracy is required in many situations. For example, the layout of building foundations or setting a road centerline can be significantly affected by deviations of only a few centimeters. Installing boundary markers or burying water and sewer pipes can lead to serious problems if positions are off by tens of centimeters. Therefore, surveyors are responsible for defining reference points with high precision and providing positioning data so that construction can proceed according to design.

Centimeter-level accuracy is also indispensable for as-built management (quality confirmation) of completed structures. To accurately determine how much pavement or earthwork elevations and slopes deviate from the plan, meter-level coarse positioning is insufficient. If errors are within a few centimeters, you can create heat maps that color-code deviations from the design or accurately calculate required fill and cut volumes; if accuracy is low, correct judgments cannot be made. High-precision survey data help prevent rework and corrections during quality control and inspections, ultimately shortening schedules and reducing costs.

High-precision positioning also plays an important role in disaster response and infrastructure maintenance. Right after a disaster, if position information has errors of several meters, it becomes difficult to identify the exact locations and extents of damage, hampering initial response and recovery planning. Similarly, when recording the locations of cracks or deformations found during routine inspections of bridges and tunnels, keeping precise coordinates enables exact reinspection at the same spots during the next inspection. In civil engineering and infrastructure, “recording and sharing accurate positions” itself is the foundation that supports safety and efficiency, and for that reason centimeter-level high-precision positioning technology has long been required.

RTK positioning technology and the evolution of smartphones

Against this backdrop of needs, RTK technology in satellite positioning and the evolution of smartphones are converging. RTK (Real Time Kinematic) is a method that compares satellite data observed at a rover (moving station) and a base station in real time and uses error information to dramatically improve positioning accuracy. This method can correct errors that were once on the order of meters down to a few centimeters, making it widely used in fields that require advanced positioning such as surveying and civil engineering, agriculture, and autonomous driving.

At the same time, GNSS chips built into recent smartphones have become higher performance. Since the late 2010s, smartphones capable of receiving multiple-frequency satellite signals such as L1 and L5 have appeared, dramatically improving standalone positioning accuracy. Traditional smartphone GPS used single-frequency reception and could not correct ionospheric errors, leaving accuracies on the order of meters, but dual-frequency support reduces pseudorange measurement error factors, and together with multi-GNSS use, smartphones alone are becoming capable of decimeter-level positioning (on the order of several tens of centimeters).

Smartphone OS improvements are also notable. Around 2016, APIs were released that allow apps to obtain raw GNSS data from smartphone-built GNSS, enabling direct processing of pseudoranges and carrier phase and other positioning data within apps. This has advanced R&D applying PPP (precise point positioning) and RTK algorithms—previously achievable only with expensive surveying equipment—to smartphones. In RTK experiments using smartphone raw data, it has been reported that centimeter accuracy can be achieved instantly over short distances, raising expectations for high-precision positioning.

That said, challenges remain for achieving stable centimeter-level positioning with a smartphone alone. Built-in smartphone antennas are small and have low sensitivity, making them susceptible to noise and multipath (reflections), so accuracy degrades in poor satellite reception environments. Also, RTK positioning requires receiving correction information from a base station, and obtaining and processing such data in real time has been a significant hurdle for general users. To address these problems, auxiliary external devices for smartphones and services for delivering corrections have advanced, enabling an environment where anyone can use high-precision positioning with a smartphone.

LRTK: turning a smartphone into a surveying instrument

Enter external GNSS receiver devices that can be used with smartphones. A representative example is the compact RTK-GNSS receiver “LRTK Phone,” which has attracted attention as a groundbreaking solution that can realize centimeter-level positioning just by attaching it to a phone. The LRTK Phone itself is compact enough to fit in the palm, with an antenna and battery built into a robust structure. By attaching it to the back of a smartphone using a dedicated adapter or case, the smartphone instantly becomes a surveying instrument capable of high-precision GNSS positioning.

Technically, LRTK Phone supports multi-GNSS and multi-frequency reception. It can use not only GPS but also Russia’s GLONASS, Europe’s Galileo, and Japan’s Quasi-Zenith Satellite System Michibiki (QZSS) simultaneously, and receive multiple bands such as L1/L2/L5, enabling stable positioning. Even in urban areas where satellites are often blocked, it captures as many satellite signals as possible to cancel error factors and ensure high accuracy. In practice, when an LRTK device is attached to a smartphone, the positioning error that was formerly about 5-10 m (16.4-32.8 ft) with built-in smartphone GPS is sharply reduced to approximately horizontal ±2 cm (±0.8 in) and vertical ±3 cm (±1.2 in). This accuracy rivals first-class standard GNSS surveying using the Geospatial Information Authority of Japan’s electronic reference stations and is more than sufficient for general civil and topographic surveying.

The key to achieving centimeter-level accuracy with LRTK is the combination of the RTK method mentioned above and Japan’s unique satellite-based augmentation service, CLAS. The LRTK Phone can obtain correction data from public and private base station networks (the network of electronic reference stations and various correction information services) via the smartphone’s communication and apply the correction data to positioning calculations in real time as a network RTK. As long as the device is within cellular coverage, the smartphone connection can always apply the latest corrections to maintain stable positioning accuracy.

Notably, LRTK Phone supports CLAS, Japan’s centimeter-level augmentation service provided by the QZSS. An LRTK device with an antenna capable of receiving the L6 band for CLAS can receive correction information broadcast directly from satellites and continue high-precision positioning even in environments where cellular communication is unavailable, such as mountainous areas or disaster-affected zones. Previously, real-time high-precision positioning was almost impossible at sites without communication coverage, but with LRTK, “centimeter-level positioning that does not depend on communication infrastructure” becomes possible—a major advantage for disaster response.

LRTK is also attractive for its ease of operation and use. Its built-in battery supports about six hours of continuous positioning, and it can be powered from a mobile battery via USB while in use. Connection to the smartphone is simply by Bluetooth pairing or cable, and launching the dedicated app lets you start positioning immediately. No complicated initial setup or special dedicated controller is required; intuitive operation is completed on the familiar smartphone screen. For anyone who can use a smartphone, the ease of starting RTK positioning with the push of a button without special knowledge is a major advantage on site.

Innovations in surveying work brought by smartphone integration

The introduction of smartphone-integrated devices like LRTK has started to broaden new surveying styles on sites. The greatest benefits of combining a smartphone with high-precision GNSS are intuitive operability and increased work efficiency through digital integration. Traditionally, data obtained with dedicated equipment had to be imported to a PC and converted to drawings with CAD software or processed in spreadsheets. With a smartphone + LRTK, positioning, plotting, and coordinate calculations are all processed automatically within the dedicated app. For example, coordinates of measured points are converted in real time to the plane rectangular coordinate system and elevation (geoid height), and are instantly digitally recorded along with point names and timestamps. There is no need to transcribe into a paper field notebook; data are organized to deliverable-level quality the moment they are measured.

Another strength of using a general-purpose device like a smartphone is its communication capability and cloud integration. Positioning point data, point clouds, photos, and other data obtained with the LRTK app can be uploaded to the cloud with one tap. Because information measured on site can be shared with the office immediately, it is no longer “measured and left unused,” and can be utilized in subsequent processes right away. In one field, point cloud data of as-built measurements obtained with LRTK in the morning were shared with design staff via the cloud, and construction plans were adjusted based on that data in the afternoon. Work that formerly involved bringing data back on a USB memory stick and emailing it—incurring delays and extra steps—was dramatically sped up by connecting site and office in real time.

It is also revolutionary that surveying has become something “anyone can do.” Even without advanced specialist knowledge, site supervisors and technicians can perform positioning tasks with their own smartphones, allowing them to easily conduct quick condition checks and as-built inspections themselves. Tasks that previously required calling a surveying team can now be done immediately with an LRTK-equipped smartphone, reducing waiting times and communication loss and improving overall productivity. For surveying specialists, delegating simple measurements to other staff allows them to focus on advanced measurements and design management, enabling efficient, high-quality work across the team.

In this way, smartphone-integrated high-precision positioning strongly promotes digital transformation (DX) on sites. It addresses traditional issues such as labor shortages, heavy manual tasks, and delays in information sharing, establishing new workflows that balance safety and efficiency. Indeed, examples have already emerged in municipalities without dedicated surveying departments where field staff use smartphone surveying tools to perform precise measurements themselves, suggesting potential widespread adoption across the industry. In the future, applications unique to a smartphone + high-precision GNSS platform—such as overlaying design models with AR and automated analysis using AI—are expected to advance, and it can be said that the fundamentals of civil surveying are being changed from the ground up.

Simple surveying with LRTK

Finally, let us discuss simple surveying with LRTK, which makes smartphone high-precision positioning easy to practice. The LRTK series was developed with a “one device per person” concept in mind, aiming for each field staff member to carry a pocket-sized device and perform surveying immediately when needed. By enabling surveying to be completed with just a smartphone, without relying on dedicated equipment, the barrier to surveying is greatly lowered. Even in situations that demand high accuracy, introducing LRTK allows on-site response without calling a specialized surveying team, directly improving the efficiency and speed of daily operations.

In practice, the effectiveness of LRTK has been demonstrated across a wide range of applications from reference point surveying to as-built management and disaster damage recording. For example, in one bridge project, the coordinate-guidance function of LRTK reduced the time required to stake pile-driving positions to less than half of the previous time. In another municipality, inspectors used LRTK and a smartphone camera to take photos with embedded coordinates during road facility inspections, enabling exact reinspection of the same spots at the next inspection. Simple surveying with LRTK is therefore expected to be a solution that dramatically improves site productivity and data accuracy. If your site has a need to “utilize high-precision positioning more easily,” consider the simple surveying solutions that LRTK enables with a smartphone.

FAQ

Q1. Why is high-precision positioning difficult with smartphone-built GPS? A. Typical smartphone GPS is a single-frequency simple receiver that cannot correct ionospheric errors, and the small antenna imposes sensitivity limits, resulting in errors on the order of several meters. There is also no mechanism to receive correction information, so standalone positioning inherently has accuracy limitations.

Q2. What is RTK positioning? How does it achieve centimeter-level accuracy? A. RTK (Real Time Kinematic) is a positioning method that uses error information measured by a base station to correct the position of a rover (measurement side) in real time. By using the differences in observations between two points to remove error factors, it can improve positional information that would otherwise have meter-level deviations with GPS alone to centimeter-level accuracy.

Q3. What is required to achieve centimeter-level positioning with a smartphone? A. Since a smartphone alone is difficult, an external high-precision GNSS receiver and a service that provides correction information are necessary. For example, combining an attachable LRTK device with base station data over the network (or satellite-delivered CLAS) makes centimeter-level positioning possible with a smartphone.

Q4. Is high-precision positioning possible in areas without communication coverage? A. Yes. Network RTK cannot be used outside communication coverage, but a receiver compatible with CLAS can achieve high-precision positioning using correction signals from satellites. Devices that support CLAS reception, such as some LRTK models, can continue centimeter-level positioning in mountainous or disaster sites beyond cellular coverage.

Q5. How do smartphone positioning and traditional surveying instruments differ? What are the advantages? A. Positioning using a smartphone plus a high-precision GNSS device differs from traditional instruments in being far more portable and easier for anyone to use. Heavy equipment and complex operations are unnecessary, and one person can complete on-site surveying. Real-time cloud sharing of data also speeds up operations. However, in terms of accuracy and stability, traditional instruments like total stations may outperform smartphone setups under some conditions, so it is advisable to choose the appropriate tool depending on the application.