RTK Surveying Using Only a Smartphone: The True Capability of Centimeter-Level Accuracy (cm level accuracy (half-inch accuracy))

Table of Contents

• Introduction

• What is RTK surveying?

• Why centimeter-level accuracy (cm level accuracy (half-inch accuracy)) is required

• Traditional RTK surveying and its challenges

• Background enabling RTK surveying with smartphones

• Advantages of smartphone RTK surveying

• What you can do with smartphone RTK surveying

• Accuracy and performance of smartphone RTK surveying

• Simple surveying with LRTK

• FAQ

Introduction

In recent years, the advent of smartphones has dramatically changed our lives. We increasingly use location information in the palm of our hands, checking our current position with map apps or embedding location tags in photos. However, ordinary smartphone GPS has errors on the order of several meters, which is insufficient for precise surveying or design. What has attracted attention is RTK surveying, a centimeter-class high-precision positioning technology. This article explains how RTK surveying that can be performed using only a smartphone works and examines the real-world capability of its centimeter-level accuracy (cm level accuracy (half-inch accuracy)), and concludes by introducing the latest solutions.

What is RTK surveying?

RTK surveying stands for Real Time Kinematic, and is one of the high-precision positioning methods using GNSS (Global Navigation Satellite Systems). Ordinary GPS positioning is done with a single receiver and therefore has errors on the order of meters, but RTK surveying simultaneously receives signals from satellites at two or more points: a base station (reference point) and a rover (mobile station). The error information obtained at the base station is sent to the rover in real time and used to correct the measurements, enabling high positioning accuracy within a few centimeters. In other words, RTK dramatically reduces conventional positioning errors by determining the high-precision relative position to a reference point.

Why centimeter-level accuracy (cm level accuracy (half-inch accuracy)) is required

So why is centimeter-class accuracy required? On civil engineering and construction sites, a deviation of several centimeters can lead to significant problems. Many tasks require precise alignment, such as staking out a building location, measuring property boundaries, and installing infrastructure equipment. In agriculture, precision farming with autonomous tractors requires position control at the centimeter level. Also, in disaster sites and topographic surveys, recording positions with high precision enables rapid and accurate restoration work and analysis. Centimeter-level accuracy (cm level accuracy (half-inch accuracy)) is the key to confidently using location information in situations that previously required specialized surveying equipment.

Traditional RTK surveying and its challenges

RTK surveying itself has existed for some time, but traditionally it required specialized and expensive equipment. Typically, a high-precision GNSS receiver is mounted on a tripod as the base station, and another receiver is used as the rover to perform the survey. These surveying instruments can cost several million yen, and transporting and setting up the equipment is laborious. Surveying expertise and experience are also required, and sometimes two or more people are needed. In addition, delivering correction information from the base station to the rover can require licenses or dedicated communication devices for radio transmission, so it was not something anyone could use easily. As a result, the benefits of RTK surveying were limited to a small number of surveyors and certain sites.

Background enabling RTK surveying with smartphones

Recently, this situation has been changing significantly. Advances in technology have produced compact and affordable RTK-capable GNSS receivers that can be used in combination with smartphones. Smartphones themselves have become high-performance devices capable of acquiring and processing raw location data. In addition, the availability of correction data via the Internet—such as Ntrip (network RTK correction services)—and services like Japan’s QZSS CLAS providing centimeter-class corrections have made correction data easy to obtain. These developments have made it possible to realize RTK surveying using only a smartphone. High-precision positioning equipment that used to be stationary can now be carried as portable devices that work with smartphones, transforming on-site surveying workflows.

Advantages of smartphone RTK surveying

Using smartphones for RTK surveying offers many advantages compared to traditional methods. The main benefits are summarized below.

• Mobility and ease of use: All you need is a smartphone and a small receiver, so there is no need to transport bulky equipment. The receiver fits in a pocket and can be taken out and used immediately when needed. It can be carried by one person, making it easy to walk around a site and perform surveys.

• Low cost: It can be introduced at a far lower cost compared to dedicated GNSS surveying instruments. There is no need to share expensive equipment among multiple people, and achieving one device per person becomes realistic, improving on-site productivity.

• Ease of operation: Intuitive smartphone app interfaces allow surveying without specialist knowledge. With just a tap, you can record points and perform various calculations, greatly lowering the barrier to surveying.

• Real-time sharing: Because smartphones have communication functions, positioning data can be uploaded to the cloud immediately and shared with office staff. This smooths information coordination between the field and the office and enables rapid decision-making.

• Integrated multifunctionality: By integrating the smartphone’s camera and sensors, a single device can perform tasks such as photography with geotagging, AR visualization, and point cloud scanning. Tasks that previously required separate devices can be handled together with smartphone RTK surveying.

What you can do with smartphone RTK surveying

Combining a smartphone with an RTK receiver for high-precision surveying enables a wide range of on-site capabilities. Below are the main functions and use cases achievable with smartphone RTK surveying.

• High-precision point surveying: Simply hold the receiver over the point to be measured and tap a button on the smartphone to record the latitude, longitude, and elevation with centimeter-level accuracy (cm level accuracy (half-inch accuracy)). You can attach timestamps, point names, and notes to measurement points for easy management when reviewing later.

• Staking out and guidance: Marking coordinates specified in design drawings or plans on site becomes easy with smartphone RTK. By moving while checking the direction and distance to the target point on the smartphone screen, one person can perform staking-out tasks that previously required a transit or total station.

• 3D point cloud scanning: Smartphones with LiDAR sensors can scan surrounding structures and terrain to obtain dense 3D point cloud data. By combining these point clouds with high-precision coordinates from RTK, accurate geographic coordinates can be assigned to the scanned data, assisting in the creation of survey maps and BIM/CIM models.

• Photogrammetry and records: Photos taken with the smartphone’s camera can be automatically tagged with positioning information and saved to the cloud. For example, if you photograph concrete cracks or disaster scenes, those locations are accurately plotted on a map and can be reviewed in the office while viewing the photos.

• Distance, area, and volume calculations: Measured coordinate data can be analyzed in smartphone apps or on the cloud. For instance, distances between measured points, the area of enclosed regions, and excavation volumes can be calculated automatically. This allows on-site estimation of quantities for quick decision-making.

• AR visualization: If design data or 3D models are imported into the smartphone, AR functionality can overlay them on real-world imagery. Thanks to high-precision positioning, models and projected views can be displayed on site without misalignment, which is powerful for pre-construction image sharing and verification.

In this way, smartphone RTK surveying is not limited to mere position measurement but is attractive because it offers an all-in-one solution from measurement to recording and construction support.

Accuracy and performance of smartphone RTK surveying

Some may wonder whether such high precision can truly be achieved with a smartphone-based RTK system. Actual verification results reveal its capability. Generally, positioning error with a smartphone plus RTK receiver is about ±1–2 cm horizontally and about ±3 cm vertically. Translate with parentheses: horizontal about ±1–2 cm (±0.4–0.8 in), vertical about ±3 cm (±1.2 in). This means that in most situations positions can be determined within a few centimeters. Moreover, by measuring continuously for a certain time and averaging the data, sub-1 cm accuracy can also be achieved. Measuring for about 30 seconds (around 60 measurements) and averaging produced an astonishing horizontal accuracy of 8 mm (8 mm (0.31 in)).

Such accuracy rivals first-class GNSS surveying instruments that use national control points. In comparisons measuring the same point with high-performance surveying equipment and a smartphone RTK device, differences in coordinates of 5 mm or less (5 mm (0.20 in) or less) have been reported. In other words, smartphone RTK surveying has been shown to offer accuracy comparable to professional equipment.

Of course, achieving high precision requires a clear view of the sky for stable satellite signal reception, but recent multi-GNSS support has increased the number of cases where positioning is possible even in mountainous areas or among high-rise buildings. Where single-frequency GPS was previously difficult, smartphone RTK using multiple satellite systems and frequency bands can often solve the problem. In practical terms, smartphone RTK demonstrates stable centimeter accuracy suitable for surveying even under challenging site conditions. Next, as a concrete example of a solution for utilizing this smartphone RTK technology on site, we introduce LRTK.

Simple surveying with LRTK

As described above, we have reviewed the technology and advantages of smartphone RTK surveying, and one notable concrete solution is LRTK. LRTK is an innovative product/service that turns a smartphone into a centimeter-class surveying instrument. A dedicated GNSS receiver small and light enough to fit in a pocket (approximately 125 g, thickness about 1–1.3 cm (0.4–0.5 in)) attaches to a smartphone, and by simply launching the LRTK app, anyone can easily start high-precision positioning.

For example, if there is a point to measure on site, place the LRTK receiver over that position and tap the button on the smartphone screen. Latitude, longitude, and elevation are recorded instantly and saved on the smartphone along with the point name, notes, and timestamp. Acquired data can be synced to the LRTK cloud with a single tap, and results can be checked in real time from an office PC. This enables field workers to conduct surveys alone and immediately share and report results.

LRTK is developed with the era of one device per person in mind, and its price range is set to be much more accessible than traditional surveying instruments. It is intuitive enough for non-specialist users, making it useful for a wide range of professionals such as civil engineering and construction workers and inspection staff in their daily tasks. LRTK supports not only iPhone but also some Android smartphones, flexibly adapting to on-site device environments.

Furthermore, LRTK is an all-in-one package that not only performs single-point positioning but also maximizes the benefits of smartphone RTK surveying with features such as point cloud scanning, AR functionality, and staking-out support. For example, point cloud data obtained with an iPhone’s LiDAR can be georeferenced so that 3D data is reflected on a map immediately after scanning. AR overlay of design models is performed seamlessly within the LRTK app, allowing confirmation of 3D models accurately aligned to the real world.

Thus, although LRTK describes its functionality as “simple surveying,” its accuracy and features rival full-scale surveying instruments. Surveying work that once required specialists has become more accessible, and the era has arrived in which anyone on site can use their smartphone to take advantage of centimeter-level positioning. If you want to experience “RTK surveying using only a smartphone,” consider trying simple surveying with LRTK.

FAQ

Q: What do I need to perform RTK surveying using only a smartphone? A: Basically, you need a smartphone, an RTK-capable small GNSS receiver, and a dedicated app. There are compatible models for both iPhone and Android, but to achieve high precision you attach a receiver that supports multi-GNSS and dual-frequency. For example, attaching a product like LRTK to your smartphone and launching the app lets you begin centimeter-level positioning immediately. You do not need to set up a special base station yourself; correction information is received via the smartphone.

Q: How is conventional GPS positioning different from RTK surveying? A: There are major differences in accuracy and mechanism. Conventional smartphone or car-navigation GPS positioning has errors of several meters because it cannot correct influences such as atmospheric and clock errors in satellite signals. RTK surveying, on the other hand, uses relative positioning with a base station to correct these error factors in real time. As a result, accuracy improves to the level of a few centimeters. RTK also markedly improves vertical (height) accuracy, enabling on-site height measurements similar to leveling.

Q: Can the accuracy of smartphone RTK surveying really be trusted? A: Yes. Under appropriate conditions, smartphone RTK surveying is highly reliable. Validation experiments have confirmed accuracy comparable to high-performance surveying instruments. Horizontal errors are generally within a few centimeters, and in some cases accuracy below 1 cm has been reported. However, to obtain high precision, it is desirable to measure in an open environment with good satellite reception. Choosing a location with few tall buildings or obstacles nearby and remaining still for a certain number of seconds during measurement will maximize accuracy.

Q: Is a communication environment required to perform RTK surveying with a smartphone? A: Basically, a mobile data connection is needed to receive correction information via the Internet. Smartphone RTK surveying acquires real-time data from national or municipal control station networks or private correction services over the Internet. Therefore, it is important that the smartphone can communicate during surveying. However, in Japan it is possible to receive corrections without Internet connection by using the QZSS CLAS signal. With a compatible receiver, positioning can continue in areas without mobile coverage, so you can choose the method according to the use case.

Q: In what situations can smartphone RTK surveying be used? A: It can be used widely from civil engineering and construction surveying to disaster-site investigations and agricultural positioning. For example, it is effective for quality control in land development, staking-out on construction sites, and progress measurement in road works. In disaster response, it helps quickly measure and record damage for restoration planning; for infrastructure inspection, it enables accurate measurement of structural displacements to understand long-term changes. In agriculture, it is useful where precise positioning is required, such as autonomous tractor control and field parceling. Because smartphone RTK surveying makes applications that previously required expensive equipment accessible, its range of use is expected to expand.

Q: Can non-specialists operate it? A: Yes. It is designed to be relatively easy to use without specialist qualifications or extensive experience. Many smartphone RTK solutions provide user-friendly apps, and you can perform surveys simply by following on-screen instructions. Difficult settings are automated, so even those unfamiliar with RTK can operate it. Basic surveying knowledge helps maximize utility, but these tools are designed for on-site personnel to use routinely, and case studies show that products like LRTK are being used by field staff for construction management and inspection tasks, improving productivity.

Q: How can surveyed data be output and used? A: Survey data collected on a smartphone can be easily utilized via the cloud. For example, with the LRTK app, measured point latitude, longitude, and elevation are automatically plotted on a cloud map and can be viewed immediately in a web browser. Data can be exported in CSV or DXF formats for use in CAD software or GIS systems. The app also automatically converts to Japan’s plane rectangular coordinate system or to the global geodetic system (WGS84) and can apply geoid height corrections, so you can obtain coordinates suitable for practical use on the spot.