Table of Contents

• Introduction

• Comparison of Conventional Surveying Instruments and Smartphone GPS Accuracy

• What Is LRTK Phone?

• Centimeter-Level Positioning Achieved by LRTK Phone

• Accuracy Comparison Between Professional Surveying Equipment and LRTK Phone

• Changes and Benefits on Site from Introducing LRTK

• Procedure for Simple Surveying with LRTK

• FAQ

Introduction

Position information from a smartphone’s GPS is perfectly practical for everyday map apps even with errors on the order of a few meters. However, civil engineering surveying and construction sites require centimeter-level accuracy. Until now, achieving centimeter accuracy required expensive, large-scale professional surveying equipment (GNSS receivers, total stations, etc.). Recently, however, a GNSS device called the LRTK Phone has appeared: a small terminal that attaches to a smartphone and easily achieves cm-accuracy positioning (cm level accuracy (half-inch accuracy)). Its accuracy and convenience have attracted attention. This article answers the question of whether the LRTK Phone’s accuracy is comparable to professional equipment by explaining comparison results with conventional surveying instruments and the technical background in detail.

Comparison of Conventional Surveying Instruments and Smartphone GPS Accuracy

First, let’s look at the difference between instruments used in conventional surveying and the GPS accuracy of a typical smartphone. When positioning with a typical smartphone’s built-in GPS receiver, errors of about 5–10 m (16.4–32.8 ft) are common. This is because satellite signals are disturbed by multiple factors before reaching the ground, such as orbit and clock errors, delays in the ionosphere and troposphere, and reflections (multipath) from buildings and the ground. With single-receiver GPS positioning, these error sources accumulate and several-meter offsets are unavoidable.

On the other hand, GNSS surveying instruments and total stations used in surveying and construction can determine positions with accuracies of a few centimeters or better. This large difference has traditionally been achieved by error corrections to satellite signals, high-quality receivers, and dedicated surveying methods.

A representative method for conventional high-precision positioning is RTK (Real-Time Kinematic). RTK uses two GNSS receivers simultaneously: a base station with a known position and a rover that measures while moving on site. The base station computes error information and sends it to the rover in real time; the rover applies corrections to its positioning results to eliminate errors that would otherwise be several meters, reducing them to a few centimeters. This technique made centimeter-level accuracy possible in GPS surveying.

However, conventional RTK surveying had several challenges. High-performance GNSS receivers and antennas, tripods, high-capacity batteries, and communications equipment (radio modems) all had to be brought to the site, and setup and operation required expertise and effort. Reliable base stations are essential for error correction; if you install your own base station you must set up and manage antennas at known points. Accuracy also degrades as you move farther from the base station, so achieving stable positioning over wide areas could require base stations every few km. In addition, conventional high-precision surveying equipment is very expensive, creating a high budget barrier to adoption.

What Is LRTK Phone?

Amid these developments came the next-generation high-precision positioning solution called LRTK. The LRTK Phone was developed as a device that, by simply attaching a small high-precision GNSS receiver (terminal) to a smartphone, makes centimeter-level positioning easy to achieve. Designed to work with a dedicated smartphone app, it allows anyone to obtain high-precision position information and point-cloud data through simple operation.

The LRTK Phone can also integrate with a smartphone’s built-in LiDAR sensor and photographic functions to rapidly scan a site and generate three-dimensional point-cloud data. It can easily measure narrow spaces, the undersides of bridges, and areas under trees—places that drones or large laser scanners find difficult to access—and a major feature is its ability to produce high-accuracy point clouds without pre-installing control points (targets).

The name LRTK represents an evolution of traditional RTK. LRTK addresses RTK’s issues—large equipment, the need for expertise, and reliance on communications—so that centimeter accuracy can be achieved “by one person, anywhere, easily.” The LRTK Phone terminal is palm-sized at about 150 g, with the battery and antenna integrated for easy carrying on site. It connects to a smartphone via Bluetooth or an attachment and begins positioning without complicated equipment setup. In short, LRTK Phone brings tasks that once required specialist surveyors and expensive equipment into the realm of smartphone-like convenience.

Centimeter-Level Positioning Achieved by LRTK Phone

Why can a palm-sized LRTK Phone deliver accuracy comparable to professional equipment? The answer lies in the use of the latest satellite technologies and positioning methods. Here are the main reasons LRTK Phone can stably maintain cm-level positioning accuracy.

• Use of QZSS Michibiki’s CLAS: LRTK Phone supports CLAS, the centimeter-level positioning augmentation service provided by Japan’s Quasi-Zenith Satellite System (QZSS, Michibiki). This lets the device receive high-precision correction information directly from satellites even in mountainous areas where cellular signals are weak. Because Michibiki satellites are always positioned over Japan, they can capture signals even in valleys and dense high-rise areas, enabling positioning in environments where conventional GPS devices produce errors of several meters.

• Dual-frequency GNSS for error reduction: The GNSS module in LRTK Phone receives multiple frequency bands such as L1 and L5. By obtaining signals at different frequencies from the same satellite and using their phase differences to cancel ionospheric delays and other errors, it achieves cm-level fixed solutions faster and more stably than single-frequency positioning. This is especially effective for maintaining vertical (height) accuracy, enabling high-precision positioning on site in a short time.

• Multi-GNSS and fusion with high-precision correction data: LRTK Phone supports not only GPS but also GLONASS, Galileo, BeiDou, and the aforementioned Michibiki—i.e., multiple GNSS systems. Constant access to signals from many satellites improves satellite geometry, making it easier to secure the necessary number of satellites even in urban or mountainous areas. It also ingests precise orbit, clock, and atmospheric correction data distributed by networks such as the Geospatial Information Authority of Japan’s Continuously Operating Reference Stations, removing error factors affecting satellite positioning. By combining CLAS augmentation signals from satellites with correction data over the Internet, LRTK can stably maintain centimeter accuracy across Japan.

Through this combination of advanced technologies, LRTK Phone consistently achieves astonishing positioning accuracy of about ±1 cm horizontally and ±2–3 cm vertically (±0.4 in horizontally and ±0.8–1.2 in vertically). This level matches that of high-performance grade-1 GNSS surveying instruments and is revolutionary in that it can be obtained from a pocket-sized device.

Accuracy Comparison Between Professional Surveying Equipment and LRTK Phone

So how does LRTK Phone actually compare to conventional professional surveying instruments? Here are the results of comparison tests conducted in-house. For the same point, positioning was performed with an LRTK Phone and a professional grade-1 GNSS receiver; the averaged position values obtained over several tens of seconds were compared, and the difference between the two was reported to be under 5 mm (0.20 in). A discrepancy of only a few millimeters effectively means the measurements from both devices are nearly identical. In another test in a mountainous area where conventional equipment experienced unstable satellite signals and errors over 5 m (16.4 ft), the LRTK Phone was still able to position consistently at centimeter-level accuracy. From these results, the reliability and accuracy performance of LRTK Phone can be said to reach a level comparable to professional surveying equipment.

Furthermore, the LRTK Phone’s catalog specification lists positioning accuracy of horizontal ±1 cm and vertical ±2 cm (RMS), indicating errors within a few centimeters. While offering specifications equivalent to conventional high-precision GNSS receivers, LRTK Phone provides overwhelming portability and ease of operation—major advantages.

Changes and Benefits on Site from Introducing LRTK

The benefits of LRTK Phone go beyond high accuracy. Actual on-site use has reported unprecedented advantages in work efficiency and operations. At one construction site, what had previously required waiting for an external surveying team to perform as-built checks could now be done instantly by the site supervisor using just an LRTK Phone and a smartphone. As a result, waiting time for surveys was greatly reduced and construction progress management became smoother. Tasks that previously required two or more people can be completed by one person with LRTK, helping mitigate labor shortages and reduce personnel costs. In this way, introducing LRTK Phone enables dramatic efficiency gains and labor savings in surveying work, significantly improving on-site productivity.

LRTK’s applications are also expanding beyond construction. For example, local governments have used LRTK Phone for rapid situation assessment at disaster sites. By recording and sharing accurate position coordinates with photos taken using LRTK, recovery responses were expedited. In underground infrastructure maintenance, LRTK’s stake-driving guidance function (guidance for driving stakes at specified coordinates) has been used to reproduce and confirm the precise positions of buried pipes. Because centimeter-precision positioning, once limited to expensive surveying equipment, is now available at low cost and with ease thanks to LRTK, its benefits are beginning to penetrate sites that previously did not utilize high-precision GNSS.

Procedure for Simple Surveying with LRTK

Finally, let’s imagine how easy surveying with LRTK Phone is. For example, consider installing a stake at a reference point specified in design drawings. Traditionally, a surveyor using a total station would carefully determine coordinates and drive the stake; with an LRTK Phone, one person can handle this in a short time.

First, call up the target point coordinates preconfigured in the LRTK app on your smartphone, power on the LRTK terminal, and connect it to the phone. Outdoors, as satellites are acquired, the positioning mode will switch to “Fix (cm accuracy)” within several tens of seconds, preparing for high-precision positioning. The app displays the bearing and distance to the target point in real time, so you navigate the site guided by that display. Approaching the point feels like using a smartphone map app: the remaining error shrinks from several tens of centimeters to several centimeters… until the display shows virtually 0 cm error—that is the precise spot to drive the stake. Install the stake there to establish the reference point.

Next, measure other points relative to that reference. Bring the LRTK terminal to the point you want to measure and tap the “Position” button in the smartphone app; the coordinates of that point are recorded with centimeter accuracy. You can enter point names and notes and save them. If you take photos with your smartphone, high-precision latitude, longitude, and orientation metadata are automatically tagged to the images, making it easy to match photos and positioning data later. The collected survey data can also be synced to the cloud from the site. By the time you return to the office, you can view the points on maps or 3D views in a cloud service on your PC, measure distances and areas, and use the data immediately.

Surveying with LRTK Phone is intuitive and speedy. Tasks that once required expensive, specialized equipment can now be performed by anyone with a smartphone in hand. LRTK Phone is a reliable partner that fully leverages centimeter-level satellite positioning on site to enable efficient and accurate surveying. As a cutting-edge solution compatible with the Ministry of Land, Infrastructure, Transport and Tourism’s i-Construction (ICT construction) initiatives, LRTK is expected to be increasingly useful on many sites going forward.

FAQ

Q1: How accurate is LRTK Phone positioning?

A1: LRTK Phone achieves positioning accuracy of about ±1 cm horizontally and ±2–3 cm vertically (RMS). In practical verification tests, accuracy was found to be nearly equivalent to professional high-performance GNSS equipment, with differences on the order of a few millimeters (under 5 mm (0.20 in)).

Q2: Why is it so much more accurate than a smartphone’s GPS?

A2: A typical smartphone GPS performs single-receiver positioning and therefore has errors of several meters. LRTK Phone uses RTK principles and the latest technologies to correct errors. By leveraging augmentation signals from the Michibiki satellites, multiple frequencies and multiple satellite systems, and integrating high-precision correction data, it eliminates error sources and achieves centimeter-level accuracy.

Q3: Does using LRTK Phone require special equipment or base stations?

A3: No. The LRTK Phone itself contains a high-precision GNSS receiver and can directly receive Michibiki’s augmentation signals (CLAS), so you do not need to install a dedicated base station on site. While it can also receive correction data from public reference station networks via the Internet, Michibiki coverage provides assurance even where cellular signals are unavailable.

Q4: Can people without surveying experience use it?

A4: Yes. LRTK Phone emphasizes simple operation so anyone on site can use it. Attach the terminal to your smartphone, launch the app, and follow the on-screen instructions to start positioning. The UI is intuitive—just press a button at the point you want to record and the coordinates are saved—so it can be used without specialized surveying knowledge.

Q5: In what situations is LRTK Phone useful?

A5: It is useful for as-built measurements and reference point installation at construction sites, land development and agricultural surveys in civil engineering, disaster site situation recording, and infrastructure maintenance. It is well suited for small- to medium-scale surveys that don’t justify deploying a drone or laser scanner, and for positioning in narrow or shaded areas. It serves as a quick-response tool for “just want to measure this” needs.

Q6: How will LRTK contribute to future surveying sites?

A6: By bringing high-precision positioning easily to the field, the LRTK series has the potential to dramatically improve productivity in surveying and construction management. With labor shortages, the ability for a single person to perform accurate surveys reduces labor. It also aligns with construction DX initiatives like i-Construction, and is expected to become an increasingly powerful partner on many future sites.

Q7: Which smartphones are supported?

A7: LRTK Phone connects to smartphones via Bluetooth, etc. The dedicated app supports both iOS (iPhone/iPad) and Android, so it can generally be used with modern smartphones. To make the most of point-cloud scanning using the phone’s built-in LiDAR sensor, using a compatible high-performance model will yield better results.

Q8: Can survey data be managed and shared?

A8: Yes. LRTK provides a dedicated cloud service. Points, tracks, photos, and point-cloud data collected on site can be synced to the cloud from the smartphone with a single tap. In the cloud you can view data alongside maps and 3D models, measure distances and areas, and stakeholders can quickly review results from the office, improving reporting and collaboration efficiency.