Is LRTK Phone Accuracy Comparable to Professional Equipment? Results of Comparison with Conventional Survey Instruments

Table of Contents

• Introduction

• Comparison of Conventional Survey Instruments and Smartphone GPS Accuracy

• What is LRTK Phone

• Centimeter-Level Positioning Achieved by LRTK Phone

• Accuracy Comparison Between Professional Survey Instruments and LRTK Phone

• Changes and Effects on Site Work from LRTK Adoption

• Simple Survey Procedure Using LRTK

• FAQ

Introduction

Position information using a smartphone’s GPS is sufficiently practical for everyday map apps even with errors on the order of a few meters. However, civil engineering surveys 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, a GNSS device called the LRTK Phone, which attaches to a smartphone and easily achieves cm-precision positioning (cm level accuracy (half-inch accuracy)), has appeared and its accuracy and convenience have attracted attention. This article answers the question of whether LRTK Phone accuracy is comparable to professional equipment by explaining comparison results with conventional surveying instruments and the technical background in detail.

Comparison of Conventional Survey Instruments and Smartphone GPS Accuracy

First, let’s look at the differences between instruments used in conventional surveying and the GPS accuracy of a typical smartphone. With a typical smartphone’s built-in GPS receiver, positioning 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, ionospheric and tropospheric delays, and reflections (multipath) from buildings and the ground. Standalone GPS positioning accumulates these error sources, so meter-level deviations are unavoidable.

On the other hand, GNSS surveying instruments and total stations used in surveying and construction can determine positions with sub-centimeter accuracy. This large difference was achieved through satellite signal error corrections, high-quality receivers, and specialized surveying methods.

A representative method for conventional high-precision positioning is “RTK positioning (real-time kinematic)”. RTK uses two GNSS receivers simultaneously: a base station (fixed station) with a known position and a rover (mobile receiver) used on site. The base station calculates error information and sends it to the rover in real time; the rover applies corrections to its positioning, canceling out errors that would otherwise be several meters down to a few centimeters. This method enabled centimeter-level accuracy in GPS surveying.

However, conventional RTK surveying had several challenges. First, the site required bringing in high-performance GNSS receivers and antennas, tripods, large-capacity batteries, and communication devices (radio modems), and setup and operation demanded expertise and effort. Also, reliable base stations were essential for error correction; if you set up your own base station you needed to install and maintain antennas at known points. Accuracy degrades with distance from the base station, so stable positioning over wide areas required placing base stations every few kilometers, and there were other constraints. In addition, conventional high-precision surveying equipment is very expensive, making adoption difficult from a budget perspective.

What is LRTK Phone

Emerging against this background is the next-generation high-precision positioning solution called LRTK. LRTK Phone was developed as a device that achieves centimeter-level positioning simply by attaching a small high-precision GNSS receiver (device) to a smartphone. It is designed so that anyone can obtain high-precision position information and point cloud data with simple operations using a dedicated app that pairs with the phone.

LRTK Phone can also integrate with a smartphone’s built-in LiDAR sensor and photographic functions to rapidly scan a site and generate 3D point cloud data. It can easily measure in confined spaces, on the undersides of bridges, or under trees—places that are difficult for drones or large laser scanners to access—and a major feature is that it can obtain highly accurate point clouds without installing reference targets in advance.

The name LRTK represents an evolution of traditional RTK. LRTK addresses the RTK challenges of “large equipment,” “need for expertise,” and “dependence on communication environments,” enabling centimeter accuracy “by one person, anywhere, easily.” The LRTK Phone device is a palm-sized unit weighing only about 150g, with battery and antenna integrated for easy portability. It connects to a smartphone via Bluetooth or an attachment and can start positioning without complicated device setup. In short, LRTK Phone enables operations that previously relied on specialized surveyors and expensive equipment to be performed with a smartphone-like experience.

Centimeter-Level Positioning Achieved by LRTK Phone

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

• Use of QZSS (Michibiki) CLAS: LRTK Phone supports the centimeter-level augmentation service (CLAS) provided by Japan’s quasi-zenith satellite system “Michibiki.” This allows reception of high-precision correction information directly from satellites even in mountainous areas where cellular signals are weak. Because Michibiki satellites are positioned over Japan, signals are relatively easy to receive in valleys and dense urban areas; cases have been reported where LRTK was able to obtain positioning in environments where conventional GPS equipment would produce meter-level errors.

• Error reduction with dual-frequency GNSS: The GNSS module in LRTK Phone receives multiple frequency bands such as L1 and L5. By receiving different frequency signals from the same satellite and using their phase differences to cancel out errors such as ionospheric delays, it can obtain centimeter-level fixed solutions (Fix) more quickly and stably than single-frequency positioning. This is particularly effective for maintaining vertical (height) accuracy, enabling high-precision positioning within a short time on site.

• Multi-GNSS and fusion of high-precision correction data: LRTK Phone supports not only GPS but also GLONASS, Galileo, BeiDou, and Michibiki, i.e., multi-GNSS. Constant reception from many satellites improves satellite geometry and makes 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 from networks such as the Geospatial Information Authority’s reference station network in real time, thoroughly removing error factors affecting satellite positioning. By combining CLAS augmentation signals from satellites and correction data via the Internet, LRTK can stably maintain centimeter accuracy across Japan.

Through this combination of cutting-edge technologies, LRTK Phone continuously achieves astonishing positioning accuracy of approximately ±1 cm horizontally and ±2–3 cm vertically. Concretely, this corresponds to about ±1 cm (±0.4 in) horizontally and ±2–3 cm (±0.8–1.2 in) vertically, a level comparable to first-class high-performance GNSS surveying instruments, and revolutionary in that this accuracy is obtainable from a pocket-sized device.

Accuracy Comparison Between Professional Survey Instruments and LRTK Phone

So how does LRTK Phone actually compare with conventional professional surveying instruments? Here are the results of internal comparison tests. For the same point, positioning was performed with an LRTK Phone and a professional class-1 GNSS receiver, and the average position values obtained over several tens of seconds were compared. The reported difference between the two was less than 5 mm (0.20 in). A mere few millimeters of error effectively means the measurement results of both devices are nearly identical. In another mountain test, where conventional instruments produced unstable satellite signals and positioning errors of 5 m or more (16.4 ft or more), LRTK Phone was able to stably achieve centimeter-level accuracy. From these results, LRTK Phone’s reliability and accuracy performance can be said to have reached a level comparable to professional surveying instruments.

Furthermore, the LRTK Phone’s catalog specification lists positioning accuracy as horizontal ±1 cm and vertical ±2 cm (RMS), indicating errors within a few centimeters. It offers specifications equivalent to conventional high-precision GNSS receivers while delivering overwhelming portability and ease of use, representing a significant advantage of the LRTK Phone.

Changes and Effects on Site Work from LRTK Adoption

The benefits LRTK Phone brings are not limited to high accuracy. Reports indicate it also provides unprecedented advantages in work efficiency and operations on site. At one construction site, site supervisors who previously had to wait for an external survey team to perform as-built confirmation measurements were able to perform those surveys immediately themselves using 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 now be completed by one person with LRTK, alleviating labor shortages and reducing personnel costs. Thus, LRTK Phone adoption enables dramatic efficiency gains and labor savings in surveying tasks, greatly contributing to on-site productivity improvement.

LRTK use is also spreading beyond construction. For example, local governments have used LRTK Phone to rapidly grasp disaster site conditions. At damaged locations, personnel used LRTK to record and share accurate coordinates with photos, helping to speed up recovery responses. In buried infrastructure maintenance, LRTK’s stake-driving guidance function (guidance when driving stakes to specified coordinates) has been used to reproduce and confirm the exact positions of buried pipes. Centimeter-level positioning that previously required expensive surveying equipment can now be obtained at low cost and with ease thanks to LRTK, so its benefits are beginning to penetrate sites that previously did not utilize high-precision GNSS.

Simple Survey Procedure Using LRTK

Finally, imagine how simple surveying with LRTK Phone can be by walking through a workflow. For example, consider driving stakes at reference points specified in design drawings. Traditionally a surveyor would carefully determine coordinates with a total station to drive stakes, but with LRTK Phone this can be handled by one person in a short time.

First, call up the target point coordinates pre-set in the smartphone’s LRTK dedicated app, turn the LRTK device on, and connect it to the smartphone. Outdoors, as satellites are acquired, the positioning mode will change to “Fix (cm precision (cm level accuracy (half-inch accuracy))))” in several tens of seconds, indicating high-precision positioning is ready. The app displays the bearing and distance to the target in real time, so move toward the point using that guidance. You approach much like navigating to a destination in a smartphone map app; the remaining error decreases from tens of centimeters to several centimeters, and when the display shows almost 0 cm error that location is the exact spot to drive the stake. Drive the stake there and establish the reference point.

Next, measure other points relative to that reference. Bring the LRTK device to the point to be measured and tap the “Position” button in the 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 the smartphone as needed, high-precision latitude/longitude and orientation information of the photo location are automatically tagged, making it easy to correlate photos and positioning data later. The acquired survey data can also be synchronized to the cloud from the site. By the time you return to the office, you can immediately view each point’s layout on a desktop cloud service in map or 3D view, and perform distance or area measurements.

Surveying with LRTK Phone is intuitive and speedy. Tasks that formerly required expensive, specialized equipment can now be performed by anyone with a smartphone. LRTK Phone is a reliable partner that fully leverages satellite positioning centimeter-level accuracy on site, enabling efficient and precise surveying. As a modern solution compatible with the Ministry of Land, Infrastructure, Transport and Tourism’s i-Construction (ICT construction), it is expected to become increasingly active on many sites.

FAQ

Q1: What is the positioning accuracy of LRTK Phone?

A1: LRTK Phone has positioning accuracy of approximately ±1 cm horizontally and ±2–3 cm vertically (RMS). Verification tests have confirmed nearly equivalent accuracy to professional high-performance GNSS equipment, with differences on the order of a few millimeters.

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

A2: A typical smartphone GPS is standalone and has meter-level errors, but LRTK Phone corrects errors using RTK principles and the latest technologies. By utilizing augmentation signals from Michibiki, multiple frequencies and multiple satellites, and integrating high-precision correction data, it systematically removes error sources to achieve centimeter-level accuracy.

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

A3: No. LRTK Phone itself contains a high-precision GNSS receiver and can directly receive Michibiki’s augmentation signals (CLAS), so there is no need to set up a dedicated base station on site. It can also receive correction information from public reference station networks via the Internet, but Michibiki coverage provides reassurance even where cellular signals are unavailable.

Q4: Can someone without surveying experience operate it?

A4: Yes. LRTK Phone emphasizes simple operability so anyone at the site can use it. Attach the device to a smartphone, launch the app, and follow the on-screen instructions to start positioning. The UI is intuitive—press a button at the point you want to measure to record coordinates—so no specialized surveying knowledge is required.

Q5: In what situations is LRTK Phone useful?

A5: It is useful in civil engineering tasks such as as-built measurements and establishment of reference points at construction sites, land development, and agricultural land surveys, as well as disaster site documentation and infrastructure maintenance. It is suitable for small- to medium-scale surveys that do not warrant deploying a drone or laser scanner and for positioning in confined or shaded locations, making it a responsive tool for “quick measurements.”

Q6: How will LRTK contribute to future surveying sites?

A6: The LRTK series has the potential to dramatically improve productivity in surveying and construction management by making high-precision positioning easily portable to the site. With labor shortages, the ability for one person to perform accurate surveys enables labor savings. It also aligns with construction DX trends such as i-Construction, and is expected to become an increasingly powerful partner at many 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 is basically compatible with modern smartphones. However, to fully utilize point cloud scanning with a smartphone’s built-in LiDAR sensor, using supported high-performance models will yield better results.

Q8: Can survey data be managed and shared?

A8: Yes, LRTK offers a dedicated cloud service. Points, traces, photos, and point cloud data acquired on site can be synchronized to the cloud with a single tap from the smartphone. You can view data on maps and 3D models in the cloud, measure distances and areas, and easily share data with stakeholders, streamlining reporting and coordination.