New Norms for RTK Positioning｜Subscription-based cm-level Accuracy Service Achievable with iPhone

Today, satellite positioning technologies such as GPS have advanced significantly. Among them, a new norm is emerging particularly for high-precision RTK positioning. RTK stands for Real Time Kinematic, a satellite positioning method that realizes centimeter-level accuracy by applying error correction information from a reference station. Initially, implementing RTK positioning on site required expensive and large-scale resources, but today, by combining smartphones (especially the iPhone) with subscription-based services, those burdens can be overcome, enabling centimeter-level positioning in everyday environments.

This article explains the overview of RTK positioning, the characteristics of subscription-based RTK services, and their compatibility with iPhones and smartphones in detail. It also considers benefits such as operational flexibility, on-site efficiency improvements, and labor reduction resulting from adoption, as well as the low adoption barrier and advantages of continuous support. Furthermore, we explore how subscription models change RTK adoption decisions and on-site utilization, and finally introduce a simple surveying method using LRTK.

Table of Contents

• What is RTK positioning?

• What is a subscription-based RTK positioning service?

• Centimeter-level positioning achievable with iPhone

• Benefits of subscription-based RTK services

• Differences from traditional RTK operations

• How RTK utilization changes with subscription models

• Simple surveying using LRTK

• Frequently Asked Questions (FAQ)

What is RTK positioning?

RTK positioning is a high-precision GPS/GNSS technique that reduces errors in real time to the order of several centimeters. Standalone positioning using a typical smartphone’s GPS (GNSS) is convenient but incurs errors of about 5–10 m. In contrast, RTK positioning can reduce errors to roughly 1/100 (about 5 cm (2.0 in)). In fact, network-type RTK services widely used in the field report horizontal errors on the order of 3–4 cm (1.2–1.6 in).

The key to RTK’s high accuracy is using two receivers simultaneously: a reference station (a fixed station with known coordinates) and a rover (a receiver mounted on and moved to the point to be measured). The reference station calculates the instantaneous positioning error by comparing its known precise position with the satellite-derived positioning results, and transmits the error information to the rover in real time. The rover applies that error correction to its own positioning results to obtain highly accurate coordinates. In short, “using two receivers instead of one allows error cancellation, improving accuracy.”

Thanks to RTK technology, centimeter-level accuracy that was difficult with conventional GPS can now be obtained in real time, so RTK is being adopted across many fields—not only civil surveying and construction sites but also agriculture and autonomous drone navigation. It is attracting attention as a key to improving work efficiency and safety.

However, performing RTK positioning on site traditionally required preparing two dedicated high-performance GNSS receivers—one for the reference station and one for the rover—and having them communicate via radio or network. The equipment was large-scale, including tripods, poles, batteries, and controller terminals, making transport to sites cumbersome. Moreover, obtaining high-precision positioning required long wait times for satellite acquisition and initial error convergence (FIX), which could sometimes take several minutes. Equipment prices were also very high, often requiring investments on the order of several million yen or subscription fees for positioning services.

Into this context, new RTK solutions utilizing smartphones have emerged.

What is a subscription-based RTK positioning service?

To use RTK positioning, you normally need to set up your own base station (reference station) or connect to an existing network of reference points to obtain correction data. In Japan today, the Geospatial Information Authority’s Continuously Operating Reference Stations (CORS) and private correction data distribution services are available; by subscribing to these, you can perform centimeter-level positioning without preparing your own reference station.

Providing such high-precision positioning data as a service that can be used as needed is the essence of a subscription-based RTK positioning service. Users pay monthly or annual fees to rent a centimeter-level positioning environment, receiving correction information and software support from the service instead of purchasing and maintaining expensive equipment. For example, by subscribing to a network-type RTK correction data distribution service and receiving corrections through a smartphone app, you can achieve high-precision positioning on site.

Recently, services have appeared that combine smartphones with ultra-compact RTK-GNSS receivers, allowing anyone to easily use centimeter-level positioning via subscription. This enables flexible operation even at sites without specialized surveying equipment, allowing high-precision positioning for only the period needed.

Centimeter-level positioning achievable with iPhone

The advent of smartphones (especially iPhone) has made RTK positioning even more accessible. The key is the ultra-compact RTK-GNSS receiver that attaches externally to the smartphone. Standalone smartphone GPS makes high-precision RTK difficult, but combining a high-performance antenna and multi-frequency positioning chip in an external receiver makes it possible.

For example, an RTK receiver designed to attach to an iPhone can weigh just over 100 grams and be about 1 cm (0.4 in) thick, fitting in a pocket. It has a built-in battery and connects to the phone via Bluetooth, so no cables are required. You can attach it to your phone with one touch to start positioning immediately, and remove it when not in use so your phone’s mobility is not compromised.

Smartphone RTK is highly mobile and eliminates the traditional hassle of unloading heavy equipment from a vehicle and mounting it on a tripod. Each person can carry a high-precision positioning tool on their own phone—one device per person—so positioning can be performed instantly when needed. Small-scale surveys or quick height checks can be handled with smartphone-like ease, significantly reducing waiting and setup time.

Moreover, combining iPhone sensors and apps enables diverse applications. If you record RTK positional data while photographing a site or scanning with the smartphone’s LiDAR, you can attach high-precision location information to photos or easily generate 3D point cloud data with absolute coordinates. Surveying and measurement can be completed with just an iPhone without expensive dedicated 3D scanners. Advanced uses are also possible, such as combining AR to display virtual markers at designed coordinates during staking or layout work.

Some Japan-based solutions support smartphone RTK receivers compatible with the QZSS “Michibiki” centimeter-class augmentation service (CLAS). This allows continued high-precision positioning by obtaining correction information directly from satellites even in areas without cellular coverage, such as mountainous regions. Scenes where high precision was previously difficult due to lack of communication can now be addressed with smartphone RTK.

By combining smartphones and RTK technology, RTK positioning now offers affordability, lightness, simplicity, and speed, revolutionizing on-site surveying styles.

Benefits of subscription-based RTK services

Introducing RTK positioning via a subscription model brings the following benefits to the field:

• Flexibility of operation: Because you can use the service only when needed and for the required period, you can flexibly secure high-precision positioning resources according to project scale and duration. It is easy to add or cancel devices and user accounts, eliminating the concern of idle assets after purchasing equipment. Additionally, as the service provider handles new technologies and features, you don’t need to replace equipment in-house and can always use the latest environment.

• Improved on-site efficiency: Subscription services enable all workers to use their own high-precision positioning tools simultaneously. Compared with the traditional approach of sharing a single device, this eliminates waiting time and personnel juggling, allowing positioning tasks to progress in parallel. Preparation time to start positioning on site is also drastically reduced, decreasing overall project delays due to waiting for surveys. As a result, project schedules shorten and productivity improves.

• Promotion of labor reduction: Easier access to high-precision positioning increases opportunities to perform surveying tasks alone that previously required two people. For example, layout work that used to rely on a total station can be handled by one person carrying a GNSS rover (smartphone + RTK receiver), enabling efficient surveying even at sites with labor shortages. Even at sites without a dedicated surveyor, on-site staff can use subscription services to perform necessary positioning, making effective use of personnel resources.

• Low adoption barrier: Subscription models greatly reduce initial investment, lowering the barrier to adopting high-precision positioning. Without seeking approvals for expensive equipment purchases, small sites or short-term projects can consider adoption easily. Intuitive smartphone app interfaces make handling possible even for staff with limited expertise, reducing training and proficiency costs.

• Continuous support and updates: Receiving technical support and system updates from the service provider is another major advantage. Software is kept up to date, and new features and improvements become available automatically. Should any trouble occur, providers can offer remote support or quickly fix bugs, minimizing downtime compared to managing equipment in-house. The reassurance of always being able to use an optimized environment for high-precision positioning is a unique benefit of subscription services.

Differences from traditional RTK operations

RTK via subscription-based services plus smartphones differs from traditional RTK operation in several ways. The main differences are as follows:

• Equipment and portability: Traditionally, bringing a full set of bulky equipment—tripods, large antennas, dedicated terminals—was necessary. In contrast, with a smartphone plus an ultra-compact receiver, the workflow is completed with a pocket-sized device and a smartphone, making transportation easy.

• Initial cost and cost structure: Traditional methods required substantial funds for equipment purchases, and the equipment had to be depreciated as assets. Subscription models allow you to start using the service with monthly fees only, reducing initial costs. Subscription fees are easier to expense, and contract periods can be adjusted as needed, offering flexible cost management.

• Operation and personnel: Conventional RTK surveying often required specialist equipment operators and assistants, and experienced personnel were needed for equipment setup and calibration. With subscription-based smartphone RTK, app-guided setup simplifies configuration and positioning can be done with one tap. As a result, on-site staff can perform positioning tasks without specialized technicians, increasing flexibility in workforce composition.

• Constraints of positioning environment: Traditionally, high precision was only achievable within the radio range of a base station, and precision degraded outside communication coverage. Smartphone RTK plus subscription services use network-based correction via cellular networks to enable wide-area positioning. Additionally, solutions supporting satellite-based augmentation (like CLAS) can maintain positioning precision even outside cellular coverage.

• Data utilization and integration: With traditional equipment, survey data often had to be transferred to a PC for processing later. Smartphone RTK can send positioning data to the cloud and share it on the spot. Real-time sharing between the field and the office allows immediate confirmation and additional measurements, smoothing workflows. Easy digital data integration is another strength of the new operational model.

How does RTK utilization change with subscription models?

The advent of subscription-based RTK services is significantly changing the use cases for high-precision positioning. Previously, because expensive surveying equipment and specialist technicians were required, RTK was often limited to dedicated surveying companies or large-scale projects. But as subscription services become widespread, a broad range of users—from major construction firms to small contractors and individual technicians—have begun incorporating centimeter-precision positioning into routine work.

Decision-making about adoption is also changing. Cases that were previously dismissed as “high precision is needed but costs don’t justify it” can now trial subscription services easily. Trial periods like “use it for a few months to evaluate the benefits” are easier to conduct, accelerating bottom-up adoption of high-precision technology from the field.

On-site work itself evolves. For example, construction managers can use an iPhone to perform ad hoc surveys to check as-built conditions or installation positions on the spot. Measurements that used to require a specialist surveying team can now be done immediately when needed, speeding decision-making and enabling earlier detection and correction of errors. Daily access to high-precision positioning is expected to raise overall construction quality control levels.

In other words, subscription-based RTK is turning “centimeter-level positioning” from a special event into a routine tool. Technology that was once exclusive to surveying specialists is becoming a common platform accessible to everyone on site, accelerating digital transformation (DX) of workflows and enabling safer, more efficient site operations.

Simple surveying using LRTK

Finally, as a concrete example of a subscription-based RTK service introduced so far, we describe simple surveying using our LRTK. LRTK is a subscription-based centimeter-level positioning service used by attaching a small RTK receiver to an iPhone/iPad, dramatically simplifying surveying tasks on civil engineering sites.

For example, baseline surveys that previously required heavy tripods and long hours with a total station can, with LRTK, begin RTK positioning immediately on arrival and obtain cm-level coordinates in a short time. Simple surveys such as height checks and as-built measurements can be completed quickly with just a smartphone. Positioning data can be shared to the cloud in real time, allowing office staff to instantly review and utilize information collected on site, enhancing convenience.

By leveraging simple surveying with LRTK, on-site surveying barriers are greatly reduced while achieving both efficiency and accuracy. Experience the new norm that subscription-based RTK positioning services bring.

Frequently Asked Questions (FAQ)

Q1. What is a subscription-based RTK positioning service? A1. It is a service that allows centimeter-level positioning by receiving correction information over a network without preparing a dedicated reference station. Provided in a subscription format such as a monthly fee, users essentially rent a high-precision positioning environment. It includes distribution of high-precision GNSS data and support via dedicated apps, enabling cm-level accuracy without purchasing expensive equipment.

Q2. Can an iPhone really achieve centimeter-level positioning by itself? A2. Standalone iPhone GPS makes this difficult, but by attaching a dedicated small RTK receiver and using correction data, it becomes possible. Recent iPhones support high-performance GNSS and handle multiple frequencies such as L1/L5. Combining an RTK receiver and network corrections can achieve planar positioning accuracy on the order of 2–3 cm (0.8–1.2 in). In practice, iPhone + external receiver setups have measured positions on survey sites with errors of a few centimeters (a few in).

Q3. Can it be used without specialized knowledge? A3. Yes, it is relatively easy to use. You only need to follow guidance on a smartphone app, so deep knowledge of GNSS or geodesy is not practically required. A basic understanding of surveying procedures and coordinate systems is desirable, but service providers typically offer tutorials and support, so beginners can start with confidence.

Q4. What is required to start using it? A4. Fundamentally, you need an RTK-GNSS receiver compatible with centimeter-level services, a smartphone (e.g., an iPhone), and a communications environment to receive correction information. Specifically, you attach a dedicated ultra-compact GNSS receiver to your phone and install a positioning app. After subscribing to the service and enabling network reception of correction data (e.g., NTRIP), you are ready. In some cases, simple tools like a monopod or pole to place the device on the survey point can make work easier.

Q5. What kinds of sites and applications can it be used for? A5. It is widely applicable to surveying scenes in construction and civil engineering—for example, baseline surveys, as-built surveys, as-built verification (post-construction shape checks), and layout works such as staking and piling. Tasks that used to be time-consuming can now measure many points in a short time with RTK positioning. Combining iPhone LiDAR and photography can also acquire 3D point cloud data for record and inspection. Beyond civil engineering, it is used in agriculture for automatic tractor guidance and in drone surveying for geotagging in photogrammetry—any application requiring centimeter-level accuracy.

Q6. Can it be used outside cellular coverage? A6. If correction data are received via the internet, cellular coverage is generally required. However, in Japan some services support satellite-based augmentation like QZSS’s CLAS, enabling direct reception of augmentation signals from satellites even outside cellular coverage. For example, LRTK includes a CLAS-compatible mode, allowing maintenance of centimeter-level positioning in mountainous areas or disaster sites where cellular networks are unavailable.

Q7. What is the positioning accuracy and how long does the initial FIX take? A7. Accuracy is typically about ±2–3 cm (±0.8–1.2 in) horizontally and ±3–5 cm (±1.2–2.0 in) vertically (depending on satellite visibility and the environment). Time to convergence (FIX) has also been dramatically reduced, and with modern multi-frequency GNSS it can start high-precision positioning in a few seconds to tens of seconds. While in the past waits of several minutes were not uncommon, with good satellite signals you can now start positioning tasks virtually without noticeable delay.

Q8. What is LRTK? A8. LRTK is a subscription-based RTK positioning service provided by Reflexia, a startup originating from Tokyo Institute of Technology. It consists of a small GNSS receiver device that can be attached to an iPhone/iPad and a dedicated app, turning a smartphone into a versatile centimeter-accurate surveying instrument. From reference point surveys to point cloud measurement, layout, and AR visualization, LRTK covers a wide range of surveying and measurement needs with a single device. It features low-cost access to the latest high-precision positioning without complex equipment management.