Table of Contents

• What RTK positioning is

• Why “RTK positioning × subscription” is drawing attention now

• Features of iPhone-compatible subscription RTK receivers

• Field challenges in the construction and surveying industries and use cases for RTK subscriptions

• Comparison with other methods

• Misconceptions and cautions when introducing RTK

• LRTK implementation cases and how the subscription works

• FAQ

What RTK positioning is

“RTK positioning,” which has attracted attention in the construction and surveying industries in recent years, is a technology that uses GNSS (Global Navigation Satellite Systems) to measure positions in real time with centimeter-level accuracy. Ordinary GPS positioning can result in position errors of about 5–10 m due to satellite signal errors. For applications like displaying your current location on a map app, an error of a few meters is acceptable, but to determine the precise location of structures in civil engineering work or to detect minute displacements in infrastructure inspections, “centimeter-level” accuracy is indispensable. RTK (Real Time Kinematic) is the positioning method that meets this requirement.

A key feature of RTK is the scheme of canceling errors by using two GNSS receivers. A base station (a receiver placed at a fixed known point) and a rover (a receiver moved to the point to be measured) are used simultaneously, and the satellite signal data received by both are compared in real time. The base station computes the positioning error from the difference between its true known position and the position calculated from GPS, then transmits that error information to the rover via radio or the internet. The rover applies the received error correction to its calculated position, allowing high-precision positioning with greatly reduced errors. Simply put, “measuring with two units at the same time cancels common error factors compared to one GPS unit,” which dramatically improves accuracy.

With RTK corrections, position errors can be reduced to roughly one-hundredth of conventional levels. Typical network RTK (described later) can achieve planar position errors of about 2–3 cm and height errors within a few centimeters. The fact that GPS can achieve “surveying-equipment-level” accuracy is revolutionary. Traditionally, expensive and specialized equipment was required, but in recent years palm-sized receivers and smartphone apps have made achieving centimeter accuracy possible.

Why “RTK positioning × subscription” is drawing attention now

RTK positioning itself is not new, but services combining it with a “subscription (flat-rate) model” have emerged recently and rapidly gained attention. Two main factors underlie this trend.

One is the lowering of adoption barriers. Historically, RTK-capable surveying equipment was very expensive, requiring a large initial investment to obtain a complete set of dedicated devices. This made it difficult for anyone other than large general contractors or surveying firms to adopt. Subscription-based services allow necessary equipment to be used for a monthly fee, greatly reducing upfront costs. The flexibility to contract only for the needed period is attractive to small and medium-sized construction companies and local governments. Since the latest feature updates are provided continuously, the risk of equipment becoming obsolete after purchase is also reduced.

The other is the growing need for workforce reduction and efficiency on site. With a decline in experienced technicians and initiatives to reform working styles, the construction industry faces the challenge of ICT construction and surveying DX (digital transformation). Policies such as the Ministry of Land, Infrastructure, Transport and Tourism’s i-Construction initiative are encouraging adoption, and alongside drone surveying and machine guidance, RTK-GNSS utilization is becoming a field standard. In this context, subscription-based RTK that delivers “high-precision positioning that anyone can use” is timely as a productivity-improving tool for work sites. The era is shifting from one in which expensive equipment was handled only by specialists to one in which easy-to-use services are routinely operated by site supervisors and workers.

Features of iPhone-compatible subscription RTK receivers

Among the recently introduced subscription RTK receivers, the particularly groundbreaking ones are the iPhone-compatible compact devices. RTK receivers that can be connected directly to smartphones have many features that traditional surveying equipment lacks.

Easy connectivity and portability: iPhone-compatible RTK receivers are compact units with built-in antennas and batteries that attach to the back of the iPhone or to the Lightning connector for use. Where fixed base station equipment or long surveying poles were previously required, this device completes the workflow with just a smartphone and receiver. Weighing only a few hundred grams, the burden of carrying it to the site is greatly reduced. One technician can carry it in a pocket and begin positioning immediately when needed—this ease of use is a major advantage.

Smartphone-native operability: Positioning and data recording are performed via a dedicated smartphone app. With an intuitive UI, high-precision measurement of the current position is possible with the push of a button even without specialized knowledge. Results are displayed on a map in real time, and photo capture and position logging can be linked with a single tap. Traditional surveying instruments required complex settings via dedicated controllers, but the clear operation system of smartphone apps allows a wide range of site staff to use them.

Cloud integration and data utilization: RTK receivers that work with iPhones seamlessly integrate with cloud services via internet connectivity. Coordinate data of measured points, photos taken on site, and even 3D point cloud data obtained by the iPhone’s LiDAR sensor can be uploaded and stored in the cloud instantly. Office staff can share site data, receive progress reports, and review survey results on the spot. Daily report creation and as-built documentation can be done efficiently in the cloud, eliminating the need to transcribe measured data onto paper and improving quality through centralized data management.

Leveraging smartphone functions: Many functions are possible precisely because the smartphone is integrated. For example, photos taken with the iPhone can be tagged with RTK-corrected high-precision position data, allowing accurate plotting and management of photos on maps later. There is also a coordinate guidance function that uses accelerometer and gyroscope sensors to navigate back to recorded points. AR (augmented reality) displays on the screen can show arrows indicating the direction to a target or notify the user when within a set distance, useful for staking or on-site guidance to target points. Moreover, LiDAR-equipped iPhones can perform 3D scans of surrounding terrain and structures, obtaining point cloud data with high-precision coordinates assigned to each point. The smartphone + RTK device combination realizes a wide range of uses that truly make it a “universal surveying instrument.”

Field challenges in the construction and surveying industries and use cases for RTK subscriptions

Now let’s look at how subscription RTK can actually be used on construction and surveying sites. Below are representative use cases that help solve field challenges.

Improving as-built accuracy: For works such as roads and land development, measurements of completed structures and ground elevation are taken to verify whether construction has been carried out according to the design (as-built). With an RTK receiver, coordinates and heights at work locations can be measured immediately on site with errors limited to a few centimeters. Where levels or total stations and multiple personnel were previously required, subscription RTK allows site supervisors themselves to check points quickly. Ensuring high precision from the initial layout (marking and staking) stage contributes to quality improvement and efficiency by preventing rework.

Photogrammetry and 3D modeling: Photogrammetry using drones or single-lens cameras is widely used to create 3D models and orthophotos of sites. RTK subscription services play an important role in supporting the accuracy of such photogrammetry. For example, equipping a drone with RTK dramatically improves the positional accuracy of aerial photos, reducing the need for ground control points (GCPs). Combining photos or LiDAR scans taken from a handheld iPhone + RTK on the ground enables efficient acquisition of detailed point cloud models. Because the resulting 3D model’s coordinate system is based on RTK measurements, it aligns with design coordinates and can be used directly for volume calculations and displacement checks.

Efficiency in staking and layout work: Traditionally, staking out positions for structures required a surveyor to calculate offsets from drawings and mark the site with tape measures or optical equipment. With an RTK receiver, the app provides position guidance based on design coordinates, allowing a single worker to perform staking or layout. The smartphone screen can display guidance like “10 cm east, 5 cm south” or show virtual marks on the ground in AR, intuitively directing users to the correct point. When many points are set over a wide area, work efficiency and accuracy improve dramatically.

Disaster sites and infrastructure inspections: In disaster zones such as those affected by earthquakes or heavy rain, rapid situation assessment and recovery planning are required. Subscription RTK receivers are useful for obtaining high-precision position information even in mountainous or disaster-affected areas where communication infrastructure has been disrupted. Devices compatible with the centimeter-class correction service (CLAS) broadcast from Japan’s Quasi-Zenith Satellite System “Michibiki” can receive correction information directly from satellites, enabling positioning even outside mobile coverage. Some local governments have used smartphone-mounted RTK receivers in post-disaster surveys to map collapsed terrain and record photos of damage. In infrastructure maintenance, high-precision 3D point clouds obtained during periodic inspections of tunnels and bridges can be compared with previous surveys to precisely identify the locations of cracks and deformations.

As shown above, the ability for “anyone to obtain high-precision position information quickly” is itself creating new value on construction and surveying sites. Subscription RTK receivers are expected to transform surveying and measurement work that previously relied on specialists and expensive equipment, enabling both labor savings and higher-level operations.

Comparison with other methods

When introducing subscription RTK, it is important to understand the differences and appropriate use cases compared with other positioning and measurement methods commonly used on sites. Below is a comparison of representative conventional methods and RTK features.

Comparison with conventional GNSS surveying equipment: Traditional GNSS surveying equipment (RTK sets) include the receiver body, antenna, data collector (control terminal), tripod or pole, and so forth, making them very expensive and requiring specialist knowledge to operate. The RTK positioning principle is the same, but conventional equipment often requires setting up your own base station or contracting external correction services and connecting for communications. The hardware is also large, so vehicles and personnel are needed to bring it to the site. In contrast, subscription-type compact RTK receivers operate with just a smartphone and do not require preparing a base station; they can obtain correction information from public control networks or satellite broadcast services (network RTK). The lowered barrier makes them much easier to use. However, conventional units can be superior in antenna performance and stability due to dedicated enclosures, making professional-grade equipment more suitable for very large sites or special environments. Consider mixing or choosing based on purpose and budget.

Comparison with 3D laser scanners: Fixed 3D laser scanners are also commonly used for high-precision terrain measurement. Laser scanners can acquire millions of distance points per second, producing millimeter-level point cloud models, but they are large and costly (hundreds of thousands to millions of yen). Also, the acquired point clouds are in the instrument’s local coordinate system (based on the scanner setup position), so aligning them to the site surveying coordinate system requires separate target placement or GNSS surveying to combine reference points. Smartphone LiDAR measurement with RTK cannot match a laser scanner in point count, but a major advantage is that acquired points are tied to a global coordinate system at the same time. For quick scans over a modest area to obtain a rough 3D model, a lightweight smartphone + RTK is sufficiently practical. Use laser scanners when detailed scanning is required, and smartphone RTK for routine as-built records or when full-scale surveys are not necessary to achieve cost-effective measurement operations.

Comparison with UAV surveying: Drone (UAV) aerial photogrammetry has been increasingly adopted on many sites. The drone’s strength is capturing large areas in a short time, but it cannot be used in no-fly zones or bad weather. Improving the accuracy of aerial data requires RTK-equipped drones or ground GCP placement. Subscription RTK receivers complement UAV surveying: when drones cannot fly in urban areas or indoors, ground-based measurement by people is necessary, and smartphone-mounted RTK is powerful in such cases. Measuring verification points on drone-derived 3D models with RTK makes model accuracy confirmation and comparison with existing topographic maps straightforward. Overall, aerial overview surveying suits UAVs, while detailed ground surveying suits RTK—combining both allows an efficient surveying system adaptable to all situations.

Misconceptions and cautions when introducing RTK

Although RTK positioning’s high accuracy is attractive, there are several points and common misconceptions to be aware of when introducing it for the first time. To ensure successful operation, the main points are summarized below.

“If you buy an RTK receiver, you’ll get cm accuracy” is a misconception: RTK does not work with a single GNSS receiver alone; the presence of a base station that provides correction information (or an equivalent service) is always required. You can prepare a mobile base station yourself, but in many cases users connect to data provided by the Geospatial Information Authority’s control points or to paid correction services offered by mobile carriers via internet connection. Subscription RTK receivers simplify these settings in the app, and users typically just log into the designated network service or automatically receive corrections if compatible satellites can be received. Keep in mind that the “one-button measurement” experience is supported by such infrastructure.

Positioning accuracy varies with the satellite environment: Because RTK uses signals from GNSS satellites, it is heavily influenced by the surrounding environment. In forests with closed canopies or in urban canyons between tall buildings, the number of received satellites can decrease or multipath (reflected signals) interference can occur, potentially degrading accuracy. RTK apps display solution quality statuses like `Fix` and `Float`, and centimeter-level accuracy is guaranteed only when the solution is `Fix` (integer-fixed). Always monitor satellite lock and solution status during positioning; if the solution falls to `Float` (errors on the order of tens of centimeters), treat measurement results with caution. Receivers that support multi-GNSS (GPS, GLONASS, Galileo, QZSS, etc.) and multi-frequency reception increase satellite availability and make it easier to maintain a `Fix` in challenging environments, so choosing a model that supports many satellites is a key point when adopting.

Basically not usable indoors or underground: GNSS signals do not reach inside buildings or tunnels, so RTK is fundamentally an outdoor technology. For underground floors or indoor positioning, other methods such as UWB or SLAM must be combined. However, recent smartphone RTK solutions have introduced features that allow short-term indoor positioning continuation through engineering. For example, if a `Fix` solution is obtained outdoors before entering a building, a phone’s inertial sensors and AR technology can estimate relative position to avoid complete loss. Even so, errors accumulate over long durations or distances, so these should be considered auxiliary functions. The basic rule is to “use where the sky is visible” and avoid overreliance in unsuitable environments.

Handling of coordinate systems and height references: GNSS-derived positioning results are usually obtained as geodetic latitude/longitude or ellipsoid heights. On Japanese construction sites, conversions to local plane coordinate systems or orthometric heights (geoid heights) are often required. Subscription RTK software supports Japan-specific coordinate transformations and geoid corrections, allowing measured points to be displayed in arbitrary coordinate systems immediately. For example, values in the “XX system (regional coordinates)” and elevations can be calculated on site, making it easy to compare received data with construction drawings. Nonetheless, for final accuracy confirmation, it is reassuring to validate important reference points by surveying known points or by averaging multiple measurements to understand instrument and system errors.

LRTK implementation cases and how the subscription works

Finally, we introduce “LRTK”, a notable example of a subscription RTK service. LRTK is an RTK solution developed by a venture originating from Tokyo Institute of Technology. It centers on smartphone-mounted devices and provides a comprehensive service combining a dedicated app and cloud services.

Service composition: The LRTK series includes hardware such as the small receiver “LRTK Phone” for use with an iPhone, a rugged pole-mounted receiver “LRTK Pro2,” and a helmet-mounted “LRTK Helmet,” offering devices suited to different uses. All devices connect to smartphones via Bluetooth or Lightning and are controlled and configured from the LRTK app. Positioning data, photos, and point clouds are automatically synchronized to the cloud service “LRTK Cloud,” and data management and sharing are possible via a web browser. The integration of hardware, software, and cloud forms an ecosystem that supports the cycle of measuring, viewing, recording, and communicating on site in a one-stop manner.

Subscription mechanism: In addition to purchase plans, LRTK offers monthly subscription plans. For example, with LRTK Phone, users can introduce the device at a low initial cost and pay monthly software usage fees. While subscribed, the app and cloud features are always provided at the latest version, with bug fixes and feature additions automatically applied. Support is also available during the contract period, giving peace of mind to sites new to RTK. The ability to increase or decrease the number of subscriptions as needed provides flexibility to match project scale and duration, allowing efficient operation of high-precision positioning environments.

Implementation cases and effects: LRTK has been implemented widely in domestic construction and surveying fields, and its benefits have been reported. For example, a mid-sized construction company that previously outsourced as-built surveys was able to have its in-house construction teams perform them after adopting LRTK, reducing work stoppages while waiting for surveys. A local government adopted LRTK for post-disaster field surveys, using satellite augmentation signals to map and photograph damaged areas even when mobile communications were down. A surveying consultant firm started operations where veteran and junior staff share site data on the same cloud, enabling remote real-time instruction and verification from separate offices. This allows new technicians to acquire measurement points without hesitation, while veterans can provide support without travel time.

Thus, subscription RTK services like LRTK not only rent equipment but also act as “solutions that revolutionize the work processes on site.” By making high-precision GNSS positioning more accessible, LRTK contributes to productivity improvements in the construction and surveying industries and will likely be a key technology supporting on-site DX going forward. If you are considering introducing centimeter-precision positioning on your site in an easy way, consider leveraging a subscription service.

FAQ

Q: Do I need any special qualifications or training to use smartphone-compatible RTK receivers? A: No specialized qualifications are required. Basic operations are performed in a smartphone app with an intuitively designed UI. Simple training or manual review is needed during initial setup, but it is significantly easier to learn than traditional surveying equipment, so site supervisors and workers can master usage in a short time.

Q: Do subscription RTK services always require an internet connection? A: Positioning may be possible without network connection in some cases. Normally, mobile data on the smartphone is used to connect to network reference stations to obtain correction information. However, devices that can receive correction signals directly from satellites, such as Michibiki’s CLAS, can achieve centimeter-class positioning even outside mobile coverage. Some services, including LRTK, support this satellite augmentation and strongly support offline use.

Q: Is positioning accuracy really a few centimeters? Does it change with weather or time of day? A: Under appropriate conditions, horizontal accuracy of about 2–3 cm can be expected. However, satellite geometry, ionospheric conditions, and surrounding obstructions can cause slight degradation or increase the time needed to obtain a `Fix` solution. Best results are obtained in open conditions on clear days, while extreme events such as thunderstorms or solar flares can increase GNSS errors. Always check the positioning status in the app and monitor environmental changes.

Q: If I cancel the subscription, what happens to the data and devices? A: Your local data remain in your possession after contract termination. Measurement data and photos stored in the cloud can be exported as the customer’s assets. Devices may be sold or rented depending on the service. In LRTK’s case, the device itself remains with the user even after subscription termination, and usage can be resumed by re-subscribing. However, during the lapse in subscription, dedicated app and cloud functions will be suspended, so if continued use is planned, maintaining the subscription is recommended.

Q: Will using a smartphone on site cause damage? Are waterproofing and battery life sufficient? A: The smartphone + RTK receiver combination is designed with field use in mind. For example, LRTK receivers are built to be dustproof and splash-resistant, and batteries provide enough runtime for a day’s work (depending on model, roughly 8–12 hours). Countermeasures on the smartphone side include waterproof cases and external battery packs. Compared to dedicated equipment, substitution with a spare smartphone is often easier in case of failure, which is an advantage. If concerned, prepare spare devices and charging options in advance for reliability.