Table of Contents

• What is iPhone RTK surveying?

• Easy centimeter-level positioning outdoors

• Surveying possible indoors as well

• Benefits of smartphone RTK surveying

• Easy deployment and operability

• Use cases for iPhone RTK surveying

• Simple surveying with LRTK

• FAQ

What is iPhone RTK surveying?

In the civil engineering and construction sectors, the use of ICT exemplified by the Ministry of Land, Infrastructure, Transport and Tourism’s i-Construction initiative has advanced in recent years, and there is a strong demand to streamline surveying work. However, traditional high-precision surveying required expensive equipment such as total stations and dedicated GNSS devices, and only a limited number of technicians could operate them, which became a burden on sites. Against this backdrop, the need for “a more accessible yet high-precision surveying method” has grown.

Recently, advances in positioning technology have brought attention to a new surveying style using smartphones. Among these, iPhone RTK surveying is a revolutionary method that achieves centimeter-level high-precision positioning comparable to conventional surveying equipment by combining a compact dedicated GNSS receiver with an iPhone. RTK (Real Time Kinematic) is a technology that dramatically improves positioning accuracy by applying correction information from a reference station in real time; whereas typical smartphone-built-in GPS has errors of around 5–10 m, RTK can localize positions with errors on the order of a few centimeters.

Traditionally, achieving this level of accuracy required expensive GNSS surveying equipment, base stations, and antennas operated by specialized technicians. However, the situation has dramatically changed with the fusion of the iPhone and external RTK devices. By attaching a small RTK receiver to a familiar smartphone and using a dedicated app, anyone can now easily perform high-precision surveying. This method, which combines the intuitive operability of a smartphone with the precision of RTK, is accelerating on-site DX (digital transformation) and greatly contributing to the efficiency and labor savings of surveying tasks.

Easy centimeter-level positioning outdoors

One advantage of iPhone RTK surveying is that in open outdoor environments, centimeter-level positioning can be achieved quickly with simple steps. Previously, surveys required setting up tripods and configuring communication with reference points, among other cumbersome preparations. With smartphone RTK, you simply turn on the power of the RTK receiver attached to the iPhone and start positioning in the app, and surveying begins. In an open sky area, an RTK Fix solution (the high-precision positioning state where a float solution is fixed) can be obtained in a matter of tens of seconds, allowing immediate confirmation of coordinate positions.

By using networked RTK services, correction information (reference station data) is automatically retrieved via the Internet from the smartphone, so there is no need to prepare an additional base station. For example, by connecting to electronic reference points (GNSS Continuous Observation System) provided by the Geospatial Information Authority of Japan or to private VRS services, real-time high-precision positioning can be performed. Also, systems that support the quasi-zenith satellite “Michibiki” centimeter-class augmentation service (CLAS) have appeared in Japan, enabling RTK positioning even in mountain areas outside mobile coverage by receiving augmentation signals from the satellite. Across wide outdoor sites, iPhone RTK surveying enables fast, accurate stakeout and dramatically streamlines site preparation and point measurement. For example, on roadwork or land development sites, walking the construction area and measuring several coordinate points with a smartphone before bringing in heavy machinery makes subsequent work planning easier. Tasks that previously required arranging a specialized surveying team for establishing reference points can be completed on-site, leading to substantial efficiency gains in field operations.

Surveying possible indoors as well

RTK-GNSS is fundamentally powerful outdoors where satellite signals can be received, but iPhone RTK surveying incorporates measures to perform positioning even indoors or in environments with many obstructions. Specifically, high-precision initial positions obtained outdoors are used as a reference, and the iPhone’s AR (augmented reality) technology and built-in sensors are utilized to track relative positions indoors. By calibrating an accurate coordinate and orientation once outdoors at the start of positioning, the system updates the current position using the smartphone camera imagery and IMU (inertial measurement unit) even when entering a building or going under a bridge.

This method allows, for short periods, positioning based on a global coordinate system indoors as well, and can be applied to equipment layout inside buildings or position checks inside tunnels. However, small errors accumulate over time, so for long-distance or long-duration movement, re-calibration outdoors as appropriate helps maintain high accuracy. Even so, the previously difficult task of seamless indoor-outdoor positional identification has become a reality through the smartphone RTK combination. For example, continuous positioning inside and outside a tunnel during tunneling work or calibrating at a building entrance before taking interior measurements can be achieved easily.

Benefits of smartphone RTK surveying

The surveying method that combines a smartphone and RTK offers many advantages not found in conventional equipment. The main benefits are summarized below.

• Centimeter-level high accuracy: With correction GNSS, current position can be obtained with positioning errors on the order of a few centimeters. Because precise stakeout and reference point measurement can be performed on-site immediately, this contributes to improved construction accuracy and faster verification tasks.

• Mobility and portability: The configuration of an iPhone and a small receiver is overwhelmingly more compact than conventional stationary surveying equipment. There is no need to carry bulky equipment, and surveying can be carried out nimbly even on narrow sites or sloped ground. With a device weighing only a few hundred grams attached to the smartphone, it is easy to carry and useful in areas difficult for people to enter.

• Intuitive operation: Since the app is operated via the smartphone’s touch UI, it is easy for people without training on specialized equipment to handle. Positioning start/stop and data saving can be done with a single tap, enabling anyone to perform high-precision positioning without confusion.

• Multifunctional measurement: The latest iPhones are equipped with high-performance cameras and LiDAR sensors, enabling a variety of measurements when combined with RTK position information. You can link photos and notes to acquired points, scan the surroundings with LiDAR to create 3D point cloud data, and use these for site records and as-built management. AR measurements, such as positioning a distant target through the camera, are also possible.

• Real-time data sharing: By integrating the smartphone with the cloud, measured coordinate data and photos can be shared from the field to the office immediately. For example, the office can instantly reflect points measured on-site into drawings, enabling real-time collaboration. Instead of taking data back on a notebook or USB, cloud saving on-site allows stakeholders to confirm information in real time and supports fast decision-making.

Easy deployment and operability

A major attraction of iPhone RTK surveying is its low barrier to entry. You can start using it simply by attaching a compatible device to an iPhone or iPad you already own, so there is no need to purchase large-scale new equipment. External RTK receivers are thin and lightweight enough to mount on the back of a smartphone (for example, weighing about 160 g), and can be carried like a mobile phone. The app is also simple in design, allowing the entire process from starting positioning to saving data to be completed in a few taps.

Because on-site staff can use the smartphones they routinely carry as surveying devices, operation is easy even without special training or expert knowledge. Complex wiring and adjustments between devices are unnecessary, and one person can walk the site and perform surveying. Even if a device is lost or damaged, the financial risk is small and devices can be swapped as needed for continued use, offering operational flexibility. Additionally, the relatively low initial investment makes it easy for staff to carry smartphone surveying devices in a one-device-per-person setup. If multiple people measure various parts of the site simultaneously, wide-area data collection can be completed in a short time, improving overall project efficiency. This ease of use and high operability make smartphone RTK surveying useful in a wide range of sites, from small surveying tasks to rapid as-is assessments for large projects.

Use cases for iPhone RTK surveying

The benefits that smartphone RTK surveying brings to the field are diverse. Below are some specific use cases.

Establishing reference points and as-built measurement at construction sites

High-precision reference point surveys and as-built (shape after construction) measurements are indispensable at roadworks and land development sites. With iPhone RTK surveying, necessary point coordinates can be acquired immediately upon arrival, and temporary reference points can be easily established. Measuring multiple key points in a short time smooths out the placement of heavy machinery and schedule management. After construction, the smartphone’s LiDAR can scan the constructed objects to obtain as-built 3D data in real time. These data can be shared on the cloud immediately, enabling rapid verification and instructions between the field and the office.

Use in infrastructure inspection and maintenance

Smartphone RTK surveying is also highly useful for inspection tasks of bridges, road facilities, and other infrastructure. For example, photographing a crack in a bridge pier or the repair location of a buried pipe with a smartphone will tag the photo with precise coordinates for record keeping. Without relying on paper drawings or distance measurements, you can record the on-site situation with high-precision positional information and reflect it in reports and maintenance plans without revisiting the site. There is also potential to use AR functions to visualize the locations of underground utilities, helping to prevent accidental damage during excavation.

Rapid situational awareness at disaster sites

At disaster sites such as earthquakes or landslides, rapid situational assessment and information sharing are essential. Using iPhone RTK surveying, measurements can begin immediately upon arrival at the affected area. For example, surveying the extent and height of collapsed soil with a smartphone and estimating soil volume on-site can help with arranging heavy equipment or sandbags. Combining drone aerial photography makes it possible to quickly create wide-area damage maps. Even if communication infrastructure is disrupted, positioning using satellite augmentation allows acquisition of location information to share with relevant agencies, greatly aiding initial response.

As shown, smartphone RTK surveying is a flexible tool that meets various on-site needs and is expected to become increasingly widespread.

Simple surveying with LRTK

One solution that realizes the iPhone RTK surveying described above is LRTK. LRTK is an integrated smartphone RTK positioning system consisting of a compact high-precision GNSS receiver called the “LRTK Phone,” an iOS app, and a cloud service. By attaching the LRTK Phone to an iPhone and launching the app, anyone can immediately start centimeter-level positioning using networked RTK or Michibiki (CLAS) augmentation information. Acquired coordinate data and point cloud models are automatically saved to the LRTK cloud, and can be viewed and downloaded from a PC.

By introducing LRTK, on-site staff themselves can perform high-precision surveying without relying on specialized surveying teams. For example, establishing reference points and checking as-built results at construction sites, or recording positions for infrastructure inspections, can be efficiently carried out with just a smartphone. It supports not only outdoor positioning but also indoor positioning assistance functions, enabling measurements under bridges and inside buildings. Surveying work that previously required expensive equipment and effort will be greatly simplified by LRTK. If you are interested in iPhone RTK surveying, consider using such solutions to easily start high-precision positioning.

FAQ

Q: Can I do RTK surveying with only an iPhone? A: Currently, an iPhone alone cannot perform centimeter-level RTK positioning. High-precision positioning requires a dedicated RTK-GNSS receiver. By using a small external device attached to the iPhone (for example: LRTK Phone), the smartphone can receive correction information and enable RTK surveying.

Q: How accurate is the positioning? A: In open outdoor conditions when an RTK Fix solution is obtained, approximately ±2 cm horizontally and about ±4 cm vertically can be expected. Accuracy varies with environmental conditions and satellite reception, but this is orders of magnitude more precise than the several-meter errors of conventional smartphone GPS. However, accuracy can degrade in areas surrounded by buildings or trees due to multipath of satellite signals.

Q: Can it really position indoors? A: Yes — while full satellite positioning is not possible, relative positioning indoors is achievable by leveraging the smartphone’s camera and sensors. By aligning the current position and orientation outdoors before entering a building, movement indoors can be tracked for a short time (error accumulation on the order of a few percent of indoor travel distance). For long-duration use or when high accuracy is required, it is recommended to re-conduct RTK positioning outdoors for correction as needed.

Q: Can it be used where there is no Internet? A: Yes. There are methods to perform high-precision positioning even without Internet connectivity. For example, in Japan, receivers that support the CLAS signal provided by the quasi-zenith satellite system “Michibiki” can receive augmentation from satellites and enable RTK positioning in mountainous areas outside mobile coverage. It is also possible to set up a mobile base station (local reference point) yourself and transmit correction data by radio. However, using network-based correction services is usually easier and provides more stable accuracy.

Q: Which smartphones or tablets are supported? A: Basically, iOS-compatible apps are provided, so iPhone and iPad can be used. The latest iPhones are optimal because of high processing performance and LiDAR availability, but positioning itself works on models without LiDAR as well. If your device meets the iOS version and hardware requirements, you can use your existing device as a high-precision surveying instrument.

Q: Can it be used with Android smartphones? A: At present, many solutions are offered for iPhone/iPad (iOS), and smartphone RTK surveying systems for Android are limited. iOS devices have advantages for positioning due to the inclusion of UWB chips and integrated high-performance sensors, so iPhone use is progressing first. Android-compatible products may increase in the future, but currently using an iPhone is mainstream.

Q: What kinds of sites and applications can it be used for? A: It can be applied to a wide range of uses involving position information, such as reference point surveying and as-built management for civil engineering, position recording of infrastructure facilities, topographic measurement in agricultural civil engineering, and situational assessment at disaster sites. Because measurement data can be obtained quickly on-site, some tasks that used to be outsourced to specialists can now be handled in-house. However, for public surveying and other legally regulated work that requires qualifications, it is still recommended to consult professional surveyors.

Q: Is there a cost advantage compared to traditional surveying equipment? A: In general, smartphone RTK solutions tend to significantly reduce initial costs compared to total stations and high-performance GNSS receivers. Reusing existing smartphones or tablets also offers cost benefits. Because there is no need to procure multiple expensive stationary instruments, these solutions are easier to introduce for small- to medium-scale projects. However, the specific cost-effectiveness depends on the services used and the scale of operation, so it is important to conduct thorough consideration before introduction.