Pocket-sized, centimeter-level positioning! iPhone RTK device ready for immediate field use

Table of Contents

• How field surveying changes with iPhone RTK

• Point cloud measurement made accessible with a smartphone

• Centimeter positioning realized by the RTK method

• Pocket-sized high-precision GNSS receiver "LRTK"

• Main scenes where iPhone RTK shines

• Efficiency and labor saving in as-built management

• Powerful in disaster response

• Easy 3D scanning of structures

• Summary

• FAQ

How field surveying changes with iPhone RTK

Traditionally, on-site measurement tasks such as civil engineering surveying and as-built management required specialized equipment and advanced skills. It was common to bring total stations, GNSS survey instruments, large 3D laser scanners, and perform measurements with multiple people. These methods required time and effort to acquire point cloud data and imposed limitations on the measurement range. However, in recent years, by combining smartphones like the iPhone with small GNSS receivers, an era has arrived in which anyone can easily obtain 3D point cloud data. On-site surveying is being dramatically streamlined, and the era in which "a smartphone becomes an all-purpose surveying instrument" is beginning.

Point cloud measurement made accessible with a smartphone

Recent iPhones are equipped with LiDAR scanners and high-performance cameras, enabling 3D scanning of surrounding structures and terrain. Even without expensive dedicated surveying equipment, simply walking around with a smartphone in hand can acquire high-density point cloud data consisting of hundreds of thousands of points. For example, using an iPhone you can scan roads or development sites while walking and visualize the terrain as a 3D model directly on the phone screen. No complicated operations are required, and the fact that non-experts can handle it intuitively is revolutionary. It is truly an innovative step toward democratizing surveying. Such smartphone surveying is attracting attention as a technology that promotes the digital transformation (DX) of construction sites.

However, there remains one major challenge with point cloud data obtained by a smartphone alone: position accuracy. Positioning with a typical smartphone’s built-in GPS is usually limited to errors on the order of several meters (several ft). This cannot assign accurate coordinates to acquired point clouds and therefore cannot be used as-is for applications that require centimeter precision, such as as-built management. In addition, scanning long distances using only the phone’s sensors can cause cumulative drift that distorts the point cloud. In short, while smartphone-based point cloud measurement is convenient, improving spatial accuracy is essential to make the results useful for surveying and construction management.

Centimeter positioning realized by the RTK method

The key to solving this positioning accuracy issue is the RTK method, a positioning technology that uses GNSS (satellite positioning). RTK (Real Time Kinematic) is a technique that uses two GNSS receivers—one as a base station (reference point) and the other as a rover—to observe simultaneously and correct errors by differencing the data, achieving centimeter-level high-precision positioning. While standard GPS positioning produces errors on the order of several meters, using RTK can specify positions with very high accuracy: about 1–2 cm (0.4–0.8 in) horizontally and within a few centimeters (a few in) vertically.

Historically, RTK positioning required installing a dedicated base station GNSS antenna on site and sending correction information wirelessly to the rover. Today, however, network RTK, which obtains reference station data via the Internet, has become mainstream. By using the smartphone’s data connection to connect to public continuously operating reference station networks or commercial correction services (Ntrip-compatible), correction information can be received in real time. For example, you can use the Geographical Survey Institute’s network of about 1,300 continuously operating reference stations in Japan or regional VRS services. This enables immediate centimeter-level positioning on site without carrying a heavy base station. Additionally, within Japan you can also use the Quasi-Zenith Satellite System "Michibiki" augmentation service for centimeter-level positioning (CLAS). With CLAS-compatible receivers, you can receive high-precision information directly from satellites and maintain centimeter-level positioning even at sites outside cellular coverage, without an Internet connection. This capability to continue high-precision positioning in places where radio does not reach—such as remote islands, mountainous construction, or immediately after a disaster when communications are unstable—is a major advantage.

Pocket-sized high-precision GNSS receiver "LRTK"

Making the RTK positioning technology described above easy to use is the pocket-sized GNSS receiver called "LRTK Phone", developed by Reflexia, a startup originating from Tokyo Institute of Technology. Commonly known as LRTK, this thin, lightweight RTK-GNSS device attaches to an iPhone or iPad and weighs approximately 125–146 g, with a thickness of about 13 mm (0.51 in). It is designed as a dedicated case that attaches to the back of the smartphone with one touch, and it houses an antenna and battery. The device connects wirelessly to the phone; simply turn on the LRTK unit and launch the app to be ready to use. With this small device, positioning errors that were several meters with the phone’s built-in GPS shrink to a few centimeters at once, instantly transforming the smartphone into a high-precision surveying instrument.

LRTK supports the earlier-mentioned network RTK, allowing you to connect to correction information distribution services from within the smartphone app. After a few tens of seconds, satellite reception stabilizes, and when the RTK solution becomes Fix, positioning accuracy is already at the centimeter level. While positioning, the smartphone screen displays latitude, longitude, and elevation in real time so you always know your position in the global coordinate system. There is no need for the conventional setup of instruments on known points or conversion to local coordinates; absolute coordinates are automatically attached to all acquired point clouds and photos.

The LRTK Phone uses a triple-frequency GNSS receiver, and models that support Michibiki’s CLAS signals are available. Therefore, even at sites outside cellular coverage or immediately after disasters where the Internet cannot be used, LRTK can receive corrections directly from satellites and continue to maintain centimeter-level accuracy.

Basic steps to quickly start iPhone RTK surveying on site:

• Attach the LRTK receiver – Attach the LRTK unit to the iPhone, turn on the power, and launch the dedicated app (LRTK App).

• Connect to correction information – From the app, connect to a public reference network or commercial service and start receiving RTK corrections. In a few tens of seconds the positioning status will become "Fix", enabling cm-level positioning.

• Scan the site – Once positioning is stable, scan the target with the iPhone’s camera and LiDAR. Simply walk around with the phone in hand and photograph the terrain or structures to obtain high-density point clouds.

• Confirm and share data – After scanning, upload the acquired point cloud data to the cloud immediately. You can view 3D point clouds on the web, measure distances and volumes, and share results with office colleagues.

Even in disaster investigations where bringing bulky equipment is impractical, a single pocket-sized LRTK can accurately record site conditions and share them instantly with stakeholders.

Furthermore, services combining smartphone surveying apps with LRTK and cloud functionality are provided. Point cloud and positioning data acquired on site can be uploaded to the cloud with a single tap and checked or downloaded from the office immediately. With a web-based 3D point cloud viewer, you can measure distances, areas, and volumes of acquired data, or overlay them with construction design data to check progress. Because point clouds can be handled in a web browser without special expensive software, the workflow is very simple. The ability to perform surveying → data sharing → analysis end-to-end using only a smartphone and LRTK will greatly contribute to DX at job sites.

Main scenes where iPhone RTK shines

Now let’s look at some concrete use cases showing how the combination of iPhone + LRTK changes field operations.

Efficiency and labor saving in as-built management

As-built management involves verifying that the finished shape and dimensions of constructed structures or land match the design drawings. Traditionally, this was done by measuring various points with tape measures or total stations and taking photos for records. However, this approach makes it difficult to cover wide areas and carries risks of missed measurements and human error.

Using an iPhone and LRTK significantly changes as-built measurement methods. When arriving on site, attach LRTK to the iPhone and start point cloud scanning immediately. With positioning in Fix, simply walking around the site with the phone allows detailed 3D measurement of the entire constructed object. Because the acquired point clouds already include high-precision coordinates, you can compare measurement results with design data on the spot to check quality. By measuring the entire site in a short time, you can greatly reduce the manpower and time required for as-built management. There is also a safety advantage in that hazardous areas can be scanned remotely without sending personnel into danger. Such digital as-built management is supported by the Ministry of Land, Infrastructure, Transport and Tourism’s i-Construction initiative, and it is expected to become a new field standard.

Powerful in disaster response

In sites affected by major earthquakes or heavy rain-induced landslides, rapid and accurate situation assessment is essential. However, it is often difficult to bring large surveying equipment into disaster zones, and communications infrastructure may be cut off.

In such situations, the iPhone and LRTK combination is highly effective. Lightweight and pocket-sized, the device allows rapid deployment to the site to scan collapsed structures and terrain and convert them to point clouds in a short time.

Even if cellular networks are unavailable, if LRTK supports CLAS reception it can receive corrections via satellite and maintain accuracy.

High-precision point cloud data can be shared instantly with stakeholders via the cloud, enabling decision-makers at remote locations to accurately understand the current situation. This facilitates prevention of secondary disasters and the planning of effective recovery measures. From initial disaster response through recovery planning, rapid on-site measurement with LRTK can be a major asset.

Easy 3D scanning of structures

3D point cloud utilization for maintenance of large structures such as bridges, tunnels, and plant equipment is advancing. Traditionally, laser scanner surveys by specialists were required, but iPhone RTK allows routine inspections to easily scan structures.

For example, an inspector can record the shape of a bridge underside or tunnel lining in detail simply by walking while holding up an iPhone. Even in locations where typical GNSS equipment cannot receive satellite signals, combining the iPhone’s LiDAR and camera can obtain the necessary point clouds.

The acquired 3D data makes it easy to objectively detect cracks or deformations and compare shapes before and after repairs. Since the data includes absolute coordinates, tracking long-term changes and integrating data across sites is straightforward. The ability to create digital twins of structures without large equipment is highly useful for infrastructure maintenance.

Summary

iPhone RTK, which combines smartphones and RTK technology, has the potential to fundamentally change on-site measurement. By simply attaching the pocket-sized LRTK unit to a smartphone, anyone can perform centimeter-accurate surveying anywhere, greatly boosting productivity across applications from point cloud measurement to as-built management and disaster investigation. The concept of "one versatile surveying device per person," which was unthinkable under traditional approaches, is becoming a reality. This allows processes that used to take days to weeks—from surveying to drawing creation and reporting—to be completed with data verification on the same day as on-site measurement.

As an easy-to-introduce solution for advancing DX at field sites, iPhone RTK is highly attractive. Because it uses familiar smartphones, user training is simple and it can be smoothly integrated into existing workflows. The ability to start without large initial investments also lowers the barriers to digitalization in the construction industry. Please take advantage of this simple surveying with LRTK to improve efficiency and sophistication in your field operations. Surveying technology that fuses smartphones and RTK will continue to evolve, and the day it becomes the standard for field surveying is not far off.

FAQ

Q: Can you really do surveying with an iPhone? A: Yes. Recent iPhones include LiDAR scanners and high-performance cameras, and using dedicated apps to 3D-scan the surroundings makes point cloud measurements similar to surveying possible. However, a standalone iPhone’s positioning accuracy is coarse—on the order of several meters (several ft)—so it is difficult to use for surveying purposes as-is. By combining an RTK-capable GNSS receiver such as LRTK, centimeter-level accuracy can be achieved, making the device usable as surveying equipment.

Q: What positioning accuracy can be achieved using LRTK? A: RTK positioning with LRTK can be expected to achieve approximately 1–2 cm (0.4–0.8 in) horizontally and about 3–4 cm (about 1.2–1.6 in) vertically (under good conditions ±1 cm (±0.4 in) horizontal, ±2 cm (±0.8 in) vertical). Actual accuracy depends on satellite reception conditions and the quality of correction information, but it is sufficient for typical civil surveying and as-built management. Considering that smartphone GPS errors are on the order of several meters (several ft), LRTK dramatically improves positioning precision.

Q: Which iPhone models are supported? A: LRTK Phone supports iPhone and iPad. Devices such as the iPhone 12 Pro series and later, and iPad Pro models equipped with LiDAR are especially suitable because they can acquire high-density point clouds via LiDAR scanning. Even models without LiDAR can generate point clouds using photogrammetry mode with the camera, so a wide range of devices can be used.

Q: How does it compare to drone or laser scanner surveys? A: Drone surveys and terrestrial laser scanners are effective for large sites and high-precision requirements, while iPhone RTK’s strengths are ease of use and mobility. Because it is easy to carry with just a smartphone and a small device, measurements can begin immediately in confined sites or locations requiring flight permissions. Other advantages include real-time result confirmation and low initial cost. For very large areas, however, drones or high-performance scanners may be more efficient; choose the appropriate tool depending on site scale and purpose.

Q: How can the acquired point cloud data be used? A: Acquired point cloud data can be viewed and measured directly on the LRTK cloud, or imported into standard point cloud processing or CAD software. Since the data contains elevation and coordinate system information, it is easy to overlay with design drawings and other survey data for analysis. For example, you can calculate earthwork volumes for as-built verification, compare terrain changes before and after construction, or record structural deterioration. Point cloud data obtained with a smartphone can be effectively used in many field scenarios.

Q: Can it be used with Android smartphones? A: Currently, LRTK Phone is intended for use with iOS devices such as iPhone and iPad. This is because the latest iPhone series include LiDAR sensors that enable standalone point cloud scanning, and stable surveying apps have been implemented in the iOS environment. Please wait for official announcements from the manufacturer regarding support plans for Android devices.

Q: How long does the LRTK battery last? A: The LRTK unit runs on an internal battery and can be used continuously for about 5–6 hours on a full charge. For typical field work, you can continue surveying for more than half a day without recharging. Using a mobile battery via the included USB cable allows for extended use.