Table of Contents

• What is iPhone RTK surveying?

• Easy centimeter-level positioning outdoors (cm level accuracy (half-inch accuracy))

• Surveying possible indoors as well

• Advantages 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 civil engineering and construction, the use of ICT represented by the Ministry of Land, Infrastructure, Transport and Tourism’s i-Construction initiative has been progressing in recent years, and there is a strong demand to streamline surveying work. However, conventional high-precision surveying has required expensive equipment such as total stations and dedicated GNSS devices, and only a limited number of technicians can operate them, making it a burden on site. Against this backdrop, the need for “a simpler yet highly accurate surveying method” has been growing.

Recent 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-class high-precision positioning comparable to conventional surveying instruments by combining a small 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; while typical smartphone-built-in GPS has errors on the order of about 5–10 m (16.4–32.8 ft), RTK can pinpoint positions with errors down to a few centimeters.

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

Easy centimeter-level positioning outdoors (cm level accuracy (half-inch accuracy))

One advantage of iPhone RTK surveying is that in open outdoor environments you can obtain centimeter-level positioning quickly with simple procedures. Traditionally, surveys required setting up a tripod and installing equipment each time, with complicated preparations such as configuring communication with reference points. With smartphone RTK, surveying starts simply by turning on the RTK receiver attached to the iPhone and starting positioning in the app. In wide open areas, you can obtain an RTK Fix solution (a high-precision position fix from a float solution) in a matter of tens of seconds, and immediately confirm the coordinates.

If you use a network-type RTK service, the smartphone can automatically obtain correction information (reference station data) via the Internet, so there is no need to prepare additional base stations. For example, by connecting to GNSS continuous observation stations provided by the Geospatial Information Authority of Japan or to private VRS services, you can perform high-precision positioning in real time. Also in Japan, systems that support the centimeter-class augmentation service (CLAS) from the Quasi-Zenith Satellite System “Michibiki” have appeared, enabling RTK positioning using augmentation signals from satellites even in mountainous areas outside cellular coverage. Across wide outdoor sites, iPhone RTK surveying enables quick and accurate stake-out and dramatically streamlines preliminary surveying and point measurements. For example, in roadworks or site development, walking the work area and measuring a few coordinates with a smartphone before bringing in heavy machinery makes subsequent work planning easier. Tasks that previously required arranging a dedicated surveying team to set reference points can be completed on the spot, leading to significant efficiency gains in field operations.

Surveying possible indoors as well

RTK-GNSS is, in principle, most effective outdoors where satellite signals can be received, but iPhone RTK surveying incorporates methods to perform positioning even indoors or in environments with many obstructions. Specifically, it uses a high-precision initial position obtained outdoors as a reference, and leverages the iPhone’s AR (augmented reality) technology and built-in sensors to track relative position indoors. By calibrating accurate coordinates and orientation outdoors at the start of positioning, the system continues to update the current position using the smartphone camera imagery and IMU (inertial measurement unit) when entering a building or going under a bridge.

This method enables positioning based on a global coordinate system indoors for short periods, and can be applied to tasks such as equipment layout inside buildings or position confirmation in tunnels. However, small errors accumulate over time, so for long-distance or long-duration movements it is recommended to re-calibrate outdoors as needed to maintain high accuracy. Even so, the seamless indoor-outdoor position identification that was previously difficult has become a reality through the combination of smartphone RTK. For example, it is now easy to perform consistent inside-outside positioning for tunnel construction or to calibrate at a building entrance and then carry out indoor dimensional measurements.

Advantages of smartphone RTK surveying

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

• Centimeter-class high precision: By using corrected GNSS, you can obtain your current position with an error on the order of a few centimeters. Since precise stake-out 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 just an iPhone and a small receiver is overwhelmingly compact compared to conventional stationary surveying instruments. There is no need to carry heavy equipment, and surveying can be performed nimbly even in narrow sites or on slopes. Because you simply attach a device weighing on the order of a few hundred grams to your phone, it is easy to carry and useful in places that are difficult for people to access.

• Intuitive operation: Since the app is operated via the smartphone’s touch UI, people without training in specialized equipment can handle it easily. With a single button you can start/stop positioning and save data, so anyone can 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 positional information. You can attach photos and notes to acquired points, or scan surroundings with LiDAR to create 3D point cloud data, which helps with site records and as-built management. AR measurement, such as positioning a distant target through the camera, is also possible.

• Real-time data sharing: By linking 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 in-field measured points on drawings. Data that used to be brought back on paper or USB can now be saved to the cloud on the spot, allowing stakeholders to check information in real time and enabling faster decision-making.

Easy deployment and operability

Another attractive point of iPhone RTK surveying is its low barrier to introduction. Since you can start using it simply by attaching a supported device to an iPhone or iPad you already own, there is no need to purchase large-scale new equipment. External RTK receivers are thin and lightweight enough to attach to the back of a smartphone (for example, weighing approximately 160 g), so you can carry them like a mobile phone. The app itself is also simply designed, allowing positioning start and data saving to be completed in a few taps.

Because field staff can use their everyday smartphones for surveying, operation is easy even without special training or expert knowledge. There is no need for complex wiring or adjustments between devices, and a single person can walk the site and perform surveying tasks. In the event a device is lost or damaged, the financial risk is small, and you can flexibly continue using a replacement terminal as needed. Also, because the initial investment is relatively small, it is easy for each staff member to carry a smartphone surveying device and operate on a one-device-per-person basis. If multiple people survey different parts of the site simultaneously, broad-area data collection can be completed in a short time, improving overall project efficiency. Because of this ease of use and high operability, smartphone RTK surveying is active across a wide range of sites—from small-scale surveys to rapid as-is assessments of large projects.

Use cases for iPhone RTK surveying

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

Setting reference points and as-built measurement on construction sites

High-precision reference point surveying and as-built (post-construction shape) measurement are indispensable in roadworks and site development. Using iPhone RTK surveying, you can obtain the coordinates of required points immediately upon arrival and easily set temporary reference points. Measuring multiple key points in a short time helps with the placement of heavy machinery and process management. After construction is completed, you can also scan the constructed objects with the phone’s LiDAR to obtain as-built 3D data in real time. This information can be shared on the cloud immediately, enabling quick verification and instruction between the field and the office.

Use in infrastructure inspection and maintenance

Smartphone RTK surveying is also highly useful for infrastructure inspections such as bridges and road facilities. For example, when photographing a crack on a bridge pier or a repair location for buried pipes, the smartphone can tag the photo with accurate coordinates for record-keeping. Without relying on paper drawings or distance measurements, you can preserve what you observed on site with high-precision positional information, allowing reports and maintenance plans to be prepared without revisiting the site. Additionally, using AR to visualize the locations of underground buried facilities can help avoid 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 required. With iPhone RTK surveying, you can start measuring damage as soon as you arrive at the affected area. For example, measuring the extent and height of collapsed soil with a smartphone and estimating the volume on site can assist in arranging heavy machinery or sandbags. Combined with drone aerial photography, you can quickly create wide-area damage maps. Even when communications infrastructure is disrupted, using satellite augmentation for positioning allows you to obtain positional information and share it with relevant agencies, supporting initial response efforts.

In this way, smartphone RTK surveying is a flexible tool that meets a variety of on-site needs and is expected to become increasingly widespread.

Simple surveying with LRTK

One solution that realizes the aforementioned iPhone RTK surveying is LRTK. LRTK is an integrated smartphone RTK positioning system consisting of a small 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 begin centimeter-class positioning using network RTK or Michibiki (CLAS) correction 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, field staff can perform high-precision surveying themselves without relying on a specialized surveying team. For example, tasks such as setting reference points and as-built checks on construction sites, and recording positions during infrastructure inspections can be efficiently carried out with a single smartphone. It supports outdoor use and also provides indoor positioning assistance for measurements under bridges or inside buildings. Surveying work that previously required expensive equipment and significant effort can be greatly simplified with LRTK. If you are interested in iPhone RTK surveying, consider using solutions like this to easily start high-precision positioning.

FAQ

Q: Can I perform RTK surveying with just an iPhone? A: At present, you cannot achieve centimeter-level RTK positioning with the iPhone alone. High-precision positioning requires a dedicated RTK-GNSS receiver. By using a small external device that attaches to the iPhone (e.g., LRTK Phone), you can receive correction information via the smartphone and realize RTK surveying.

Q: How accurate is the positioning? A: In open outdoor environments when an RTK Fix solution is obtained, you can expect approximately ±2 cm (±0.8 in) in horizontal position and ±4 cm (±1.6 in) in vertical direction. 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. Note that 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 indoors, relative positioning indoors is achievable by utilizing the smartphone’s camera and sensors. By aligning the current position and orientation outdoors with high precision before entering, you can track movement indoors for short periods (errors accumulate on the order of a few percent of indoor travel distance). For long-duration use or when high precision is required, it is recommended to perform RTK positioning outdoors again as needed for correction.

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 signals provided by the Quasi-Zenith Satellite System “Michibiki” can obtain augmentation information from satellites for RTK positioning even in mountain areas outside cellular coverage. It is also possible to set up your own mobile base station (local reference point) and transmit correction data via radio. However, using network-based correction services is generally easier and offers more stable accuracy.

Q: Which smartphones or tablets are supported? A: Basically, iOS-compatible apps are provided, and iPhones and iPads can be used. The latest iPhones are optimal due to high processing performance and built-in LiDAR, but position measurement itself works on models without LiDAR as well. If your device meets the required iOS version and hardware requirements, you can use your existing device as a high-precision surveying tool.

Q: Can Android smartphones be used? A: Currently, many solutions are provided for iPhone/iPad (iOS), and smartphone RTK surveying systems for Android are limited. iOS devices have advantages for positioning such as integrated UWB chips and high-performance sensors, so iPhone use is progressing first. Android-compatible products may increase in the future, but at present using an iPhone is mainstream.

Q: What kinds of sites and applications can it be used for? A: It can be used for a wide range of applications that require positional information, such as reference point surveying and as-built management in civil engineering, position recording of infrastructure facilities, topographic measurement in agricultural civil engineering, and situational assessment in disaster response. Because surveying data can be obtained quickly on site, some tasks that previously required outsourcing to specialists can be handled in-house. However, for public surveying work that legally requires qualification, it is still recommended to seek cooperation from licensed surveyors and other experts.

Q: Is there a cost advantage compared to conventional surveying equipment? A: In general, smartphone RTK solutions tend to significantly reduce initial costs compared to total stations and high-performance GNSS receivers. Being able to reuse existing smartphones and tablets is also a cost benefit. Because there is no need to prepare multiple expensive stationary instruments, it is easier to introduce for small- to medium-scale projects. However, the specific cost-effectiveness varies depending on the services used and the scale of operations, so careful consideration before introduction is important.