Usable Indoors and Outdoors! Easy High-Precision Measurements with iPhone RTK Surveying

Table of Contents

• What is iPhone RTK surveying?

• Easy centimeter-level positioning outdoors

• Surveying possible indoors as well

• Benefits of smartphone RTK surveying

• Easy implementation and operability

• Use cases for iPhone RTK surveying

• Simple surveying with LRTK

• FAQ

What is iPhone RTK surveying?

In civil engineering and construction, the adoption of ICT exemplified by the Ministry of Land, Infrastructure, Transport and Tourism’s i-Construction initiative has been advancing in recent years, and there is strong demand for streamlining surveying tasks. However, traditional high-precision surveying required expensive equipment such as total stations and dedicated GNSS devices, and technicians capable of operating them were limited, placing a burden on sites. Against this backdrop, there has been growing demand for “a more accessible yet high-precision surveying method.”

With recent advances in positioning technology, a new surveying style using smartphones has attracted attention. Among these, iPhone RTK surveying is a revolutionary method that achieves centimeter-class high-precision positioning comparable to conventional surveying instruments by combining a dedicated compact GNSS receiver with an iPhone. RTK (Real Time Kinematic) is a technology that dramatically improves positioning accuracy by applying correction information from a base station in real time; while typical smartphone-built-in GPS has errors of about 5-10 m (16.4-32.8 ft), RTK can pinpoint positions with errors of only a few centimeters (a few inches). Note: centimeter-level accuracy (cm level accuracy (half-inch accuracy)).

Until now, achieving this level of accuracy required preparing expensive GNSS surveying instruments, base stations, and antennas, and having specialized technicians operate them. But the situation is changing thanks to the fusion of iPhone and external RTK devices. By attaching a compact RTK receiver to a familiar smartphone and using a dedicated app, a new era is arriving in which anyone can easily perform high-precision surveying. Combining the intuitive operation of smartphones with the precision of RTK promotes DX (digital transformation) on sites and greatly contributes to improved efficiency and labor savings in 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 procedures. Traditionally, each survey required setting up tripods and equipment, and complex preparations such as configuring communications with control points. With smartphone RTK, measurement starts simply by powering on the RTK receiver attached to the iPhone and starting positioning in the app. In a wide-open area the RTK Fix solution (the high-precision state where the float solution is resolved to a Fix) can be obtained in tens of seconds, allowing you to immediately confirm coordinate positions.

If you use a network-type RTK service, correction information (base station data) can be automatically acquired over the Internet from the smartphone, so you do not need to prepare an additional base station. 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 real-time high-precision positioning. In Japan, systems that also support the quasi-zenith satellite “Michibiki” centimeter-class augmentation service (CLAS) have emerged, allowing RTK positioning to be possible even in mountainous areas beyond cell coverage by receiving augmentation signals from satellites. Across wide outdoor sites, iPhone RTK surveying enables fast and accurate stakeout and dramatically streamlines preparatory surveying and point measurements. For example, on roadworks or land development sites, walking key points in the construction area and measuring several coordinates with a smartphone before bringing in heavy machinery makes subsequent work planning easier. Tasks such as establishing control points, which previously required a specialized surveying team, can now be completed on the spot, significantly improving on-site work efficiency.

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, 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 positions indoors. By calibrating accurate coordinates and orientation outdoors at the start of positioning, the system continues to update the current position using the smartphone’s camera images and IMU (inertial measurement unit) even when entering buildings or going under bridges.

This method allows short-term indoor positioning in the global coordinate system, making it applicable to tasks such as equipment placement inside buildings and location verification inside tunnels. However, small errors accumulate over time, so for long-distance or long-duration movements, periodically re-calibrating outdoors maintains high accuracy. Even so, the previously difficult “seamless positioning between indoors and outdoors” has become a reality through the combination of smartphone RTK. For example, it is now easy to perform continuous positioning inside and outside a tunnel or to calibrate at a building entrance and then measure interior dimensions.

Benefits of smartphone RTK surveying

Combining a smartphone with RTK brings many advantages not found in conventional equipment. The main benefits are summarized below.

• Centimeter-class high accuracy: With correction GNSS, you can obtain current positions with positioning errors on the order of a few cm (a few inches). Because precise stakeout and control point measurement can be done on site immediately, this contributes to improved construction accuracy and faster verification tasks. Note: centimeter-level accuracy (cm level accuracy (half-inch accuracy)).

• Mobility and portability: Configured only with an iPhone and a compact receiver, the system is overwhelmingly more compact than conventional fixed surveying equipment. There is no need to carry heavy equipment, enabling agile surveying in narrow sites or on slopes. Because you simply attach a device weighing several hundred grams to your smartphone, it is easy to carry and effective in areas hard to access.

• Intuitive operation: Operation is done via a smartphone’s touch UI, so even people without specialized equipment training can use it easily. Measurement start/stop and data saving can be done with a single tap, allowing anyone to perform high-precision positioning without confusion.

• Multifunctional measurement: Newer iPhones have high-performance cameras and LiDAR sensors, enabling diverse measurements when combined with RTK position information. You can attach photos and notes to collected points or scan surroundings with LiDAR to create 3D point cloud data, which is useful 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 linking the smartphone to the cloud, measured coordinate data and photos can be shared with the office immediately from the field. For example, the office can instantly reflect field-obtained point coordinates on drawings, enabling real-time collaboration. Data that previously had to be carried back on paper or USB can be saved to the cloud on site, allowing stakeholders to check information in real time and make quick decisions.

Easy implementation and operability

A major appeal of iPhone RTK surveying is its low implementation barrier. You can start using it simply by attaching a compatible device to the iPhone or iPad you already own, eliminating the need to purchase new large-scale equipment. External RTK receivers are thin and lightweight enough to be attached to the back of a smartphone (for example, weighing about 160 g), and can be carried around like a mobile phone. The app is also designed simply, allowing you to complete positioning start and data saving in a few taps.

Since field staff can use the smartphones they already use daily for surveying, operation is easy even without special training or expertise. There is no need for complex wiring or adjustments between devices, and a single person can walk the site and perform surveying tasks. Even if a device is lost or damaged, the cost risk is low and you can flexibly replace the terminal as needed to continue operations. Because the initial investment is relatively small, it is also easy to equip each staff member with a smartphone surveying device in a one-person-one-device setup. If multiple people measure different areas 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 across a wide range of sites, from small surveying tasks to rapid as-built assessments for large projects.

Use cases for iPhone RTK surveying

The benefits that smartphone RTK surveying brings to sites are diverse. Below are some concrete use cases.

Establishing control points and as-built measurement on construction sites

High-precision control point surveying and as-built (post-construction shape) measurement are indispensable for roadworks and land development sites. Using iPhone RTK surveying, you can obtain coordinates for required points immediately upon arrival and easily establish temporary control points. Measuring multiple key points in a short time facilitates the placement of heavy machinery and process management. After construction is complete, you can use the smartphone’s LiDAR to scan the shape of the constructed object and acquire as-built 3D data in real time. This information can be shared on the cloud instantly, enabling rapid verification and instruction between the field and the office.

Use in infrastructure inspection and maintenance

Smartphone RTK surveying is also very useful for inspecting bridges, road facilities, and other infrastructure. For example, photographing crack locations on a bridge pier or repair points for buried pipes with a smartphone will record photos with precise coordinates attached. Without relying on paper drawings or distance measurements, you can preserve the on-site situation with high-precision location information, allowing reports and maintenance plans to be updated without revisiting the site. Using AR, you can visualize the location of buried utilities to prevent accidental damage during excavation, which is another promising application.

Rapid situation assessment at disaster sites

At disaster sites such as earthquakes or landslides, rapid situation assessment and information sharing are required. With iPhone RTK surveying, measurement of damage can begin immediately upon arrival at the affected area. For example, measuring the extent and height of collapsed soil with a smartphone and estimating volume on site can help arrange heavy machinery or sandbags. Combined with drone aerial photography, you can quickly create wide-area damage maps. Even when communication infrastructure is disrupted, positioning using satellite augmentation can provide location information to share with relevant agencies, greatly aiding initial response.

Thus, smartphone RTK surveying is expected to become increasingly widespread as a flexible tool that meets a variety of on-site needs.

Simple surveying with LRTK

One solution that realizes the iPhone RTK surveying described above is LRTK. LRTK is an integrated smartphone RTK positioning system composed of a compact high-precision GNSS receiver called the “LRTK Phone,” an iOS app, and a cloud service. Simply attach the LRTK Phone to your iPhone and launch the app to immediately start centimeter-level positioning using network RTK or Michibiki (CLAS) correction data. Collected coordinate data and point cloud models are automatically saved to the LRTK cloud and can be viewed or downloaded from a PC.

By introducing LRTK, field staff can perform high-precision surveying without relying on a specialized surveying team. For example, tasks such as establishing control points and checking as-built conditions on construction sites, or recording positions for infrastructure inspections, can be performed efficiently with a single smartphone. LRTK also includes positioning assistance features for indoor use, enabling measurements under bridges and inside buildings as well. Surveying tasks that previously required expensive equipment and significant effort are greatly simplified with LRTK. If you are interested in iPhone RTK surveying, consider using such solutions to easily begin high-precision positioning.

FAQ

Q: Can RTK surveying be done with the iPhone alone? A: Currently, you cannot achieve centimeter-level RTK positioning with only the iPhone itself. 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 through the smartphone and realize RTK surveying.

Q: How accurate is the positioning? A: In open outdoor conditions when an RTK Fix solution is obtained, you can expect approximately ±2 cm (±0.8 in) horizontally and ±4 cm (±1.6 in) vertically. Accuracy varies with environmental conditions and satellite reception, but this is orders of magnitude more precise than typical smartphone GPS errors of several meters. Accuracy can degrade in locations surrounded by buildings or trees due to multipath reflection of satellite signals.

Q: Can you really position indoors? A: Yes—while full satellite positioning is not possible indoors, using the smartphone’s camera and sensors enables relative indoor positioning. By aligning your position and orientation precisely outdoors before entering, you can track movement indoors for a short time and perform positioning (errors accumulate at about a few percent of indoor travel distance). For long-duration use or when high accuracy is required, we recommend periodically performing RTK positioning outdoors to reapply corrections.

Q: Can it be used without the Internet? A: Yes. There are methods to perform high-precision positioning even without an Internet connection. In Japan, for example, using a receiver compatible with the “Michibiki” CLAS signals allows RTK positioning in mountainous or out-of-coverage areas by receiving augmentation signals directly from satellites. It is also possible to set up your own mobile base station (local control point) and transmit correction data via radio. However, using network-based correction services is typically easier and provides more stable accuracy.

Q: Which smartphone or tablet models are supported? A: Generally, iOS-compatible apps are provided, allowing use on iPhone and iPad. The latest iPhones are optimal due to high processing performance and built-in LiDAR, but positioning itself works on models without LiDAR as well. As long as your device meets the app’s iOS version and hardware requirements, you can use your existing device as a high-precision surveying instrument.

Q: Is it available on Android smartphones? A: Currently, many solutions are offered 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 usage is currently more widespread. 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 requiring location information, such as control point surveying and as-built management in civil engineering, recording positions of infrastructure equipment, topographic measurement in agricultural civil engineering, and disaster site assessment. Because you can obtain survey data quickly on site, some tasks previously outsourced to specialists can be handled in-house. However, for public surveying or other legally regulated tasks requiring qualifications, we recommend continuing to work with licensed surveyors and other specialists.

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. Reusing existing smartphones and tablets also provides a cost advantage. Because you do not need to purchase multiple expensive fixed instruments, adoption is easier even for small- to medium-scale projects. That said, the specific cost-effectiveness depends on the services used and the scale of operations, so thorough consideration before introduction is important.