Labor- and time-saving with a single smartphone! One-person surveying with centimeter-level accuracy made possible by the iPhone RTK device

Table of Contents

• What is one-person surveying?

• What is centimeter-level positioning with RTK?

• Labor reduction and time-saving benefits of smartphone surveying

• What is an iPhone RTK device?

• Features of the iPhone RTK device

• Use cases for the iPhone RTK device

• Recommendations for simple surveying with LRTK

• FAQ

What is one-person surveying

Surveying has traditionally been conducted by teams of two or more people. In conventional surveying methods, a technician who operates optical instruments such as a total station pairs with an assistant who holds a staff (staff) or a prism. Because large, heavy equipment must be set up and measurement points recorded while mutually checking positions and targets, the work inevitably requires manpower and time. Also, in hazardous locations such as mountainous areas or disaster sites, having multiple people enter the area increases the risk of accidents. In this way, conventional surveying has relied heavily on manual labor, and there has always been a need to reduce personnel and improve safety.

Against this backdrop, the concept attracting attention is "solo surveying". As the name implies, this refers to surveying work carried out by a single person, and it is becoming feasible thanks to recent technological innovations. In particular, the spread of surveying methods that utilize GNSS (Global Navigation Satellite Systems) has opened the door to solo surveying. GNSS surveying, which can determine your position anywhere using GPS satellites as long as the sky is open, eliminates the need to carry heavy equipment and maintain lines of sight, and in principle allows a single worker to perform position staking. In other words, the era in which satellite positioning technology enables "one-man (single-person) surveying" has arrived.

However, conventional GNSS surveying also had limitations. With typical commercial GPS receivers, errors can reach several meters, and they fall far short of the level required for measuring boundary points and stake-driving work with centimeter-level accuracy (half-inch accuracy). Therefore, more precise positioning technology is indispensable for practical use. The condition for surveying alone is 'the ability to perform high-precision positioning without an assistant,' and the technology that makes this possible is RTK (Real-Time Kinematic).

Centimeter-level positioning with RTK

RTK stands for *Real Time Kinematic*, and is a correction technique that dramatically improves the accuracy of satellite positioning systems such as GPS. A standalone GPS fix can be off by several meters due to satellite signal errors, but the RTK method uses satellite data observed simultaneously by a base station (reference station) and a rover (mobile station) to correct those errors in real time. Specifically, the base station generates correction information from the difference between its known accurate position and the received satellite signals, and transmits this to the rover (the surveyor side). The rover uses the received correction information to adjust its observations, achieving centimeter-level positioning.

With the advent of the RTK method, GPS has become capable of providing positioning with accuracy sufficient for surveying. Traditionally, it was necessary to prepare dedicated, expensive RTK-capable GNSS receivers and communication devices and to obtain correction data via radio communication with a base station or via cellular networks. However, in recent years, advances in satellite positioning technology and cost reductions have made RTK positioning increasingly accessible even with small, inexpensive devices. Furthermore, in Japan the quasi-zenith satellite system "Michibiki" provides centimeter-level augmentation signals (CLAS, cm level accuracy (half-inch accuracy)), making high-precision positioning possible even in mountainous areas where it is difficult to install base stations. Thanks to these developments, centimeter-class RTK positioning (cm level accuracy (half-inch accuracy)) has begun to spread not only among traditional specialized organizations but also into general surveying work.

Labor Reduction and Time-Saving Effects of Smartphone Surveying

Although RTK laid the groundwork for high-precision single-person surveying, using it in the field still required specialized knowledge, such as handling equipment and processing positioning data. In addition, many traditional RTK-GNSS receivers cost several million yen just for the device, making it difficult for small and medium-sized operators to adopt them easily. In recent years, a new approach has emerged: smartphone-based surveying.

If a single smartphone can be used as surveying equipment, the barriers—both in terms of operability and cost—drop dramatically. Because position information can be viewed and recorded on the screen of a smartphone that everyone is familiar with, no special training like that required for specialized equipment is necessary. With a system that combines a dedicated terminal and a smartphone, complex processes such as reception from satellites and correction processing are automated in the background, so the user simply follows on-screen instructions to move and record points and the survey is completed. It should also be noted that this does not require the costly initial investment associated with existing high-precision surveying equipment, and you can make use of the smartphone you already own. Because it can be implemented simply by providing a small receiver and an app, small and medium-sized businesses can easily take advantage of the latest technology. This has made the labor-saving (personnel reduction) and time-saving (shorter work times) of surveying operations suddenly much more realistic.

In actual cases where smartphone surveying was adopted, there have been reports of site measurements that previously required 2–3 people and more than half a day being completed by a single person within tens of minutes. For example, at a civil engineering construction site, checking the overall as-built condition (final finished shape) of a developed area used to involve setting survey points and performing leveling surveys, taking more than half a day to finish. When they switched to a method of scanning the site on foot with an iPhone equipped with a high-precision GNSS receiver, they were able to acquire terrain data (point cloud) for the entire site in mere minutes and instantly visualize elevation differences from the design surface. Because they could perform additional measurements and adjustments on the spot and rescan to confirm in short cycles, this also led to a significant reduction in rework. Thus, smartphone surveying has the potential to deliver dramatic labor savings and efficiency improvements, and it is attracting considerable attention from industry stakeholders.

What is an iPhone RTK terminal?

So, what exactly does a practical method for enabling single-person surveying using a smartphone look like? The key is a device called "iPhone RTK terminal". In simple terms, it's an ultra-compact RTK-GNSS receiver that attaches to an iPhone or iPad, a device that turns a smartphone into a high-precision surveying instrument. By mounting this device on a smartphone, the phone can perform centimeter-level positioning comparable to conventional dedicated GNSS equipment.

The LRTK Phone, developed by a Japan-based startup, is a prime example of such an iPhone RTK device. It consists of a compact receiver weighing about 165 g that attaches to the iPhone and a dedicated app, realizing a smartphone-integrated surveying system. The high-precision positioning data received by the LRTK unit is sent to the app in real time and displayed and saved on the screen as position coordinates. Users can acquire precise location information, including latitude, longitude, and height, with the same ease as operating their everyday smartphone.

Features of the iPhone RTK Terminal

The main features of the iPhone RTK terminal (LRTK) are summarized as follows.

• Ultra-compact, lightweight design: A compact size that can almost integrate with a smartphone, weighing approximately 165 g and with a thickness of about 1 cm (0.4 in). Its pocketable, lightweight design allows you to carry it on-site at all times and take it out for use whenever needed.

• Built-in battery for long operation: The device includes a built-in battery that enables approximately 6 hours of continuous measurement. Charging is via USB Type-C and it also supports power from a power bank, so it can be used reliably outdoors where external power is hard to obtain.

• One-touch attach/detach: Dedicated smartphone cases and magnetic attachments are provided, allowing the device to be attached to or removed from an iPhone or iPad with one touch. It can be easily attached only when needed and removed when not in use, preserving the smartphone’s original portability.

• Centimeter-level positioning accuracy: A high-performance multi-band GNSS antenna is built in, and real-time corrections via RTK enable high-precision positioning of about ±1〜2 cm (±0.4〜0.8 in) horizontally. In the vertical direction (elevation), 3D coordinates can be obtained with an accuracy of about ±3 cm (±1.2 in). This achieves survey-grade accuracy that cannot be obtained with built-in smartphone GPS.

• Supports Michibiki CLAS and network RTK: It can receive the high-precision positioning augmentation service (CLAS) provided by Japan’s Quasi-Zenith Satellite “Michibiki,” allowing centimeter-level positioning even in areas without cellular coverage such as mountainous regions. It also supports network RTK (Ntrip) over the Internet, enabling real-time error corrections anywhere in Japan.

• Supports solo operation: A smartphone with the device attached can be fixed to a dedicated pole or a monopod and used like a conventional surveying instrument to perform high-precision point measurements and stake-out (positioning) tasks. Height offset correction can be easily set in the app, and by simply supporting it with one hand while watching a bubble level, you can accurately measure ground points. Full-scale surveying work can be performed by a single person without an assistant.

• Versatile surveying app features: Using the dedicated iOS app, you can utilize a variety of functions beyond simple position measurement. In addition to acquiring and recording current coordinates, it supports averaging from several seconds of continuous measurement, track log recording, 3D point-cloud scan surveying using the iPhone camera and LiDAR, navigation (guidance) to preset target coordinates, and AR features that overlay design drawings and 3D models onto live site imagery. With just one smartphone, you can complete surveying and the visualization of surveying results.

Use Cases for iPhone RTK Devices

How can iPhone RTK devices with these kinds of features be utilized in real-world fieldwork? Below are some anticipated scenarios and the benefits they provide.

1. As-built management on civil engineering and construction sites: "As-built management," the process of confirming whether the terrain and structures after construction have been finished according to the design, has traditionally been a labor-intensive task. Using an iPhone RTK device, a single person can walk the site while performing a 3D scan to acquire wide-area terrain data in a short time. Because the acquired point cloud data is georeferenced from the outset (latitude/longitude and elevation), you can check differences from the design data on-site with a color-coded heatmap display without bringing the data back to the office for coordinate conversion. For example, areas where the ground is higher than the design elevation appear red and lower areas appear blue, making it immediately obvious on the smartphone screen. If necessary, you can instantly perform additional measurements or construction rework and re-scan to confirm, enabling a rapid PDCA cycle. As a result, you can greatly reduce the manpower and days required for as-built inspections while ensuring quality.

2. Situational awareness at disaster sites: At disaster sites such as landslides and floods, surveying is indispensable for assessing and recording damage. However, it is difficult to send a large number of people into hazardous areas. With smartphone surveying, a single mobile worker can move around the site and perform measurements from safe positions. With centimeter-level positioning using an iPhone RTK device (cm level accuracy, half-inch accuracy), it is possible to record the terrain of the affected area with high precision to support subsequent recovery planning. In fact, Fukui City, Fukui Prefecture, was quick to introduce a field surveying system using iPhones and RTK positioning for disaster response, successfully mapping damage faster and at lower cost than traditional methods. Its ability to efficiently cover wide areas with limited personnel has been valued.

3. Public Surveying and Infrastructure Inspection: Local governments and others are considering smartphone-based surveying for various purposes. For maintenance and management of infrastructure such as roads and bridges, geotagged photo records and 3D modeling are useful. Using an iPhone RTK device makes it easy to tag captured photos with accurate coordinates and orientation, and to share point cloud data on the cloud. Because staff without specialized surveying equipment can take measurements with a smartphone, the burden of personnel training is also reduced. As a platform for promoting the DX (digital transformation) of surveying operations, the smartphone — a device anyone can use — will be a powerful tool.

Besides these, it can be applied to a wide range of situations depending on the idea, such as verifying land boundaries, conducting field measurements in agriculture, and even indoor positioning (relative positions can be measured with AR technology even when outside GPS coverage). The important point is that high-precision positioning and measurement can be carried out easily by a single person. Tasks that were previously abandoned due to manpower or cost issues may also become feasible with the combination of a smartphone and an iPhone RTK device.

Recommendation for Simple Surveying Using LRTK

As we have seen, smartphone surveying that combines an iPhone with an RTK unit represents an innovative approach that overturns conventional practices. With only a small device that a single person can carry and a smartphone app, you can carry out surveying of large sites, 3D recording, and even comparisons with design data in a short time. In addition to reduced personnel and time savings, ancillary benefits—such as the immediate use of survey data and improved safety—are also very significant.

As a solution that makes such simple surveying easy to carry out, LRTK is a highly compelling choice. Developed as a surveying system that can be completed with a single smartphone, the LRTK Phone combines accuracy and features comparable to professional surveying instruments with a usability designed to be easy for anyone to handle. If your company is looking to reduce labor or improve efficiency in its surveying operations, why not consider adopting this kind of smartphone surveying? One-person surveying that leverages the latest technology should dramatically increase on-site productivity.

FAQ

Q: Can you really perform surveying with just a smartphone? A: Yes. By combining a dedicated RTK receiver device with an app, a smartphone can function as a high-precision surveying instrument. If you attach a compact RTK receiver to an iPhone, it can achieve centimeter-level positioning (cm-level, about 0.4 in) based on signals from satellites. Simply bring the phone to the point you want to measure and tap the screen to record latitude, longitude, and elevation.

Q: Why can't the GPS in a typical smartphone achieve high accuracy? A: The GPS built into most smartphones suffers positioning errors of several meters due to satellite signal errors and ionospheric effects. That is fine for showing your current location in map apps or using it as a car navigation system, but it is insufficient for surveying. By using an RTK device and applying correction information to cancel these errors, you can obtain dramatically higher‑precision positions.

Q: Is a communication connection required for RTK surveying? A: If you receive correction information (differential data) via a network, a smartphone data connection (4G/5G) is required. However, within Japan, even in areas without cellular coverage you can achieve high-precision positioning by directly receiving the CLAS signal from the Quasi-Zenith Satellite System Michibiki. LRTK terminals support this CLAS, so centimeter-level positioning is possible without a base station even in mountainous areas.

Q: Can it be used with smartphones other than the iPhone? A: At present, this is a solution for iPhone and iPad iOS/iPadOS devices. It has been developed to take advantage of Apple products’ high-performance sensors and stable hardware environment, and a dedicated app is available from the App Store. Please look forward to future developments regarding support for Android devices.

Q: Can it be used without surveying knowledge or qualifications? A: Because basic operations are completed within a smartphone app, it is considerably easier than handling specialized surveying equipment. Tap the screen at the point you want to measure to record the coordinates, and calculations and corrections are performed automatically. However, qualifications such as a licensed surveyor are required to perform legal surveying work like official control point surveys or boundary determinations. Smartphone surveying should be used primarily as an aid for simple on-site measurements and preparing materials; if you intend to submit results as formal survey deliverables, it is desirable to have them verified by a professional.

Q: Can you really perform stake driving and setting out by yourself? A: Yes. With a combination of an iPhone RTK device and an app, there is a guidance (navigation) feature that displays arrows and distances on the smartphone screen toward the set target coordinates. If you follow this while carrying the smartphone, you can reach the target point. On site, if you mount the smartphone on a pole, stake driving that previously required two people can be done by one person. Using AR technology, the lines and points from the design drawings can also be displayed on the real-world view, visually assisting accurate positioning.