Easily achieve high-precision positioning with smartphone-linked GNSS devices! The way surveying is done will change

In recent years, the field of surveying has seen growing attention to "one-person surveying," which allows a single person to complete a survey. This is because, amid labor shortages and the aging of technicians, there is increasing demand to conduct surveys efficiently with small teams. Behind this trend are advances in technologies such as robotic total stations and high-precision GNSS positioning. An era is approaching in which surveying tasks that were traditionally carried out by multiple people can be performed by a single person thanks to technology.

In particular, the advent of GNSS terminals that link with smartphones is bringing a major transformation to the style of field surveying. By simply attaching a compact RTK-GNSS receiver to a smartphone, the smartphone can quickly be transformed into a surveying instrument with centimeter-level accuracy (cm level accuracy (half-inch accuracy)). For example, using a smartphone-linked GNSS terminal, a single person can perform everything from high-precision positioning to 3D point cloud scanning, stake driving (layout marking), and construction management using AR, and measurement data can be shared to the cloud instantly. Complicated surveying tasks become easy, and truly 「Easy high-precision positioning」 is realized.

In this article, we focus on GNSS devices that can be paired with smartphones and explain their features and the benefits of deploying them in the field. Centered on keywords such as improved surveying efficiency, labor savings, cloud integration, AR utilization, point cloud processing, and remote support, we examine how smartphone-based high-precision positioning is changing surveying workflows. Finally, as a concrete example, we introduce how to use the smartphone-connected RTK-GNSS terminal "LRTK" and its advantages.

What is a smartphone-connected GNSS device?

First, let's confirm what a smartphone-linked GNSS device is. A GNSS device is a device that measures your position using satellite positioning systems such as GPS, GLONASS, Galileo, and Michibiki (QZSS). A high-precision GNSS device that supports the RTK (Real Time Kinematic) method can reduce positioning errors to a few centimeters by using correction information from a reference station. Using this high-precision GNSS device together with a smartphone is what a smartphone-linked GNSS device is.

Specifically, a small RTK-GNSS receiver is connected to a smartphone via Bluetooth or cable, and positioning and data processing are performed using a dedicated app on the smartphone. The smartphone acts as a dedicated controller that also serves as the antenna and computing unit, and with just a palm-sized device and a smartphone, surveying tasks that previously required tripod setup and multiple people can be performed by a single person. By leveraging the smartphone's communication functions to receive network RTK correction information (for example, an electronic reference point network via Ntrip or Michibiki's centimeter-class augmentation service "CLAS"), real-time positioning to within a few centimeters (a few cm; about 1 in) can be achieved anywhere in the country.

Conventional smartphones' built-in GPS had errors of about 5-10 m (16.4-32.8 ft), but using a smartphone-connected GNSS unit dramatically improves positioning accuracy, making it easy to achieve the accuracy required for surveying — a few centimeters (a few in). The GNSS unit itself contains a battery and can perform continuous measurements for several hours, so ease of use in the field has also been taken into account. The major appeal is the convenience of being able to start high-precision positioning on the spot simply by taking a smartphone and a small GNSS unit.

Improving Survey Efficiency and Reducing Labor Requirements

One of the biggest benefits of smartphone-linked GNSS terminals is the efficiency and reduced manpower of surveying operations. Traditionally, surveying with a total station required a two-person team: a technician operating the surveying instrument and an assistant who set the prism at the distant target point. In some cases it was not uncommon for sites to require three or more people, including a recorder, working for an entire day. In situations with such labor and time costs, the inefficiency was especially severe at sites already suffering from chronic labor shortages.

By introducing a smartphone-linked GNSS terminal, such surveying can be handled by one person. With a high-precision GNSS, maintaining a direct line of sight is not required, so even on sites with many obstacles, a single person can move around and measure survey points one after another. Measurement operations are simple—just press a button on the smartphone screen—and recording survey point names and notes is automated, so no assistants or recorders are needed. As a result, limited staff can work on multiple sites in parallel, or a single technician can complete surveying over a wide area in a short time.

Labor-saving through personnel reductions not only leads to direct cuts in personnel costs, but also helps address chronic labor shortages. The mindset that "surveying is better if it can be done by one person" is spreading on sites, and attention to such solutions is growing as expectations for reduced manpower increase. The Ministry of Land, Infrastructure, Transport and Tourism’s *i-Construction* promotion and the construction industry's DX (digital transformation) are also supporting this, and one-person surveying is becoming a realistic option. Smartphone-connected GNSS terminals can be said to be a powerful tool supporting this one-person surveying.

Real-time Sharing and Remote Assistance via Cloud Integration

By leveraging smartphones and Internet connectivity, a major advantage is that surveying data collected on site can be shared to the cloud in real time. When measurements are taken with a dedicated app, survey points' latitude, longitude, and height, acquisition time, notes, related photos, and other information are immediately stored on the smartphone. If those data are uploaded to the cloud on site, they can be shared immediately with staff and stakeholders in the office. If you send the results from your smartphone before leaving the site, supervisors and colleagues can review the data and provide feedback while you are en route or before you arrive at the office.

Cloud integration enables smoother remote support and instruction. For example, if a measurement was missed or additional points are needed, the office can check the data and immediately contact the field to request supplementary measurements. This minimizes rework such as “going back to the site to remeasure after reviewing data brought back.”

Also, at disaster sites, a single person can perform surveying and photographic recording with a smartphone and a GNSS terminal and share it with headquarters via the cloud, enabling remote technicians to instantly grasp the situation and create drawings—realizing remote support. Point cloud data and coordinates obtained on site can be viewed on cloud-based maps and 3D views, allowing people who are not present to understand the spatial data and make appropriate judgments and give instructions.

In this way, cloud sharing of data eliminates the time lag between the field and the office and significantly reduces the lead time from surveying to deliverable preparation. Immediate information sharing among stakeholders enables early detection of errors and rapid decision-making, contributing to the overall efficiency of operations.

Intuitive Positioning and Construction Management Using AR

AR (augmented reality) technology, which overlays information onto the real world through a smartphone screen, can also bring new levels of convenience to surveying and construction management when combined with smartphone-linked GNSS terminals. By providing high-precision self-positioning, AR displays on the smartphone enable intuitive guidance and verification.

For example, by using the dedicated app's AR feature, you can display real-time guidance on the screen such as "east by ○ cm (○ in)" and "north by ○ cm (○ in)" for a pre-set target point. By simply following this guidance, stake-setting (positioning and marking) work that used to require several people can be carried out accurately by a single person. With a smartphone in one hand, if you move toward the arrows and target marks displayed on the screen, you can reach the designated coordinates without hesitation, enabling even less experienced workers to perform highly accurate layout work.

Additionally, by importing design data and drawings as 3D models into a smartphone and projecting them onto the actual site scenery with AR, you can visualize the finished form on the spot. For example, overlaying design models of road embankments or structures onto the site enables operators, workers, and clients to intuitively share the completed image, helping to prevent construction mistakes and resolve misunderstandings. Comparing surveyed terrain data with the design model on-site to check deviations and estimate embankment volumes on the spot — this kind of immediate as-built management is also easy with AR.

By leveraging AR, tasks such as "measuring", "recording", and "comparing" can be performed visually and in real time on-site. Processes that previously required taking measurement points back and cross-checking them against drawings can be completed on the spot with AR, leading to a reduction in rework and do-overs.

Point Cloud Processing Made Easy with Smartphone LiDAR and Photogrammetry

By utilizing the LiDAR sensors and high-performance cameras built into the latest smartphones, on-site 3D point cloud data acquisition can be carried out easily. By using a smartphone-connected GNSS receiver, precise position coordinates (latitude, longitude, and height) can be assigned to the point clouds captured with the smartphone, so the acquired point clouds immediately become 3D surveying data in the geodetic coordinate system.

A single person can walk around holding a smartphone and, simply by scanning the surroundings, record terrain and structures as high-density point clouds. In traditional topographic surveying, positions between survey points were visually interpolated, but point cloud measurement captures the surface’s irregularities down to every nook and cranny, enabling more reliable as-built verification and the creation of detailed digital twins. Large amounts of point cloud data become a powerful resource for checking arbitrary cross-sections later and verifying details that would be overlooked in plan views.

Furthermore, using the acquired point cloud data, analyses such as earthwork volume calculations can be carried out immediately on-site. For example, if the ground before and after excavation is scanned and the point clouds are compared, calculating cut-and-fill volumes on the spot can dramatically improve earthwork management efficiency. Point cloud measurements that used to require dedicated 3D laser scanners can increasingly be substituted with just a smartphone and a GNSS device. This lowers the barrier to 3D surveying and further accelerates on-site digitization.

How to Use and Advantages of the Smartphone-Connected RTK-GNSS Device "LRTK"

Finally, as a concrete example of a smartphone-linked GNSS device, I will introduce a product called "LRTK" and explain how to use it and its advantages. LRTK is a pocket-sized RTK-GNSS receiver developed by a startup originating from Tokyo Institute of Technology, and it is used in combination with commercially available smartphones. Weighing about 165 g, and with a thickness of about 1 cm (0.4 in), it has an ultra-compact design that can be attached to a smartphone, yet it achieves centimeter-level positioning accuracy comparable to professional surveying GNSS equipment. It attaches to the back of an iPhone with a dedicated holder and operates via a Bluetooth connection.

The basic steps for using LRTK are as follows:

• Preparation – Attach the LRTK receiver to your smartphone. Mount it to the back of an iPhone or iPad using a dedicated holder or case, and beforehand install the free dedicated app "LRTK" from the App Store.

• Startup – When you arrive at the survey site, turn on the LRTK device. Launch the app on your smartphone and connect to the device; satellite acquisition will begin. Within tens of seconds it will reach RTK "FIX" status, enabling centimeter-level positioning (cm level accuracy, half-inch accuracy).

• Measurement – Move to the point you want to measure and tap the "Positioning" button in the app to record the high-precision coordinates for that location (single-point positioning). No assistant is required. If you want to continuously measure a wide area, simply walk around holding the smartphone and points will be automatically measured and recorded at regular intervals. If the smartphone is LiDAR-equipped, you can also scan surrounding point clouds by pointing the camera.

• Data verification & sharing – The measured coordinates and generated point clouds are displayed on the app screen on site, and two-point distances and area calculations can be performed instantly. If you take photos of the site as needed, they will be saved with location information. After work, use the app’s sync feature to upload data to the cloud so results can be viewed and shared via the web from PCs in the office.

To summarize the main benefits gained from implementing LRTK, the following points can be highlighted:

• Centimeter-level high-precision positioning (cm level accuracy (half-inch accuracy)) – Achieves positioning accuracy within several cm (several in) (cm level accuracy (half-inch accuracy)), improving the quality of survey deliverables. It stands apart from conventional smartphone GPS errors of several m (several ft), and offers sufficient accuracy for as-built control and stakeout/layout marking.

• One-person surveying – Measurements can be completed with a smartphone in hand, allowing tasks that previously required multiple people to be handled by a single person. This enables efficient work even on sites facing personnel shortages.

• Intuitive operation – The simple UI of the smartphone app enables intuitive operation, and even first-time users can handle it after a short training. Positioning is primarily button-driven and requires no complex settings, so stable results can be obtained without experienced personnel.

• Integration of diverse functions – Not only position measurement, but coordinate navigation via AR, point cloud scanning, photo recording, and various measurements (distance, area, volume calculations) — all features necessary for field surveying are integrated into a single app. You can complete on-site tasks in a one-stop manner without using separate devices or software.

• Cloud sharing and data management – Measurement data can be automatically synced with the cloud, making it easy to share results on the spot and reducing the hassle of data organization. Transcribing to paper field notebooks or taking data back is no longer necessary, reducing human error.

• Ease of adoption – Compared to conventional high-precision GNSS survey instruments, the combination of a smartphone and a compact terminal can greatly reduce initial investment and operating costs. The dedicated app is provided free of charge, and because you can use an existing smartphone, there is no need to acquire new dedicated equipment. As a result, small and medium-sized enterprises and local governments can more easily adopt it and benefit from high-precision positioning.

• Improved safety – Speeding up surveying work can shorten time spent in hazardous areas. Also, even when working alone, utilizing AR features allows targets to be measured from a safe distance, which helps reduce burden in dangerous environments such as roadways or slopes.

By leveraging smartphone-connected GNSS devices such as LRTK, labor savings, improved efficiency, and higher accuracy in surveying can be achieved simultaneously, and on-site work styles are being transformed. As these single-operator surveying solutions become increasingly widespread, the digital transformation (DX) of the construction and surveying industries will advance further. Easy, high-precision positioning with smartphones and GNSS is becoming the new standard at worksites.