One device for point surveying and 3D scanning! RTK devices are the all-purpose survey instruments for the field

In the construction industry in recent years, the promotion of i-Construction and DX (digital transformation) has accelerated the introduction of ICT devices into on-site surveying operations. On surveying sites today, RTK devices, which can handle both "point surveying" and "3D scanning" with a single unit, are attracting attention. Thanks to high-precision GNSS positioning using the RTK (real-time kinematic) method, tasks that were traditionally carried out separately can be performed together. Such RTK-capable positioning devices are truly versatile as onsite surveying instruments, and their ease of use even for beginners is also an appealing point.

Table of Contents

• What is an RTK device?

• Achieving point surveying and 3D scanning with one device

• Comparison with traditional surveying methods

• Benefits of introducing RTK devices

• Use cases for RTK devices

• Simple surveying with LRTK

• FAQ

What is an RTK device?

RTK stands for Real Time Kinematic, a high-precision positioning technology that uses GNSS (satellite positioning systems). Two receivers, a base station and a rover, observe simultaneously; the base station sends error information measured at its location to the rover in real time to correct errors, dramatically reducing position error. Normally, standalone GPS positioning can have errors of several meters (several ft), but by using RTK it is possible to reduce errors to the order of a few centimeters (a few in).

An RTK device is a terminal that makes RTK positioning easy to accomplish on site. Traditionally, RTK positioning required large GNSS receivers and fixed equipment, but recent miniaturization of electronic components has produced palm-sized RTK-capable GNSS receivers. By using network RTK correction services (such as VRS) or CLAS augmentation signals from Japan’s Quasi-Zenith Satellite System "Michibiki," centimeter-class positioning (cm level accuracy (half-inch accuracy)) is possible without installing a dedicated base station. For example, there are RTK devices that attach to a smartphone or tablet; they are portable for the field and start high-precision positioning simply by turning on the power. With such RTK devices, even users without special skills can easily obtain highly accurate position information.

Achieving point surveying and 3D scanning with one device

Traditionally, surveying operations typically performed point surveying (measuring accurate coordinates of individual points) and 3D scanning (capturing the site’s shape as three-dimensional point cloud data) with separate equipment and methods. For example, to determine the elevation of a control point or the position of a boundary, point surveying would be carried out using an optical total station or GNSS survey instrument, while to record the overall terrain or the shape of structures you would need a terrestrial laser scanner or photogrammetry from drone images for 3D scanning.

However, by using an RTK device, you can perform both point surveying and 3D scanning with a single unit. One device can handle everything from pinpoint positioning to wide-area shape measurement, greatly reducing the amount of equipment you need to carry on site. Specifically, by leveraging the centimeter-level position information provided by the RTK device and capturing the surroundings with a smartphone camera or LiDAR sensor, you can acquire point cloud data with high-precision position coordinates. Individual survey point coordinates and 3D models are recorded in the same reference coordinate system, so there is no additional effort to integrate data later. Survey tasks that used to be done separately are increasingly being completed in a single site visit thanks to the introduction of RTK devices.

Comparison with traditional surveying methods

With the advent of RTK devices, field surveying workflows are changing significantly. Here we summarize the differences compared with traditional surveying methods.

• Required equipment: Traditionally, you needed to bring in a total station, large GNSS receivers, tripods, targets, external batteries, and many other pieces of equipment. In some cases, a separate laser scanner for 3D scanning was also required, making transport and setup at the site a major chore. With an RTK device, surveying can be done with a small receiver and a smartphone, significantly reducing the quantity and weight of equipment.

• Personnel and skills: In traditional precision surveying, it was common for several skilled surveyors to divide roles during work (for example, one person operating the instrument while another holds the prism). Instrument operation required specialized knowledge and adjustments. With an RTK device, one person can handle tasks easily, and intuitive smartphone app operation guides the measurement. Even without specialized knowledge, measurements can be made by following on-screen instructions, making RTK devices suitable for sites with labor shortages.

• Work time: Traditionally, time-consuming setup such as installing equipment and establishing control points was required before surveying could begin. Point surveying and 3D scanning were sometimes done on different days, requiring multiple site visits. With an RTK device, positioning starts immediately after power-up, and point cloud capture can be performed on the spot, leading to significant time savings.

• Data processing: Traditionally, point cloud data required later alignment to control points through georeferencing. Integrating multiple datasets also involved manual alignment work. Point clouds and photographic data acquired with an RTK device have accurate position coordinates attached from the start, so post-capture coordinate alignment is unnecessary. This allows immediate onsite verification of as-built conditions and smooth import into CAD or BIM software back at the office.

In this way, workflows using RTK devices achieve efficiency and simplification across equipment, personnel, time, and data processing compared with traditional methods. They lower the barrier to surveying and enable faster, more flexible field responses.

Benefits of introducing RTK devices

Introducing RTK devices to the field yields many benefits, such as:

• Dramatic improvement in work efficiency: Point surveying and 3D scanning can be performed together in a single site visit, greatly shortening surveying time. Equipment setup and movement are reduced, allowing rapid data acquisition regardless of weather or schedule. Because positioning results and point cloud data can be checked in real time, additional measurements or rework can be handled flexibly on the spot.

• Cost reduction: Conducting surveys with fewer people and in less time reduces labor and transport costs. There is no need to procure multiple expensive specialized surveying instruments; introducing a relatively affordable RTK device can lower initial investment. If work previously outsourced to specialist surveyors can be done in-house, outsourcing costs are also reduced.

• Improved accuracy and data quality: RTK centimeter accuracy enables far more precise positional information than before. This increases the reliability of stakeout and as-built management, minimizing manual errors and human mistakes. Acquired 3D point clouds are tagged with absolute coordinates, allowing accurate overlay of data collected in multiple sessions and high-precision time-series change analysis.

• Expanded data utilization: Survey data obtained with RTK devices can be output in formats matching public coordinate systems. As a result, point cloud models and survey point coordinates can be overlaid onto GIS maps or integrated with BIM/CIM design models to support construction planning. With photogrammetry, detailed 3D models of the site can be generated immediately, making volume calculations and distance measurements easy in digital form.

• Versatility and future potential: RTK devices can handle a wide range of uses, from point surveying to terrain scanning and even AR-based overlay of design data, all with a single device. In the coming construction DX era, they are promising tools for immediately acquiring and sharing onsite digital data. Compact devices are easy to carry and offer the mobility to survey whenever needed, which is a major advantage.

Use cases for RTK devices

RTK devices are used in various scenarios. Here are some representative examples.

• Surveying for small-scale construction and land development: RTK devices are useful for surveying relatively small sites such as residential development lots and road improvement projects. Measuring the as-built condition of ground shaped by heavy machinery on site and creating a 3D model to calculate volumes enables quick earthwork quantity management and verification of embankment and excavation. Tasks that traditionally required a surveying team after construction are increasingly being completed quickly by site supervisors themselves.

• Rapid damage recording at disaster sites: RTK devices are used to record site conditions immediately after earthquakes, floods, and other disasters. For example, they can be used to document ground subsidence or liquefaction-induced surface changes, as well as building tilts and crack conditions, in detail with photos and point clouds and share the data to the cloud immediately. Even where communication infrastructure is lacking, devices compatible with Japan’s augmentation services can perform high-precision surveys on site, aiding initial response.

• Infrastructure inspection and maintenance: 3D scanning is effective for inspecting bridges, tunnels, and plant equipment. High-precision point clouds obtained with RTK-enabled scanning allow quantitative identification of crack locations and deformation amounts. Scanning the same locations during periodic inspections enables visualization of aging-related changes. High-precision displacement measurements that used to require specialist contractors can now be performed by site personnel using their own devices.

• Surveying in remote locations: RTK devices are powerful in remote sites that were traditionally difficult to survey, such as mountain construction sites or former golf course land planned for solar power plants. Devices compatible with CLAS signals can receive corrections even outside cellular coverage, allowing wide-area surveys to be conducted independently. In areas where drones cannot capture ground beneath trees, a walking survey with an RTK device can acquire dense ground point clouds and reduce the number of additional survey visits.

Simple surveying with LRTK

Among the many RTK devices, LRTK is attracting attention as a product that can be easily used with a smartphone. Developed by a startup from Tokyo Institute of Technology, it is a small device that attaches to an iPhone. It consists of an antenna-and-battery integrated receiver and a dedicated app, and supports network RTK and "Michibiki" CLAS signals, enabling centimeter-class positioning (cm level accuracy (half-inch accuracy)) even outside communication coverage. By simply attaching LRTK to an iPhone, an ordinary smartphone quickly becomes an RTK-capable all-purpose surveying tool.

With LRTK you can perform everything from point positioning to 3D point cloud scanning and even AR-assisted stakeout navigation with a single device. Photos and LiDAR-scanned point clouds are tagged in real time with high-precision position coordinates, so site-acquired data can be uploaded to the cloud and shared with stakeholders or checked against CAD drawings for as-built verification seamlessly. The app is designed to be intuitive for users without specialized knowledge, enabling a labor-saving and high-precision form of simple surveying. LRTK has been used in investigations of disaster areas such as the Noto Peninsula earthquake, and its practicality and ease of use have quietly made it popular among field personnel. As a tool that makes high-precision surveying more accessible, LRTK is expected to see expanding applications. The official LRTK website also publishes case studies and demonstration videos, so interested readers should check it out.

FAQ

Q1. What is the difference between RTK and ordinary GPS positioning? A1. Ordinary GPS (GNSS) positioning typically produces errors on the order of several meters (several ft), whereas RTK (real-time kinematic) uses correction information from a base station to reduce errors to the order of a few centimeters (a few in). Specifically, RTK observes satellite signals simultaneously at both a base station and a rover and cancels common error factors between the two points. As a result, RTK provides dramatically higher real-time positioning accuracy compared with standalone positioning.

Q2. What preparations or environment are required to use an RTK device? A2. Basically, you need the RTK device itself, a smartphone or tablet to pair with it, and a means of receiving correction information. If you use network RTK, you will need internet connectivity and a communication contract. However, within Japan, devices that support "Michibiki" augmentation signals can receive corrections even at sites without cellular coverage, such as mountainous areas. Initial setup and installation of the dedicated app are required when using the device for the first time, but once configured, positioning starts simply by turning on the power at the site. Many smartphone-connected RTK devices connect via Bluetooth and control positioning and data checks through a dedicated app.

Q3. Can surveying beginners handle it? A3. Yes. Modern RTK devices are designed for intuitive operation. Measurements can be performed by following guidance on the dedicated smartphone app, and complex surveying calculations and adjustments are automated. Therefore, even users with limited experience or without surveying qualifications can perform basic measurements. However, surveying knowledge can be helpful for interpreting and utilizing the obtained data, so gradually deepening one’s understanding will make use more effective.

Q4. What level of accuracy can RTK devices achieve? A4. Under favorable conditions, RTK devices can be expected to achieve approximately 1–3 centimeters (0.4–1.2 in) horizontally and a few centimeters (a few in) vertically. Accuracy varies with surrounding obstructions and radio conditions. Open-sky environments provide the highest accuracy, while forests or dense urban areas with tall buildings can cause multipath and signal attenuation, increasing errors somewhat. Even so, RTK is far more accurate than standalone positioning (errors of several meters (several ft)) and offers practical precision for many surveying tasks.

Q5. Can RTK devices be used where satellites cannot be received or indoors? A5. Unfortunately, RTK devices that use GNSS cannot perform positioning where satellite signals are unavailable. In forests or building shadows, satellite signals may be blocked, degrading accuracy or interrupting positioning. Indoors or inside tunnels, GNSS signals generally cannot be received at all, so RTK is unusable. In such environments, it is necessary to use other surveying instruments or methods, such as total stations. However, in some cases you can work around the issue by performing RTK positioning at a nearby open location and measuring relative positions to the inaccessible area.

Q6. What types of RTK devices are available? A6. Broadly speaking, there are RTK devices designed to work with smartphones or tablets and dedicated units (handheld or pole-mounted RTK receivers). Smartphone-connected types leverage the phone’s display and processing power, making them compact and lightweight with excellent portability and usability. Dedicated units are ruggedly built for harsh outdoor environments and include models optimized for long-duration surveying and stable positioning accuracy. There are also specialized RTK receivers for drone integration or surveying robots. Choose the type that fits your use case; for first-time adopters, smartphone-connected models that balance ease of use and versatility are recommended.

Q7. Is there a cost to use RTK correction information? A7. It depends on the correction source. Receiving correction data from network RTK services (VRS, etc.) often requires paid membership or monthly fees from surveying companies or GNSS service providers. For example, services using private reference station networks charge according to usage time or monthly contracts. On the other hand, RTK devices compatible with Japan’s Quasi-Zenith Satellite System "Michibiki" can receive free centimeter-level augmentation signals (CLAS) directly from satellites without internet, enabling centimeter-class positioning without additional usage fees. Consider which correction source suits your needs and region.