RTK Use Cases in Construction: Improved Work Quality with High-Precision Positioning

Table of Contents

• What is RTK?

• Benefits of Using RTK on Construction Sites

• What RTK Can Do (Use Cases)

• How to Introduce RTK and Key Points

• Recommendation: Simple Surveying with LRTK

• FAQ

Accurate surveying is indispensable in construction and civil engineering sites, but it is not always realistic to have a full surveying crew on site at all times or to outsource to specialist surveyors. With labor shortages and budget constraints, it is necessary to devise ways to carry out surveying with a limited number of personnel. However, neglecting surveying accuracy can cause positional deviations that lead to construction mistakes and rework, resulting in reduced work quality and schedule delays.

In recent years, high-precision GNSS positioning technology using the RTK (Real Time Kinematic) method has advanced, making centimeter-level (half-inch accuracy) surveying possible even with a small crew. Even without large dedicated equipment or advanced specialist knowledge, an RTK-compatible receiver enables immediate high-precision position measurements on site. As a result, tasks that were previously entrusted to surveying teams can now be easily handled in-house.

This article explains what RTK is, how it works, and how it differs from ordinary GPS positioning in an easy-to-understand way. It also details concrete tasks where RTK can be used on construction sites and key points for its introduction. At the end of the article, we touch on "LRTK" as a solution that allows anyone to start high-precision positioning easily, exploring its potential to improve productivity and construction quality.

What is RTK?

RTK stands for Real Time Kinematic, a positioning technology that corrects satellite positioning errors in real time to obtain centimeter-level (half-inch accuracy) high-precision position information. In Japanese it is also called "dynamic interference positioning" (動的干渉測位). Standalone GPS positioning typically has errors of about 5–10 m (16.4–32.8 ft), but RTK can reduce errors to within a few centimeters (a few inches). This increase in precision enables precise surveying tasks that were previously difficult to perform to be carried out immediately on site.

The basic principle of RTK is relative positioning using two GNSS receivers: a base station and a rover. First, a base-station receiver is installed at a known, accurate coordinate, and another receiver is carried around as the rover to take measurements. Both receivers simultaneously receive signals from satellites, and the difference between the position obtained at the base station and the known coordinate (the positioning error) is sent in real time to the rover, canceling out the errors included in the rover’s positioning results. This differential correction substantially offsets satellite-signal-derived errors, allowing the rover to determine its position horizontally and vertically with an accuracy of a few centimeters (a few inches). RTK positioning technology has recently attracted significant attention, especially in construction and civil engineering sites.

Benefits of Using RTK on Construction Sites

On construction and civil engineering sites, accurate surveying is often required, but it is not easy to always place an experienced surveying team or to outsource the work. With labor shortages and cost constraints, there is an increasing need for site technicians themselves to perform surveying efficiently. High-precision positioning with RTK can be the trump card to solve these issues. Below are the main benefits of introducing RTK.

• Labor savings and efficiency in surveying: With RTK, surveying tasks that previously required multiple people can be performed by a single person. There is no need to carry heavy surveying equipment or have another person hold a staff rod, so personnel can be allocated to other tasks. Waiting for a surveying team to arrive or coordinating personnel becomes unnecessary, improving overall site productivity.

• Rapid data acquisition and shorter schedules: By simply walking the site with a GNSS rover (the rover receiver), many survey points can be measured in a short time even across a large area. This is far quicker than measuring one point at a time with a total station, allowing tasks such as batter board setting and as-built verification to proceed rapidly. Because coordinates are obtained in real time, differences from design values can be checked on the spot and immediately reflected in construction, reducing rework.

• Reduced outsourcing costs: Fees for hiring surveying companies and the personnel and equipment costs to maintain an in-house surveying team are significant. Once RTK-capable positioning equipment is introduced, many surveying tasks can be handled internally, reducing the frequency of outsourcing. Also, you may not need to purchase all expensive optical surveying instruments (total stations or levels), thereby suppressing initial investment costs.

• Quality improvement through high precision: Centimeter-level (half-inch accuracy) precision from RTK allows batter board setting (layout) and installation of structures to be done far more accurately than before. Minimizing deviation from references prevents construction mistakes and rework, making it easier to ensure the quality specified in the design. Detailed measurement data can also be obtained for as-built management, aiding in creating quality certificates and responding to inspections. Improved precision directly translates to improved overall construction quality.

• Stronger capability for digital construction: Initiatives such as *i-Construction* promoted by the Ministry of Land, Infrastructure, Transport and Tourism are advancing ICT and 3D-data-based "digital construction." Introducing RTK on site is the first step toward 3D surveying and ICT construction. If your company can handle digital surveying data in-house, it can increase trust and evaluation from clients and contribute to strengthening future competitiveness.

What RTK Can Do (Use Cases)

By utilizing RTK's high-precision positioning on site, many tasks that previously relied on specialized surveying teams can be performed in-house. Here are several particularly useful use cases on construction sites.

• As-built surveying / topographic measurement: Using RTK to survey the current topography of road land or planned development areas allows workers to efficiently collect topographic data while walking the site themselves. Tasks that used to require time-consuming cross-section surveying with a total station can be completed in a short time with an RTK-GNSS rover, which can measure many points quickly. For example, there are reports that a topographic survey of about 50 points that previously took two people half a day could be completed by one person in a few hours using RTK.

• Batter board setting and layout (staking out): RTK is also useful for staking out the positions and elevations of buildings and structures shown in design drawings. GNSS positioning can sometimes provide positioning even when optical surveying instruments struggle due to lack of line of sight. Even on sites with complex terrain or many obstacles, design coordinates can be marked quickly and accurately, improving the efficiency and accuracy of batter board and layout work.

• As-built measurement and earthwork volume calculation: For embankment or excavation works such as dam construction or land development, RTK can be used to measure the as-built terrain area-wise, enabling detailed records of the completed terrain. From the many measured points obtained, 3D data (point clouds) can be generated to accurately calculate earthwork volumes. Because wide areas can be measured in a short time, embankment and excavation volumes that were previously estimated from partial cross sections can be calculated with greater reliability. Furthermore, by measuring required locations immediately after construction in-house and comparing them with design data on the spot, as-built inspections that used to be done later can be completed immediately.

• Infrastructure inspection and maintenance management: RTK positioning is useful for maintenance and management of public infrastructure such as roads and bridges. If the locations of cracks or pavement displacement are recorded with high precision, exactly the same points can be remeasured later to track changes. Keeping digital coordinate data instead of roughly marking positions on paper drawings improves management accuracy and supports comparison of inspection results and future repair planning.

• Simple 3D surveying (point cloud acquisition): By combining RTK with smartphones or drones, it is possible to obtain 3D survey data easily. For example, aerial photogrammetry with an RTK-capable drone can create high-precision terrain models without installing many ground control points. Also, by linking a smartphone’s built-in LiDAR scanner or camera with RTK, site 3D point cloud data can be obtained without using an expensive laser scanner. By using these technologies, 3D surveying that formerly required specialists can now be realized at relatively low cost.

How to Introduce RTK and Key Points

When actually introducing RTK positioning technology on site, there are several key points to keep in mind. In the past, setting up dedicated equipment and radio devices was necessary, but today there are products that are easy to use. Below are the basic procedures and preparations you should know when using RTK for the first time.

• Prepare RTK-compatible equipment: First, obtain a GNSS receiver that supports high-precision positioning. If you set up your own base station, you need two units: one for the base and one for the rover. However, if you use existing base stations such as the Geographical Survey Institute’s Continuously Operating Reference Stations, you may only need a rover. Recently, small GNSS receivers that can connect to smartphones have become available; choosing such devices improves portability and ease of handling on site.

• How to receive correction information: In RTK positioning, the rover receives correction information sent from the base station to correct its position. There are two main communication methods: radio and the Internet. In the radio method, communication devices such as low-power radios are attached to both the base and rover to transmit correction information directly by radio (a radio station license may be required depending on the frequency band). If cellular communication is available on site, it is easy to connect to networks such as the Continuously Operating Reference Station network or private correction services (VRS) via the rover-side smartphone and receive correction data over the Internet. In Japan, the Quasi-Zenith Satellite System "Michibiki" also offers a centimeter-level augmentation service (CLAS) that can provide correction information directly from satellites even in mountainous areas without cellular coverage. Choose the method that best fits your site environment.

• Setting base points: If you install your own base station, select a nearby known point with accurate coordinates as the antenna installation location for the base station. If there are no public control points or known points near the site, it is still possible to set a temporary base point and perform RTK surveying (in that case, the obtained coordinates will be relative to the temporary reference point, so you will need to link them to public coordinate system known points later for correction calculations). In any case, install the base station antenna in a stable spot with as open a sky as possible to ensure accuracy (when using network RTK, setting your own base point is unnecessary).

• Use surveying apps: To check and record positioning data obtained by a GNSS receiver, use dedicated software or apps. Many manufacturers provide surveying apps that run on smartphones or tablets, allowing Bluetooth-connected receivers to display coordinates in real time and save data together with point names and notes. Coordinate transformations to Japanese geodetic systems (plane rectangular coordinate system or geoid height) can also be done easily within the app, allowing the obtained survey data to be used directly for drawing creation and as-built management.

• Pre-checks and practice: When introducing new RTK equipment, perform operational checks and practice before using it on an actual site. For example, use a known point on your company premises as the base station and try surveying several nearby points to check the differences from the known coordinates and verify proper equipment operation. Also, by checking in advance how long it takes for the rover to obtain a "FIX solution" (integer solution, the state where errors are resolved) and the satellite acquisition situation, you can avoid confusion on the actual site. It is also important to test positioning accuracy in environments where GNSS signals may weaken, such as in mountainous areas or near trees, and adjust measurement locations or timing as necessary.

Recommendation: Simple Surveying with LRTK

Finally, as an example of a solution that makes RTK technology easy to introduce, we present LRTK. LRTK is a pocket-sized RTK-GNSS receiver developed by a startup from Tokyo Institute of Technology that attaches to smart devices such as iPhones and iPads. It weighs just 125 g and has a thickness of approximately 13 mm (0.51 in), making it an ultra-compact, lightweight device that, when paired with a smartphone, achieves centimeter-level (half-inch accuracy) precision comparable to traditional tripod-mounted surveying instruments. No large tripods or external power supplies are required; it runs on an internal battery, so it can be quickly taken out and used for surveying whenever needed on site.

By attaching a single LRTK to a smartphone, you can cover most of the positioning and surveying tasks discussed above. Place the receiver at the point to be measured and press the button on the smartphone to record latitude, longitude, and elevation with centimeter-level (half-inch accuracy) precision on the spot. Obtained coordinates are automatically converted to the Japanese plane rectangular coordinate system and geoid height, and saved together with point names, timestamps, and notes. The smartphone app also includes functions such as calculating the distance between two points or area, and guiding to a target point (coordinate) on design drawings to indicate staking positions. It can perform 3D scanning of the site in cooperation with the smartphone’s camera or LiDAR sensor, and includes AR features that overlay design BIM models onto the real scene, meeting a wide range of site needs.

Survey data collected on site can be uploaded to a dedicated web page in the cloud with a single tap, making it possible to share information with colleagues in remote offices in real time. The LRTK receiver supports multiple GNSS frequency bands and can receive the CLAS signal provided by Japan’s Quasi-Zenith Satellite "Michibiki," so high-precision positioning can be maintained even in locations without cellular coverage as long as CLAS can be received. Compared with traditional surveying instruments, the introduction cost is significantly lower, making LRTK truly a DX tool that can realize "one device per person." By using LRTK for simple surveying, even sites that cannot organize large surveying teams can perform high-precision surveying, potentially dramatically improving productivity and construction quality.

FAQ

Q: Do I need any special qualifications to perform RTK surveying? A: There are no national qualifications specifically required to operate the equipment. Once the basic operation is learned, anyone can perform RTK surveying tasks. However, note that when using radio communication between base and rover, a radio station license may be required depending on the frequency band used (network RTK or CLAS use does not require a license). Also, for legally binding surveys such as boundary determinations, procedures by qualified surveyors may be required separately.

Q: Can I substitute a smartphone’s built-in GPS? A: General smartphone built-in GPS (standalone positioning) has an accuracy of about 5–10 m (16.4–32.8 ft), which does not meet the precision required for construction surveying. By using an RTK-capable GNSS receiver, even a smartphone can achieve centimeter-level (half-inch accuracy) positioning. In other words, you add RTK high-precision positioning capability to a regular smartphone GPS. For example, attaching an ultra-compact receiver like LRTK to a smartphone enables easy high-precision surveying on the spot.

Q: How accurate is RTK positioning? A: Under favorable conditions, RTK can reduce horizontal position errors to a few centimeters (a few inches). This is orders of magnitude more precise than conventional standalone GPS, which has errors of several meters. However, accuracy can degrade if satellites cannot be adequately acquired due to surrounding conditions. Vertical accuracy in particular is more susceptible to ground-environment effects and may sometimes show errors greater than a few centimeters (a few inches).

Q: Can RTK be used in mountainous sites without cellular coverage? A: Yes, RTK positioning is possible even at sites outside cellular coverage. By using the CLAS centimeter-level correction service provided by Japan’s Quasi-Zenith Satellite "Michibiki," correction data can be received directly from satellites without Internet connectivity. Installing a mobile base station and operating by radio is another effective method. By selecting the optimal operation method according to the site’s communication conditions, high-precision positioning can be achieved in mountainous areas.

Q: Is it difficult to perform surveying alone? A: Recently introduced smartphone-linked RTK equipment is designed to make solo surveying easy. Surveying apps provide user interfaces that help beginners, for example notifying you by sound or screen display when you approach the target point while carrying the receiver and watching the map screen. There is no need to carry heavy objects or perform complicated equipment operations; with a little practice, one person can carry out high-precision surveying sufficiently.

Q: If we have RTK, do we no longer need total stations or levels? A: Satellite positioning is not万能 and cannot completely replace traditional surveying instruments in all cases. For example, in tunnels or inside buildings where GNSS signals do not reach, measurements with total stations (TS) or auto levels are still necessary. Also, in situations requiring millimeter-level precision over short distances (such as precise leveling or machine installation measurements), optical instruments may be more reliable. RTK is a powerful new tool, but it is important to use it in combination with conventional technologies depending on the situation.