For Small Contractors: What You Can Do with RTK Without a Full Survey Team

Table of Contents

• What is RTK?

• Benefits for Small Contractors Using RTK

• What You Can Do with RTK (Use Cases)

• How to Introduce RTK and Key Points

• Recommendation: Simple Surveying with LRTK

• FAQ

On small construction and civil engineering sites, precise surveying is often required. However, it is not always realistic to station a full survey team or to hire a specialist surveyor. With limited personnel and budget, small contractors need to find ways to perform surveying tasks themselves. Neglecting accurate surveying can lead to positional errors, construction mistakes, and rework.

In recent years, advances in satellite positioning technology known as RTK (Real Time Kinematic) have made high-precision surveying possible even with a small crew. Without dedicated large equipment or advanced expertise, RTK-capable devices can measure positions with centimeter-level (half-inch accuracy) precision. As a result, tasks that used to rely on a survey team can now be handled in-house more easily.

This article explains, for small contractors, what RTK is, how it works, and how it differs from ordinary GPS. It also details the tasks you can perform with RTK without a full survey team, and explains methods and key points for introducing RTK. At the end of the article, we introduce a simple surveying solution called “LRTK,” showing the possibility of high-precision surveying that anyone can start using.

What is RTK?

RTK stands for Real Time Kinematic, a positioning technique that obtains high-precision position information by correcting satellite positioning errors in real time. In Japanese it is also called “dynamic interference positioning,” and while standalone GPS positioning can have errors of several meters, RTK can reduce those errors to within a few centimeters (half-inch accuracy). Recently, RTK technology has drawn attention in civil engineering and construction sites.

The basic principle of RTK is relative positioning using two GNSS receivers. One receiver is set up at a known coordinate point as the base station, and the other is operated as a mobile station (rover) to perform measurements. Both receivers simultaneously observe signals from satellites; the difference between the position obtained at the base station and the actual known point coordinates (the error) is sent in real time to the rover, cancelling out the errors contained in the rover’s positioning results. This differential correction greatly offsets various error sources in satellite signals, enabling centimeter-level (half-inch accuracy) high-precision positioning. Precision surveying that was previously difficult can now be performed on-site immediately with RTK.

Benefits for Small Contractors Using RTK

With labor shortages caused by population aging and an aging workforce, “labor saving” has become a major issue on construction sites. Surveying tasks that traditionally required two experienced surveyors are increasingly required to be completed efficiently by fewer people as it becomes harder to secure personnel. It is said that the number of workers in the construction industry has decreased by about 30% since its peak in the late 1990s, and the desire to complete surveying alone is growing year by year. RTK is expected to be a trump card to address these challenges.

Key benefits small contractors gain by adopting RTK technology are summarized below:

• Measurement labor reduction and efficiency: With RTK, surveying that previously required multiple people can be done by one person. There is no need to assign staff to set up equipment or hold targets, allowing other staff to be deployed to different tasks. Waiting for a survey team or adjusting personnel is no longer necessary, improving overall site productivity.

• Shorter schedules due to rapid data acquisition: By walking around with a GNSS rover, many points across a wide site can be measured in a short time. It is far faster than measuring one point at a time with a total station, allowing tasks such as batter board setting and as-built checks to proceed quickly. Because coordinates are available in real time, differences from design values can be checked on the spot and reflected immediately in construction, reducing rework.

• Reduced outsourcing costs: For small businesses, the cost of requesting a surveying company or maintaining an in-house survey team is a significant burden. Once RTK equipment is introduced, many surveying tasks can be handled internally, reducing the number of times outsourcing is required. Also, since expensive optical surveying equipment (such as total stations) is not necessary, initial investment can be relatively restrained.

• Quality improvement through high precision: RTK’s centimeter-level (half-inch accuracy) precision enables more accurate batter board positioning and installation of structures. This prevents construction errors and rework and makes it easier to ensure the quality specified in design drawings. Detailed measurement data obtained for as-built management also supports quality assurance and inspections.

• Digital construction readiness and competitive advantage: With the Ministry of Land, Infrastructure, Transport and Tourism promoting *i-Construction*, site digitization is advancing. Introducing RTK is the first step toward 3D surveying and ICT-based construction. If your company can handle digital data in-house, it builds trust and evaluation from clients and contributes to future competitiveness.

What You Can Do with RTK (Use Cases)

Using RTK on site allows you to perform many tasks that previously relied on a survey team. Here are several use cases particularly useful on small sites.

• Current-condition surveying and topographic measurement: Using RTK for current-condition surveys to understand the shape of roads and sites enables a surveyor to efficiently acquire terrain data while walking the site. Tasks that used to take time with total station cross-section surveys can be done in much less time with an RTK-GNSS rover, allowing rapid collection of baseline data for map creation and construction planning. For example, a roughly 50-point terrain survey that used to take two people half a day has been reported to be completed by one person in a few hours with RTK.

• Batter board and layout staking: RTK is also useful for staking out the position and elevation of buildings and structures shown on design drawings. Where optical surveying has line-of-sight issues due to obstructions, GNSS can still perform positioning. Even on sites with complex terrain or many obstacles, design coordinates can be quickly and accurately marked, improving the efficiency and accuracy of layout work.

• As-built measurement and earthwork volume calculation: If you use RTK to measure the surfaces of embankments or excavations (e.g., dams or development sites), you can record finished shapes in detail. From many acquired 3D points, accurate calculations of fill and excavation volumes are possible. Because large areas can be measured quickly, volumes that were previously estimated from partial measurements can now be calculated more reliably. In addition, the person in charge can measure required locations immediately after construction and check differences from design values on the spot, allowing inspections that used to be postponed to be completed then and there.

• Infrastructure inspection and maintenance: RTK positioning is useful for maintenance of roads, bridges, and other infrastructure. Accurately recording the locations of cracks or displacements allows repeat measurements at the same points later to track changes. Storing digital coordinate data rather than roughly marking locations on paper drawings improves the accuracy of maintenance records.

• Simple 3D surveying (point cloud acquisition): Combining smartphones or drones with RTK makes it possible to obtain 3D survey data easily. For example, an RTK-capable drone conducting photogrammetry can create highly accurate terrain models without placing many ground control points. Also, by linking smartphone LiDAR or cameras with RTK, you can obtain point cloud data without using an expensive laser scanner.

How to Introduce RTK and Key Points

When you actually introduce RTK positioning on a small site, there are several key points to keep in mind. Traditionally, a set of specialized surveying equipment and radio devices was required, but now there are easy-to-use solutions available. Below are the basic steps and preparations for first-time RTK users.

• Preparing RTK-capable equipment: First, prepare a GNSS receiver that supports high-precision positioning. Traditionally, a two-receiver set for base and rover was standard, but if you do not set up your own base station, a single rover receiver plus a correction service subscription is acceptable. Choosing a compact GNSS receiver that can link with a smartphone rather than a large fixed unit improves mobility and portability on site.

• Methods for receiving correction information: RTK requires a communication method to transmit correction information from the base station to the rover. There are radio-based and internet-based methods. With radio, specific low-power radio devices are installed on both base and rover to send correction information directly by radio (note that radio station licenses may be required depending on frequency bands). If site communications are available, a convenient method is connecting the rover’s smartphone to the Geospatial Information Authority of Japan’s reference station network or to commercial correction services (such as VRS) via the internet to receive data. In Japan, you can also use the centimeter-class augmentation service (CLAS) provided by the Quasi-Zenith Satellite System “Michibiki,” which allows reception of correction information via satellite in mountain areas out of cellular range. Choose the optimal method according to your operational environment.

• Setting reference points: If you set up your own base station, prepare a known point near the site with accurately known coordinates and mount the antenna there as the base station. If there are no public reference points or known points at the site, you can still create a temporary reference point and perform RTK surveying; however, measured coordinates will be relative to the temporary reference and you will need to later tie them to public coordinate systems through correction calculations. In any case, place the base station antenna in an open location with good visibility and secure it firmly to ensure accuracy (this step is unnecessary when using network RTK).

• Utilizing surveying apps: To check and record data obtained by the GNSS receiver, use dedicated software or apps. Many surveying apps run on smartphones or tablets, connect to receivers via Bluetooth, display coordinates in real time, and save point names and notes. Coordinate system settings tailored to Japanese geodetic systems (such as plane rectangular coordinates and geoid heights) can be configured easily in the app, enabling direct use of measurements in drawing creation and as-built management.

• Pre-checks and practice: After introducing new RTK equipment, always perform operation checks and practice before going to site. For example, using a known point on company property as a base station and surveying several nearby points lets you check the device’s operation by comparing measured values with known coordinates. Knowing how long it takes for the rover to achieve a “FIX solution” (integer ambiguity resolution) and typical satellite acquisition conditions helps avoid surprises in the field. Also test positioning in environments with poor GNSS signal such as mountainous or wooded areas, and, if necessary, adjust measurement locations or times.

Recommendation: Simple Surveying with LRTK

Finally, as an example of an RTK solution that small contractors can easily adopt, we introduce LRTK. LRTK is a pocket-sized RTK-GNSS receiver developed by a startup originating from Tokyo Institute of Technology, designed to be attached to smartphone devices such as iPhone and iPad. It is an ultra-compact device weighing just 125 g and about 13 mm (0.51 in) thick, and when paired with a smartphone it quickly transforms into a centimeter-level (half-inch accuracy) high-precision surveying instrument. It does not require large tripods or external power supplies, runs on an internal battery, and is convenient to pull out and use on site whenever needed.

With just one LRTK unit attached to a smartphone, you can cover almost all the surveying and positioning tasks introduced above. By placing the receiver at the point you want to measure and pressing a button on the smartphone, latitude, longitude, and elevation can be recorded with centimeter accuracy (half-inch accuracy). Acquired coordinates are automatically converted to Japan’s plane rectangular coordinate system and geoid heights, and saved with titles, dates, and notes. It can calculate distances and areas between two points on the spot, and provides navigation to design target points to guide staking positions. It also includes 3D scanning functions using the smartphone’s camera or LiDAR and AR features that overlay design models on the real world, meeting a wide range of site needs. Measurement data can be uploaded to a dedicated cloud page with one tap for real-time sharing with office staff. LRTK receivers support multi-frequency GNSS signals and can receive the Quasi-Zenith Satellite System “Michibiki” CLAS centimeter-class augmentation service, meaning high-precision positioning can continue even where cellular communication is out of range if CLAS signals are receivable. Compared with conventional surveying equipment, introduction costs are dramatically lower, making it an ideal DX tool for the era of “one device per person.” By using LRTK for simple surveying, sites unable to form a full survey team can still perform high-precision surveying and dramatically improve productivity and construction quality.

FAQ

Q: Do I need qualifications to perform RTK surveying? A: No special national license is required to operate the equipment. Anyone can perform RTK surveying once they learn the basic operation. However, note that if you use radio devices, a radio station license may be required depending on the frequency band (network RTK via communication lines or CLAS use does not require a license). Also, if you need survey results that have legal validity such as land boundary determination, separate procedures by licensed surveyors may be required.

Q: Can I substitute the GPS built into a smartphone? A: Smartphone GPS (standalone positioning) typically has errors of about 5–10 m and does not meet the accuracy required for construction surveying. By using an RTK-capable receiver, a smartphone can achieve centimeter-level (half-inch accuracy) positioning. In other words, RTK adds high-precision positioning capability to a normal smartphone GPS. Attaching an ultra-compact receiver like LRTK to a smartphone enables easy on-site high-precision surveying.

Q: How accurate is RTK positioning? A: Under good conditions, RTK can reduce horizontal positional errors to the order of a few centimeters (half-inch accuracy). This is orders of magnitude more precise than typical standalone GPS, which has meter-level errors. However, accuracy can degrade if satellites cannot be adequately acquired due to the surrounding environment; vertical accuracy in particular can have errors on the order of several centimeters.

Q: Can RTK be used in mountainous sites without cellular coverage? A: Yes, RTK positioning is possible even in areas without cellular coverage. For example, by using the “CLAS” service provided by Japan’s Michibiki satellites, correction information can be received directly from satellites without internet connection. Alternatively, setting up a base station in advance and operating via radio communication is effective. By choosing the appropriate operation method for the site’s communication conditions, high-precision positioning can be achieved even in mountainous areas.

Q: Is it difficult to perform surveying alone? A: Modern smartphone-linked RTK devices are designed for single-person operation. Survey apps provide user interfaces that alert you by sound or display when you approach a target point, making them easy for anyone to use. There is no need to carry heavy equipment or perform complex operations, and with a little practice a single person can perform high-precision surveying adequately.

Q: Do weather or surrounding obstacles affect positioning? A: Severe weather such as heavy rain or snow has relatively little direct effect on satellite positioning, but surrounding environments must be considered. In forests or near tall buildings, satellite signals can be blocked or reflected, reducing RTK accuracy or preventing a solution. Taking measurements in open sky conditions as much as possible and choosing times when satellite geometry is favorable help prevent accuracy degradation.

Q: Will RTK make total stations or levels unnecessary? A: In locations where satellite signals cannot reach, such as inside tunnels or buildings, traditional total stations (TS) and levels continue to be useful. Also, for very short-distance tasks requiring millimeter-level accuracy (such as precise leveling or coordinate measurements for equipment setup), optical instruments may still be more reliable. Therefore, while RTK can streamline many tasks, it does not entirely replace all traditional tools. Using both optical instruments (TS and levels) and RTK as appropriate for each application is the realistic approach.

Q: How much does it cost to introduce RTK? A: In the past, a full set of RTK surveying equipment required an investment of several million yen, but compact and affordable devices are now available, making RTK more accessible to small businesses. Actual costs vary depending on the model and operation method, but it is now much more economical to adopt high-precision positioning than before. Additionally, correction services such as the Geospatial Information Authority’s VRS and Michibiki’s CLAS are available, some free of charge, helping to reduce operating costs.