RTK GNSS Benefits: How cm-Level Accuracy Transforms Construction Surveying

Table of Contents

• What is RTK GNSS?

• How RTK GNSS Works and Its Features

• Benefits of Introducing RTK GNSS

• Simple Surveying with LRTK

• Frequently Asked Questions

What is RTK GNSS?

RTK GNSS stands for Real Time Kinematic, a high-precision positioning technique that uses Global Navigation Satellite Systems (GNSS). GNSS, typified by GPS, measures positions on the ground using signals from multiple satellites, but standalone positioning typically suffers from errors of several meters (several ft) due to atmospheric effects and satellite geometry. In construction and precision surveying, such errors cannot be ignored and traditionally required advanced corrections and skilled technicians.

RTK GNSS uses two GNSS receivers—a base station and a rover—that exchange satellite signal data received simultaneously to correct errors in real time. The base station is installed at a pre-surveyed accurate coordinate and calculates the difference (error information) between its measured position and the known position. This error information is sent to the rover via radio or the Internet, and the rover applies corrections to its measurements, reducing positioning errors to within a few centimeters (within a few in). The ability to correct in real time and obtain high-precision position information on site is a major characteristic of RTK.

While standalone GPS positioning can sometimes reach errors of several tens of centimeters, using RTK can achieve accuracies of about 2–3 cm (0.8–1.2 in) horizontally/planimetrically and about 3–5 cm (1.2–2.0 in) vertically. Such centimeter-level high-precision positioning brings dramatic quality improvements to construction sites and surveying operations. For example, in civil engineering, traditional GPS surveys could cause positional and construction errors, but RTK enables accurate layout and as-built measurements that match design drawings. RTK-GNSS is expanding its use in surveying, construction management, infrastructure maintenance, drone surveying, and even agriculture and autonomous driving—wherever “more accurate position information” is required.

How RTK GNSS Works and Its Features

The core of RTK GNSS is the method of differential correction. The base station and rover receive signals from the same satellites simultaneously; the base station sends its computed error information to the rover to correct the rover’s measurements, reducing errors that were several meters in standalone positioning down to a few centimeters. This makes it possible to achieve the high-precision positioning that previously required post-processing or many known control points, now in real time on site. Because positioning data are corrected as they are acquired, there is no need for time-consuming office post-processing, resulting in significant time savings and labor reduction.

RTK can also correct errors from ionospheric delay and multipath (signal reflections), providing stable accuracy even in urban high-rise areas or mountainous regions. However, to obtain accuracy the rover must continuously receive a sufficient number of satellite signals, so an open sky view is preferable, as with ordinary GNSS. Attention should also be paid to the communication range between the base and rover, but generally high-precision positioning is possible within a range of several kilometers (several thousand ft).

RTK can be broadly categorized into two types: installing your own base station, or network RTK, which receives correction information from existing electronic reference point networks. With the former, you place a base station on site and communicate by radio; with network RTK, correction data are obtained from the Geospatial Information Authority of Japan’s (GSI) electronic reference points or private base station services via mobile networks, making positioning possible with just a single receiver without placing a base station on site. Recently, services such as the QZSS “CLAS” and paid correction services from telecom carriers have made it easier to obtain high-precision positioning over the network. The spread of these systems has lowered the barrier to RTK-GNSS adoption, making it more accessible even for small- and medium-scale sites.

Benefits of Introducing RTK GNSS

Introducing RTK real-time high-precision positioning to construction and surveying sites brings various benefits, including improved positioning accuracy and work efficiency. The main benefits are explained below.

Dramatic Improvement in Positioning Accuracy

The greatest advantage of RTK is the dramatic improvement in positioning accuracy. Conventional GPS or optical surveying could allow small survey errors that affect subsequent construction accuracy. With RTK, coordinate deviations can be kept to a few centimeters or less, allowing construction and surveying to be carried out to the accuracy of the design drawings. For example, RTK-based positioning for building foundations or road centerline layouts can minimize human-induced deviations. When surveyors set up batter boards (reference points for elevation and position), using RTK coordinates yields more accurate reference positions.

RTK also excels in as-built (finished-shape) management. Measuring embankment heights or the shapes of structures after concrete placement with RTK-equipped devices can quickly produce dense point clouds and coordinate data to immediately identify deviations from the design model. Because high-precision as-built data can be obtained on site, costly re-measurements due to insufficient accuracy at later inspections can be avoided. The GSI-recommended methods also indicate that using RTK-GNSS makes it easier to keep as-built measurements within specified tolerances, which is effective for quality assurance.

As a concrete example of accuracy improvement, one surveying firm achieved exceptionally high positioning accuracy of about 8–12 mm (0.31–0.47 in) horizontally after introducing RTK. When sub-centimeter errors that were previously unattainable by standalone positioning become possible, even very small displacements or tilts in structures can be detected immediately. This greatly enhances quality control and effectively eliminates “very small errors that could not be measured before.” Introducing RTK GNSS elevates on-site positioning accuracy to a different level and directly improves the reliability of construction and surveying.

Major Improvement in Work Efficiency

RTK GNSS is also a tool that dramatically increases on-site work efficiency. Because high-precision positioning results are available in real time, many complex surveying procedures and post-processing calculations can be greatly simplified. For example, conventional total station surveys require repeatedly repositioning the instrument to maintain line-of-sight and an assistant to handle the prism at each survey point. With RTK-GNSS, as long as the sky is open and satellites are visible, you can observe positions continuously while moving without repositioning the instrument. One person can walk across a large development site and complete the survey, eliminating the repeated setup and aiming required by a total station. As a result, surveying time is greatly reduced and personnel needs decrease.

The advantage of obtaining high-precision data in real time also applies to marking out (laying out positions and elevations on site) and as-built verification processes. With RTK you can always know your current position to centimeter accuracy, allowing stakes and markings to be set while checking deviations from design values on the spot. Since the instrument does not need to be reconfigured when moving between points, there is no wasted waiting time, which reduces burdens during hot or cold work. In one site, introducing RTK changed surveying that previously required one round-trip each with a total station and a level into a single round-trip survey using RTK and a level. Cutting procedures in half reduced surveying time by about 50%, and sites reported that it saved considerable time. Thus, RTK streamlines surveying and measurement steps, shortening work time and contributing to shorter project schedules and reduced labor costs. Because it enables more output with fewer personnel and less time, RTK delivers great productivity benefits.

Addressing Labor Shortages and Reducing Costs

RTK GNSS also has a significant impact on the construction industry’s worsening labor shortages. High-precision surveying and measurement can be performed by fewer people, allowing technology to compensate for the shortage or busyness of skilled surveyors. Traditionally, installing batter boards and performing as-built measurements required 2–3 people, but cases where a single person with an RTK receiver and a tablet can complete surveying and recording are increasing. This not only reduces labor costs but also frees limited personnel for other important tasks.

RTK use also reduces surveying costs. For example, on small construction sites that previously required hiring external surveyors for high-precision surveys, on-site staff equipped with RTK devices can now handle the work, saving outsourcing fees. Recently, inexpensive RTK services and low-cost receivers have appeared, lowering initial investment and making adoption easier. As a result, “the barrier to RTK adoption has dropped, making the technology familiar to many companies.” Compared to the expensive traditional GNSS surveying equipment, the spread of monthly network RTK services and affordable receivers has led to more small and medium contractors adopting RTK on-site.

Moreover, RTK reduces construction mistakes and rework. If positions and measurements are accurate from the start, you can avoid later rework caused by “deviations from the reference.” This directly reduces wasted materials and unnecessary labor. Getting construction and surveying right the first time leads to overall cost savings across the project. In this way, RTK improves efficiency both in manpower and cost, helping complete more projects with limited resources.

Improved Safety and Quality Control

Introducing RTK GNSS improves on-site safety and quality control. Because high-precision surveying can be done quickly, the time workers spend in hazardous locations can be reduced. For example, installing batter boards beside busy roads or surveying steep slopes can be done from a safe distance with RTK by positioning target points remotely. Being able to measure required points from the edge of the site reduces the risk of people entering hazardous areas. Additionally, equipping drones with RTK receivers enables aerial surveying of slopes at risk of collapse or riverbeds during high water—areas where humans cannot safely enter—allowing replacement of previous hazardous field surveys and enhancing worker safety.

RTK is also a powerful tool for quality control. With centimeter-accurate data available in real time, deviations in as-built conditions can be detected and corrected immediately during construction. For example, during paving work you can instantly check and adjust deviations from design elevations while rolling, or verify and fine-tune the accurate position of bridge girders and columns during installation—enabling immediate measurement and correction. This helps prevent nonconformities flagged in final inspections and greatly reduces quality defects and construction errors.

Furthermore, RTK positioning data are easy to share and record via the cloud. Digital records of who measured what, where, and with what accuracy improve transparency and traceability in construction management. Automatically embedding position information in survey photos and combining RTK with AR technology raise the accuracy of construction records and inspection documents, enabling objective, data-driven quality control. Overall, RTK GNSS contributes to building a safer, higher-quality construction management system and increases on-site trustworthiness.

Contribution to ICT Construction and DX Promotion

RTK GNSS is not just a means to improve surveying accuracy; it is also a foundational technology for promoting ICT construction and digital transformation (DX) in the construction and surveying industries. Initiatives such as the Ministry of Land, Infrastructure, Transport and Tourism’s i-Construction and CIM (Construction Information Modeling) emphasize the use of 3D data on site, and RTK is indispensable as a means to obtain high-precision position information in real time. For example, using RTK enables drone photogrammetry to acquire high-precision 3D point clouds with fewer control points, drastically reducing the need for many ground control points. This achieves both labor savings and accuracy assurance in digital construction.

RTK is also widely used in ICT construction machinery for machine guidance and machine control (automatic control of earthmoving machines). Systems that mount RTK-GNSS antennas and design data on bulldozers or excavators to automatically adjust blade height and position rely on continuously knowing the precise current position. RTK enables real-time centimeter-level positioning of construction machinery, allowing high-precision automatic construction that keeps errors within a few centimeters. This is a step toward future unmanned construction and automation of construction machinery; RTK is already indispensable in drone surveying and autonomous vehicles.

By linking high-precision data with BIM/CIM models, digital data can be used consistently from design and construction to maintenance. For example, point cloud data from as-built surveys collected with RTK can be imported into a CIM 3D model for as-built verification or future renovation planning. Such data-driven construction management improves infrastructure asset management and facility management. Thus, introducing RTK is the first step to digitalizing and smartening your construction process and offers major benefits for aligning with next-generation industry standards.

Simple Surveying with LRTK

As described above, RTK GNSS is extremely useful for improving accuracy, efficiency, and safety, but some may worry “Isn’t the equipment expensive?” or “Is it hard to use?” LRTK addresses these concerns and enables anyone to easily start RTK surveying. LRTK is a pocket-sized RTK-GNSS receiver developed by Refixia Inc., a startup from Tokyo Institute of Technology, and is notable for being usable with a smartphone or tablet. By attaching a dedicated small receiver to a smartphone and launching an app, centimeter-level positioning can be achieved on site immediately.

The main benefits of LRTK are as follows:

• High-precision positioning: Using a smartphone and LRTK receiver can correct smartphone position information that used to have errors of several meters to cm-level accuracy (half-inch accuracy). Field trials recorded astonishing accuracy of about 8–12 mm (0.31–0.47 in) horizontally, and averaging multiple measurements achieved about 8 mm (0.31 in), reaching positioning accuracy comparable to conventional high-end bench-mounted GNSS equipment in a palm-sized device.

• Multifunctionality: LRTK is not just a surveying instrument—it offers point-cloud measurement, support for marking-out work, high-precision geotagging of photos, AR-based completed-structure simulation displays, and more. Data acquired on site can be immediately shared to the cloud, enabling real-time information coordination with remote offices. With this single device you can complete surveying, recording, and sharing, strongly supporting on-site DX.

• Cost performance: LRTK is set at a dramatically lower introduction cost than traditional RTK surveying equipment, allowing high-precision positioning with a modest budget. Because it is affordable, providing units to multiple site staff is realistic. Designed to be operable without large-scale equipment or specialist knowledge, it requires little training effort, enabling anyone to use RTK surveying as an extension of daily tasks.

Thus, LRTK can be an optimal solution for construction and surveying personnel who want to introduce RTK-GNSS. With a pocket-sized device and a smartphone, centimeter-level surveying can be done on the spot, dramatically streamlining on-site layout and measurement work. Field supervisors and workers have expressed expectations such as “If each person had an LRTK, productivity would dramatically increase,” and it is becoming a new trend in on-site DX. Detailed product information is available on the LRTK official website for those interested. Consultations and inquiries about introduction are also accepted at any time. LRTK can help take your site’s surveying accuracy and operational efficiency to the next stage.

Frequently Asked Questions (FAQ)

Q. What is needed to perform RTK-GNSS positioning? A. Basically, two RTK-capable GNSS receivers (a base station and a rover) and a communication method connecting them are required. Traditionally, a base station was set up near the site and correction data were transmitted to the rover via low-power radio or UHF radio. However, network RTK, which uses correction information from the GSI electronic reference point network or private providers, has become common, so you can perform RTK positioning with only one rover if you have Internet connectivity and a service contract. In summary, RTK positioning requires “base station error data” and “correction computation at the rover,” and to obtain these you need either radio communication equipment or a network connection.

Q. How accurate is RTK-GNSS? A. Accuracy varies with equipment and environmental conditions, but using a typical network RTK service can provide about 2–3 cm (0.8–1.2 in) horizontally and about 3–5 cm (1.2–2.0 in) vertically. In open-sky environments with stable reception of many satellites, it is not uncommon to achieve errors within 2 cm for both horizontal and vertical. Conversely, in areas where satellite signals are blocked—such as between high-rise buildings or inside forests—RTK solutions can become unstable and accuracy may decline. Still, RTK displays quality indicators (estimated accuracy) in real time, so you can monitor error magnitude during measurement. The latest equipment, using multi-GNSS reception and tilt compensation, can more stably achieve errors of nearly 1–2 cm.

Q. Can RTK positioning be used in mountainous areas without network coverage? A. Yes, RTK positioning itself is possible without network coverage. However, in that case network RTK is unavailable and you must set up your own base station on site and send correction data via radio. For example, in mountainous construction sites a base station antenna may be mounted at a high point and communicate with the rover via special small-power radio (digital simple radio). As communication distance increases, accuracy decreases, so the key is to keep the base and rover as close as possible. Alternatively, if you have equipment that can receive CLAS augmentation signals from Japan’s QZSS directly from satellites, you can obtain correction information without the Internet, enabling operation similar to network RTK even in areas without cellular coverage. Note, however, that in environments where satellites themselves cannot be received—such as deep forests—RTK also becomes unusable, so ensuring sky visibility or switching to alternative surveying methods (non-GNSS) should be considered.

Q. Isn’t RTK equipment expensive to introduce? A. Professional RTK-GNSS equipment used to cost several million yen, but costs have fallen in recent years. Options such as monthly subscriptions to network RTK services or purchasing reasonably priced receivers have increased, lowering both initial and operating cost barriers. In particular, small receivers that work with smartphones (such as LRTK) are offered at far more affordable price ranges than traditional units. From an operational cost perspective, you can also use free correction data from the GSI (real-time data from electronic reference points) to perform RTK positioning without communication or service fees. By choosing an introduction form that fits site size and purpose, you can use RTK cost-effectively.

Q. Can beginners handle RTK-GNSS? A. Yes. Recent RTK-GNSS equipment and software have become user-friendly, and basic operations are not that difficult. Even first-time users can perform positioning tasks by following procedures after understanding the principles roughly. Products like LRTK provide smartphone apps that guide users through reception of correction information to positioning automatically, so intuitive operation is possible without specialized knowledge. Nevertheless, because RTK is precise positioning, you should pay attention to satellite reception status and correct device setup; with manufacturer manuals and training, beginners can handle it. Initially receiving a brief in-house lecture from an experienced colleague and practicing will help you gain confidence. The key is to use it continuously and gain experience—once mastered, you will appreciate RTK-GNSS’s convenience and usefulness.