What is RTK?
The Basics of High-Precision Positioning You Need to Know in Civil Engineering Surveying

This article takes an average of 2 minutes and 30 seconds to read
Published March 13, 2025

In recent years, high-precision positioning technology known as "RTK" has gained attention in the construction and infrastructure sectors. While traditional GPS positioning can result in errors of several meters, using RTK allows positioning errors to be reduced to just a few centimeters.
This article explains what RTK is, its mechanism and features, the reasons why RTK is needed in civil engineering surveying, specific surveying methods, the differences and accuracy comparisons with traditional GPS, and the challenges and solutions related to RTK operation.
What is RTK?
RTK stands for "Real Time Kinematic," a positioning technology that corrects satellite positioning errors in real-time to achieve centimeter-level accuracy.
Specifically, it uses two GNSS receivers: a reference station (base station) that is fixed on the ground and a mobile station (rover) that moves while performing positioning. These two receivers communicate measurement data between each other to perform high-precision relative positioning.
The reference station is installed at a location with known, accurate coordinates, and it receives signals from multiple satellites such as GPS and GLONASS simultaneously with the mobile station. The positioning information obtained from both the reference and mobile stations is used to correct errors by calculating the difference, enabling real-time, high-precision calculation of the mobile station's position.
In standalone GPS positioning (standalone positioning), errors of several meters can occur due to signal delay from satellites and atmospheric influences. However, with RTK, these error factors are neutralized by receiving correction data from the reference station, allowing for positioning with centimeter-level accuracy. In other words, RTK achieves much higher accuracy than standalone positioning by using "relative positioning with two receivers," which is the basic principle behind RTK.
The Mechanism and Features of RTK Positioning
Let’s take a closer look at the mechanism of RTK positioning. In RTK, both the reference station and the mobile station simultaneously receive signals from at least four positioning satellites and exchange data between the two receivers. The reference station generates correction data based on its own accurate location and the phase data of the observed satellite signals, which is then transmitted to the mobile station via radio or the internet. The mobile station combines its own observed data with the received correction data and applies real-time error correction to calculate high-precision position coordinates. By utilizing the relative distance between the two stations and the phase difference of the satellite signals, RTK compensates for satellite signal propagation errors (such as ionospheric and tropospheric delays, and satellite clock errors), achieving high precision.
The key features of RTK are its immediacy and high accuracy. Since the corrections are applied in real-time, positioning results can be obtained on-site with centimeter-level accuracy. The typical accuracy is approximately 2-3 cm horizontally and 3-4 cm vertically. This is orders of magnitude more precise compared to the accuracy of standalone positioning (which has errors on the order of meters). Additionally, GNSS satellites can use multiple positioning systems (in addition to GPS, such as GLONASS, Galileo, and Michibiki (QZSS)), and with an RTK receiver compatible with multi-GNSS, the number of satellites used increases, further enhancing the stability and precision of positioning. The accuracy improves as the satellite geometry (positioning) improves, and the use of multi-GNSS can mitigate the effects of unfavorable satellite configurations.
There are several types of RTK systems, but they can be broadly classified into standalone RTK (base & rover method) and network RTK. Standalone RTK involves setting up a reference station locally and exchanging correction data with the rover. On the other hand, network RTK (Network RTK, VRS method, etc.) obtains correction data via the internet from a network of reference stations provided by government or private organizations. With network RTK, there is no need to install a reference station on-site; instead, correction is received by transmitting virtual reference station data to the user near their location. While the operational methods differ, the fundamental mechanism of both is the same: "Using the reference station's correction data to compensate for the positioning errors of the mobile station."
Why RTK is Needed in Civil Engineering Surveying
So, why is RTK so essential in civil engineering surveying? The background lies in the growing demand for improved accuracy and productivity in the construction industry.
First, in terms of accuracy, there are many situations in infrastructure construction and surveying work where centimeter-level precision is required. Traditional surveying methods using transit or optical distance measuring instruments (total stations) can achieve high accuracy, but they require multiple people and take time. By utilizing RTK-GNSS, a single person can conduct extensive surveys in a short time, significantly improving work efficiency. For example, with network-based RTK (VRS), tasks that previously required a three-person team can be completed by one person, and since 3D coordinates (XYZ) are directly obtained, leveling surveys are no longer needed.
This leads to a reduction in manpower and a shortened work schedule, making RTK a very useful technology in the civil engineering industry, where chronic labor shortages are a problem.
Moreover, the spread of RTK is closely tied to the ICT construction and i-Construction initiatives promoted by the Ministry of Land, Infrastructure, Transport and Tourism. The Ministry is promoting the use of 3D surveying and machine guidance. For instance, "a method of performing low-cost 3D surveying by combining the LiDAR function of smartphones or tablets with RTK receivers" is officially recommended, further advancing digital transformation on construction sites. With RTK providing high-precision location data, detailed terrain modeling through drone surveying, precise construction via semi-automatic control of heavy machinery (machine control), and advanced as-built management become possible, simultaneously enhancing both the quality and efficiency of construction. High-precision surveying is indispensable in construction to minimize errors and rework, making RTK an essential technology for achieving this.
In addition, the need for RTK is increasing in the field of infrastructure maintenance. For example, in highway and railway maintenance, there are many situations that require high positioning accuracy, such as measuring displacement of bridges and railways, monitoring ground subsidence, and recording the exact locations of buried utilities. Traditionally, leveling surveys and total station-based fixed-point observations were mainstream, but by utilizing RTK, multiple points can be measured in a short time, enabling the capture of area-based displacement. GNSS positioning is effective for surveying large bridges and railway tracks with minimal obstacles, and the mobility and accuracy unique to RTK contribute to improving the precision and efficiency of infrastructure inspections.
Thus, from both the "high precision" and "efficiency" perspectives, RTK has become an indispensable tool in civil engineering surveying. In fact, more small-to-medium-sized general contractors and civil engineering companies are adopting RTK systems, internalizing surveying tasks within their own operations. The use of RTK is expanding not only at large sites but also at smaller ones.
Specific Surveying Methods Using RTK
By utilizing RTK, various new approaches are possible in civil engineering surveying methods. Here, we will introduce representative surveying methods and applications using RTK.
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Reference Point Surveying (Measuring and Setting Known Points):
With RTK, the coordinates of reference points on a construction site can be quickly measured and set. For example, by using known points from the Geospatial Information Authority of Japan's electronic reference point network or a public coordinate system as the reference station, and observing the site’s arbitrary points with a rover, that point can be instantly set as a high-precision reference point. Traditionally, reference point surveying, which took half a day using leveling or traverse surveying, can now be completed in a short time with RTK. This is a crucial task that serves as the foundation for the accuracy of subsequent surveying and construction, and the introduction of RTK significantly improves efficiency. -
Current Condition Surveying and Terrain Surveying:
RTK is highly effective for surveying large areas of terrain or as-built conditions. By simply having a worker carry a rover receiver (with a GNSS antenna and controller mounted on a pole) and walk around the site, 3D coordinates with centimeter-level accuracy can be obtained. Compared to traditional plane surveying or point cloud surveying using total stations, RTK enables the collection of a large amount of point data at an overwhelming speed, and surveying can be done safely even on uneven terrain. Especially in as-built management of embankments and cuttings, RTK rovers can be used to measure the surface in detail and calculate volumes. Since surface data can be obtained in a short time, it is also useful for post-construction verification and creating as-built drawings. -
Coordinate Setting for Stringlines and Stake Driving:
RTK surveying can be applied not only for measuring completed terrain but also for construction "stake-out" tasks. By importing coordinate data for structures, road centerlines, and other elements from design drawings into the controller in advance, stake-driving tasks at the designated coordinates can be performed on-site using a rover. When using GNSS surveying equipment for stake driving, the difference between the receiver’s current position and the target position (in terms of direction and height) is displayed in real-time to guide the process, allowing the worker to simply move the pole according to the on-screen instructions to mark the designated position. Utilizing the advantages of RTK, which can provide positioning even in large sites with difficult visibility or at night, efficient and accurate stake-out can be performed. -
UAV Photogrammetry (Drone Surveying):
RTK is also being used in photogrammetry with drones, which has become increasingly popular in recent years. RTK-enabled drones (which are equipped with GNSS receivers and perform high-precision positioning while receiving corrections during flight) or PPK (Post Processed Kinematic) methods, which provide RTK-level corrections through post-processing, can greatly enhance the positional accuracy of orthophotos and point cloud models created from aerial photographs. In traditional drone surveying, it was necessary to install numerous ground control points (known coordinate markers), but with RTK drones, the number of control points can be minimized or even eliminated, significantly reducing the time required for survey preparation. In large-scale land development sites or forest surveys, RTK-equipped drones can quickly acquire high-precision terrain data from the air, improving both safety and efficiency. -
3D Scanning Using Mobile Devices:
As a recent application, there is a method that combines smartphones or tablets with RTK. For example, by using an RTK-enabled device and the built-in LiDAR on an iPhone or iPad, 3D point cloud surveying can be easily performed. By using a dedicated app, photos taken with the smartphone’s camera can be tagged with high-precision RTK coordinates, and point clouds scanned with LiDAR can be given location information, allowing for the instant generation of a 3D model of the site. This enables 3D surveying using a smartphone + RTK without the need for expensive laser scanners, and the Ministry of Land, Infrastructure, Transport and Tourism is supporting the on-site adoption of this technology. It is especially effective for surveying small sites or narrow spaces, and its use is expected to grow further in the future.
As mentioned above, there are a wide variety of surveying methods utilizing RTK. From setting up reference points and terrain surveying to stake driving, aerial surveying with drones, and even easy 3D measurements using smartphones, RTK has greatly expanded the scope of modern surveying technology. By choosing between setting up your own reference station or using network-based RTK services, high-precision positioning can be performed flexibly in various environments. It can truly be said that we are entering an era where "RTK cannot be overlooked."
Differences and Accuracy Comparison with Traditional GPS
When comparing RTK with traditional GPS positioning (standalone positioning), the following points can be highlighted:
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Difference in Positioning Accuracy:
The biggest difference is the positioning accuracy. With standalone GPS, the error is typically several meters (approximately 5 meters for smartphone GPS, and about 2-3 meters for dedicated devices). In contrast, RTK positioning provides high-precision location within a few centimeters, as mentioned earlier. The vertical accuracy of RTK is also superior, although it tends to have slightly larger errors compared to horizontal accuracy. Even so, the impact of the difference between a few centimeters and several meters on application is significant, and the improved accuracy of RTK has made tasks that were difficult with GPS possible. -
Required Equipment and Setup:
Standalone positioning only requires one receiver, but RTK positioning requires two receivers: a reference station and a mobile station, or correction data from a network service. Therefore, RTK operation requires equipment for the reference station (which may include mobile communication devices or radios, depending on the case) and the data reception environment for the mobile station. On the other hand, in recent years, network-based RTK services provided by private companies and mobile carriers have been established, making it possible to obtain correction data without having to set up your own base station. Additionally, in Japan, the quasi-zenith satellite "Michibiki" provides a centimeter-level augmentation service (CLAS), and by using compatible receivers, correction data can be obtained directly from satellites without the need for the internet. -
Positioning Stability:
Standalone GPS positioning can always provide a location, but the accuracy is low, leading to fluctuations in the position and drift over time. RTK generally offers stable high precision, but it is highly dependent on the satellite signal reception environment. In urban areas with tall buildings or within forests, the reception of multiple satellites and the exchange of signals necessary for RTK may be obstructed, leading to a "float solution" (a state where a fixed solution cannot be obtained). Therefore, RTK requires attention to the number of visible satellites and the geometry (DOP values), and if necessary, repositioning or reinitializing the positioning (ambiguity resolution) should be performed. Additionally, if the distance from the reference station is too far, the correction effect will weaken and the accuracy will decrease. In such cases, when using a reference station several tens of kilometers away, a network-based RTK system may generate a virtual reference station nearby as a workaround. -
Real-Time Capability:
Both systems can provide real-time positioning, but in the case of RTK, an initial convergence time is required to achieve high-precision positioning. Immediately after powering on the receiver or exiting a tunnel, the RTK solution typically takes several tens of seconds to a few minutes to reach a "fixed (FIX)" state, enabling high-precision positioning. On the other hand, standalone positioning can always calculate a position instantly, but the accuracy is lower, so the practical significance differs. RTK, which provides centimeter-level accuracy in real time, is suitable for surveying and construction applications, while standalone positioning, with meter-level accuracy, is sufficient for uses like car navigation or general positioning.
In summary, the distinction lies in "ease of use" and "required accuracy." Standalone GPS is simple in terms of equipment and can be used anywhere, but the accuracy is low, while RTK, though requiring specific equipment and environmental conditions, offers very high accuracy. In civil engineering surveying and construction ICT, RTK is chosen because high precision is required.
Challenges and Solutions of RTK
While RTK positioning offers high precision, there are several challenges in its practical use. Here, we will introduce points to be aware of when using RTK, along with their solutions and countermeasures.
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Challenge 1: Dependence on Satellite Reception Environment
Since RTK relies on receiving signals from GNSS satellites, positioning is difficult in areas that are not open to the sky. In tunnels, behind buildings, or within forests, satellite signals may be blocked or weakened, making it impossible to perform high-precision positioning, or even any positioning at all. Additionally, signal reflections (multipath) can increase errors and make it more difficult to obtain a fixed solution. Solution: During the survey planning phase, check for satellite obstructions caused by man-made structures or terrain, and consider conducting observations in open areas or combining RTK with other methods as needed. For example, in mountainous areas, it is effective to use a total station only in blocked areas of valleys and RTK for the rest of the survey. Additionally, modern receivers offer improved multipath removal performance and the ability to receive multiple frequencies for faster re-positioning, which increases the chances of maintaining a stable fixed solution even in partially obstructed environments. In locations where GNSS cannot be used, such as indoors or underground, alternative positioning systems that combine total stations, laser scanners, and IMUs are used to complement GNSS. -
Challenge 2: Communication Infrastructure and Access to Correction Data
RTK requires the transmission of correction data from the reference station to the mobile station, and the method used for this data transmission presents different challenges. When using a private radio system, the coverage area is limited by the constraints of radio laws, and in large sites, a radio repeater may be necessary. On the other hand, network-based RTK, which uses mobile networks, faces the issue of being unable to position in areas without mobile phone coverage, such as in mountainous regions. In fact, there are many cases in civil engineering, construction, and infrastructure management where there is no coverage, creating a need for operations that are independent of communication networks. Solution: It is crucial to secure the appropriate method of obtaining correction data based on the site. In the case of a private reference station combined with specific low-power radio, optimizing the radio reach by installing antennas at high locations or setting up relay stations can help. For network-based systems, in areas where mobile phone coverage is unavailable, one option is to use the CLAS (Centimeter-Level Augmentation Service) from Japan's quasi-zenith satellite Michibiki. With a CLAS-compatible receiver, correction data can be received directly from satellites, enabling RTK positioning even without mobile network coverage. For example, Lefixea's LRTK device, a compact RTK receiver that attaches to a smartphone, offers a model that can receive Michibiki’s CLAS signal through a mobile network outage option. Using such devices, RTK surveying can continue reliably even in remote areas where mobile signals do not reach. -
Challenge 3: Equipment Costs and Operational Effort
Traditionally, performing RTK surveying required two high-performance GNSS receivers (one for the reference station and one for the mobile station), resulting in high equipment costs. Additionally, the setup of base stations, communication configurations, and battery management required significant operational effort, making the barrier to adoption high for small and medium-sized businesses. Solution: In recent years, solutions that achieve low cost and simple operation have been emerging. By utilizing network-based RTK services, only one receiver is needed, and the use of inexpensive digital simple radios or correction data reception via Ntrip over the internet helps reduce running costs. Moreover, ultra-compact RTK receivers, like the LRTK mentioned earlier, which can be integrated with smartphones, have been made practical. The LRTK device is a palm-sized receiver with an integrated antenna and battery, and by simply attaching it to an iPhone or similar device and connecting via Bluetooth, centimeter-level positioning is possible, eliminating the need for complex wiring or installation work. The user interface has also been improved with features such as one-tap positioning and continuous logging on the dedicated app, making it easier to operate without specialized knowledge. Equipment costs have been significantly reduced compared to traditional systems, and more products are now available at price points that are accessible to smaller companies. With these new tools, the barrier to RTK adoption has been significantly lowered compared to before. -
Challenge 4: Operational Expertise and Accuracy Management
In RTK surveying, it is important that humans manage the accuracy, rather than relying solely on the equipment. For example, if the coordinates of the reference station are incorrectly set, that error will affect all subsequent positioning results. Additionally, during positioning, it is essential to periodically check known points to verify errors, observe multiple times to confirm repeatability, and ensure proper quality control. Attention must also be paid to GNSS-specific phenomena (such as poor satellite geometry or ionospheric disturbances), and if necessary, decisions to pause or postpone measurements should be made. Solution: To accumulate knowledge in surveying planning and accuracy management, attend training sessions hosted by equipment manufacturers or service providers, and develop internal operational manuals. The work regulations and manuals created by the Geospatial Information Authority of Japan are also useful references. Fortunately, modern RTK systems are equipped with features such as real-time display of positioning status (FIX/Float) and warning alarms to notify users of any accuracy degradation. Services that automatically correct reference station coordinates through connections with electronic reference points are also available, reducing human errors. By making double-checking a standard practice and not relying solely on the equipment, users can fully harness the strengths of RTK.
In summary, we have provided a broad explanation of RTK, from its basics to practical applications. RTK is a technology that is revolutionizing civil engineering surveying, and by leveraging high-precision positioning, productivity on construction sites can be dramatically improved.
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