Positioning accuracy has finally reached the centimeter level! Precision surveying made possible with RTK devices

Table of Contents

• The Importance of Precision Surveying and Expectations for RTK Devices

• Positioning Accuracy and Challenges of Conventional Technologies

• What is RTK (Real-Time Kinematic)?

• How RTK Positioning Works

• Evolution of RTK Devices and Latest Technology Trends

• Use Cases of RTK Devices in Precision Surveying

• Benefits of Implementing RTK Devices

• Precautions When Using RTK Positioning

• Future Prospects for RTK Devices and Surveying

• Simple Surveying with LRTK

• FAQ

The Importance of Precision Surveying and Expectations for RTK Devices

On construction and civil engineering sites, even a positional deviation of just a few centimeters (a few inches) can lead to major problems. If the placement of bridge piers or foundations is off by a few centimeters (a few inches), it can affect the entire structure, and surveying errors in roadworks can result in rework and additional costs. Therefore, centimeter-class precision surveying (half-inch accuracy) is indispensable for ensuring quality and safety. Traditionally, optical total stations and levels have been used to pursue millimeter-level accuracy (0.04 in), but these methods are time-consuming and labor-intensive and require work by skilled surveyors.

On the other hand, the recently introduced RTK devices (high-precision GNSS positioning devices) have attracted great expectations as a technology that dramatically increases positioning accuracy while improving work efficiency. Centimeter-level positioning, which traditionally required specialized equipment and highly skilled technicians, can now be easily achieved by anyone with nothing more than a palm-sized receiver and a smartphone. In the field of precision surveying, RTK devices are combining the two values of "high accuracy" and "ease of use," and are pioneering a new style of surveying.

Accuracy and Challenges of Conventional Positioning Technologies

Positioning using artificial satellites has long been expected to have errors on the order of several meters. With standard GPS standalone positioning, delays and reflections of satellite signals cause errors of around 5～10 m (16.4～32.8 ft). This level of accuracy is insufficient for precise construction and civil engineering surveys, so detailed work ultimately had to be completed using conventional optical distance measurement and leveling surveys. In addition, conventional technologies used to achieve high accuracy (total stations and large GNSS receivers) involve bulky, expensive equipment that requires manpower to transport and set up on site. Projects had to rely on specialized surveying teams, and site personnel could not easily verify positions themselves.

Furthermore, with conventional GNSS positioning (using GPS), achieving high accuracy in real time was difficult, and cases requiring post-processing (PPP or static surveying) were common. Although surveying methods that combine "ease of use" and "accuracy" have long been sought after, previously there were few solutions that satisfied both simultaneously.

What is RTK (Real-Time Kinematic)?

An innovative technology that emerged in this context is RTK positioning (Real-Time Kinematic). RTK refers to a method that achieves centimeter-level positioning accuracy (half-inch-level accuracy) — which conventional GPS could not provide — by correcting positioning signals from satellites in real time. Specifically, a receiver called a rover and a base station installed at a known, precise coordinate location simultaneously receive GNSS signals, and by calculating the difference between their positioning data they cancel out errors. By applying correction information in real time, RTK largely compensates for error sources associated with satellite positioning (ionospheric and tropospheric delays, satellite clock errors, etc.) and enables identification of highly precise positions.

In other words, the reference station calculates the discrepancy between its own precise position and the position information received from the satellites, and transmits that correction data to the mobile station. By adding that correction value to its own positioning result, the mobile station can instantly obtain a position coordinate with much smaller error. With this RTK method, an accuracy of approximately ±2–3 cm (±0.8–1.2 in) horizontally and on the order of ±a few centimeters (±a few in) vertically can be achieved. Because errors that were traditionally on the order of several meters (several ft) are reduced to within a few centimeters (a few in), RTK technology has begun to be used in a wide range of fields that require "high-precision positioning," including surveying, civil engineering and construction, agriculture, facility management, and autonomous driving.

How RTK Positioning Works

To use RTK positioning, you basically need to deliver real-time correction information to the rover. The two typical methods for that mechanism are as follows.

• Local reference station method: The user prepares known-coordinate points (locations whose exact coordinates are known) at the survey site and installs a GNSS receiver for the reference station there. The reference station transmits correction information obtained in real time to the rover by radio or similar means, and the rover receives it and applies it to positioning. Because you provide your own base station, stable corrections can be obtained, but there are challenges such as the labor involved in installing the base station and the decrease in accuracy as you move away from the base station (errors increase when more than a few km (a few mi) away).

• Network RTK method: This is a method that does not require installing your own base station and acquires correction information from a public reference station network via the internet. For example, in Japan, correction services using the "VRS method" are provided, such as the Geospatial Information Authority of Japan’s CORS (Continuously Operating Reference Station) network, which integrates data from reference stations installed at various locations and sets a virtual reference station around the user. The rover receives correction information from the server via cellular communication (delivered using protocols such as Ntrip) and performs high-precision positioning. With this network RTK method, stable accuracy over a wide area can be achieved, and there is the advantage that setting up base stations is unnecessary. However, on the other hand, there are constraints such as the need for a subscription or monthly fee for the correction service, and it cannot be used in locations without cellular coverage.

In other words, to achieve centimeter-level (half-inch accuracy) precision with RTK, it was essential either to set up a base station or to obtain correction information via communication. However, in recent years, advances in technology have produced new approaches that greatly relax these requirements. The key is Japan’s Quasi-Zenith Satellite System “Michibiki” and its centimeter-level (half-inch accuracy) positioning augmentation service (CLAS). CLAS is a satellite-delivered correction information service that covers all of Japan, and as long as a receiver supports it, it enables real-time high-precision positioning without relying on the Internet. Because the augmentation signal can be obtained simply by receiving the L6-band radio waves transmitted from Michibiki (QZSS), it is a groundbreaking system that can maintain centimeter-level (half-inch accuracy) precision even in areas outside communication coverage, such as mountainous regions and disaster sites. For example, during the 2024 Noto Peninsula earthquake, there were reports of CLAS-compatible RTK receivers proving useful for field surveys while communication networks were down in the affected areas. Thus, in the world of RTK positioning, diversification of means for obtaining correction information has made it possible to secure high precision more flexibly than before.

Evolution of RTK Devices and the Latest Technology Trends

Behind making high-precision positioning by RTK available to everyone are the evolution of the devices themselves and the development of surrounding technologies. On the hardware side, the miniaturization and performance improvement of GNSS receivers and antennas have progressed dramatically. Not long ago, centimeter-class GNSS receivers (centimeter-class / half-inch-class) including batteries and enclosures were very large and heavy, but recently high-sensitivity multi-GNSS modules have become small enough to fit on palm-sized PCBs. Chips that can support multiple satellite positioning systems (GPS, GLONASS, Galileo, BeiDou, Michibiki, etc.) and multiple frequency bands (L1/L2/L5, etc.) simultaneously have been commercialized, allowing stable reception of many satellite signals even in urban or mountainous areas where the number of satellites used to be insufficient before. As a result, RTK devices can now more readily obtain high-precision solutions even in environments that were previously difficult for positioning.

There have also been major advances in software and infrastructure. Improved positioning performance of smartphones is one such advance: Android models supporting dual-frequency GNSS have appeared, and techniques for acquiring and analyzing raw GNSS data are being researched. Although accuracy with a smartphone alone has improved to the sub-meter level (sub-1 m (sub-3.3 ft)), limitations of built-in antennas make it difficult to consistently achieve centimeter-level (cm-level (0.39 in)) accuracy. This led to the approach of combining smartphones and high-performance external GNSS receivers. The latest RTK devices are designed with smartphone integration in mind, fusing a smartphone's communication and processing capabilities with the dedicated unit's high-precision positioning performance.

For example, our developed compact RTK device series "LRTK" is one such example. It is a palm-sized receiver that can be attached to a smartphone, and by simply connecting via Bluetooth the smartphone quickly becomes a surveying instrument with centimeter-level accuracy (half-inch accuracy). The high-performance multi-GNSS receiver can stably obtain RTK fixed solutions outdoors (errors within a few cm (a few in)), and in supported areas CLAS satellite augmentation signals can also be received directly. On sites with communication coverage it can use network RTK, and outside coverage it can use satellite augmentation — the ability to flexibly achieve high accuracy depending on the situation is also a strength of modern RTK devices. Integration with smartphone apps has greatly improved usability. Because positioning and recording can be performed intuitively on the familiar smartphone screen, even technicians with limited specialized knowledge can handle it easily. As a result of these technological trends, RTK devices have evolved into practical tools that are “compact, inexpensive, and easy to carry” “easy to set up and ready to measure immediately”.

Use cases of RTK devices for precision surveying

As high-precision RTK devices have become more accessible, the range of on-site applications has expanded dramatically. Below are some of the main application scenarios.

• Construction and civil engineering sites: RTK devices are used for establishing control points (stakeout/batter boards) and verifying as-built conditions. Tasks that previously required total station measurements by surveyors can now be carried out by site supervisors or workers themselves using RTK-enabled devices, allowing positioning and elevation checks to be completed in a short time. Because precise surveying can be performed in real time during construction, this helps prevent rework and shortens project schedules.

• Agriculture (precision agriculture): Examples are increasing of mounting RTK devices on tractors and drones to perform autonomous driving and to control seeding positions with an accuracy of a few centimeters (a few in). Because they can maintain travel lines with minimal error even in vast fields, efficient farm work without overlap or unevenness is possible. In the agricultural sector, RTK's centimeter-level accuracy (half-inch accuracy) also contributes to improved quality and productivity.

• Drone surveying and mapping: In photogrammetry that creates terrain models from aerial photographs, accuracy is improved by RTK-equipped drones and GCPs (ground control points) with RTK receivers. RTK-capable drones can record while correcting their position during flight, enabling the generation of high-accuracy 3D models aligned with map coordinates without post-processing. This can eliminate many ground control points that were previously required, improving survey efficiency and safety.

• Infrastructure inspection and maintenance: RTK devices are also playing an active role in infrastructure upkeep, such as roads and buried pipelines. For example, when performing on-site AR (augmented reality) displays based on the position information of buried objects, high-precision RTK positioning allows virtual models to be overlaid without even a displacement of a few centimeters (a few in). RTK devices are becoming a powerful tool in any situation where accurate position measurement is required, such as displacement measurement of bridges and dams and monitoring terrain changes at disaster sites.

In this way, RTK devices meet the needs for precision surveying across a range of fields, primarily construction and surveying. They not only measure the coordinates of points but, when combined with other technologies, also support the centralization of measurement data and real-time on-site decision-making, acting as a driving force that simultaneously boosts productivity and accuracy on site.

Benefits of Introducing RTK Devices

Based on what has been discussed so far, let's summarize the main benefits that can be gained by introducing RTK devices.

• Dramatic improvement in positioning accuracy: Needless to say, the biggest advantage is the ability to achieve high precision at the centimeter level. Position measurements that previously had large errors can be performed reliably with RTK devices, so they can be confidently used even in construction projects and surveys with strict quality control.

• Improved work efficiency and speed: Because high-precision positioning is possible in real time, there is no waiting time for results. You can measure on the spot and immediately move on to the next task, reducing construction schedule delays caused by waiting for surveys. In addition, many devices can be carried and operated by a single person, so surveying can be completed with the minimum number of personnel, which also helps alleviate labor shortages.

• Usability and responsiveness: The latest RTK devices come with refined user interfaces such as smartphone apps, enabling intuitive operation. Some products allow positioning to be started with a single button, without having to worry about obscure technical terms or settings. They serve as simple surveying tools that even first-time users can handle after a short familiarization, allowing anyone on site to perform surveys whenever needed and achieving immediate responsiveness.

• Data integration and multifunctionality: Positioning data from GNSS are recorded in a global coordinate system, which makes them easy to integrate with other geospatial data. RTK devices that combine multiple functions—such as photography, point cloud scanning, and navigation—have emerged, enabling all-in-one measurement with a single unit. The coordinate data of measured points can be immediately shared to the cloud or cross-checked with drawing data, enabling smooth digital information integration.

• Cost savings and improved safety: Small RTK devices are generally less expensive than traditional large surveying instruments, and maintenance costs are often lower. Also, because of their high precision they can reduce surveying errors and rework, so a reduction in overall operational costs can be expected. Being able to survey quickly on site also shortens the time spent working in hazardous areas, providing safety benefits.

Precautions when using RTK positioning

RTK devices are extremely useful, but there are some points to keep in mind to reliably achieve centimeter-level accuracy.

First, speaking generally about GNSS positioning, the reception environment for satellite radio signals has a large impact on accuracy. In open areas with a clear sky you can receive satellite signals stably, but in the canyon-like gaps between high-rise buildings (urban canyons) or in forests the signals can be blocked or cause multipath (reflections), making accuracy prone to degradation. With RTK, if satellites cannot be sufficiently acquired you cannot obtain a fixed solution and will remain at a float solution, so errors can worsen to the order of several tens of centimeters to about 1 m (3.3 ft). Therefore, when performing positioning you should take measures such as choosing locations with as wide a view of the sky as possible, installing the antenna high overhead, and avoiding obstacles.

Next, the reception status of correction information is also important. With a local base station configuration, take care that the wireless communication distance between the base station and the rover does not become too long, and with a network RTK configuration, pay attention to the signal quality of mobile communications. If communication is interrupted, it may take some time after correction information is received again to obtain a fixed solution. Also, when positioning while moving, be mindful of sudden changes in orientation and differences in elevation. The latest RTK devices improve robustness through tilt compensation features and the simultaneous use of multiple satellites, but depending on device specifications, tilting at extreme angles may fall outside the guaranteed accuracy.

Finally, an understanding of reference frames and coordinate transformations is also indispensable. Coordinates obtained with RTK are basically in a global geodetic reference frame (such as WGS84 or Japan’s corresponding JGD2011). Because surveying coordinate systems differ by country or region, you may need to transform your results into the required coordinate system as necessary. In domestic public surveying, conversion to a plane rectangular coordinate system or height corrections using geoid heights may be required, so pay careful attention to how coordinate systems are handled in order to correctly utilize high‑precision positioning results.

Future Prospects for RTK Devices and Surveying

As centimeter-level positioning (half-inch-level positioning) using RTK devices begins to become widespread, the field of surveying is entering a major period of transformation. As technology advances further, an era in which high-precision positioning is taken for granted will arrive. For example, the addition of further Michibiki (Quasi-Zenith Satellite) satellites and the expansion of other countries' satellite systems are expected to further improve the coverage and stability of satellite positioning. In addition, the development of advanced correction services (such as PPP-RTK) that integrate and process vast reference-station data in the cloud and deliver corrections in real time is expected to shorten initialization times and further improve accuracy.

In terms of hardware, smartphones themselves may soon come standard with RTK-equivalent positioning capabilities. Some of the latest smartphones have already begun to include high-precision positioning modes, and in the future centimetre-level accuracy may be obtainable without dedicated devices. If that happens, an era will arrive in which not only surveying professionals but also everyone involved in field work will use high-precision GNSS routinely.

What lies ahead as RTK devices become widespread is a further DX (digital transformation) of surveying work. By being able to obtain spatial coordinates in real time, onsite progress management and as-built management can be shared in real time, and automated construction that links position information with construction machinery and robots can be carried out, leading to new applications one after another. As high-precision positioning information is utilized across all areas of society—such as infrastructure maintenance, disaster prevention, and urban planning—efficiency and safety are expected to improve dramatically.

Simplified surveying with LRTK

As expectations for RTK devices grow toward the future, one solution that is already significantly transforming field operations is simplified surveying with LRTK. LRTK is the name of the compact, high-accuracy GNSS device and service our company provides, developed with the goal that anyone can easily achieve centimeter-level positioning without using specialized surveying equipment. Specifically, it consists of a compact receiver that can be attached to a smartphone (LRTK terminal) and a dedicated app, allowing high-accuracy positioning to begin within seconds of powering on without the hassle of setting up equipment on site.

The strengths of simplified surveying with LRTK are on-site responsiveness and all-in-one measurement capabilities. Tasks that traditionally required separate equipment—positioning, recording, and mapping—can be performed end-to-end with just an LRTK and a smartphone, simplifying the surveying workflow. For example, when you measure a point on the smartphone screen it is simultaneously plotted on the map, and when you take a photo that photo is automatically tagged with high-precision position coordinates and orientation. You can directly calculate distances and areas from the acquired point data and share them with your team via the cloud, enabling smooth information flow between the field and the office.

So that even those conducting surveying on site for the first time can use it easily, the LRTK app features an intuitive user interface, and Japanese operation manuals and support are provided. Its price is more affordable than large surveying instruments, and because corrections can use the free CLAS satellite service, running costs are almost nonexistent. As a result, LRTK serves as an easy-to-use and powerful tool in situations where the barrier to adopting high-precision positioning has been high — such as surveying small construction sites, surveying on remote islands and in mountainous areas, and routine inspection work.

In a trend that could be called the democratization of precision surveying, LRTK is providing an environment where "anyone, anywhere, immediately" can measure. If you have not yet experienced simple surveying with an RTK device, please take this opportunity to experience its convenience and accuracy. You will surely realize that the conventional wisdom of surveying will change dramatically.

FAQ (Frequently Asked Questions)

Q: What is the difference between RTK and conventional GPS positioning? A: Standalone GPS positioning typically incurs errors on the order of several meters, but RTK positioning uses correction information from a base station to reduce errors to a few centimeters. The major difference is that RTK applies corrections in real time and can achieve positioning accuracy that is orders of magnitude higher than conventional GPS.

Q: What is needed to perform RTK positioning? A: Essentially, you need an RTK receiver for the mobile station (rover) and a base station that provides correction information. The base station can be set up yourself or you can obtain correction data from a network RTK service. You also need a means of communication (a radio or an internet connection) for the rover to receive the correction information. Recently, integrated RTK devices that can be connected to smartphones have appeared, making it easy to start RTK positioning without needing dedicated equipment.

Q: Is high-precision positioning with RTK possible in areas without mobile-phone coverage? A: Network RTK services cannot be used where cellular communications do not reach, but there are several alternatives. One is a local RTK method in which a base station is set up on site and correction information is sent via radio communication. Another is to use CLAS, Japan's satellite augmentation service. With a CLAS-compatible receiver you can receive correction signals directly from the Michibiki satellites without the Internet, allowing real-time centimeter-level accuracy (half-inch accuracy) even in mountainous areas.

Q: Can beginners use RTK devices? A: Yes, recent RTK devices are designed to be easy for beginners to use. They feature intuitive operation that links with smartphone apps and functions that automatically connect to correction data, so you can begin positioning without specialized knowledge. For example, products like LRTK complete positioning simply by following guidance in Japanese, so even those encountering high-precision surveying for the first time can feel secure.

Q: What kind of device is LRTK? A: LRTK is a compact, high-precision GNSS receiver designed to attach to and be used with a smartphone. It connects to the smartphone via Bluetooth and performs RTK positioning using a dedicated app. It supports multi-GNSS and multi-frequency, enabling real-time acquisition of highly accurate positions with errors of several cm (several in). It also supports reception of CLAS satellite augmentation signals, allowing it to continue centimeter-level positioning (half-inch accuracy) even outside communication coverage. Compared with conventional surveying instruments, it is highly portable and easy to operate, and is attracting attention as a simple surveying tool that can be used even by non-experts.