RTK devices now affordable! Achieving high-precision positioning at low cost

Table of Contents

• What is an RTK device?

• Why high-precision positioning is required

• Challenges of conventional RTK surveying

• Why RTK devices can now be introduced at low cost

• Types and features of low-cost RTK devices

• Application areas and benefits of RTK devices

• Points for introducing RTK devices

• Simple surveying with LRTK

• FAQ

In recent years, advances in positioning technology have made RTK (Real Time Kinematic) positioning equipment, once expensive, available at affordable prices. There are many situations in surveying and civil engineering sites where centimeter-level (approx. inch-level) high-precision positioning is required, but until now specialized high-priced equipment was necessary. Thanks to the emergence of low-cost RTK devices, it is now possible for individuals and small sites to achieve high-precision positioning at low cost. This article explains in detail what RTK devices are, why they are important, the challenges of conventional approaches, the background to the price reductions, and the types and uses of the latest low-cost RTK devices. At the end of the article we also introduce the simple surveying solution “LRTK,” which uses the latest technologies, so please refer to it.

What is an RTK device?

An RTK device is equipment that uses a positioning technique called RTK (Real Time Kinematic) to obtain high-precision location information. RTK is a method for dramatically improving positioning accuracy in satellite positioning systems such as GPS by comparing in real time the data received at a reference station (a fixed receiver) and a rover (the receiver on the object being measured) and correcting errors. As a result, where standalone positioning would normally result in errors of several meters (several ft), RTK can reduce errors to about several centimeters (several in) horizontally. RTK devices refer to equipment that includes receivers, antennas, and communication devices for performing RTK positioning; traditionally, expensive sets from surveying equipment manufacturers were mainstream. Recently, however, with the advent of small, low-cost GNSS receiver modules and easy-to-use RTK equipment that can be used in conjunction with smartphones, RTK devices are becoming more accessible.

Why high-precision positioning is required

Why is centimeter-level (approx. inch-level) high-precision positioning needed in the first place? One reason is that small positional deviations in surveying and civil engineering/construction sites can lead to significant problems. For example, if errors of several centimeters (several in) occur in land boundary determination or foundation work, they can cause construction mistakes or boundary disputes later on. Also, in as-built verification (checking whether a completed structure matches the design), high-precision coordinate data are required. In situations formerly handled by leveling or total stations, RTK-GNSS allows one person to survey efficiently. Furthermore, advanced technologies that have recently become common—such as drone aerial surveying and machine guidance (automatic control of construction machinery)—require centimeter-level (approx. inch-level) accuracy. High-precision positioning directly contributes to improved safety, ensured construction quality, and increased productivity, so it is valued in many fields.

Challenges of conventional RTK surveying

RTK enables high-precision positioning, but conventional adoption had several challenges. First, the cost of equipment was extremely high. Dedicated RTK surveying sets (base station and rover, communication equipment, dedicated controller, etc.) were priced in the millions of yen, making them out of reach for small businesses or individuals. Second, operational effort and specialist knowledge were required. When installing a base station, it needed to be set up on an accurately known point and preliminarily positioned, which took time and effort for configuration and adjustment. On the rover side, wireless communication settings with the base station and application of received correction information required specialized operations, making the equipment difficult to handle without skilled personnel. Moreover, conventional RTK surveying typically required a two-person team to manage the base station and rover and divide surveying tasks. Because of these high costs and burdens, RTK adoption was limited in many places.

Why RTK devices can now be introduced at low cost

In recent years the situation surrounding RTK devices has changed significantly, and the cost of introduction has been greatly reduced. Several technical and environmental factors are behind this.

GNSS receiver cost reduction: GNSS receiver chips and modules, including those for GPS, have become dramatically cheaper. In the past, specialized high-end receivers were required for high-precision positioning, but now commercially available small chips support multiple frequencies and multiple satellite systems (not only GPS but GLONASS, Galileo, QZSS, etc.) and can obtain the observation data necessary for RTK. Mass production and technological innovation have made these modules far cheaper than conventional specialized equipment.

Wider availability of correction information services: RTK positioning requires correction data from base stations to correct positioning errors, and ways to obtain this data have become more abundant. Previously, you had to prepare your own base station or subscribe to paid positioning services. Now, national and private reference station networks have been established, and relatively inexpensive internet-based correction information services are available. For example, network RTK services that use reference points installed nationwide by mobile carriers are offered for a monthly fee of several thousand yen, enabling high-precision positioning without bringing a base station to the site. Furthermore, in Japan the Quasi-Zenith Satellite System “Michibiki” has begun a centimeter-class positioning augmentation service (CLAS), and with a compatible receiver it is possible to obtain correction information directly from satellites and perform RTK positioning even at sites outside internet coverage, such as mountainous areas. The easier access to correction information is one factor lowering RTK adoption barriers.

Smartphone integration and improved usability: Another factor is integration with smartphones and tablets. Products that allow RTK-capable GNSS receivers to be connected to a smartphone via Bluetooth or cable and operated/data-logged through dedicated apps have increased. Leveraging smartphones’ intuitive UIs and high-resolution screens has made tasks such as starting/stopping positioning, recording points, and checking on maps much easier. With a smartphone, it is also easy to upload positioning data to the cloud and share it instantly. This makes devices easier to use for non-experts and ultimately reduces adoption hurdles.

Competition and new entrants driving innovation: New companies and startups entering the GNSS surveying field and introducing innovative RTK devices are also notable. In addition to established surveying-equipment manufacturers, domestic and international ventures using low-cost GNSS modules are developing unique RTK solutions. Intensified competition has led to products on the market that improve performance while suppressing price. Users now have more choices and can more easily find RTK devices suited to their purposes and budgets.

Types and features of low-cost RTK devices

There are several types of low-cost RTK devices currently available. Each has different characteristics, so choosing according to intended use is important.

• Smartphone-mounted RTK devices: Small GNSS receivers that attach to the back or top of a smartphone are now available. By integrating with the smartphone, there is no need to carry a dedicated terminal, and positioning through to data storage can be completed within an app. Batteries and antennas are built-in or included, enabling centimeter-level (approx. inch-level) positioning with just a smartphone. The convenience of being able to walk around holding the phone and survey with one hand is a strong attraction.

• Handheld GNSS receivers and data loggers: Compared to conventional receivers, a variety of small, lightweight GNSS receivers that can be hand-held or mounted on a pole tip have been released. Many models link with smartphones or tablets via Bluetooth to receive correction data and display results, and there are more affordable models that require no complicated setup. Some offer durability and waterproof/dustproof specifications suitable for construction sites, and prices have been reduced to a fraction of conventional equipment.

• RTK-capable drones and surveying equipment: Drone models with RTK receivers built in and RTK modules that can be retrofitted to existing drones have appeared. This enables aerial photos to be geotagged with high-precision location information, reducing the number of ground control points required for photogrammetry. There are also simple base station kits and pedestal receivers with integrated antennas that can be brought to a site and used immediately as reference stations. By combining these devices, it is possible to build low-cost reference signals for drone surveying and machine control.

• Other new form factors: Novel RTK device forms are being developed, such as GNSS receivers that can be mounted on helmets, wearable high-precision GNSS backpacks, and systems that integrate with smart glasses to display positioning results in AR. These are designed to fit site work styles and support solo operations and improved safety.

Application areas and benefits of RTK devices

The spread of low-cost RTK devices is expected to enable their use in many fields. Below are the main application areas and their benefits.

Civil engineering and construction surveying: RTK devices are useful in many construction tasks such as as-built verification, stakeout, and checking land boundaries. Tasks that surveyors used to perform with total stations can be done much faster with RTK because coordinates can be obtained instantly by placing the receiver. One-person surveying becomes possible, reducing labor costs and improving safety (no need to accompany workers in hazardous areas).

Land surveying and map creation: RTK can be used for cadastral surveys and on-site collection of GIS data. Where handheld GPS with large errors was previously used, RTK devices can acquire high-accuracy location data from the start, reducing post-processing and data uncertainty. With low-cost RTK devices, anyone can perform precise positioning for tasks such as forest and farmland parcel measuring and infrastructure asset location recording.

Drone surveying and spatial data acquisition: As mentioned, combining RTK-equipped drones and ground reference stations allows aerial photos to carry high-precision location information. This reduces the need to place many ground control points for photogrammetry. Using low-cost RTK devices for drone surveying enables small sites to quickly acquire high-precision 3D survey data for purposes such as as-built checks and earthwork volume calculations.

Agriculture and other fields: In precision agriculture (smart farming), high-precision position information from RTK is important. RTK devices are used for position control of autonomous tractors, field parcel measurement, and fixed-point observations for crop growth management. Because these technologies have become cheaper, small-scale farmers can now more easily adopt them. Other areas where high-precision positioning is useful—such as logistics, earthquake and volcano monitoring, and disaster-area mapping—can also benefit from low-cost RTK devices.

Points for introducing RTK devices

Even though RTK devices have become cheaper, there are several points to keep in mind to use them effectively.

Check the operating environment: RTK positioning is most effective outdoors with a clear view of the sky. In the shadow of buildings or within forests, satellite signals are obstructed and accuracy drops, so it is important to choose measurement locations carefully or install external antennas as needed. In urban canyons, multipath (satellite signal reflections) can cause errors, and even after correction centimeter-level (approx. inch-level) accuracy might not be guaranteed. Understand in advance whether RTK is suitable for your site and what accuracy limits to expect.

Decide how to obtain correction information: Determine how you will obtain correction information for RTK devices. Where internet is available at the site, subscribing to a network RTK service (such as NTRIP) is convenient. In mountainous areas without cellular coverage, options include setting up a base station in advance or using equipment that supports Michibiki’s CLAS signal. Choose the method that fits your needs and prepare the necessary equipment and subscriptions.

Evaluate device performance: Low-cost RTK devices vary in performance. Differences between products include the number of satellite systems supported (GPS/GLONASS/QZSS, etc.), frequency bands, time to initial fix (time to obtain a fix solution), positioning update rate, battery life, and waterproofing. Select a device with specifications that match the required accuracy and usage. If possible, try a demo unit before purchasing to verify performance in actual field conditions.

Data utilization and integration: Consider how you will use the data obtained from RTK devices. Dedicated apps and cloud services allow coordinate data to be shared immediately from the field and compared with office CAD drawings. Confirm that the chosen equipment integrates smoothly with your workflow (e.g., design software or GIS systems). Also pay attention to the data formats you will acquire (latitude/longitude, plane rectangular coordinates, height systems, etc.) and be prepared to perform coordinate transformations or geoid height conversions if necessary.

Simple surveying with LRTK

One solution that has emerged in this context is “LRTK.” LRTK is a type of RTK device designed to be attached to a smartphone so that anyone can easily perform centimeter-level (approx. inch-level) positioning. By attaching a dedicated small GNSS receiver to the back of a smartphone and taking it to the site and turning it on, high-precision positioning can be achieved. Where network connectivity is available, correction services are accessed via the smartphone; in areas without coverage, the device can receive Michibiki’s augmentation signal, enabling stable positioning even in mountainous or communication-deprived sites. Because LRTK integrates battery and antenna, complicated equipment connections are unnecessary and time to start positioning is greatly reduced.

Using LRTK’s dedicated app, acquired point coordinates are displayed on a map in real time so you can check survey results on the spot. Cloud integration is supported, and measured data can be synced to the cloud with one tap for immediate access and sharing on office PCs. Combined with AR (augmented reality) technology, you can overlay design locations on the on-site view on your smartphone screen to intuitively guide stakeout positions or perform as-built checks. These features enable efficient single-person surveying without specialist knowledge.

For those who have hesitated to adopt high-precision positioning due to cost or manpower concerns, LRTK makes it easy to get started. As a new surveying style enabled by low-cost RTK devices, LRTK can greatly improve on-site productivity. Consider including such cutting-edge devices as options to enjoy the benefits of high-precision positioning.

FAQ

Q. What is the difference between RTK and regular GPS positioning? A. Standalone GPS positioning typically has errors of several meters (several ft), while RTK reduces errors to several centimeters (several in) by using correction information from a reference station. Because corrections are applied in real time, RTK provides high-precision positions on the spot.

Q. What is needed to use an RTK device? A. Basically you need an RTK-capable GNSS receiver (the RTK device) and correction data to correct positioning errors. Correction data can be obtained by setting up your own base station or by using an internet-based network RTK service. Many modern products can obtain correction data via the internet just by connecting to a smartphone, so separate dedicated communication equipment is not always necessary.

Q. Can low-cost RTK devices really achieve high-precision positioning? A. Yes—under appropriate conditions. Even low-cost equipment can achieve several-centimeter (several in) accuracy in open-sky environments. However, compared with high-end machines, they may be inferior in antenna performance and reception sensitivity, so in environments with many obstructions it may take longer to obtain a Fix solution (centimeter-level solution) or accuracy may temporarily degrade. When using inexpensive devices, securing the best possible measurement environment helps achieve high precision.

Q. In what environments can RTK be used? Can it be used indoors or in forests? A. RTK is basically intended for outdoor use with a clear view of the sky. It cannot be used indoors or inside tunnels where satellite signals do not reach. In forests, signal blockage and reflections from trees can degrade accuracy and cause large errors. On the other hand, if there are only some obstacles, a multi-GNSS receiver can continue positioning by receiving signals from multiple satellites. In short, the more open the sky, the better RTK can perform.

Q. What price range do RTK devices fall into? A. It depends on the product, but in recent years RTK-capable receivers have become available from around tens of thousands of yen. Even higher-performance models or those with combined functions (e.g., GNSS + IMU + LiDAR) can be in the hundreds of thousands of yen, which is significantly more affordable compared to traditional dedicated surveying equipment. Choose a model that fits your needs and budget.

Q. Do I need specialist knowledge or qualifications to introduce RTK? A. Basic operations have become relatively simple, and special qualifications are not required to operate them. However, understanding the principles of high-precision positioning and coordinate systems makes it easier to make full use of the devices. First-time adopters can usually become proficient in a short time by utilizing manufacturer- or dealer-provided training and manuals. If you plan to use results for official surveying work, having verification performed by qualified surveyors can give greater confidence in the introduction.