Centimeter-Level High Precision!
Features and Selection Guide for Compact GNSS Devices for RTK Surveying in Construction

In construction site surveying, high-precision centimeter-level positioning using RTK (Real-Time Kinematic) technology is becoming increasingly important. With the advancement of infrastructure and the need for more efficient construction processes, there is a strong demand for higher accuracy in positioning information, and situations where errors of a few meters are unacceptable are on the rise. For example, on construction sites promoting ICT construction (also known as construction DX) by the Ministry of Land, Infrastructure, Transport and Tourism, GNSS receivers are mounted on construction machinery to enable real-time positioning during construction. To meet these high-precision surveying needs, compact GNSS devices with RTK positioning capabilities have been developed.

RTK positioning is strong because it enables real-time error correction between the base station and moving stations, allowing accurate coordinates to be obtained immediately on-site. This dramatically improves the efficiency of surveying tasks, making previously labor-intensive tasks like layout marking and as-built management much quicker. In fact, when RTK surveying technology is properly utilized, reports show that it can speed up work and reduce costs compared to traditional surveying methods.

This article explains the mechanism and technology behind high-precision RTK surveying, the features and selection criteria for compact GNSS devices, and compares them with traditional equipment. Finally, we introduce the LRTK series, a notable product for the construction industry, and provide a guide for requesting more information. Please use this as a reference to accelerate construction DX through high-precision positioning.

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The Mechanism and Technology of High-Precision RTK Surveying

RTK surveying is a real-time high-precision positioning technology that utilizes GNSS (Global Navigation Satellite System). As the name "Real-Time Kinematic" suggests, it refers to dynamic real-time positioning, and it involves the simultaneous use of at least two GNSS receivers (a moving station and a reference station). The reference station (base station) is installed at a location with a known, accurate coordinate and continuously receives satellite signals to determine its position. On the other hand, the moving station (rover) is carried to the point to be surveyed and receives correction information from the reference station via communication to calculate its position.

The accuracy of standalone positioning (with a single GNSS receiver) is typically a few meters. However, RTK improves this accuracy to within a few centimeters through error correction. The reference station and moving station share the signal errors from the same satellites (such as satellite clock errors or ionospheric delays), and by subtracting these errors, high precision is achieved. The two stations communicate data in real-time via radio or internet connection (typically using UHF specific low-power radio or mobile communication), and the moving station instantly calculates its position. This allows surveyors to obtain centimeter-level positioning results almost immediately, even while moving around the site.

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Features and Selection Guide for Compact GNSS Devices

GNSS receivers for RTK surveying were once dominated by large stationary equipment or expensive surveying-specific devices. However, recent advancements in technology have led to the development of compact and lightweight GNSS devices that are easy to carry and use. With models that are small enough to fit in the palm of your hand or can be integrated with smartphones, the barrier to introducing these devices to the field has significantly decreased. Here, we outline the key points to consider when selecting a compact GNSS device.

• Positioning Accuracy: The most important factor is accuracy. RTK-compatible devices can achieve high-precision positioning, typically within 1-3 cm horizontally and a few centimeters vertically. Always check if the device specifies "centimeter-level (cm)" accuracy in the product specifications. Actual positioning accuracy is influenced by satellite reception conditions and the environment, but a GNSS receiver that supports multi-band frequencies (such as L1/L2) will help mitigate ionospheric errors and provide more stable and precise results. Since positioning accuracy directly affects the quality of the work on-site, it’s crucial to select a device that offers sufficient performance without compromise.

• Supported GNSS Satellites and Frequencies: It’s ideal to select a device that supports multi-GNSS systems, such as GPS, GLONASS (Russia), Galileo (Europe), BeiDou (China), and Japan’s quasi-zenith satellite system, Michibiki (QZSS). The more satellites a device can receive, the more satellites can be captured overhead, improving positioning even in areas with obstructions like building shadows or mountainous regions. Additionally, consider the supported frequency bands. Some low-cost receivers only support the L1 single frequency, but ideally, choose a device that supports dual frequencies, such as L1/L2. Devices that support Michibiki’s CLAS signal (L6 band) offer the advantage of maintaining high-precision positioning even in remote areas, such as mountain regions, by receiving correction signals from satellites, even when communication networks are unavailable. Always check the number of satellites and frequency bands the device can support, especially with an eye toward future positioning improvements.

• Communication Methods and Correction Data Acquisition: RTK surveying requires correction data from the reference station. Therefore, it’s important to check which communication methods the device supports. A typical option is a device that supports RTK correction services delivered over the internet (such as Ntrip), which connects the device to cloud-based reference station networks via smartphone tethering or built-in SIM. This method allows correction data to be received anywhere in the country. Additionally, when working in areas without communication coverage, it's crucial to have options for direct communication via radio (RF). For example, you can use paired devices—one for the base station and the other for the moving station—and transmit correction data via specific low-power radio frequencies (such as 920 MHz). Some compact GNSS devices can even act as a base station themselves, sending correction data to other devices. If the device supports Michibiki CLAS, it can receive correction data directly from satellites without the need for an internet connection, which is especially useful in mountainous regions. Consider whether your use case requires an internet-based or local wireless solution or a combination of both.

• Price and Setup Costs: Compact GNSS devices come in a wide range of prices. High-performance devices are generally more expensive, but recent advances, particularly from overseas manufacturers, have driven prices down, with some RTK receivers now available for a few hundred thousand yen. On the other hand, traditional surveying equipment can cost several million yen per unit, so it’s important to select a device that fits your budget. When evaluating setup costs, be sure to consider not only the price of the hardware but also any operational costs, such as fees for correction data services, communication costs, and software usage fees. Recently, some products have adopted subscription-based models, offering plans that significantly reduce initial costs. These are more affordable compared to traditional high-end GNSS equipment, making them accessible even for small to medium-sized companies.

• Battery Life: For long-term use on-site, battery life is essential. Check how long the device can operate continuously on a full charge. Due to their compact size, these devices have limited internal battery capacity, but some models designed with low power consumption can last over 8 hours, with some wearable RTK devices offering up to 12 hours of operation. Also, check whether the device supports USB charging or mobile power banks for extended use, and whether battery replacement is possible. Be sure to choose a device with a power design that suits the on-site needs, including measures against battery performance degradation in extreme temperatures or cold environments.

• Durability and Dust/Water Resistance: Construction sites are harsh environments with rain, wind, dust, and impact. Even compact GNSS devices need to be durable enough for industrial use. When selecting a device, check its waterproof and dustproof ratings (at least IP65 or higher) and whether it has shock resistance. It’s important to ensure the device is well-constructed, with adequate protection for connectors. Devices designed for field use often feature waterproof structures that allow them to be washed off even after getting muddy, and are guaranteed to operate under extreme temperatures and humidity. For example, the LRTK Pro2, despite being an integrated antenna and battery design, is built to withstand harsh use on construction sites, ensuring it can be relied upon. Durability is a must-have condition for field equipment, as the device should withstand rough handling without damage.

• Additional Features (Inclination Compensation, etc.): Some recent compact GNSS devices are equipped with IMUs (Inertial Measurement Units) that provide automatic compensation for tilt, allowing the device to measure accurate coordinates even when the pole is tilted. This feature is useful when avoiding obstacles or when positioning at an angle, without the need for leveling the device. It is especially useful in narrow or uneven measurement points and improves surveying efficiency. Additionally, features like photo capturing with position tagging and cloud synchronization for data sharing are available on some models. Be sure to compare devices and check for any additional convenient features that suit your workflow.

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RTK-GNSS surveying excels at providing high-precision measurements over large areas in a short amount of time, making it ideal for open civil engineering surveys and similar tasks. On the other hand, total stations are better suited for measuring local points with extremely high accuracy and are essential for tasks such as establishing benchmarks in construction or detailed measurements. Drone surveying is adept at capturing aerial data (such as terrain models or images) and is useful for getting an overall view of the site or for remote surveying in hazardous areas. Since each method excels in different areas, the ideal approach is to use a combination of them for synergistic effects, rather than treating them as direct competitors. For example, drones can be used to capture a broad overview of a large area, RTK-GNSS for key point observations, and a total station for detailed measurements of critical areas.

When comparing traditional stationary GNSS surveying equipment with the latest compact GNSS devices, there is no significant difference in basic RTK positioning accuracy. While the miniaturization and cost reduction of compact devices have made them more user-friendly, large-scale equipment may still have advantages in terms of environmental durability and expandability. However, recent compact devices can now support external antennas and wireless connectivity, and often come equipped with the latest positioning engines, offering comparable performance. Therefore, compact GNSS devices are expected to gradually replace traditional equipment and become the primary surveying tool on-site.

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Introduction to LRTK Products

Finally, let's introduce the LRTK series, which has garnered attention among compact RTK-GNSS devices. LRTK is a product line developed by Refexia Inc., aiming to create advanced GNSS devices that allow anyone to easily utilize centimeter-level positioning. The differentiating features compared to other traditional products are as follows:

• Smartphone Integration and Ease of Use: LRTK is designed to seamlessly integrate with smartphones. By using a dedicated app, positioning can be initiated by using the smartphone as a controller, eliminating the need to carry a separate receiver device. For example, the "LRTK Phone" is a receiver that can be directly attached to the smartphone. When taking a photo with the smartphone, the coordinates of the subject are automatically recorded with centimeter-level accuracy and saved to the cloud. The intuitive user interface makes it easy to use, even for those who are not professional surveyors.

• All-in-One Design and Portability: The devices in the LRTK series feature a compact design that integrates the antenna, GNSS receiver, battery, and communication module. The representative model, "LRTK Pro2," fits all components into a disc-shaped body approximately 10 cm in diameter, and positioning can start immediately by attaching it to the end of a pole. With its lightweight design, it offers high mobility, making it easy to carry and use while walking around the site. This is a major departure from traditional stationary GNSS devices (which require large tripods and external power sources) and represents a revolution in surveying methods.

• CLAS Support and Offline Operation: The LRTK Pro2 supports the reception of the CLAS signal from Japan's satellite positioning service, Michibiki, allowing for high-precision positioning with just satellite correction data, even when there is no internet connection. This feature allows surveying in mountainous areas or places with no communication infrastructure, and proves invaluable for emergency surveying during disasters. Additionally, the LRTK series includes a unique function called "L-Link," which allows multiple LRTK devices to communicate wirelessly, turning one unit into a simple reference station and the others into moving stations, enabling the creation of a local RTK network on-site.

• Inclination Compensation Feature: The LRTK Pro2 is equipped with the latest IMU sensors and features an inclination compensation function that automatically corrects the positioning point at the end of the pole, even if the pole is slightly tilted. This eliminates the need to constantly straighten the pole when avoiding obstacles, significantly improving efficiency when surveying in tight spaces. The fact that this feature, previously only available on expensive high-end international models, is now easily accessible on a domestic compact device is a significant advantage.

• Integration with Cloud Services: LRTK also supports cloud integration for positioning data, providing a system where location data and photo data collected on-site can be instantly shared and managed within the company. For example, photos taken with the LRTK Phone are saved to the cloud with centimeter-level location tags, allowing them to be reviewed from office PCs. Additionally, data from worker's trajectories collected by the LRTK Helmet (helmet-mounted receiver) can be sent in real-time to the server, allowing remote supervisors to monitor progress. This ensures seamless data connectivity between the field and the office, promoting DX in reporting and instructions.

 

As shown above, the LRTK products are groundbreaking in that they offer high-precision GNSS surveying in a more accessible way and directly contribute to the digital transformation (DX) of the site. Compared to traditional RTK devices from competing companies, LRTK stands out with the convenience of smartphone integration, a variety of form factors (such as smartphone-mounted, pole-mounted, and helmet-mounted models), and CLAS support optimized for the Japanese market. The pricing structure has also been designed to make it easy for a wide range of users, from general contractors to small and medium-sized civil contractors, surveyors, and infrastructure maintenance personnel, to adopt.