Utilizing RTK GPS and Implementation Costs: Key Points for Applying High-Precision Positioning on Site

Table of Contents

• What is RTK GPS?

• Mechanism and Characteristics of RTK GPS

• Application Areas of RTK GPS

• Equipment Required for RTK GPS Implementation

• Costs of Implementing RTK GPS

• Key Points for Applying High-Precision Positioning on Site

• Simple Surveying with LRTK

• FAQ

What is RTK GPS?

RTK GPS stands for Real-Time Kinematic GPS, a technique that identifies positions with centimeter-level accuracy using satellite positioning. With ordinary GPS (standalone positioning), errors of several meters (several ft) commonly occur due to signal delays from buildings or terrain and atmospheric effects. In contrast, the RTK method corrects errors in real time, enabling positioning with an accuracy of about 2–3 cm (0.8–1.2 in). Tasks that were difficult due to large GPS errors—such as precisely identifying boundaries or automatic control of machines—become feasible with RTK. Because RTK GPS provides highly accurate position information, it is attracting attention in civil surveying, construction sites, agriculture, and other fields where precise alignment and measurement are required.

Mechanism and Characteristics of RTK GPS

RTK GPS achieves high accuracy by using two GNSS receivers called a base station and a rover, comparing their observation data and correcting errors. First, the receiver serving as the base station is installed at a precisely known position; the difference (error) between the coordinates calculated from the satellite signals received there and the actual installation coordinates is determined. That correction information is transmitted to the rover via radio or the Internet, and the rover applies the correction to the GNSS data it receives, producing a highly accurate position with the errors removed. Because this processing is done in real time, the rover can immediately perform high-precision positioning on site.

Another feature of RTK positioning is that the high accuracy is achieved through relative positioning with respect to the base station. In other words, the rover’s position is determined precisely as coordinates relative to the base station. If the base station’s absolute coordinates are known, the rover’s absolute coordinates can also be obtained with high accuracy. This enables surveying and construction based on map coordinate systems. However, to obtain high accuracy, it is necessary to consistently receive good signals from multiple satellites, and positioning accuracy may decrease in environments with tall buildings or trees nearby.

In recent years, GNSS correction information services provided by governments and companies (so-called network RTK) have appeared, making it increasingly possible to use RTK positioning without installing a dedicated base station. For example, Japan’s Quasi-Zenith Satellite System "Michibiki" provides a centimeter-level augmentation service (CLAS), and paid high-precision positioning services from mobile carriers can allow single receivers to achieve centimeter-level accuracy. These infrastructure improvements are gradually lowering the barriers to using RTK GPS.

Application Areas of RTK GPS

High-precision RTK positioning is being applied across various fields. Examples of main application areas are listed below.

• Surveying: RTK GPS is used in topographic and land surveying to accurately measure land boundaries and terrain. Surveying tasks that used to take a long time with conventional total stations can obtain coordinates instantly with RTK, greatly improving work efficiency.

• Construction (ICT construction): On construction sites, high-precision GNSS positioning is utilized as part of ICT construction (information-based construction). Machine guidance systems installed on excavators and bulldozers allow accurate construction by comparing design drawings with actual positions, improving quality and reducing rework. Also, using GNSS receivers for on-site stakeout (marking) work to efficiently establish references is increasingly common.

• Agriculture (smart agriculture): RTK GPS is used in automatic steering systems for tractors and other equipment to enable autonomous driving over large fields. With centimeter-level accuracy, straight driving and position control can be performed so that seeding and fertilization are applied evenly. This not only shortens work time and reduces labor but also enables precision agriculture that makes effective use of farmland.

• Drone surveying: Equipping drones (unmanned aerial vehicles) with RTK-capable GPS enables high-precision positioning for aerial photos. Without placing many ground control points (GCP) in ground surveys, accurate terrain models and orthoimages can be generated from drone photos, improving efficiency in civil planning and disaster surveys.

• Autonomous driving and logistics: High-precision position information is essential for vehicle autonomous driving and navigation of automated guided vehicles (AGVs). RTK GPS enables lane-level accuracy in self-positioning, supporting safe and efficient route navigation. RTK is particularly advancing in scenes where centimeter-level offsets are critical, such as platooning of long-haul trucks and autonomous operation of agricultural machinery.

Equipment Required for RTK GPS Implementation

To implement RTK GPS, specialized equipment and systems for high-precision positioning are required. Prepare the following equipment and environments.

• Base station GNSS receiver: A high-precision GNSS receiver for the base station to be fixed in place. Install the antenna at an accurately known coordinate and generate correction information from the satellite signal data received here. High-performance receivers and antennas with high positioning accuracy are used for base stations.

• Rover GNSS receiver: The GNSS receiver on the rover that is the object of positioning. It is used in handheld surveying instruments, machines, drones, etc. An RTK-capable receiver that can apply correction data sent from the base station is required.

• Communication means (data link): A communication method to transmit correction information from the base station to the rover is indispensable. Commonly, a data link is secured via low-power radio, digital simple radio, or Internet-based methods such as NTRIP. On the rover side, a radio modem or mobile router is used to receive base station data in real time.

• GNSS correction information services: If you do not set up your own base station, use external correction information distribution services. Various services exist, including the Geospatial Information Authority’s network of continuously operating reference stations, paid services from private providers, and free base station data published by local governments and universities. Configure receivers and software according to the service used to obtain correction information.

• Positioning software and apps: Software or applications are also necessary to record and utilize coordinates obtained from RTK positioning. Survey controllers or tablet/smartphone surveying apps can be used to check positioning results on maps and save data in real time.

Additionally, having a good view of the sky is important for high-precision positioning. Position in as open a location as possible to avoid blocked satellite signals or multipath reflections so accuracy remains stable. For long-term stable operation, ensure sufficient power supply for the base station and prepare tripods and poles for mounting positioning equipment.

Costs of Implementing RTK GPS

When introducing high-precision RTK GPS, it is necessary to comprehensively consider various cost factors such as equipment costs, communication costs, and personnel training. Traditionally, this type of system required significant initial investment due to the high cost of dedicated equipment.

However, recent technological innovations have reduced costs. The main cost items and their trends are explained below.

Equipment purchase cost: The main costs are purchasing GNSS receivers and antennas for both base and rover and communication modems required for RTK positioning. Professional GNSS receivers capable of high-precision positioning used to cost several hundred thousand to several million yen per set. Recently, however, low-cost high-precision GNSS modules and simplified receivers have appeared, allowing substitution with more affordable equipment depending on the application.

Communication and service fees: Running costs for transmitting base station data should not be overlooked. For radio communication, license application and equipment costs may be required, and for Internet use, mobile data charges apply. When using external correction information services, subscription fees or service usage fees may be required. For example, high-precision positioning services from carriers or private cloud RTK services may have monthly fees.

Personnel and operational costs: Operating high-precision positioning on site requires personnel training and establishment of operational rules. Consider the human costs of training operators to become proficient with equipment and setting up procedures for accuracy control. Especially when introducing RTK for the first time, there will be a learning period until the system can be used smoothly on site.

Although these cost hurdles exist, the benefits of introduction can be significant and may produce returns exceeding costs over the long term. If RTK GPS improves surveying and construction efficiency and reduces labor and work time, the investment can be recovered overall. There are also cases of cost reduction by utilizing open correction information (free satellite augmentation signals and Internet base stations). Demonstrations by local governments and research institutions report that combining inexpensive GNSS receivers with free services can achieve nearly the same accuracy at much lower cost compared to conventional systems. Advances in technology are making RTK GPS increasingly accessible.

Key Points for Applying High-Precision Positioning on Site

To make the most of high-precision RTK positioning on site, pay attention to the following points.

• Receive satellite signals well: The basis of high-precision positioning is to receive as many GNSS satellite signals as possible stably. In environments with poor radio conditions, such as in the shadow of buildings or in forests, accuracy tends to decline, so adjust the positioning location and ensure correction information does not drop out. Improve reception by using a pole to raise the antenna when necessary.

• Manage reference points and coordinate systems: Accurately know the coordinates of the known point where the base station is installed. Also, perform positioning and data recording in the appropriate coordinate system for the purpose, such as Japan’s plane rectangular coordinate system or the World Geodetic System (WGS84). If you position without understanding base point errors or differences in coordinate systems, the high-precision data may not be useful on site.

• Ensure stable communication environment: Since RTK requires receiving correction information in real time, take care to prevent communication interruptions. For radio communication, check the distance between base and rover and whether obstacles exist; for Internet communication, consider coverage areas and data limits. Installing relay stations or using alternate communication methods as needed can improve stability.

• Verify and record accuracy: Make it a habit to verify that the coordinates measured on site really meet the required accuracy. Pre-measure known control points to check errors, and during positioning, check real-time accuracy indicators (whether RTK is a fixed or float solution, estimated errors, etc.). When recording positioning results, also store the date and time, the type of correction information used, and the solution status (Fixed/Float), which makes it easier to verify data reliability later.

• Equipment handling and personnel development: To use high-precision equipment stably, site personnel need to become proficient in handling equipment. Do not neglect basic maintenance such as periodic calibration, battery management, and dust/water protection. When operating with a team, share operation procedures and troubleshooting information so that anyone can handle the system to a required level of accuracy.

Simple Surveying with LRTK

Recently introduced LRTK is a solution developed to make RTK-GNSS technology easier to use on site. LRTK is a compact RTK-capable GNSS receiver that can be attached to a smartphone (iPhone/iPad), turning a smartphone into a centimeter-accuracy surveying instrument. Using a dedicated app, it enables not only position coordinate measurement but also 3D point cloud measurement using the phone’s camera and LiDAR, on-site stakeout (position marking), and AR verification using design data—many functions in one device. Measured data can be saved and shared to the cloud in real time, making it easy to instantly share field-acquired information with the office and collaborate with stakeholders.

A major attraction of the LRTK system is its ease of use and cost performance. Because all you need is a pocket-sized receiver and a smartphone, there is no need for bulky surveying equipment or multiple personnel as before. The device weighs a few hundred grams and has a built-in battery, so power supply is easy. Prices are also very affordable compared to conventional surveying instruments, and the system is designed so each field worker can have one device per person. The user-friendly interface allows even non-specialist surveyors to operate it intuitively, making it possible to take it out and measure immediately when needed, greatly lowering the barrier to incorporating high-precision positioning into daily field work. By using simple surveying with LRTK, tasks that require high precision will become more accessible and efficient. The spread of such advanced tools is expected to make high-precision positioning commonplace across more field sites in the future.

FAQ

Q: What is RTK GPS? A: RTK GPS stands for Real-Time Kinematic GPS. It is a method that uses two GNSS receivers—a base station and a rover—to correct errors and perform position measurements with centimeter-level accuracy. It is far more accurate than ordinary GPS positioning and is used in fields that require precise position information, such as surveying and construction.

Q: What is needed for RTK positioning? A: To perform RTK positioning, you broadly need three things: a GNSS receiver for the base station, a GNSS receiver for the rover, and a communication means to transmit correction information from the base station. If you do not set up your own base station, you can connect via the Internet to correction information distribution services provided by public or private entities to supplement the role of the base station. In any case, an RTK-compatible high-precision GNSS receiver and an environment to receive correction data are indispensable.

Q: How much does it cost to introduce RTK-GPS? A: Costs vary depending on the implementation form and application. Equipping a conventional professional RTK-GPS system can require initial costs on the order of several million yen. Purchasing high-performance base and rover sets and dedicated controllers can be a large investment. However, lower-cost receivers and services have appeared recently, and for small-scale surveying it can be built for under several hundred thousand yen. By selecting equipment appropriate to the required accuracy and functions, you can introduce RTK while keeping costs down.

Q: Can you achieve high-precision positioning with only a smartphone? A: At present, it is difficult to obtain RTK-level accuracy using only the standard GPS chip built into a smartphone. Smartphone antennas are small and reception stability is poor, and designs often process satellite data intermittently to conserve power. However, combining a smartphone with an external RTK-capable receiver enables high-precision positioning. For example, attaching a device like LRTK to a smartphone can transform it into a tool capable of centimeter-level positioning.

Q: What is the accuracy of RTK-GPS? A: RTK-GPS typically provides accuracy within about 2–3 cm (0.8–1.2 in) horizontally (under ideal conditions when a “fixed” solution is obtained). Vertical accuracy is typically several centimeters to several tens of centimeters. Ordinary GPS (standalone positioning) has an accuracy of about 5–10 m (16.4–32.8 ft), so RTK offers vastly higher precision. However, actual accuracy depends on satellite geometry, surrounding environment, and the equipment used, so careful accuracy management is always important.