In recent years, the introduction of RTK (Real Time Kinematic) positioning has been accelerating in the construction and surveying sectors. The centimeter-level (cm level accuracy (half-inch accuracy)) high-precision positioning achieved by RTK contributes greatly to improving efficiency and reducing labor in field operations—outcomes that conventional GPS positioning could not achieve. High-precision position information is also indispensable for smart construction sites such as i-Construction (ICT construction) promoted by the Ministry of Land, Infrastructure, Transport and Tourism, so demand for RTK technology will likely continue to grow. However, deciding whether to install your own reference station (base station) at each site as in the traditional method, or to use a network RTK correction service that receives correction information via mobile communication networks, is a difficult decision for many field stakeholders such as surveyors, construction contractors, and municipal employees.

This article compares the traditional site-installed RTK base station (so-called “local station”) and the increasingly widespread network RTK correction services, focusing on the benefits obtained by migrating to network-based services.

Table of Contents

• Site-installed RTK base stations

• People involved in surveying work such as surveyors, construction contractors, and municipal employees

• FAQ

Site-installed RTK base stations

In the conventional RTK positioning method, it was necessary to install your own reference station (base station) near the work site. A base station is set up on a known point with precisely determined coordinates and receives GNSS satellite signals simultaneously with the rover (mobile station). The base station computes errors from the satellite signal data measured at its known position and sends correction information to the rover in real time via radio communication. The rover applies the received correction information to cancel out positioning errors, reducing the errors that were several meters to a few centimeters (a few cm (≈ a few in)), and thereby obtaining high-precision positions. Because atmospheric errors and the like can be common-mode over short baseline lengths between the base and rover, it is ideal to install the base station within a few kilometers of the work area. For this reason, in many cases operators have prepared reference stations for each site and performed relative positioning with the rover at as short a distance as possible.

However, operating your own RTK base station entails various burdens. Major challenges include the following:

• Initial cost is high: The initial investment to procure a high-precision GNSS receiver for the base station, a survey antenna, communication equipment, and so on can be substantial; in some cases the equipment set can cost several million yen. In addition, costs are incurred for infrastructure such as poles and mounting brackets for the antenna, power supply construction, lightning protection, and waterproof cases.

• Maintenance burden: There is the burden of managing equipment in-house, including periodic inspection and calibration of base station equipment and firmware updates. The antenna location must be chosen to be an “open site with a clear view of the sky,” and you must ensure an environment without strong sources of radio noise nearby. If the station is permanently installed, the user must also take measures against equipment failure from wind, rain, or lightning, and against theft or vandalism. If the base station fails, work may have to stop, so risk management must always be considered.

• Limited coverage area: The area where correction information from a base station is valid is limited to the vicinity of the base station (rough guideline: a radius of a few km to about 20 km). When performing RTK positioning at a distant site, it is necessary to install a new base station on site or relocate an existing one, which requires additional effort.

• Setup work each time: If you cannot keep a fixed station permanently, you need to set up and configure a base station at each work site. The time required to install and remove a reference station occurs each time, adding extra work and time before surveying can begin.

That said, operating your own base station has several advantages. Because there is no monthly fee for a correction service, you can reduce running costs over the long term. One base station can deliver data to multiple rovers simultaneously, so on sites where multiple surveying instruments or construction machines use RTK, you can operate without worrying about additional user contracts for each terminal. Moreover, in environments without communication infrastructure—such as mountainous areas or at sea—RTK positioning is possible with your own base station and radio communication. For these reasons, for large-scale operators who use RTK constantly over wide areas or for special sites outside mobile network coverage, operating your own base station can still be an effective option.

On the other hand, for surveying work that moves from site to site or for small operators introducing RTK for the first time, the ease and low initial hurdle of network services are attractive. Recently, network RTK correction services that eliminate the need for users to install base stations themselves have become widespread. By receiving correction data from a provider’s reference point network via a mobile connection, there is no need to place your own base station at the site, and you can start centimeter-level surveying immediately with only a rover receiver.

People involved in surveying work such as surveyors, construction contractors, and municipal employees

Using a network RTK service significantly improves work efficiency compared to traditional methods. The cumbersome preparation of a base station is no longer required, and because the necessary equipment is limited to the rover, the setup is simplified—resulting in a substantial reduction in burden for surveyors and site managers. Network RTK generates correction information by creating a virtual reference station (VRS) near the user, enabling consistent high-precision positioning over a wide area. What specific benefits can be gained by migrating to network RTK? Here are the main points.

• Low initial introduction barrier: Because you do not need to purchase and install expensive base station equipment and antennas, you can start RTK surveying at relatively low cost with just a GNSS rover receiver. The barrier to adopting high-precision positioning is greatly reduced, making it easier for small businesses and municipal organizations to utilize high-precision surveying even if they cannot afford dedicated equipment.

• Reduced site preparation time: Because you do not need to set up a reference station before starting work, you can begin surveying or machine guidance as soon as you arrive on site. Eliminating the need to transport and install dedicated base station equipment saves personnel and time.

• Consistent positioning over a wide area: Within the service coverage area, you can receive common correction information nationwide, so there is no need to relocate a base station for each site. Even if you are transferred or travel for work to distant sites, you can perform RTK positioning with the same accuracy everywhere by simply switching the rover’s settings. In addition, all correction information is based on the World Geodetic System (Japan Geodetic Datum 2011), so you can acquire positions in a unified coordinate system across regions, ensuring the consistency of surveying data.

• Reduced equipment management burden: The provider operates and monitors the base station network, so users do not have to worry about equipment maintenance or fault handling. You can always use stable correction data supported by professionals and avoid positioning troubles caused by equipment failure or calibration errors. The service provider also handles updates to the latest correction methods, eliminating the need for you to update your own system. Many providers offer 24-hour monitoring and fault response, and if a failure occurs it is quickly recovered, allowing安心して利用できます。

• Usable without specialized knowledge: Network services are simple to configure and operate, making them easy for personnel with limited RTK experience to handle. You can incorporate high-precision positioning into field work without struggling with radio frequencies or base station coordinate settings as in the past. There is no need to obtain radio licenses or set base station coordinates.

For example, on construction sites the morning task of setting up a base station is no longer needed, so personnel can immediately begin surveying and machine positioning tasks. Previously, surveyors had to transport equipment to a known point on site early in the morning and spend time installing the base station and checking radio communication; with network RTK, simply powering on the rover receiver is enough to start work immediately. If the roughly 30 minutes per day previously spent installing a base station is eliminated, that adds up to over 100 hours per year saved, directly improving overall site productivity. When municipal employees survey roads or rivers, they can perform detailed on-site positioning with only a rover and a communication device without carrying a base station. Because there is no need to prepare your own base station, a small team can conduct surveys quickly and efficiently. The advent of network RTK has made high-precision positioning an accessible technology that does not require special equipment or large teams, dramatically lowering the barrier to RTK adoption.

Of course, because this method uses a communication line, you cannot receive correction information in locations without mobile phone coverage. However, mobile network coverage in Japan is very broad, and situations where coverage is a problem during normal operations are rare. Even if communication is temporarily interrupted, positioning itself continues as standalone (GPS) positioning, so work does not stop immediately (accuracy is reduced).

As a service that leverages the convenience of network RTK, our company offers a simple surveying solution called LRTK. By using LRTK, you can achieve centimeter-level positioning easily on site without complicated equipment or specialized knowledge. With up-to-date correction information available via the network, you can begin high-precision surveying as soon as you have the necessary equipment. If you want to introduce high-precision RTK surveying to your sites with less effort, please consider using LRTK.

FAQ

Q: Which satellite positioning systems (GNSS) are used for RTK positioning? A: RTK positioning generally uses multiple satellite systems in combination, not just GPS—such as Russia’s GLONASS, Europe’s Galileo, and Japan’s QZSS (Michibiki). The greater the number of satellites that can be received, the more stable high-precision positioning becomes, so most recent RTK-capable GNSS receivers support multi-GNSS. Network RTK service providers also supply correction information based on these various satellite signals, so you can use the service with confidence.

Q: What is the difference between traditional site-installed RTK and network RTK? A: With the traditional method, you must prepare your own base station (fixed station) and exchange correction information with the rover via radio communication. In contrast, network RTK obtains correction information over the Internet from a provider-operated network of reference stations, so the user does not have to install a base station. Simply put, the difference is whether you use your own base station or receive correction data from a service. (For example, in a network RTK service, the provider integrates data from multiple fixed stations around the user on the server side and provides correction information as if a nearby reference station were present.)

Q: What do I need to use a network RTK service? A: You need a GNSS receiver (rover) that supports centimeter-level positioning and a communication device to receive correction data via mobile communications. In many cases, a SIM-compatible communication module is installed in the rover, or a tablet/smartphone is connected via Bluetooth to access the Internet. Then you sign a contract with a correction data service (network RTK correction service) and configure the specified connection settings (server information for Ntrip, ID/password, etc.), and the receiver will begin obtaining correction data in real time. Recently, products that integrate a communication module into the GNSS receiver itself and can connect to correction services as a standalone device have become more common.

Q: Can RTK positioning be performed outside mobile phone coverage? A: Unfortunately, real-time network RTK corrections cannot be used. In areas without coverage you cannot receive correction data, so positioning falls back to regular standalone positioning (GPS) during that time. However, except in special environments such as mountainous regions, areas without mobile coverage are limited domestically, and this rarely poses a problem for routine surveying. If communication cannot be secured, countermeasures include installing a base station on site in advance or using post-processing kinematic (PPK) methods.

Q: Does network RTK provide sufficient positioning accuracy? A: Yes. Network RTK services achieve correction effects equivalent to having a local base station by methods such as virtual reference stations (VRS). By interpolating data from multiple surrounding reference stations, they can provide homogeneous centimeter-level positioning over a wide area comparable to the traditional single-base-station method. When used properly, horizontal and vertical accuracy within a few centimeters (a few cm (≈ a few in)) can be obtained. In practice, under clear-sky conditions and with proper positioning, horizontal accuracy of about 1–2 cm (0.4–0.8 in) and vertical accuracy of about 2–3 cm (0.8–1.2 in) can be achieved.

Q: Can RTK positioning be performed even if there are no known reference points at the survey site? A: Yes, with a network RTK service. The provider’s reference station network has pre-determined, rigorously computed coordinates, so a rover alone can obtain positions in a public coordinate system (World Geodetic System) even if there are no known points on site. Conversely, with the traditional self-operated base station method, if the coordinates of the chosen base station location are unknown, the positioning results will be offset into an arbitrary local coordinate system. In that case, you must either measure and set the base station coordinates beforehand or later transform the survey results to match known reference points.

Q: How much does a network RTK service cost? A: Generally, centimeter-level RTK correction services can be contracted for a monthly fee on the order of several thousand yen. Costs vary by provider and region, but compared with the cost of building and operating your own base station, network services offer a very inexpensive way to use high-precision positioning. Some services offer short-term contracts or pay-as-you-go plans, allowing you to subscribe only for the period you need.

Q: Are there cases where using your own base station is better? A: Yes—under certain conditions, operating your own base station may be more appropriate. For example, in large-scale projects spanning several years, the initial investment can be recovered and may yield sufficient benefits. In mountainous regions, remote islands, or offshore areas where mobile communications do not reach, RTK using your own base station plus radio communication is a practical option. On the other hand, for surveying work that moves from site to site or for first-time RTK adopters, the ease and low initial cost of network services are significant advantages. In many cases network RTK is more efficient, but choose based on your operational conditions.

Q: What should I be careful about when using network RTK? A: While service use simplifies procedures, the basic precautions for high-precision positioning remain the same. Install the GNSS receiver’s antenna in a location with as open a view of the sky as possible, and avoid multipath and signal blockage caused by surrounding high-rise buildings or trees. Also ensure that the rover’s communication device maintains signal during positioning by working in areas with good reception. If you have doubts about the measurement, verify accuracy by measuring a known point or taking multiple measurements at a single point.

Q: What is an easy way to introduce RTK surveying? A: Using a network RTK correction service is the quickest path. For example, by using our LRTK service, you can start centimeter-level positioning with your existing GNSS receiver and a communication device without installing special equipment. LRTK is an all-in-one solution integrating receiver, communication module, and correction service, and its ease of use—just power on on site and begin positioning—is a key feature. Because initial costs are low, it is advisable to start with a network RTK service and expand its use according to your work needs.

Q: How will RTK technology develop in the future? A: Satellite positioning is advancing daily, and RTK is expected to become even more sophisticated. For example, developments are underway for wide-area augmentation using satellite communications (PPP-RTK) and centimeter-level augmentation services from Japan’s quasi-zenith satellite Michibiki (CLAS), which perform high-precision positioning without relying on terrestrial base station networks. However, in terms of immediacy and convenience, network RTK is currently the most practical solution, and correction services using base station networks are likely to remain the mainstream method for high-precision positioning for the foreseeable future.