Comparison of Old and New RTK Correction Services: Advantages of Local Stations → Network RTK

In recent years, the adoption of RTK (Real Time Kinematic) positioning has accelerated in the construction and surveying sectors. The centimeter-level (cm level accuracy (half-inch accuracy)) high-precision positioning provided by RTK has greatly contributed to efficiency and labor savings in field work that conventional GPS positioning could not achieve. High-precision positioning 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 is expected to grow further. However, whether to use the traditional method of installing a reference station (base station) at each site yourself or a network-type RTK correction service that receives correction information via mobile communication networks is a troubling decision for many field personnel, including surveyors, construction contractors, and municipal employees.

This article compares the traditional site-installed RTK base station (so-called “local station”) with the increasingly prevalent network-type RTK correction services and explains mainly the benefits of migrating to network-type 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 whose coordinates have been determined in advance, and it receives GNSS satellite signals simultaneously with the rover (mobile station). The base station calculates errors from the satellite signal data measured at its position and sends that correction information to the rover in real time via radio communication. The rover cancels out the positioning errors using the received correction information, reducing errors that were several meters in standalone positioning to several centimeters (a few centimeters (a few cm (~1 in))) and obtaining high-precision positions. Because atmospheric errors and the like can be common when the baseline between the base station and the rover is short, it is ideal to install the base station within a few kilometers (a few km (a few thousand ft)) of the work area. For this reason, in many cases operators have prepared a reference station for each site and conducted relative positioning with the rover at the shortest possible distance.

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

• High initial cost: The initial investment to acquire a high-precision GNSS receiver for the base station, survey antenna, communication devices, and so on can be large, and in some cases the full set of equipment can cost several million yen. In addition, infrastructure costs are incurred for poles and mounting hardware to install the antenna, power supply work, lightning protection, waterproof cases, and so forth.

• Maintenance and management effort: There is a burden of managing equipment in-house, including periodic inspections and calibrations of base station equipment and firmware updates. You must also select an antenna installation location with “an open view of the sky” and ensure there are no strong sources of radio noise nearby. For permanently installed stations, users themselves must take measures against equipment failure due to wind, rain, or lightning strikes, as well as theft and vandalism. If the base station malfunctions, work itself will stop, so risk management must always be considered.

• Limited coverage area: The area where correction information transmitted from a base station is effective is limited to the vicinity of the base station (a guideline is a radius of several km to about 20 km (20 km (65,616.8 ft))). When performing RTK positioning at a distant separate site, you must either install a new base station on site or relocate an existing one, which involves effort.

• Setup work each time: If a permanent fixed station cannot be maintained, it is necessary to set up and configure a base station for each work site. Because time is required each time to install and remove the reference station, additional labor and time are required before surveying can begin.

That said, operating your own base station has some advantages. Because there is no monthly fee for correction services, you can reduce long-term running costs, and a single base station can simultaneously distribute data to multiple rovers, so on sites using RTK with multiple surveying devices or construction machinery you can operate without worrying about additional subscriptions for each terminal. Moreover, RTK positioning is possible in environments without communication infrastructure, such as mountainous areas or at sea, as long as you provide your own base station and radio communication. For these reasons, for large-scale operators that use RTK constantly over wide areas or special sites outside mobile communication coverage, the self-operated base station method 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 convenience and low initial barrier of network-type services are attractive. Recently, network-type RTK correction services that eliminate the need for users to install base stations themselves have been spreading. Because correction data can be received from an operator’s network of reference points via mobile lines, there is no need to place your own base station at the site, and you can start centimeter-level (cm level accuracy (half-inch accuracy)) surveying immediately as long as you have a receiver (rover).

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

Using network-type RTK services significantly improves work efficiency compared to the traditional method. The complicated preparation work for base stations is no longer necessary, and required equipment is simplified to the rover side only, greatly reducing the burden on surveyors and site supervisors. In network-type RTK, a virtual reference station (Virtual Reference Station) is created near the user to generate correction information, enabling uniform high-precision positioning over a wide area. What specific benefits can you gain by migrating to network-type 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 positioning at relatively low cost as long as you have a GNSS rover receiver. The hurdle for introducing high-precision positioning is greatly reduced, making it easier for small businesses and municipalities without funds to acquire dedicated equipment to utilize high-precision surveying.

• Reduced site preparation time: Because you no longer need to set up a reference station before starting work, you can start surveying and machine guidance immediately upon arrival at the site. Eliminating the need to transport and install dedicated base station equipment saves personnel and time.

• Consistent positioning over wide areas: Within the service coverage area, you can receive common correction information anywhere in Japan, so there is no need to re-establish a base station at each site. Even when surveying distant sites for transfers or business trips, you can perform RTK positioning with the same accuracy throughout by simply switching the rover settings. In addition, all correction information is based on the World Geodetic System (Japanese Geodetic Datum 2011), so positions are obtained in a unified coordinate system everywhere, ensuring consistency of survey data.

• Reduced equipment management burden: Operation and monitoring of the base station network are handled by the service provider, so users do not have to worry about equipment maintenance or fault response. You can always use stable correction data backed by professional support and avoid positioning problems caused by equipment failures or calibration mistakes. The service provider also supports the latest correction methods, eliminating the need for you to update an in-house system. Many services provide 24/7 system monitoring and fault response, so even if a failure occurs it is quickly restored and you can use it with confidence.

• Usable without specialized knowledge: Network-type services are simple to configure and operate, making them easy to handle even for personnel with limited RTK experience. Unlike the conventional approach, you do not have to worry about radio frequencies or base station coordinates and can incorporate high-precision positioning into field operations without obtaining radio licenses or setting base station coordinates.

For example, on construction sites you no longer need to perform the base station setup that used to be done first thing in the morning, so staff can immediately start surveying or machine positioning. Previously, surveyors had to transport equipment to a known point at the site first thing in the morning and spend time setting up the base station and checking radio connections, but with network RTK they can start work simply by powering on the rover receiver. Eliminating about 30 minutes per day of preparation time spent on base station setup translates to more than 100 hours of saved work time annually, directly improving overall site productivity. Even when municipal staff survey roads or rivers, they can achieve detailed on-site positioning with only a rover and a communication device without carrying a base station. Because no base station setup is required, limited personnel can quickly and efficiently proceed with surveying. The advent of network-type RTK has made high-precision positioning an accessible technology that does not require special equipment or large crews, significantly lowering the barrier to RTK adoption.

Of course, because this method uses a communication line, correction information cannot be received in locations without mobile phone reception. However, mobile communication coverage in Japan is very wide, and cases where being out of coverage poses a problem during regular operations are rare. Even if communication is temporarily interrupted, positioning itself continues in standalone mode, so work does not stop immediately (accuracy is reduced).

As a service that leverages the convenience of network-type RTK, our company offers a simple surveying solution using LRTK. By using LRTK, you can achieve centimeter-level (cm level accuracy (half-inch accuracy)) positioning in the field easily without complicated equipment preparation or specialized knowledge. You always receive the latest correction information via the network, and you can start high-precision surveying immediately once you have the necessary equipment. If you want to introduce high-precision RTK positioning more easily to your sites, please consider using LRTK.

FAQ

Q: Which satellite positioning systems (GNSS) are used for RTK positioning? A: In general, RTK positioning uses not only GPS but also multiple satellite systems such as Russia’s GLONASS, Europe’s Galileo, and Japan’s QZSS (Michibiki). The more satellites you can receive, the greater the stability of high-precision positioning, so most modern RTK-capable GNSS receivers support multi-GNSS. Network-type RTK service providers also provide correction information based on these various satellite signals, so you can use them with confidence.

Q: What is the difference between the conventional site-installed RTK and network-type RTK? A: In the conventional method, you must provide your own base station (fixed station) and exchange correction information with the rover via radio. In contrast, network-type RTK obtains correction information over the Internet from a provider-operated network of reference stations, so users do not need to set up their own base stations. Simply put, the difference is whether you use your own base station or receive correction data from a service. (For example, in network-type RTK, the server integrates data from multiple fixed stations around the user and provides correction information as if a nearby reference station existed.)

Q: What do I need to use network-type RTK? A: You need a GNSS receiver (rover) that supports centimeter-level positioning and a communication device to receive correction data via mobile communication. In many cases, you either install a SIM-capable communication module in the rover or connect to a tablet or smartphone via Bluetooth to access the Internet. Then you sign a contract with a correction data provider (network-type RTK correction service) and configure the specified connection settings (Ntrip server information, ID and password, etc.), and the receiver will begin obtaining correction data in real time. Recently, devices with built-in communication modules that can connect to correction services standalone have become common.

Q: Can RTK positioning be performed outside mobile phone coverage? A: Unfortunately, real-time network-type RTK corrections cannot be used. In areas without coverage you cannot receive correction data, so you will fall back to normal standalone positioning (GPS) during that time. However, outside special environments such as mountainous areas, regions without mobile coverage within the country are limited, and it rarely becomes a problem in routine surveying work. If you cannot secure communication, countermeasures include installing a base station on site in advance or using post-processing kinematic (PPK).

Q: Can network-type RTK still provide sufficient positioning accuracy? A: Yes. Network-type RTK services achieve correction effects equivalent to “having a base station on site” by using methods such as virtual reference stations (VRS). By interpolating data from multiple nearby reference stations, they can provide uniform centimeter-level accuracy over wide areas, allowing positioning comparable to the traditional single-base-station method. When used appropriately, horizontal and vertical accuracies within a few centimeters can be obtained. In practice, under clear-sight conditions and with proper positioning, horizontal accuracy is about 1–2 cm (0.4–0.8 in) and vertical accuracy is about 2–3 cm (0.8–1.2 in).

Q: Can RTK positioning be performed even if there are no known reference points at the survey site? A: Yes, by using a network-type RTK service. The provider’s reference station network has coordinates determined in advance, so even without known points on site, the rover alone can obtain positions in the public coordinate system (World Geodetic System). In contrast, with the traditional self-operated base station method, if the coordinates of the base station location are unknown, positioning results may be shifted into an arbitrary local coordinate system. In that case, you must either measure known point coordinates on site and set the base station accordingly in advance or later transform the survey results to match known reference points.

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

Q: Are there cases where using your own base station is better? A: In certain conditions, the self-operated base station method may be appropriate. For example, for large projects spanning several years, the initial investment can be justified by the long-term benefits. Also, in environments without mobile coverage, such as mountainous areas, remote islands, or offshore sites, RTK via your own base station plus radio communication is a practical option. Conversely, for surveying work that moves from site to site or for those introducing RTK for the first time, the ease and low initial cost of network-type services are major advantages. In many cases network-type RTK is more efficient, but you should choose according to your operational conditions.

Q: What should I be careful about when using network-type RTK? A: Although procedures are simplified by using the service, basic precautions for high-precision positioning remain the same. Place the GNSS receiver antenna in as open a location as possible, and avoid signal reflection (multipath) and blockage from surrounding high-rise buildings or trees. Also ensure the rover’s communication device maintains good signal during positioning. If you have doubts about measurement results, verify accuracy by measuring a known point or by performing multiple measurements at the same point.

Q: Is there an easy way to introduce RTK surveying? A: Using a network-type RTK correction service is the quickest route. 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 that integrates the receiver, communication module, and correction service, and its ease of just powering on at the site to start surveying is a major feature. Because you can try high-precision positioning with low initial cost, we recommend starting with a network-type service and expanding its use according to your needs.

Q: How will RTK technology evolve in the future? A: Satellite positioning is continually advancing, and RTK is expected to become even more sophisticated. For example, developments are progressing in wide-area augmentation using satellite communications (PPP-RTK) and centimeter-level augmentation services via Japan’s QZSS Michibiki (such as CLAS), enabling high-precision positioning without relying on terrestrial base station networks. However, in terms of immediacy and convenience, network-type RTK is currently the most practical solution, and for the foreseeable future, correction services using base station networks will remain the mainstream for high-precision positioning.