Speeding Up On-Site Layout with Network RTK: Instant Positioning without a Base Station

In surveying work on construction sites, network RTK has attracted attention as a groundbreaking technology. Traditional GNSS surveying required installing a base station on site and determining positions by relative positioning with a rover. However, by leveraging network RTK, centimeter-level (inch-level) high-precision positioning can be achieved in real time without preparing a base station, greatly streamlining on-site layout (marking design positions and staking out coordinates). This article explains the mechanism and benefits of network RTK from technical and practical perspectives, and touches on topics such as GNSS positioning accuracy control, labor-saving measures in field surveying, and integration with ICT construction machinery. Finally, we introduce emerging trends such as simplified surveying with LRTK and position verification using RTK-enabled AR (augmented reality).

Basics of GNSS Positioning and RTK

First, as a prerequisite for understanding network RTK, let us review the basics of GNSS positioning and RTK. GNSS (Global Navigation Satellite System) refers to systems that use multiple positioning satellites such as GPS, GLONASS, Galileo, and QZSS (Michibiki) to determine positions on Earth. Standalone positioning with a single GNSS receiver typically incurs errors of several meters due to ionospheric and tropospheric delays affecting satellite signals and multipath from reflections off buildings and the ground. This level of accuracy is insufficient for the precise layout required on construction sites.

This is where RTK positioning (Real Time Kinematic) comes in. RTK observes GNSS signals simultaneously with a base station (a receiver with known coordinates) and a rover, and transmits error information obtained at the base station to the rover in real time, enabling the rover’s position to be calculated with centimeter-level accuracy. In general, RTK-GNSS can achieve horizontal errors on the order of about 2-3 cm (0.8-1.2 in) and vertical errors of about 3-4 cm (1.2-1.6 in), representing a dramatic accuracy improvement over standalone positioning. This has allowed RTK to be used in civil engineering surveying tasks that require high precision, such as accurate layout of structures and as-built verification.

However, conventional RTK surveying required setting up a base station near the site each time, which was laborious. Installing a base station requires a point with known public coordinates, necessitating prior surveying or establishing a temporary base point to define a local coordinate system. It also requires preparing and configuring equipment for radio communication between the base and rover (digital radios or dedicated communication devices). These preparations took time and effort, so even after arranging an RTK-capable environment, many steps were needed before surveying could begin. Network RTK addresses these issues.

What Is Network RTK?

Network RTK (network-based RTK-GNSS) is, as the name implies, an RTK positioning method that uses a network. Its key feature is that there is no need to install a physical base station on site. While conventional RTK performs relative positioning with an actual base station and a rover, network RTK uses data from multiple permanently installed electronic reference stations (GNSS reference station networks) across the country. The user (rover) transmits their approximate location via communication, and the correction data service server computes a virtual reference station (virtual reference station) near the user’s location. The server generates high-precision correction data corresponding to this virtual reference station using real-time observations collected from multiple known electronic reference stations, and transmits it to the rover. On the rover side, an environment is virtually recreated as if a local base station were nearby, allowing the rover to obtain precise real-time positioning solutions (coordinates).

This mechanism enables users to perform RTK surveying without a physical base station. For example, in Japan the Geospatial Information Authority maintains about 1,300 electronic reference stations (GEONET) deployed at an average interval of 25 km, and VRS (Virtual Reference Station) network RTK services using these stations are offered. The VRS method models ionospheric and tropospheric errors from data of multiple surrounding reference stations and corrects them, thereby suppressing the phenomenon in which accuracy degrades as baseline distance increases when using a single base station. A national-scale network of reference stations provides homogeneous accuracy regardless of location, which is another advantage of network RTK.

Using network RTK requires a contract with a correction data service provider, and the rover needs a communication method to connect to that service (typically a mobile internet connection). In practice, it is common to insert a SIM card into an RTK-capable GNSS receiver to use mobile data communication and receive corrections via a protocol called Ntrip. Although this preparation is needed, the major advantage is the immediacy of surveying once on site—because there is no physical base equipment to worry about, you can start surveying immediately.

Benefits of Instant Positioning without a Base Station

The greatest benefit of introducing network RTK is the dramatic reduction in preparation time before surveying begins. On arrival at a site, you can power on your equipment, connect to the network, and obtain an RTK fixed solution (Fix) within tens of seconds to a few minutes. There is no need to mount a base station on a tripod and check it against known points, nor to tune radio frequencies. This directly translates into faster layout work. For example, on a building site to stake out foundation positions, conventionally surveyors would mark points using a total station from established site control points or set up their own RTK base station. With network RTK, the person in charge can simply carry a receiver to the site, immediately measure the design coordinates, and mark positions on the ground. Because waiting time from startup to positioning is short, layout can be done efficiently without deploying many personnel.

Being base-station-free also contributes to enabling one-person operations. Previously, setting up a base station sometimes required another technician or assistant, but with network RTK a single person carrying a receiver can complete the survey. Only one rover is needed, reducing equipment transport and making surveying light and agile even on confined or remote sites. Additionally, there is no need to manage base station equipment (power supply, theft prevention, etc.), so workers can concentrate on the task.

Effects in Wide-Area Surveying and Multiple Sites

Network RTK demonstrates its true value in wide-area construction surveying and operations that move between multiple sites. For linear projects such as roads and rivers that extend several kilometers to tens of kilometers, conventional RTK typically maintains accuracy within a few kilometers to a dozen kilometers radius from the base station; beyond that range it becomes difficult to maintain accuracy, requiring the construction site to be divided into sections and base stations to be relocated sequentially. With network RTK, unified-accuracy RTK surveying across the entire construction corridor becomes possible without repeatedly resetting base stations. As a result, long route surveys can proceed continuously without interruption, reducing total work time.

Similarly, for large-area sites such as solar power plants or residential land development, the ability to survey uniformly to every corner of the site is an advantage. There is no need to search for new base station locations within the site or consider repeaters for radio coverage. Carrying out reference point surveys or staking boundary posts across vast properties can be handled smoothly with a single rover.

Furthermore, network RTK is effective when surveying companies or technicians visit multiple sites in a single day. Conventional methods could incur 15–30 minutes loss per site just to set up and dismantle base stations, but network RTK eliminates the need to stow or set up equipment during travel. Teams can begin measuring upon arrival and quickly move to the next site after finishing. Accumulated over time, this yields significant time savings and enables completion of more surveying tasks. For organizations with limited personnel handling multiple projects, shorter preparation time = labor savings leads to reduced personnel costs and greater operational efficiency.

Also, data obtained via network RTK are directly linked to public surveying coordinate systems (global geodetic systems / JGD), making later verification and alignment with other datasets easier. Since results are always obtained on a nationwide common coordinate system, they can be submitted as highly reliable surveying deliverables when providing electronic as-built records. Compared to operating only on locally defined coordinates tied to private base points, network RTK contributes to improving the reliability of surveying results.

Real-Time Accuracy Control and Handling Error Factors

Network RTK can maintain high accuracy through error corrections based on multiple reference stations, but basic knowledge of accuracy control is still necessary for users. GNSS positioning error sources include the previously mentioned ionospheric and tropospheric delays and multipath. Network RTK models ionospheric and tropospheric effects on the server side and reflects corrections in the data, which largely eliminates accuracy degradation due to distance from a base station. Nevertheless, there are still important considerations depending on the field environment.

One is the satellite signal reception environment. Under elevated roadways, in forests, or in proximity to buildings where the sky is not open, the number of tracked GNSS satellites may decrease and multipath effects may increase, preventing a stable fixed solution. Even with network RTK, positioning becomes unstable in environments with insufficient satellites. During positioning, monitor the number of satellites and DOP values (dilution of precision) on the receiver controller screen, and if necessary, move the measurement position or change the timing to mitigate issues.

Another is the communication environment. Because network RTK receives correction data via cellular networks, positioning cannot continue in areas without signal or during communication outages. At sites where cell coverage is expected to be unavailable—such as mountainous areas or tunnels—consider alternatives like conventional RTK (setting up a local base station) or PPP positioning that improves accuracy after long-duration static observations. However, in typical urban and suburban work areas, cellular coverage is usually available and operation is often possible without major issues. It is important to check the service provider’s coverage area in advance and confirm whether stable mobile communication is available on site.

From the perspective of real-time accuracy control, always check the solution status output by the RTK receiver. Only when a fixed solution (Fix) is achieved is centimeter accuracy (half-inch accuracy) guaranteed; a float solution (Float) is not suitable for layout. In network RTK, reaching Fix usually takes a few seconds to tens of seconds, but if initialization takes longer, inspect satellite reception and communication conditions. If possible, perform a one-point verification survey using a known point on site and check the difference from the obtained coordinates for reassurance. Properly managing these error controls on site will allow network RTK to consistently maintain reliable positioning accuracy.

Use on Construction Sites and Integration with ICT Construction Machinery

Introducing network RTK not only streamlines surveyor tasks but also improves productivity across the entire construction site. High-precision position information is essential in the field of ICT construction (information-driven construction), for example by eliminating pegging with measuring staffs or automating as-built inspections using GPS surveying equipment. Modern ICT construction machinery (GNSS-equipped bulldozers and excavators, etc.) operate by continuously comparing 3D design data with real-time self-positioning, enabling high-precision work independent of operator skill. RTK-GNSS is used to obtain this self-positioning, and by leveraging network RTK there is no need to provide separate base stations for each machine—every machine can share high-precision position information. When construction machines and surveying personnel use the same correction data service, people and machines operate in the same coordinate system and maintain consistent positioning.

For example, when excavating with a network RTK-enabled hydraulic excavator, design surfaces and machine position are continuously maintained at centimeter accuracy, so the operator can follow guidance displayed on the screen to achieve the required shape precisely. Previously, survey crews installed batter boards or strings to indicate slopes and widths before work began, but that labor is greatly reduced. Also, if surveyors continuously measure as-built conditions with RTK and share data to the cloud, remote construction managers can instantly grasp progress and quality. Centering operations around network RTK accelerates site digitization, creating next-generation construction workflows where machine operators, survey technicians, and construction managers share information in real time.

Thus, network RTK realizes its greatest value when combined with ICT construction machinery and cloud-based site management systems. When precise position information is shared with everyone on site, rework is minimized and errors are detected early, improving overall productivity and quality. Amid labor shortages and workstyle reforms in the construction industry, network RTK’s ability to provide labor savings and technological advancement makes it a powerful solution.

Possibilities of Simple Surveying with LRTK and AR Position Verification

Finally, we touch on LRTK, an emerging application of network RTK. LRTK refers to compact RTK-GNSS receivers that attach to smartphones, providing an easy way to achieve centimeter-level (inch-level) positioning. With LRTK, baseline surveying and as-built checks can be performed using only a smartphone without dedicated surveying instruments. For example, using an attachable LRTK device and a dedicated app, a smartphone can receive network RTK corrections and function as a high-precision positioning terminal. Coordinates obtained on site are directly in the public coordinate system, greatly reducing the need for manual measurement with tape measures or conventional instruments.

A major feature of LRTK is the ability to combine a smartphone camera with AR (augmented reality) position verification. A smartphone capable of high-precision RTK positioning can overlay positions from design drawings or 3D models onto the real world. Conventional AR apps required marker placement or plane recognition calibration and often suffered from positional drift. However, by using precise self-position coordinates and heading information from RTK, AR displays with reduced model-to-reality offsets can be achieved. For example, showing the route of buried pipes or the positions of future structures as CG overlays on the smartphone screen allows less-experienced workers to intuitively understand where to install elements. By simply pointing a smartphone at the site, you can visually confirm design positions on the spot, enabling position checks without complex staking or batter boards in some situations.

Technologies like LRTK further broaden the convenience of network RTK and are reshaping field surveying. Because they operate with small, lightweight devices and smartphone apps, they are easy to use even for non-experts and are well suited to routine construction management and as-built checks. As smartphone RTK and AR position verification methods become more widespread, more technicians will be able to enjoy the benefits of network RTK’s ease of accuracy control without a base station. As the flow toward handling position information digitally from surveying through construction and maintenance accelerates, network RTK and its application LRTK hold the potential to be key drivers of a productivity revolution in the civil engineering and construction industries. Why not consider adopting the latest tools centered on network RTK to achieve instant on-site positioning?