What is RTK positioning?
RTK (Real-Time Kinematic) positioning is a technique that uses GNSS satellites to measure location in real time with centimetre-level accuracy. Standard stand-alone GPS typically has errors of several metres, but RTK employs two GNSS receivers—the base station and the rover—operating simultaneously. By taking the difference between their observations, RTK eliminates common error sources and achieves high-precision positioning.The base station—installed at a point whose coordinates are already known precisely—compares the satellite signals it receives with its true position to generate correction data, which it transmits to the rover via radio or the internet. The rover applies those corrections to the signals it is receiving, enabling it to compute highly accurate coordinates in real time. Thanks to this RTK workflow, centimetre-level accuracy—once unattainable with stand-alone GPS—is now routinely achieved and is widely used in civil-engineering surveys, drone navigation, construction machine guidance, and many other fields.

Difference from standard GPS positioning:
The main differences between RTK and ordinary stand-alone GPS lie in accuracy and underlying method. A single-receiver GPS fix derives position from signals broadcast by multiple satellites, but factors such as signal-propagation delays, satellite-orbit errors, and clock offsets introduce errors of several metres. RTK, by contrast, performs differential (relative) positioning with two receivers. Because both units observe the same satellites at nearly the same time, common error sources—satellite-orbit and clock errors, ionospheric and tropospheric delays, and so on—can be cancelled out, reducing the residual error to just a few centimetres. In short, RTK dramatically boosts GPS accuracy by coupling two receivers and exchanging real-time correction data between them.

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What happens to RTK when satellite count drops?

For RTK positioning to succeed, the rover must receive a steady stream of signals from enough GNSS satellites. In city canyons or mountainous terrain, however, buildings and topography block the sky, reducing the number of satellites in view. When too few satellites are tracked—or when observation conditions worsen—RTK encounters several problems:

• Satellite-visibility limits in cities:In urban “canyons” lined with tall buildings, only a small slice of the sky is visible, so few GPS satellites can be tracked. GNSS positioning requires at least four satellites, but stable centimetre-level RTK typically needs eight or more in view. When the visible sky narrows, even the minimum four may disappear, making not only RTK but even stand-alone positioning difficult. With only the bare minimum, satellite geometry is poor (see below), so the RTK fix solution becomes hard to obtain. In practice, achieving centimetre-grade RTK accuracy demands five or six usable satellites at a minimum; with fewer, the solution grows unstable and is likely to remain in the float state.

• Errors from the multipath phenomenon: In built-up areas, satellite signals often bounce off building façades and glass before reaching the receiver—a situation known as multipath. Because the radio wave arrives not only along the direct line-of-sight but also via one or more reflected detours, the receiver sees multiple copies of what should be a single signal. The reflected path is longer, so it arrives later; when this delayed wave combines with the direct wave, it shifts the measured pseudorange. The resulting error contaminates the RTK solution, and in the worst case the direct signal is blocked entirely and only a reflected NLOS (Non-Line-of-Sight) signal is received, causing large position errors or even loss of the fix. In downtown high-rise environments, multipath and NLOS are therefore major factors that degrade RTK accuracy.

• Effect of satellite geometry:RTK accuracy is also influenced by how the tracked satellites are arranged in the sky. Even if you have enough satellites, poor geometry—such as when they cluster in one sector or all sit low on the horizon—reduces positioning quality. Generally, the more evenly the satellites are spread across the sky, the better the solution; uneven distributions raise the DOP (Dilution of Precision) value and increase position error. In city environments, where only a few satellites are visible through narrow sky openings, geometry tends to be skewed, and vertical accuracy often suffers the most (vertical error is typically about 1.5 × the horizontal error because all satellites are above the horizon). When a low satellite count combines with poor geometry, the RTK solution becomes unstable and prone to large errors.

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As you can see, when only a few satellites are in view the RTK “fix” success rate drops sharply. In city canyons, depending on the time of day and exact location, you may fail to obtain a fix at all and accuracy will degrade. This limitation has to be kept in mind when using RTK.

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3. Strategies for Raising RTK Fix Success

Even when RTK becomes unstable because too few satellites are visible or because of urban-environment errors, you can boost the fix success rate with several practical measures. Below are the main tactics for improving RTK accuracy and reliability in the field.

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Additional antenna-placement strategy
The first step is to improve the antenna’s installation environment. On sites where tall buildings or trees surround you, reposition the receiving antenna so it faces the most open patch of sky available.

For instance, if you’re working on a street hemmed in by buildings, shifting the antenna toward an intersection or a wider break between structures can increase the number of satellites in view. Extending the antenna pole and mounting it higher is also effective. Elevating and distancing the antenna from obstacles reduces multipath and blockage, leading to more stable signal reception.

If required, you can set up an additional, temporary base-station antenna on site and keep it as close as possible to the relay station or rovers (in a confined area, one elevated base can cover several rovers). The key is to maximise the “visible sky.” Position the antenna so that nothing obstructs the 360° horizon above the elevation mask (explained later). Doing so increases the number of satellites in view, improves signal quality, and boosts the RTK fix-success rate.

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What is an elevation-mask setting?
The elevation mask defines a cutoff angle above the horizon: satellites whose elevation is below that angle are excluded from the positioning solution. Low-elevation satellites pass through more atmosphere, so their signals degrade, and they are more prone to reflections from buildings or the ground—both sources of error. For that reason, survey-grade GNSS receivers typically ignore, say, satellites below 15 degrees of elevation.

By excluding these low-quality signals, the receiver performs its calculations using only higher-elevation satellites, yielding a more stable solution. Setting an appropriate elevation mask reduces multipath errors and noise, thereby improving RTK accuracy and raising the fix rate. Be careful, however: if you set the mask too high, you may eliminate too many satellites. Choose a value suited to your site conditions—typically in the 10 ° – 15 ° range.

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Using Network RTK (VRS)

A highly effective approach is to rely on network RTK correction services. Network RTK delivers real-time corrections—often in the form of a VRS (Virtual Reference Station) stream—generated from an array of reference stations maintained by government agencies or commercial providers and transmitted over the internet.

In practical terms, you can achieve RTK accuracy without installing your own base station: the rover simply receives the VRS corrections derived from nearby reference-station data. In urban areas, receiving corrections via the cellular network is more reliable than using a local radio link, because it avoids building-related signal blockage. Network RTK also blends observations from multiple bases, so it maintains accuracy over longer baselines.

In Japan, you can tap into the Geospatial Information Authority’s nationwide CORS network as well as commercial correction services—such as NTT Docomo’s GNSS augmentation and SoftBank’s “ichimill.” These offerings make network RTK readily available even on urban job sites. By using a network RTK feed, you eliminate the need to set up and transport a base station for every project while always receiving the right corrections to boost your fix-success rate.

* Because network RTK combines data from multiple reference stations, it mitigates wide-area errors—such as ionospheric delay—and helps maintain accuracy even when the rover is far from any single base station.

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[Industry Case Studies] Implementing RTK in Urban Surveying and Infrastructure Management
RTK positioning technology is increasingly being applied in day-to-day operations across the construction and infrastructure sectors. This section highlights RTK adoption by general contractors, civil-engineering firms, and railway and highway maintenance teams, and examines the benefits they have achieved.

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Using RTK on Construction Sites—From Large Contractors to Small Civil Firms

In the construction sector, tasks once handled entirely with optical instruments—total stations, levels, and so on—are increasingly being replaced by RTK-GNSS. A prime example is as-built verification on civil-engineering projects, where RTK surveying excels at capturing heights and positions over a wide area in a short time.

A surveyor can walk the site with a rover receiver and obtain coordinates for each point instantly, greatly streamlining workflows compared with traditional leveling. Because several crews can work in parallel—each carrying a rover that references the same base station—RTK also shortens schedules on large earth-moving or land-development sites.

Among small and mid-sized civil contractors, adoption has accelerated as affordable, user-friendly RTK units have appeared. Crews now use RTK to lay out batter boards, set stakes, and establish reference lines quickly. Machine-guidance and machine-control systems—excavators and graders fitted with GNSS rovers—are also becoming common, allowing operators to monitor cut-and-fill volumes in real time and boosting site productivity.

Even on urban jobs, where high-rise buildings or elevated structures can hamper GNSS reception, contractors are overcoming the challenge by optimising antenna placement and tapping network-RTK services. As a result, RTK’s range of practical applications continues to expand.

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Case Study – Railway and Expressway Infrastructure Maintenance
RTK positioning is increasingly being adopted for the upkeep of linear infrastructure such as railways and expressways.For example, some railway operators have introduced mobile inspection systems equipped with RTK receivers for their routine track-geometry surveys. While traveling along the line, the system continuously logs elevation and position, enabling centimeter-level monitoring of track deformation and settlement. This approach eliminates the labor-intensive control-point surveys once required along long routes and allows anomalies to be detected far more efficiently.

In highway maintenance, RTK is likewise used to measure displacements in bridges and tunnels. Receivers fixed at reference points track vertical and horizontal movements of bridge decks or pavement settlement; by following these changes to the nearest centimeter over time, engineers can draw up timely repair plans.

Moreover, RTK is being used to build GIS databases of roadside assets—such as signposts and lighting towers—by registering each item’s information at precise coordinates. Urban-infrastructure managers face huge numbers of points, but with handheld GNSS units linked to a network-RTK service, field staff can walk their routes, position each asset, and enter the data instantly, avoiding the need for a full survey crew while still meeting accuracy requirements.

Even in railway and highway work, where satellite reception is challenging, stable RTK operation is now possible in cities by increasing the number of visible satellites—combining Japan’s high-elevation Quasi-Zenith satellites (Michibiki) with GLONASS, for example.​