Easier positioning accuracy management with Network RTK: always cm-level accuracy with real-time corrections (cm level accuracy (half-inch accuracy))

In recent years, positioning technologies using Global Navigation Satellite Systems (GNSS) have advanced dramatically, significantly improving construction accuracy and work efficiency in civil engineering surveying and infrastructure management. Among these, Network RTK, which enables real-time centimeter-level high-precision positioning, has attracted particular attention. RTK (Real Time Kinematic) is a method that corrects GNSS positioning errors to obtain precise coordinates, and its adoption is spreading across a wide range of sites—from major general contractors to small and medium-sized construction firms, surveyors, and infrastructure maintenance personnel for railways and highways. By leveraging Network RTK, real-time corrections can maintain centimeter-level positioning accuracy (cm level accuracy (half-inch accuracy)) at all times, making it dramatically easier to manage positioning accuracy.

This article explains GNSS positioning principles and limitations, how RTK corrections work, and how Network RTK enables real-time accuracy management. It also covers the practical benefits of high-precision positioning, including understanding error sources, avoiding re-surveying, improving quality assurance and data traceability, and reducing labor and increasing efficiency. At the end of the article, we introduce new developments that can be used on-site, such as the smartphone-compatible RTK device "LRTK" for simple surveying and AR (augmented reality) functions integrated with RTK. Please use this as a reference for adopting high-precision positioning technologies on-site.

How GNSS positioning works and its accuracy challenges

GNSS (Global Navigation Satellite System) determines your current position by receiving radio signals from multiple artificial satellites. Representative systems include GPS (United States), Russia's GLONASS, Europe's Galileo, and Japan's QZSS (Michibiki); these satellite positioning systems are collectively called GNSS. A GNSS receiver typically obtains distance information from four or more satellites and calculates its three-dimensional position (latitude, longitude, altitude). Using multiple satellite systems increases the number of observable satellites and improves positioning stability, but systematic error sources remain unless corrections are applied, so there are limits to the achievable accuracy.

Standalone GNSS positioning has limits. Satellite signals contain various error sources, so if no corrections are applied, positioning results can often be off by several meters. Errors arise from satellite orbit and clock errors, signal delays in the ionosphere and troposphere, atmospheric disturbances, and multipath (signal reflection/refraction) caused by buildings and terrain. Poor satellite geometry can also destabilize positioning, and in tunnels or urban canyons signals may be unobtainable. Thus, typical standalone GNSS accuracy is at best a few meters, which is insufficient for civil engineering construction or precision surveying. This is where RTK—technology that corrects GNSS errors to dramatically improve positional accuracy—comes into play.

What is RTK (Real Time Kinematic)?

RTK (Real Time Kinematic) is a technique that corrects GNSS positioning errors in real time to dramatically improve positional accuracy. Specifically, a base station (reference station) GNSS receiver with a known accurate coordinate is set up, and the satellite data observed at the mobile receiver (rover) at the same time are compared. The base station calculates the error by comparing its known accurate position with the GNSS-derived position and sends that correction information to the rover via radio or communications. The rover applies the received corrections to its positioning results, effectively cancelling out much of the error. By observing the same satellites simultaneously, common error sources such as satellite orbit errors and atmospheric delays are cancelled out between the two receivers, leaving mainly receiver-specific noise and local multipath errors. This relative positioning between two receivers and real-time correction typically yields about 2–3 cm (0.8–1.2 in) accuracy horizontally and about 3–4 cm (1.2–1.6 in) vertically. The most notable feature of RTK is that errors that were once on the order of meters are reduced to within a few centimeters.

RTK also uses the carrier phase of GNSS satellite signals, which allows much more precise ranging than standalone positioning (although resolving the integer number of wavelengths—integer ambiguity—is required). Putting the complex principles aside, introducing RTK enables surveying tasks that previously worried about centimeter-scale deviations to perform stakeout and as-built measurements almost exactly to design specifications. RTK-GNSS as a method for as-built management is being incorporated into standards by the Ministry of Land, Infrastructure, Transport and Tourism, and its use is expanding in fields that require accurate position information, such as drone surveying, machine guidance, and precision agriculture.

How Network RTK works and its advantages

RTK can be implemented by users setting up their own base and rover stations, or via Network RTK, which receives correction information from an existing network of reference stations. With Network RTK, there is no need to set up a local base station on-site. Observations from multiple reference stations deployed over a wide area—such as about 1,300 Continuously Operating Reference Stations (CORS) installed nationwide by the Geospatial Information Authority of Japan—are integrated to generate a Virtual Reference Station (VRS) near the user and provide correction information. The rover receives this correction data in real time via a cellular connection or other communications and applies it to its positioning. Simply put, you continuously receive from the base station network the correction values for “if there were a reference station right where you are.”

The advantage of this network approach is that it eliminates the effort of installing and surveying your own base station at every site. With just one receiver and a communication environment, high-precision positioning can be achieved anywhere in the country. Because the network model is based on data from multiple reference stations and models large-area error trends, it maintains accuracy better than traditional single-base methods even at locations distant from a single reference station. In Japan, centimeter-level augmentation services provided by QZSS (CLAS) and high-precision positioning services from telecommunications carriers have been developed, making Network RTK increasingly easy to use. As a result, centimeter-level positioning that once required specialized surveying equipment is becoming possible with simpler gear and smaller devices.

Manage accuracy in real time and avoid re-surveying

Network RTK enables real-time management of positioning accuracy on-site. The screens of GNSS receivers and surveying controllers constantly display the current positioning mode (fixed solution Fix or float solution Float) and estimated error. A Fix indicates RTK corrections are stable and centimeter-level accuracy (cm level accuracy (half-inch accuracy)) is being achieved; a Float indicates the solution is not yet stable and accuracy is degraded. By checking these indicators during work and recording points only when the status is Fix, you can ensure that you always obtain data with guaranteed high accuracy. If accuracy becomes unstable, you can wait on-site or improve radio conditions to regain Fix and resume measurement. Previously, points measured on-site might be found later to have large errors, requiring re-measurement. With RTK, accuracy verification is performed during measurement, preventing situations where “we only noticed the deviation later and had to re-survey.” Completing accurate surveying in one pass reduces rework, thereby shortening schedules and cutting costs. The peace of mind from knowing accuracy in real time is a major benefit for quality assurance in surveying.

Improved quality assurance and data traceability

Introducing RTK directly improves construction quality control and recording accuracy. Since high-precision data are available in real time, immediate inspections that detect and correct as-built deviations on the spot become possible. For example, during road paving operations, you can check deviations from design elevations sequentially while paving, or measure and confirm the installation position of structures on-site and adjust immediately if necessary. This greatly reduces the risk of receiving “position is wrong; redo it” comments during post-construction inspections.

RTK-acquired positioning data can also be digitally recorded and shared, which is useful for ensuring traceability. Historical information about who measured what, when, where, and at what accuracy is retained, making it easy for third parties to later verify data or use it as documentation for quality control. Recently, systems that integrate RTK receivers with tablet devices and upload acquired point clouds and coordinate data to the cloud in real time have been spreading. Linking photos or 3D scans with positional information dramatically improves the accuracy of construction records and as-built drawings. Moreover, there is a growing trend to import RTK-derived as-built point cloud data into BIM/CIM 3D models for verification or to use them in digital ledgers for maintenance management. Consistently using high-precision measured data throughout design, construction, and maintenance contributes to advanced infrastructure management. Objective proof of quality based on such data can also enhance trust from clients and inspection agencies.

Streamlining surveying operations and reducing labor

Network RTK dramatically increases productivity in surveying and layout tasks. Because high-precision positioning is available in real time, many of the cumbersome steps and post-processing that were previously necessary can be greatly simplified. For example, total station surveying required re-setup and post-calculations for each line of sight, but with RTK-GNSS, as long as line-of-sight is maintained, points can be collected continuously while moving. On large earthwork sites, a single person carrying a GNSS rover can complete surveying, eliminating the need to repeatedly reconfigure heavy equipment. In one field example, introducing RTK reduced surveying time by about 50% compared to conventional methods. In another case, as-built measurement staff were reduced from two people to one, and the time required was shortened to less than one-third.

Labor shortages at construction sites make the labor-saving effect of RTK extremely valuable. Even without many experienced surveyors, a small team can perform high-precision surveys, raising overall technical capability. Tasks that previously required teams to set out batter boards and confirm as-built conditions can now often be completed by a single person who can operate an RTK receiver and tablet. This reduces labor costs and allows personnel to be reassigned to other important tasks. It also offers potential savings in outsourced surveying costs; small-scale precision surveys that were once subcontracted to specialized survey companies can now be handled by in-house staff using RTK equipment. Continuing reductions in device and service costs have lowered the barrier to entry. By measuring accurately in one pass, RTK reduces material waste and rework labor, enabling more work to be completed with limited resources.

New on-site uses with smartphone RTK and AR

Recently, new devices and applications have made RTK positioning more accessible. A representative example is the smartphone-compatible compact GNSS receiver LRTK. LRTK is a pocket-sized RTK-GNSS unit that attaches to mobile devices like iPhones and iPads. Simply attaching the dedicated receiver to a smartphone allows centimeter-level positioning accuracy (cm level accuracy (half-inch accuracy)) comparable to traditional stationary surveying instruments. In a demonstration experiment, RTK positioning with a smartphone equipped with LRTK recorded a single-measurement horizontal error of about 12 mm (0.47 in), and by averaging 60 measurements the error was reduced to about 8 mm (0.31 in)—very high accuracy. This technology, which transforms your smartphone into a high-precision surveying instrument without relying on expensive dedicated gear, is bringing major changes to on-site surveying styles.

Furthermore, AR (augmented reality) features that leverage RTK's high precision are beginning to be used on-site. Construction AR apps now exist that overlay 3D design models or construction lines on live camera views from smartphones or tablets; RTK positioning enables digital information to be precisely aligned with the physical world. For example, you can superimpose a completed-model rendering of a bridge or retaining wall onto the actual site to intuitively share the finished appearance, or visualize the buried location of sewer pipes on the ground via AR to mark excavation points. RTK-enabled AR minimizes positional drift, so information that was hard to convey with traditional plans or batter boards can be accurately visualized on-site.

Thus, the combination of smartphones plus RTK devices and AR technology is turning cutting-edge positioning into a more familiar tool for many on-site staff. Not only specialized surveyors but also site supervisors and craftsmen can use centimeter-accuracy positioning and digital construction assistance in daily work. These Network RTK-based solutions are expected to spread further and support DX in civil engineering and infrastructure at the field level.

Conclusion

Network RTK is an innovative technology that brings centimeter-level positioning to the field through real-time corrections, greatly reducing the effort required for accuracy management. By suppressing GNSS errors, surveying tasks that were previously uncertain become reliable, supporting construction sites in both quality and efficiency. Shorter work times and reduced personnel also contribute to lowering risks associated with hazardous work. Additionally, accessible devices like LRTK and AR functions are opening up high-precision positioning—once reserved for specialists—to general technicians. By smartly utilizing Network RTK, promote DX in surveying and construction to further improve on-site productivity and reliability. The new possibilities that Network RTK creates for the field will continue to expand.