Infrastructure Surveying Using RTK Accuracy: On-site Effects and Benefits

Table of Contents

• What is RTK accuracy?

• The importance of high accuracy in infrastructure surveying

• How RTK positioning works and how it differs from standard GPS

• How field work changes with RTK implementation

• Main benefits of RTK implementation

• Simple surveying enabled by the latest RTK technology “LRTK”

• Frequently Asked Questions

What is RTK accuracy?

RTK stands for “Real Time Kinematic,” a technology that enables high-precision satellite positioning. This method is also referred to as RTK-GNSS positioning or the interferometric positioning method (real-time differential positioning). Normally, standalone GPS positioning can be affected by atmospheric and satellite clock errors, producing errors on the order of 5–10 m (16.4–32.8 ft). However, RTK achieves vastly higher accuracy by simultaneously observing GNSS satellite signals at two points—the reference station (base station) and the rover (mobile station)—and cancelling errors common to both. As a result, position errors can be reduced to about 1–2 cm (0.4–0.8 in) horizontally and within about 3 cm (1.2 in) vertically. In other words, RTK accuracy refers to centimeter-level positioning precision that conventional GPS could not achieve.

Originally developed in the surveying field, this high-precision RTK technology is now used widely across infrastructure sectors such as construction, civil engineering, agriculture, and drone surveying. While skilled surveyors and expensive dedicated equipment were previously required, recent technological advances have made RTK adoption more accessible for small and medium-sized businesses. As field digitization progresses, centimeter-level accuracy like that provided by RTK is becoming indispensable for infrastructure surveying. This article explains what RTK positioning is, how it works, and the benefits it brings to infrastructure surveying in an easy-to-understand way. It also touches on simple surveying using the latest LRTK technology and offers practical tips for leveraging high precision on site.

The importance of high accuracy in infrastructure surveying

Accuracy in surveying is critically important for infrastructure construction and maintenance—such as roads, bridges, water and sewer systems, and power facilities. Acquiring highly accurate survey data at the design stage enables precise planning of construction, allowing structures to be placed at the correct positions and elevations as designed. If survey accuracy is low, positional and elevation errors can occur at construction sites, leading to rework and wasted materials in later stages. For example, if a road is paved several tens of centimeters off the reference line, repairs can incur significant cost and time. Even slight misalignments can create mismatched joints or steps when multiple sections are connected later, greatly affecting infrastructure quality.

High-precision positioning is also indispensable for infrastructure inspection. Accurately knowing the positions of buried pipes and cables reduces the risk of damaging existing infrastructure during excavation. Centimeter-level surveying proves powerful for investigations that need to detect small changes, such as displacement measurements of bridges and tunnels. For instance, when monitoring tunnel settlement on an annual basis, a few centimeters of error may prevent detection of changes; with millimeter precision, even minute displacement trends can be captured. Thus, high-accuracy survey data are directly linked to ensuring quality and safety across all phases of planning, construction, and maintenance. In short, improving survey accuracy directly contributes to efficient construction and safe operation.

How RTK positioning works and how it differs from standard GPS

To understand why RTK can achieve such high accuracy, let’s compare its mechanism with standard GPS positioning. In standard GPS positioning (standalone GNSS positioning), a receiver independently receives signals from multiple satellites and computes position. This method, as mentioned earlier, is susceptible to errors from atmospheric refraction, satellite orbit errors, and clock errors, resulting in errors on the order of meters. The reason map apps on smartphones sometimes show your location shifted from the actual position is precisely this standalone positioning error.

In contrast, RTK positioning uses two receivers: a reference station and a rover. The reference station is installed at a point with a pre-known accurate coordinate, while the rover is carried to the point to be surveyed. When both receivers receive signals from the same satellites at the same times, error components common to both (such as ionospheric and tropospheric effects) can be determined in real time. Error information computed at the reference station is sent to the rover via radio communication or the Internet, and the rover applies those corrections to its measurements to cancel out most errors. The result is extremely accurate positioning with only centimeter-level residual errors.

The key aspects of RTK are relative positioning and real-time application of correction information. Whereas standalone positioning computes positions independently at each receiver, RTK leverages the difference between two points to greatly enhance accuracy. RTK also incorporates advanced techniques such as analyzing the carrier-phase of satellite signals—a wave with a wavelength of about 20 cm (7.9 in). By using carrier-phase differences, displacements down to the millimeter level can be detected, allowing final position accuracy to improve from several centimeters to, in some cases, a few millimeters. However, to realize high-precision RTK positioning, a communication link between the reference station and rover and a sufficient number of satellite signals under open sky are required. In urban canyons or mountainous areas where satellites are difficult to observe, accuracy may degrade or positioning may become unstable (such cases can be mitigated by combining other techniques described later).

How field work changes with RTK implementation

Applying RTK accuracy on site can significantly change surveying workflows and construction management methods. First, work time is reduced. Traditionally, infrastructure surveying involved many steps such as placing staffs at survey points and observing with total stations, or performing leveling surveys to measure elevation differences. With RTK surveying, surveyors can obtain coordinates and elevations in real time simply by carrying the rover (GNSS receiver) to points. Steps such as handwriting measurements for later calculation and plotting are reduced, and digital survey data can be obtained on the spot, enabling immediate verification and reflection in construction.

RTK also enables reduced manpower. One person can walk with a GNSS rover and survey wide areas with a small crew. Even when a reference station is set up, once a fixed station is established on site, only the rover needs to be operated, greatly reducing the effort of installing equipment or ensuring line-of-sight by multiple people. For example, in a demonstration of ICT construction for a road project, the use of RTK and machine control reportedly halved the required surveying personnel and substantially shortened construction days. Improved surveying efficiency gives the overall schedule more flexibility and makes coordination with other tasks smoother.

Moreover, RTK is powerful for on-the-spot as-built verification and pile-driving assistance. Comparing design coordinates with on-site positioning data allows immediate confirmation of whether structures or piles are positioned and elevated as designed. If misalignment is found, corrections can be made during construction, preventing rework. Traditionally, as-built checks were done after construction by a survey team, and discrepancies found might necessitate rework, but RTK allows on-site checking and correction. This increases confidence in quality control and the reliability of survey results, improving overall site efficiency and final quality. Additionally, reduced surveying time decreases workers’ on-site exposure, contributing to improved safety—reducing heatstroke risk and the chance of collisions with heavy machinery.

Main benefits of RTK implementation

The main benefits obtainable by leveraging RTK accuracy can be summarized as follows:

• Dramatic improvement in surveying accuracy: Compared with conventional GPS surveying with meter-level errors, RTK achieves errors within a few centimeters. This greatly enhances the reliability of facility positioning and as-built management for infrastructure.

• Improved work efficiency: Real-time positioning data reduces post-processing and redundant measurements. Large areas can be surveyed quickly and construction management decisions can be made promptly, directly contributing to shorter construction periods and reduced labor costs.

• Labor reduction and safety improvement: Fewer personnel are needed for surveying, making it easier to cope with labor shortages. Shorter survey times also reduce on-site exposure—improving measures against heatstroke and lowering the risk of contact with heavy machinery.

• Compatibility with digital construction: High-precision data obtained by RTK can be directly imported into CAD drawings, BIM/CIM models, and GIS systems. Comparing with 3D design data and integrating with machine guidance becomes smooth, promoting ICT-driven (digital) construction.

• Optimization of quality and cost: High accuracy reduces rework and over-construction, preventing waste of materials and expenses. Accurate first-time construction simplifies quality management and leads to cost reduction.

In fact, the Ministry of Land, Infrastructure, Transport and Tourism’s initiative i-Construction recommends ICT construction using RTK-GNSS because high-precision positioning can simultaneously improve productivity and quality. RTK introduction is bringing a revolutionary combination of “speed, simplicity, and high precision” to infrastructure sites, and its use is expanding not only in large-scale projects but also in small and medium-sized construction and local government maintenance operations. Its utilization is expected to continue growing.

Simple surveying enabled by the latest RTK technology “LRTK”

Recently introduced LRTK has drawn attention as a technology that makes RTK surveying even easier. LRTK is a solution that enables centimeter-level positioning without specialized equipment by combining a smartphone with a compact GNSS device. Instead of requiring large surveying instruments and complex setup, a lightweight receiver is attached to a smartphone to perform high-precision surveying. Its weight is only a few hundred grams, making it easy to carry on site.

For example, using LRTK one person can quickly walk and measure many points on site and confirm results on the spot. Test results have shown coordinates obtained with errors below 10 mm (0.39 in) from reference points, achieving accuracy comparable to professional GNSS equipment. Operation is simple—just press the start button in a smartphone app. Because it is intuitive to use without advanced surveying knowledge, not only veteran surveyors but also site managers and inspection staff can perform simple surveying.

In one municipality, LRTK was used in disaster recovery to immediately record and share damage conditions using a smartphone-based high-precision surveying system. Tasks that previously required manual effort and time were greatly streamlined by LRTK, contributing to faster recovery and cost savings. LRTK therefore enhances on-site responsiveness and is excellent for rapid response in disasters or sudden surveying needs.

Furthermore, LRTK can integrate with cloud services to instantly save and share high-precision data collected on site. This allows office staff to review survey data remotely and share information among multiple stakeholders, improving workflow efficiency. Introducing the latest RTK technology LRTK makes it easier to enjoy the benefits of high-precision surveying. Those interested should consider adopting this new solution to experience DX (digital transformation) at infrastructure sites.

Frequently Asked Questions

Q: What kind of positioning technology is RTK? A: RTK stands for “Real Time Kinematic” and is a technique to obtain centimeter-level high-precision position information in real time by correcting GNSS satellite positioning errors. Using two receivers—a reference station and a rover—and subtracting errors observed simultaneously by both reduces the multi-meter errors typical of ordinary GPS to within a few centimeters.

Q: How accurate is RTK positioning? A: Generally, RTK positioning achieves about 1–3 cm (0.4–1.2 in) horizontal accuracy and about 3–5 cm (1.2–2.0 in) vertical accuracy. However, accuracy varies with environmental conditions and equipment used. In environments with good visibility and stable satellite reception, even higher accuracy (in some cases below 1 cm (0.4 in)) is possible.

Q: Why is RTK required for infrastructure surveying? A: Infrastructure surveying requires placing and maintaining structures such as roads and bridges at precise positions and elevations, so high-precision data are essential. RTK’s centimeter-level positioning enables accurate construction, strict as-built control, and minimal deviation from existing facilities—providing significant benefits in quality and safety. Allowing errors of several meters would be unacceptable for infrastructure works.

Q: What is needed to perform RTK surveying? A: Basically, two GNSS receivers are needed: one for the reference station and one for the rover. The reference station is set at a point with known coordinates, and the rover is used at the locations to be surveyed. A communication method linking the two stations (radio or Internet-based correction data) is also required. Accurate reference point coordinates and conversion to Japan’s geodetic systems (JGD2011/2022) should also be considered. Recently, however, network RTK services that use public GNSS reference station networks have become widespread, allowing positioning without deploying a private reference station. Solutions like LRTK can also enable smartphone-based RTK positioning without dedicated large equipment.

Q: Are there weaknesses or precautions for RTK positioning? A: RTK performs best in open-sky environments; in urban canyons or forests satellite reception can degrade and positioning accuracy may fall or fail. If communication with the reference station is lost, correction data cannot be received and real-time positioning becomes unstable. To address these issues, effective measures include using multi-GNSS receivers that combine multiple satellite systems (not only GPS but also GLONASS, Galileo, etc.), combining optical surveying instruments such as total stations in areas where GNSS observation is difficult, or using augmentation signals from quasi-zenith satellites (PPP-RTK). Development of advanced RTK equipment and services continues to improve positioning performance even in urban and mountainous areas.

Q: How should total stations (TS) and RTK surveying be used differently? A: Total stations (optical surveying instruments) can achieve millimeter-level precision and are suitable for detailed measurements in construction and civil engineering within line-of-sight areas. RTK is advantageous for quickly surveying many points over wide areas or for long-distance surveys. For example, RTK is efficient for measuring distant points from reference stations in open sites, while total stations are indispensable for surveys inside tunnels or places where satellites cannot be observed. Ideally, use RTK and total stations according to site conditions. Also, because total stations require visual contact with a prism target, they often operate in teams of two, whereas RTK often allows single-person surveying and can reduce manpower. Combining both allows flexible surveying—using TS to cover areas with poor visibility and RTK for broad coverage.

Q: What is LRTK? A: LRTK is one of the latest RTK surveying solutions that consists of a small, high-precision GNSS receiver usable with a smartphone. It is easier to handle than conventional RTK equipment and can measure positions with centimeter-level accuracy. Cloud integration and simple app-based operation make it usable even by those without specialist knowledge. In the infrastructure field, LRTK is expected to improve surveying efficiency and reduce labor.