How to Use RTK for On-site Verification to Reduce Rework

Table of Contents

• Introduction

• What is RTK?

• Utilizing RTK for pre-construction site surveys and stakeout

• Utilizing RTK for on-site verification (as-built management) during construction

• Simple surveying with LRTK

• Conclusion: Toward sites with zero rework

• FAQ

Introduction

On construction sites, even when work seems to be proceeding according to plan, it is not uncommon for rework to become necessary afterward. Rework not only consumes unnecessary labor but also leads directly to extra material use and schedule delays, making it a cost factor that sites want to avoid as much as possible. In particular, rework caused by surveying or stakeout errors can have a major impact on overall schedules and budgets, posing a serious problem for construction managers.

To reduce such needless rework and keep construction running smoothly, it is important to improve the accuracy of the on-site surveying and verification processes themselves and prevent mistakes before they occur. This article reviews common issues that arise in on-site verification situations such as pre-construction site surveys and in-process checks (as-built management), and explains how RTK (a high-precision GNSS positioning technique), which is attracting attention as a key to solving these problems, can be used. Let’s look from a site perspective at how surveying DX using the latest digital technologies can achieve quality improvement and rework reduction.

What is RTK?

RTK stands for Real Time Kinematic, a high-precision positioning method that dramatically improves the accuracy of satellite positioning (GNSS), typified by GPS. Typically, GPS used in smartphones or car navigation systems can have positioning errors on the order of several meters (several ft), but RTK applies correction data from a reference station in real time to reduce errors to within a few centimeters (within a few in). In other words, RTK enables the precise stakeout and measurement required in civil engineering works.

Specifically, a mobile reference station (also called a base station) is set up near the work site, and a GNSS receiver acting as the rover receives correction information sent from that reference station while positioning. Alternatively, it is also possible to use a network of electronic reference points (GNSS reference stations) provided by the Geospatial Information Authority of Japan or private operators via the internet. In Japan, the Quasi-Zenith Satellite System "Michibiki" also offers a centimeter-class positioning augmentation service (CLAS), and with a compatible receiver, high-precision positioning is possible without preparing a dedicated base station. In recent years, with initiatives such as the Ministry of Land, Infrastructure, Transport and Tourism's *i-Construction* (ICT construction), high-precision surveying using RTK is rapidly spreading throughout the civil engineering and construction industries. RTK equipment, which used to require large, expensive antennas and specialist knowledge, has become smaller and cheaper, making one-person-one-unit operation realistic.

Utilizing RTK for pre-construction site surveys and stakeout

First, let’s look at the benefits of using RTK for pre-construction site surveys and stakeout work. Traditional analog surveying methods required time and manpower to obtain sufficient existing-condition data, and there was a risk of missing information needed at the planning stage. For example, in site surveys for land development or road design, it is common to survey only limited spots and infer the terrain, and later find unexpected depressions or obstacles in unsurveyed areas that force design revisions.

Also, at the start of construction, stakeout work using conventional methods such as total stations typically requires two or more personnel; during analog procedures like measuring distances with a tape measure and signaling by radio or gestures, human error can occur. There are many stories of positions for piles being misplaced because someone misread a number on a paper drawing or misunderstood an instruction, resulting in having to measure repeatedly.

Introducing RTK can greatly reduce the effort and risk involved in such pre-construction surveying tasks. With a high-precision GNSS receiver and surveying apps on a tablet or smartphone, you can reproduce coordinates from design drawings directly on site and perform surveying and stakeout efficiently by one person. For example, when you select a target point’s coordinates in an RTK-enabled app, the direction and distance from the current position to that point are displayed on the screen. The worker follows the displayed arrow and drives a stake or marks the spot where the distance reaches zero, which is exactly the design position. Even without a skilled surveyor standing beside them to give instructions, following the device’s guidance allows accurate stakeout, eliminating mistakes due to communication misunderstandings and reducing waiting time. Also, with RTK positioning you don’t need to carry heavy tripods or optical equipment to maintain line-of-sight; simply powering up the receiver in a place with a view of the sky allows you to survey a wide area in a short time. As a result, site surveys can measure more points in greater detail, reducing the risk of overlooking terrain variations at the planning stage. In stakeout, accurate staking can be completed once before construction, minimizing the possibility that rework such as "the foundation position was off" will be discovered after construction.

Utilizing RTK for on-site verification (as-built management) during construction

Next, RTK is also a powerful tool for as-built measurement and quality inspection during construction. In conventional as-built management, staff typically measure subgrade heights or structural dimensions point by point using levels and tape measures and record them by hand on paper forms. Because this method requires tremendous effort for measurements, only a small portion of the site is sampled, and there is a risk of overlooking differences from the design in unmeasured areas. Analog record-keeping also carries the possibility of human error. Common human errors include:

• Mishearing or miswriting numbers read out on site

• Omission or transcription errors when cleaning up or copying handwritten notes

When such surveying record errors occur, it may be necessary to correct the survey data later or go back to the site and re-measure—i.e., rework. Interrupting a construction schedule to revert to surveying is a major loss that leads to schedule delays and extra costs.

On the other hand, by using RTK, the process from as-built measurement to recording and verification can be completed digitally, greatly reducing the above kinds of mistakes. Coordinate values of measured points obtained by the RTK receiver are automatically recorded on a tablet and saved to the cloud. Because data recording is completed simultaneously with measurement, there is no need to worry about transcription errors or missing records.

Also, RTK can measure many points in a short time, so, for example, subgrade thickness that was previously judged by measuring heights at only a few spots spaced every several tens of meters (every several ft) and averaging can now be checked by acquiring areal measurement data while walking the entire road. As-built data acquired on site can be immediately compared to design values in the cloud, and it is possible to automatically determine whether measurements fall within allowable tolerances. Of course, you can immediately confirm whether the measured values meet the required standards on the spot, and if any out-of-spec areas are found, you can promptly perform remedial work and re-measure. By using RTK in this way, you can create an environment where verification is performed immediately on site without measurement omissions or oversights, greatly reducing the risk that defects such as "some areas were too thin" will be discovered at the inspection stage.

Furthermore, with a cloud-linked digital surveying system, the numeric data and photos collected on site are automatically shared, enabling immediate information sharing with stakeholders in the office or at remote locations. This reduces the effort of site supervisors returning to the office to prepare reports, shortening lead time for inspections and reporting. As quality management DX progresses, overall productivity and quality standards on construction sites will improve, bringing operations closer to smart site management without unnecessary rework.

Simple surveying with LRTK

To maximize the advantages of RTK, it is important to choose user-friendly equipment that anyone on site can operate. LRTK was developed to meet such needs as a next-generation "one-person surveying" solution. By combining a smartphone with a small RTK-GNSS receiver, LRTK enables centimeter-level positioning (half-inch accuracy) with simple operations even by non-experts. Heavy tripods and complicated setup are unnecessary; by mounting the device on a helmet and walking the site, you can even obtain 3D survey data.

In sites where LRTK has already been introduced, surveying workload has been dramatically reduced. For example, one civil engineering site reported that surveying time was reduced by about 30% from the first week of using LRTK. For companies struggling with manpower shortages, LRTK that allows one person to survey quickly can be a powerful helper. LRTK enables simple surveying that can be done whenever needed without tedious preparatory work, and it is highly effective for various applications such as road alignment surveys, slope inspections, buried water and sewer pipe investigations, and maintenance of infrastructure structures such as bridges. As a new surveying style using RTK, LRTK may become the new common sense on future sites.

Conclusion: Toward sites with zero rework

In today’s construction sites, where labor shortages and pressure to shorten schedules are increasing, RTK surveying can be a true savior. The effects of "fewer people required for surveying," "less rework due to mistakes," and "completion with a single survey" bring speed and accuracy to sites that traditional methods could not achieve. By improving surveying accuracy and enabling immediate on-site verification, the risk of rework after construction is minimized, making it possible to balance quality assurance and efficiency. RTK utilization is beginning to advance in all civil and construction fields—road works, land development, water and sewer installations, bridges, and more—and by actively adopting the digital technologies promoted by the government, site productivity and safety will dramatically improve.

Also, using intuitive modern surveying equipment allows younger staff or staff from other disciplines to perform surveying even when skilled personnel are scarce. This prevents work from concentrating on specific technicians and reduces situations where the entire construction is delayed waiting for surveying. It is not an exaggeration to say that embracing new technologies rather than clinging to traditional methods will be the key to future site management. Consider trying RTK on site to experience its efficiency gains firsthand. When introducing it for the first time, trialing it on a small project will allow you to directly feel its benefits. Use the latest RTK technologies and solutions like LRTK to aim for smart sites with zero rework.

FAQ

Q: What is the difference between RTK and normal GPS positioning? A: Normal GPS can have errors of several meters (several ft) due to satellite signal errors, but RTK uses correction data from a reference station to reduce those errors to a few centimeters (a few in). Simply put, RTK is a method to make GPS more accurate, and it is powerful for applications requiring high precision such as civil surveying.

Q: What equipment and environment are required to use RTK? A: RTK surveying requires a GNSS receiver (rover) that supports centimeter-level positioning (half-inch accuracy) and correction information from a reference station to improve positioning accuracy. Typical methods include deploying a mobile base station on site, or using correction services such as electronic reference point data or VRS via mobile communications. Recently, small RTK receivers that attach to smartphones have become commercially available, and combined with dedicated apps, they allow easy centimeter-class positioning on site.

Q: How accurate is RTK positioning? A: Accuracy depends on the equipment used and satellite reception conditions, but generally RTK provides about 2–3 cm (0.8–1.2 in) accuracy horizontally and several cm to 5 cm (a few in to 2.0 in) vertically. In open-sky conditions with sufficient satellite reception, RTK provides accuracy adequate for most civil engineering as-built management. However, in areas where satellite visibility is blocked, such as among tall buildings or in forests, accuracy degrades and sometimes a positioning solution may not be obtainable.

Q: Can RTK be used in rainy weather or environments with many obstructions? A: If used outdoors with a view of the sky, RTK positioning is not greatly affected by light rain or cloudy weather. However, in extreme weather like thunderstorms or typhoons, radio conditions can become unstable and positioning accuracy may decline. Also, in areas surrounded by high-rise buildings or dense trees, satellite signals are blocked and RTK tends to function unstably. As with satellite positioning in general, it is ideal to use RTK where the sky is as open as possible.

Q: Can less experienced technicians handle RTK? A: Yes. Modern smartphone-linked RTK systems are designed with intuitive interfaces, and with basic training, site supervisors and junior engineers can use them effectively. Unlike conventional total station surveying, they do not require advanced specialist skills; as long as users have basic knowledge of coordinates and surveying, the device provides navigation and makes surveying intuitive. Creating an environment where anyone on site can perform surveying prevents work from concentrating on specific staff, reducing waiting times and improving personnel allocation efficiency.

Q: Is there a difference in accuracy between total station surveying and RTK surveying? A: In some cases, optical instruments like total stations (TS) can be more accurate. For example, millimeter-level precision is required in steel erection or machinery alignment, and in those cases TS or leveling instruments remain indispensable. However, for routine as-built measurements and stakeout in typical civil works, RTK positioning with centimeter accuracy (half-inch accuracy) is sufficient in most cases. Because RTK can position without line-of-sight and cover wide areas by one person, it is effective to streamline everyday surveying with RTK and complement with optical surveying only for processes that require millimeter-level confirmation.

Q: I’m worried about the high cost of introducing RTK equipment. Is there an easy way to start? A: RTK equipment used to be very expensive, but affordable and easy-to-use devices are now available. Products combining high-performance smartphones with small GNSS receivers make RTK more accessible. Also, using government or private reference station services removes the need to install an expensive base station, reducing operational costs. More companies are introducing RTK at relatively low cost by taking advantage of subsidies or rental services.

Q: Is RTK surveying possible in mountainous areas without cellular coverage? A: There are ways to perform RTK surveying without internet connectivity. For example, you can set up a simple mobile base station on site and transmit correction information to the rover via radio communication, enabling positioning without relying on the internet. In Japan, you can also use the Michibiki centimeter-class augmentation service (CLAS) to perform high-precision positioning without a base station. With a CLAS-compatible receiver, you can achieve near-RTK accuracy even in remote mountain areas or on isolated islands where cellular signals do not reach.