RTK Inspection Procedure Guide: Thorough Explanation of an Efficient Field Workflow

Table of Contents

• Introduction

• Current State and Challenges of Infrastructure Inspections

• What is RTK Technology

• Basic Procedures for RTK Inspections

• Benefits of RTK Inspections

• Simple Surveying with LRTK

• FAQ

Introduction

In Japan, many infrastructure structures such as expressways, bridges, tunnels, and buildings were concentratedly developed during the high economic growth period. Decades have passed since then, and the number of aging structures has now increased. Regular inspections and maintenance are essential to safely extend the service life of social infrastructure. However, field inspection work has largely relied on the experience of veteran engineers and manual labor, and analog methods such as paper records and tape-measure measurements have been mainstream. With limited personnel and budget, how to carry out inspections efficiently and accurately has become a major challenge.

In response to these challenges, "on-site DX (digital transformation)" using digital technologies has attracted attention in recent years. In particular, the use of high-precision positioning technology called RTK (Real Time Kinematic) is set to greatly change the norms of inspection work. RTK is a technique that corrects positioning errors from GNSS (satellite positioning) in real time and enables positioning with centimeter-level accuracy (half-inch accuracy). Centimeter-level positioning, which previously required expensive dedicated equipment, can now be realized by anyone using handheld devices such as smartphones or tablets combined with a small receiver. As a result, methods for on-site measurement, recording, and information sharing are rapidly evolving.

This article provides a thorough explanation of the procedures for an inspection workflow that leverages RTK technology and the efficiency benefits it brings. It compares the issues of traditional inspection methods with the improvements introduced by RTK and presents concrete steps on how to carry out tasks at actual sites. At the end of the article, we also introduce LRTK, a solution that allows easy access to high-precision positioning, and propose methods for its on-site adoption.

Current State and Challenges of Infrastructure Inspections

Inspection work for social infrastructure has been carried out for many years with little major methodological change. In a typical field inspection, engineers visit the structure, visually check for degradation or damage, take photos of problem areas with a digital camera, and handwrite the photo locations and directions onto paper drawings. When measuring the length of a crack, they use a tape measure, and records of damage locations often become vague expressions relying on experience, such as "at the point ◯ m from the south side of pier XX." Information collected at the site is brought back to the office, organized, and transcribed into Excel or Word to create reports. Such work is very time-consuming, and variability in recording accuracy and expression between people is inevitable.

One of the problems with conventional methods is the lack of precision in position information. Records made with simple handheld GPS or visual estimation can make it difficult to reproduce the exact damaged point on a structure later. When re-inspecting the same location several years later, you often have to rely on intuition using past records like "probably around here," and it is nearly impossible to photograph from exactly the same position and angle as before. As a result, comparisons of long-term changes become uncertain, and issues may be overlooked. Additionally, inspecting locations that are difficult for people to approach—such as high bridge members or recessed slopes—poses a major challenge. In many cases, detailed observation or measurement cannot be performed without arranging an aerial work platform or installing temporary scaffolding, presenting significant costs and safety burdens. Furthermore, a shortage of field personnel and the aging of technicians are becoming more serious, and there is concern that the traditional analog approach alone will not be able to meet the growing inspection needs in the future.

What is RTK Technology

RTK (Real Time Kinematic) is a technology that dramatically improves the accuracy of GNSS positioning. Normal GPS or GNSS positioning can have errors on the order of several meters due to atmospheric effects, satellite clock errors, and other factors. RTK, however, uses a reference station (base station) with known accurate coordinates and calculates the relative position between that base station and a mobile receiver (rover) to correct errors in real time. By applying correction data transmitted from the base station to the rover, RTK enables positioning with accuracy on the order of centimeters.

Traditional RTK methods required two GNSS receivers from the same manufacturer (one for the base station and one for the rover) and communication between them via UHF radio, which necessitated expensive equipment. Recently, network RTK services that distribute correction information via the Internet have become more widespread. For example, infrastructure such as the VRS method using the network of continuously operating reference stations provided nationwide by the Geospatial Information Authority of Japan, or the centimeter-level augmentation service (CLAS) provided by Japan’s quasi-zenith satellite system "Michibiki," allow base station data to be obtained via network or satellite. This has made high-precision GNSS positioning easier to use without installing dedicated radios or local base stations.

Basic Procedures for RTK Inspections

By leveraging RTK technology, the accuracy and efficiency of field inspections can improve dramatically. Below are the general steps to perform inspection work using RTK.

• Preparation: Plan according to the purpose of the inspection and the target object, and prepare the necessary equipment. Bring GNSS receivers (RTK-capable antenna), mobile devices (tablets or smartphones), survey poles or tripods, spare batteries, and other items to the site. Confirm the coordinate system and coordinates of reference points to be used in advance, and prepare information on any known reference points near the site. Also decide beforehand how to obtain RTK correction information (whether to set up a local base station, use a network service such as VRS, or use Michibiki’s CLAS signal). Check device battery levels and firmware updates so you can arrive on site fully prepared.

• Setting up the base station or connecting to a correction service: If using your own base station, choose an open, well-sighted location on site and set it up. Place a tripod on stable ground with minimal obstruction from surrounding buildings or trees, and mount the GNSS antenna vertically. Accurately measure the antenna height (the height from the ground to the antenna reference point) and input it into the controller. If you can set it on a known point, input that coordinate; if not, determine an average coordinate from several minutes of static observation to use as a provisional reference position. Start the base station to begin broadcasting correction data so the rover can receive it. When using network RTK, connect to the correction service via an Ntrip client or similar from the rover’s device. Enter the necessary login information and select a mount point to start receiving correction data. If your receiver supports CLAS, configure it to receive the augmentation signal directly from satellites.

• Starting the rover and beginning positioning: Power on the rover receiver and confirm that it is receiving correction data from the base station via radio or the network. Launch the dedicated app on your tablet or smartphone and check the current RTK status. When satellites are sufficiently tracked and correction data is applied, the solution will soon reach FIX status. A FIX indicates that a high-precision solution has been obtained; in this state, centimeter-level position measurement (half-inch accuracy) is possible. For reassurance, if there are known reference points or markers on site, you can perform positioning on them to confirm correct coordinates are obtained.

• Measuring and recording inspection points: Once ready, record the position information of the inspection targets consecutively. For each point you observe—such as cracks or spalling—place the rover at that location and press the record button in the dedicated app to capture coordinates. If photo capture and note entry are possible simultaneously, save the coordinate, photo, and annotation together as one data item for each crack location. With RTK position records, it becomes clear on a map where the damage in each photo corresponds, making later comparison and sharing straightforward. For inspections over wide structures, RTK-equipped drones may be used to collect aerial photos or point clouds; applying RTK corrections during flight will attach high absolute-accuracy position information to all acquired data.

• On-site verification of measurement results: After measuring all required points, verify and validate the data on site. Check via the app’s map or list that no records are missing and that all important points are covered. Perform additional measurements as needed to complement the data. If positioning accuracy is in doubt, re-measure the same points to confirm value stability or re-check errors at known points. RTK positioning can temporarily degrade if satellite visibility is blocked or radio signals are interrupted, but because you can notice such issues immediately on site, you can retake measurements as needed. Confirming data quality thoroughly on site makes later analysis and report preparation smoother.

• Data storage, sharing, and reporting: Once measurements are complete, securely save the collected data. Uploading from the dedicated app to the cloud allows office PCs to access the data immediately. For example, lists of crack coordinates and photos can be automatically plotted on maps or drawings and used directly as source material for reports. High-precision data obtained by RTK can be imported into CAD drawings or asset management systems to support repair planning and analysis of long-term deterioration. Eliminating the need to bring paper records back for manual input connects the field and office with digital data, dramatically improving work efficiency and information accuracy.

Benefits of RTK Inspections

Introducing RTK brings the following major benefits to field inspections:

• High-precision data recording and reproducibility: Position information can be recorded with centimeter-level accuracy, allowing damage locations to be precisely identified and preserved as objective data. Revisiting the same coordinates at subsequent inspections becomes easy, and the ability to compare and monitor long-term deterioration improves dramatically. Records no longer rely on vague human intuition, increasing the reliability of reports.

• Dramatic improvement in work efficiency: Because measurement and recording can be done on site simultaneously, double entry and transcription to paper are unnecessary. Digitization is completed during inspection, significantly reducing office work time afterward. Tasks that were previously divided among several people can increasingly be handled efficiently by a single person, helping to alleviate personnel shortages. Data can be shared instantly via the cloud, smoothing information flow between the field and the office.

• Enhanced safety: Remote positioning and digital recording via RTK reduce the number of times workers must enter hazardous areas. For inspections at height or in confined spaces, necessary data can be obtained and the team withdrawn quickly, minimizing worker risk. Reduced frequency of temporary scaffolding or aerial work platforms lowers accident risk. Fast, accurate inspections directly contribute to improved infrastructure safety.

• Low cost and ease of introduction: High-precision positioning equipment that was once expensive can now be replaced by small, affordable RTK receivers paired with general-purpose tablets. Initial investment can be greatly reduced, making it realistic to equip many sites with a “one-per-person” device. As a result, organizational IT literacy improves and it becomes easier to adapt to digital construction initiatives such as the Ministry of Land, Infrastructure, Transport and Tourism’s i-Construction. Low-cost RTK has the potential to become the standard for future inspection work.

Simple Surveying with LRTK

One concrete solution for easily utilizing RTK in the field is the LRTK series. LRTK is an integrated system of a compact GNSS receiver and a mobile app developed by a startup originating from the Tokyo Institute of Technology. Simply attaching it to a commercially available iPad or iPhone turns your device into a versatile surveying instrument. Weighing about 125 g and with a thickness of just 13 mm (0.51 in), the pocket-size device houses a high-performance RTK-GNSS module and a battery, and achieves centimeter-level positioning through a dedicated app.

With LRTK, you can immediately enjoy the benefits of high-precision positioning for inspection tasks described in this article. It supports single-point measurements as well as continuous trajectory logging, point cloud scanning, AR-based visualization of stake-out positions, and change detection by overlaying past data—an all-in-one set of functions useful on site. Measurement data can be uploaded to a dedicated cloud with a single tap, enabling real-time situational awareness of the field from the office.

Additionally, because the LRTK device is a triple-frequency GNSS receiver, it can continue high-precision positioning even in areas without cellular coverage or immediately after a disaster when the Internet is down by receiving the centimeter-level augmentation service (CLAS) broadcast from Japan’s quasi-zenith satellite Michibiki directly. This feature is a major advantage for infrastructure inspection and disaster response sites where stable positioning is required regardless of radio or communication conditions.

LRTK has already been introduced at construction and civil engineering sites in Japan, and its ease of use and practicality have quietly made it popular as a “one-per-person field surveying tool.” Using a dedicated case to attach it to a tablet and turning on the power is all it takes to start surveying on arrival at the site, enabling precise measurements whenever needed. Without expensive equipment or special training, field staff themselves can drive the DX of infrastructure inspections—an innovative shift.

In this way, LRTK makes it easy for anyone to start using high-precision positioning that can revolutionize infrastructure inspection. If you feel inefficiencies in your current field operations, consider adopting this new approach. Your usual tablet will become a high-precision surveying instrument, and your field workflow will be transformed.

FAQ

Q: What is RTK inspection? A: RTK inspection uses RTK, a high-precision GNSS positioning technology, to inspect infrastructure and structures. Traditional inspections tended to record locations roughly, but RTK inspection acquires coordinates of damage points and measurement points in real time at centimeter-level accuracy (half-inch accuracy). This allows inspection results to be recorded with precise position information, making later comparisons and analysis easy. In short, it is an inspection method that records the inspection target’s location with accurate coordinate data.

Q: What do I need to start using it? A: Basically, you need a high-precision GNSS receiver (RTK-capable), a terminal to display and record the positioning results (e.g., tablet or smartphone), and either a communication environment to receive correction information or a base station. Specifically, prepare a rover receiver and either connect to a network RTK service via mobile data or set up your own base station and use radio communication. In recent years, small RTK devices that work with smartphones and tablets have emerged; with a device paired with a dedicated app, you can operate by simply powering on the device at the site and starting positioning.

Q: What level of positioning accuracy can be obtained? A: Under favorable conditions, RTK positioning can achieve horizontal errors of a few centimeters and vertical accuracy of a few centimeters to at most a few tens of centimeters. This is far more accurate than standalone GPS positioning, which has errors of several meters. For example, even small cracks on a bridge can be recorded with coordinates within a few centimeters of error. However, accuracy depends on satellite visibility and radio conditions. In environments surrounded by tall buildings or inside tunnels, accuracy may degrade; in such cases, countermeasures such as performing averaged positioning at a well-sighted location can partially mitigate the issue.

Q: Can RTK positioning be used at sites outside cellular coverage? A: Yes. Even without Internet connectivity, high-precision positioning can be maintained in several ways. One method is to use the centimeter-level augmentation service (CLAS) provided by Japan’s quasi-zenith satellite system Michibiki. Receivers that support CLAS can directly receive correction information from the satellite, allowing real-time positioning to continue even in areas without cellular coverage. Another method is to set up a portable local base station on site and transmit correction data to the rover via UHF radio. In this way, RTK operation is possible without network connectivity, and it has been used in disaster sites where relying on communication networks is not feasible.

Q: Does operation require specialized knowledge or qualifications? A: No. Systems are designed to be usable without special qualifications or advanced technical knowledge. Dedicated apps have intuitive interfaces that allow simple operations like pressing a start-positioning button and tapping a record button at the point you want to measure. While precise surveying traditionally required licensed surveyors or skilled technicians, RTK inspection systems can be mastered by field workers with short training. However, when submitting official results for public reference point surveys, verification by qualified personnel may be required in some cases.

Q: How does it differ from drone-based inspections? A: Drone inspections excel at high-altitude and wide-area imaging, but they require flight permits and specialized operators, and are subject to weather conditions. RTK-equipped drones can attach high-precision position information to aerial photos, but operation is limited in urban areas or indoors where flight is difficult. Ground-based RTK inspections, where a person carries the receiver, have fewer regulations and are less affected by weather, making them flexible for routine inspections. The two are complementary: using drones to capture an overall view from above and ground RTK positioning for detailed measurements and verification is an effective combination.

Q: Isn’t the introduction cost high? A: It is significantly lower than before. RTK systems once required investments of several million yen, but now you can start with an affordable small receiver like LRTK and a smartphone. Additionally, some government-provided correction services (such as continuously operating reference station data or CLAS) are available free of charge, keeping maintenance costs down. Most importantly, RTK introduction improves work efficiency, reducing re-measurements and revisits, which saves labor and time and yields a strong return on investment. Because initial costs are low, it’s easy to start with a pilot introduction and scale up.

For more details on LRTK, please visit the link below.

• [LRTK official site](https://www.lrtk.lefixea.com)