Construction management is changing! Accelerating site visualization with LRTK coordinate-tagged point clouds

Table of contents

• Basics of RTK surveying and challenges of traditional methods

• Mechanism and features of RTK point-cloud scanning that produces coordinate-tagged point clouds

• New norms for point-cloud scanning × construction management

• Workflow of field surveying with LRTK and convenience of smartphone operation

• Application examples: cloud sharing, AR display, photo geotagging, heatmap use, CAD integration

• Real-world implementation cases and their effects

• Barriers to adoption and ease of introduction

• Summary: recommending simple surveying with LRTK

• FAQ

Basics of RTK surveying and challenges of traditional methods

In construction-site surveying, it is required to measure positions accurately to millimeter-to-centimeter-level accuracy (cm level accuracy (half-inch accuracy)). However, conventional high-precision surveying has required specialized instruments such as total stations (TS) and high-performance GNSS survey receivers (GPS receivers) and advanced skills. For example, surveying using a TS requires placing a prism at each survey point and measuring one point at a time, so on large sites the instrument must be repositioned many times. Even with GNSS surveying, traditionally it was necessary to set up your own reference station (base) near the site and exchange correction information with the rover via radio communication. Both methods demanded time and manpower, relied on experienced surveyors, and limited the number of points that could be acquired at once, so it was common to sample-measure only the minimum required points.

Several issues have been pointed out with these traditional methods. First is the problem of efficiency. For example, when checking the as-built geometry of embankments or slopes after construction, the conventional approach measured heights at key locations with a TS or level to create cross-sections and check differences from design values. This method acquires only a very small number of survey points at once, making it difficult to grasp the entire surface or three-dimensional shape. Second is the issue of time and labor costs. Each survey required arranging a specialized team and spending time installing control points and adjusting equipment, and it was not uncommon for as-built inspection results to take several days to be delivered. For construction managers, "waiting several days for a few-centimeter accuracy check" became commonplace and slowed the overall schedule. Safety is another non-negligible issue. It was risky to perform detailed measurements on steep slopes or in areas where heavy equipment was operating, and with limited personnel it was difficult to safely and quickly understand the as-built condition using traditional methods.

Mechanism and features of RTK point-cloud scanning that produces coordinate-tagged point clouds

In recent years, RTK-based point-cloud scanning has attracted attention as a technology that addresses these issues all at once. RTK (Real Time Kinematic) is a real-time error correction technology in satellite positioning (GNSS) whereby a rover uses correction data from a base station to reduce positioning error to the centimeter level. Previously, RTK positioning required expensive receivers and dedicated base stations, but network RTK methods such as VRS (virtual reference station) have become widespread, allowing correction information to be obtained via the Internet. This removes the need to install a dedicated base station on site and makes it possible to achieve centimeter-level high-precision positioning in real time anywhere in Japan provided there is a suitable communication environment.

Combined with RTK positioning is the use of 3D point-cloud data measurement. Point-cloud measurement is a technology that digitally records terrain and structures as a large collection of points (point cloud); traditionally, photogrammetry from drone aerial photography and ground-based laser scanners were widely used. Recently, some smartphones such as iPhone and iPad Pro have been equipped with LiDAR sensors (laser-based high-speed distance measurement sensors), enabling easy acquisition of surrounding 3D point-cloud data with familiar devices. However, LiDAR scans performed on a smartphone alone usually record the acquired point cloud in the smartphone’s local coordinate system, leaving the issue of not knowing where on a map the data corresponds to. Additionally, walking around while scanning with the phone can gradually accumulate error and cause distortion in the overall point cloud.

The solution that emerged is a method that combines RTK positioning with smartphone point-cloud scanning. By attaching a pocket-sized high-precision GNSS receiver to a smartphone and scanning the surroundings with LiDAR or camera while knowing the precise position in real time to centimeter accuracy, each acquired point can be immediately assigned absolute coordinates (geodetic coordinates). This method is realized by Reflexia’s "LRTK" series, which consists of a small RTK-GNSS device that attaches to a smartphone and a dedicated app. When scanning with a smartphone + LRTK, a major feature is that position shifts and distortions do not occur in the point cloud even if the operator walks around carrying the device. Because the entire dataset is always recorded tied to the correct latitude, longitude, and elevation, there is no need for cumbersome post-processing or coordinate transformations. It is truly a revolutionary system that enables anyone to obtain precise on-site 3D point clouds with positional information (coordinate-tagged point clouds) on the spot.

This RTK-enabled point-cloud scanning technology is making high-precision 3D surveying, which previously required specialists, much more accessible. Construction managers and young technicians without special training can simply attach an LRTK receiver to a smartphone and walk the site to comprehensively survey terrain and structures in a short time. The effective range of the obtainable point cloud reaches tens of meters, covering wide-area terrain down to detailed structures. LRTK also allows the use of known points (control points) for correction to verify and further improve accuracy, ensuring precision and reliability comparable to traditional methods. Measurement time is only a few minutes, and the immediacy of being able to check results in real time is a significant advantage on site.

New norms for point-cloud scanning × construction management

With the advent of RTK coordinate-tagged point-cloud scanning, construction management—especially as-built control—is encountering a new norm. Traditionally, after construction was complete, a survey team would visit the site to measure elevations at important points and cross-sections, then report differences from design values on paper forms. By using point-cloud scanning, however, the overall shape of structures and ground can be recorded as digital data, making it possible to check construction results down to the details.

For example, high-precision point-cloud data obtained with LRTK can be immediately overlaid and compared with pre-prepared design 3D models or design surface data. Using a dedicated app or in the cloud, you can automatically create a heatmap that color-codes differences between the current point cloud and the design model, so areas constructed as designed appear blue or green, while deficits or excesses appear red, making it obvious at a glance where errors exist. This makes it easy to detect local unevenness or overfilling that might have been overlooked. Moreover, from the heatmap difference data, deficient or excess earthwork volumes can be automatically calculated, providing immediate information such as "how many cubic meters of fill are needed at which location." As-built inspection, which used to be empirically estimated from a few survey points, can now be conducted quantitatively and visually using point-cloud data.

This new measurement method aligns with the Ministry of Land, Infrastructure, Transport and Tourism’s i-Construction and the ICT construction trend, and the utilization of 3D measurement technology is being incorporated into as-built control procedures. Point-cloud data acquired with LRTK has accuracy that meets the as-built control standards (grades) defined by the MLIT and can be submitted as official inspection deliverables. In other words, as-built management using RTK point-cloud scanning is becoming the new norm that rivals traditional methods in accuracy and reliability while excelling in immediacy and comprehensiveness. Because client and contractor can share the same 3D data to confirm as-built conditions, it is also effective in preventing misunderstandings and ensuring quality.

Workflow of field surveying with LRTK and convenience of smartphone operation

Now let’s look at the actual procedure for surveying with a smartphone + LRTK. It is characterized by intuitive smartphone operation and simple steps that complete high-precision surveying. The following is a typical basic flow of LRTK surveying on a general site.

• Device mounting: Using a dedicated attachment or holder, attach the LRTK receiver to the smartphone. It is a compact device weighing approximately 125 g and can be attached to the back of the phone with one touch. After mounting, preparation is complete by simply turning on the LRTK device (the battery is built-in so no external power is required).

• Launch the app: When you start the dedicated LRTK app on the smartphone, it automatically connects to the device via Bluetooth or Wi-Fi and begins GNSS satellite acquisition. The app screen displays the current positioning mode (single, float, fix, etc.) and the number of satellites being tracked, allowing you to check GNSS reception status.

• Obtaining correction information: If the smartphone has Internet access, it will automatically access the configured correction information service (such as VRS-style reference station data distribution) and receive virtual reference point correction data in real time based on the current position. With good satellite reception, a Fix (RTK fixed solution) can be obtained within 30 seconds, establishing centimeter-class positioning (cm level accuracy (half-inch accuracy)).

• Start surveying: Once RTK is fixed, select the measurement mode required in the app and begin measurement. For example, to measure the coordinates of a single point, simply tap the "Measure" button on the screen and the three-dimensional coordinate values of that point are recorded. In point-cloud scan mode, the point cloud acquired by LiDAR is displayed in real time over the smartphone camera feed, and you can continuously record surrounding shapes while walking. In AR mode, you can overlay design data on the live camera view to compare with current conditions or navigate stake positions. All operations are performed by touching buttons or moving sliders on the smartphone screen, so you do not need to handle complicated settings.

• Data saving and sharing: After surveying, you can upload the acquired point-cloud data, coordinate measurement data, photos, and so on to the cloud with a single tap. Data measured on site can be shared instantly with the office or the client, and the office can view results immediately via a browser. You can also save data locally on the smartphone and later extract it via USB or export from the app for import into CAD software.

As described above, surveying with LRTK completes preparation to data acquisition in only a few minutes. There is no need to set up tripods and precisely position instruments like with a TS, so first-time users will be surprised by the speed. From powering on to position establishment, measurement, saving, and sharing, the process is largely automated and simplified, giving you the mobility to respond immediately when you want to measure something now. High intuitive usability—anyone familiar with smartphone touch operation can use it—is another major advantage, avoiding time spent on complicated equipment operation. In other words, LRTK brings the “ease of surveying with a smartphone” to the field.

Application examples: cloud sharing, AR display, photo geotagging, heatmap use, CAD integration

LRTK is not just for measuring points on the spot; it is a platform that allows acquired data to be used in various aspects of site management and construction. Here are representative application examples.

• Cloud sharing: Survey data acquired with the LRTK app can be synchronized and saved to the cloud instantly. After uploading, you can view point clouds, photos, and coordinate lists in a browser without installing dedicated software. By issuing a share link, you can share data with clients or subcontractors who do not have an LRTK license with one click. Recipients do not need a high-performance PC or special viewer; they can view the site’s 3D data from their existing PC or tablet, facilitating smooth information sharing.

• AR display: LRTK’s AR function overlays design data and guidelines on the real-world site image shown on the smartphone screen. For example, you can project a pre-imported design 3D model or lines from drawings as a virtual benchmark (height reference) or excavation line on site. Machine operators can move an excavator according to the lines displayed on the smartphone screen to achieve the gradient and depth specified in the drawings. This function can eliminate the need for skilled stakeout tasks and enable less-experienced workers to construct accurately without relying on intuition. It is also effective to display the acquired point cloud in AR on site so that client and contractor can share the completion image. Since LRTK’s AR display is based on absolute coordinates, once a virtual object is placed, it stays in the correct position without shifting even as the user walks around.

• Photo geotagging (geolocated photos): High-precision position information can be attached to photos taken with the smartphone camera. Using the LRTK app’s “geotagged photo” function, the photo’s shuttered image is saved with automatic tagging of the capture location’s latitude, longitude, elevation, and camera orientation. For example, when photographing cracks during bridge inspections, the photo file records exactly where and in which direction the photo was taken with centimeter precision (cm level accuracy (half-inch accuracy)). Information that used to be written as notes like “5 m east from control point XX” can be shared as position information that anyone can understand. This is a new digital recording method useful for later repair planning and time-series comparisons.

• Heatmap usage: The as-built heatmap mentioned earlier can be easily created on LRTK’s cloud. If you upload design 3D data (or design cross-section models), the acquired current point cloud is automatically overlaid, allowing confirmation of as-built management documents as colorized 3D data. You can inspect deviations between point cloud and design surfaces at arbitrary cross-sections, or generate cross-sectional drawings from point-cloud data and output them as CAD drawings. Heatmaps provide an intuitive grasp of site quality and are useful as as-built management report materials.

• CAD/GIS integration: Data acquired with LRTK can be exported in various formats for use with other CAD software and GIS systems. For example, point-cloud data can be output in LAS or PLY format for import into design software, and coordinate lists can be exported as CSV or DXF for inclusion in deliverables. In the LRTK cloud you can display design drawings as a background, visualize registered control-point coordinates on site with AR, and make the flow between site and design data seamless. With an eye toward future BIM/CIM and digital-twin deployment, LRTK’s flexibility in utilizing site data is another strength.

Real-world implementation cases and their effects

Sites that have already introduced LRTK report many effects such as reduced work time, reduced personnel, and improved visualization of operations. Here are some concrete examples.

At a road construction site, a single smartphone equipped with LRTK performed everything from control-point surveying to point-cloud scanning of the as-built area and on-site verification against the design model. Work that previously required several days—where a survey team set control points with a TS, a 3D laser scanner acquired point clouds, then data was taken back to the office for comparison with design data—was completed in just one day. Because the site supervisor could measure and confirm on the spot, there was no “waiting for results,” contributing significantly to schedule reduction and labor saving. Immediate as-built checks at the needed timing also helped prevent rework and ensured quality.

At another bridge repair site, LRTK’s AR function was used for excavations by heavy equipment. A 3D model of the planned excavation line was pre-imported into the app, and the virtual excavation guideline was displayed in AR on the smartphone during work. The operator simply followed that line with the excavator to achieve the design gradient and depth. This method allowed omission of physical benchmarks (stakes and strings) while maintaining accuracy, resulting in shorter construction time and reduced personnel. Visual guidance on the screen also enabled inexperienced operators to perform high-precision work without relying on veterans’ intuition.

Effects have also appeared outside of construction. In disaster response, after heavy rains caused landslides, staff immediately went to the damaged site and used LRTK-equipped smartphones to convert the collapsed terrain into point-cloud data and rapidly record damage. Traditionally, selecting control points and planning surveys took time, but with LRTK measurement could begin as soon as the team arrived—truly a “measure while moving” speed of data collection. The acquired point-cloud data was shared in real time to the cloud and immediately shared with headquarters and related agencies to support restoration planning. Even when communication infrastructure was cut off, some higher-end LRTK models can directly receive the centimeter-class augmentation service (CLAS signal) provided by Japan’s quasi-zenith satellite system (Michibiki), allowing RTK positioning to continue outside mobile coverage. These features enable emergency surveying and rapid situation assessment in isolated areas.

In infrastructure inspection, LRTK-equipped tablets have been used in regular inspections of bridges and tunnels to record crack locations as geotagged photos. Locations of deterioration, which were often ambiguous on paper drawings or ledgers, are now recorded with centimeter-level precision (cm level accuracy (half-inch accuracy)). As a result, comparisons at the next inspection are easier and repair planning accuracy has improved. This is a case in which data-driven maintenance promoted both safety and operational efficiency.

Across sites that have implemented LRTK, users perceive multifaceted benefits such as major reductions in time and cost, improved safety, and advanced quality control. Cost-wise, LRTK is substantially less expensive than traditional high-precision surveying equipment, making one-device-per-person deployment feasible. Some companies have begun equipping all site supervisors and foremen with LRTK devices for daily as-built checks and progress management. As everyone on site can acquire and share high-precision survey data in real time, the style of construction management itself is undergoing transformation.

Barriers to adoption and ease of introduction

When introducing new surveying technologies, concerns such as "will we be able to use it well?" and "will the investment pay off?" are common. However, for LRTK, the low barrier to adoption is also a major attraction that dispels such worries.

First, on cost: assembling a conventional RTK surveying set (high-precision GNSS receiver, radio, dedicated controller, etc.) used to require an investment of several million yen. LRTK simplifies dedicated equipment by leveraging smartphones, making the price orders of magnitude more affordable than conventional systems. This makes LRTK accessible even to small and medium-sized enterprises and provides high cost-effectiveness.

Next, ease of handling should not be overlooked. LRTK devices are robustly designed with dustproof, waterproof, and shock-resistant properties, making them less likely to break in harsh site environments. Yet they are lightweight and compact at only a few hundred grams, so carrying them to the site is not burdensome. The battery is built-in and can run continuously for a full day of site work. The antenna is integrated into the body, eliminating the need for wiring and assembly on site. The convenience of needing only a single smartphone greatly lowers the psychological barrier to introducing technology on site.

In terms of operability and learning cost, LRTK is also very accessible. The dedicated app UI is designed to be intuitive for non-surveying personnel, and many users report that they “got used to it immediately.” The steps are as described above and are completed in a few steps; complex settings are automated in the background so there is little to memorize. The manufacturer provides manuals and support, so any issues can be resolved quickly. In short, LRTK is designed so that anyone can master it with short training, making it easy to introduce even at sites without veteran surveyors.

LRTK also coexists and complements existing surveying workflows and equipment. For example, if you already use drone photogrammetry, you can combine large-scale terrain models from aerial surveys with ground point clouds obtained by LRTK for mutual accuracy verification, or use LRTK to complement areas under trees or beneath bridges that drones cannot capture well. For millimeter-level precision or minute displacement monitoring required in control point surveys, TS and other instruments still play a role, but for as-built management, daily terrain surveys, and quantity calculations where centimeter-level accuracy suffices, LRTK can improve efficiency. Because LRTK supports open data integration, it can be introduced gradually while leveraging existing assets. For these reasons, LRTK—“affordable,” “easy,” and “ready to use”—is likely to be accepted even by those previously reluctant to adopt new technologies, symbolizing the democratization of high-precision positioning. In construction sites facing severe labor shortages, it is undoubtedly a major tailwind.

Summary: recommending simple surveying with LRTK

LRTK, which makes RTK coordinate-tagged point-cloud measurement easy, is dramatically transforming as-built management and surveying work on construction and civil engineering sites. The revolutionary style of turning a smartphone directly into a high-precision surveying instrument can be said to symbolize on-site digital transformation (DX). The significance of lowering surveying and measurement tasks—previously outsourced to specialists—to a level that anyone on site can handle daily is great, and LRTK is expected as a next-generation site tool that directly contributes to strengthened quality control and improved productivity.

With LRTK, there is no need to pause work to wait for as-built confirmation or to perform dangerous manual measurements on steep slopes. The freedom to measure anytime, anywhere, and by one person dramatically accelerates the PDCA cycle on site. Fully utilizing 3D point-cloud data as a captured snapshot of the site also brings powerful visualization effects: early detection of previously unseen issues and smoother information sharing among stakeholders. In safety management and environmental measures, precise positional data supports rapid decision-making and contributes to building a safer, more secure construction environment.

Despite the many advantages of RTK point-cloud scanning, its true value is realized when used on site. We recommend trying it out even in a small area first. By proactively adopting new technology and not being bound by conventional norms, your site can evolve to the next stage. The smartphone-based surveying style that LRTK enables has the potential to become the new standard in future surveying work. Why not take this opportunity to experience the power of RTK coordinate-tagged point-cloud scanning? Construction management and surveying concepts will be transformed, and you will realize significant benefits in both operational efficiency and deliverable quality.

Finally, we supplement frequently asked questions about RTK surveying and LRTK in a Q&A format.

FAQ

Q. What is RTK surveying? How is it different from conventional GPS positioning? A. RTK surveying is a method that obtains centimeter-class high-precision positions by correcting errors in GNSS (such as GPS) positioning in real time. Standalone positioning typically yields errors of several meters, but RTK receives error information of satellite signals from a nearby reference station and performs correction calculations at the rover to reduce errors to a few centimeters. Traditionally it was necessary to set up your own reference station at each site, but the currently mainstream network RTK (VRS method) allows you to obtain nearby reference station data via the Internet, enabling high-precision positioning without placing a dedicated base station. In short, RTK surveying virtually creates the condition of having a reference point right next to you, providing much more precise positions in real time compared to conventional GPS positioning.

Q. Can someone without surveying expertise operate LRTK? A. Yes. LRTK is designed to be easy to operate so that non-surveying site personnel can use it. The app displays and buttons are straightforward, and complex settings and calculations are processed automatically in the background. Once you learn the basic steps, anyone with smartphone experience can handle it. Manufacturers also provide support and training materials, so questions can be resolved quickly. There are many reported cases in which construction management specialists and junior staff use LRTK for surveying and achieve satisfactory results.

Q. What is needed to introduce LRTK? A. Basically, you only need a smartphone and the LRTK receiver unit to get started. Recommended smartphones are iPhone or iPad Pro series equipped with LiDAR scanners; newer models have higher sensor performance and are advantageous in terms of accuracy (for example, iPhone 15 Pro). GNSS positioning is possible with Android devices, but smartphone LiDAR-based point-cloud scanning is currently mainly supported on high-end iOS models. In addition, subscribing to a correction information service is necessary for high-precision positioning. Contract services include the Geospatial Information Authority’s reference station network (GEONET), commercial VRS services (Ntrip), and carrier high-precision positioning services (e.g., NTT Docomo’s “Ichimiru”). Guidance or trial tickets for compatible correction services may be provided when purchasing an LRTK receiver. Initial setup is not difficult; once required information is entered, centimeter-level positioning is available immediately.

Q. What level of positioning and point-cloud accuracy can be obtained? A. Under good conditions, errors are generally within a few centimeters horizontally and vertically. RTK itself has a nominal accuracy of several centimeters, and LRTK has confirmed similar accuracy in field checks. The relative accuracy within the acquired point cloud depends on the smartphone’s LiDAR performance, but absolute coordinates reflect RTK accuracy, so the overall dataset is highly precise. For stricter verification, compare with known points or set control points on site to evaluate error tendencies. LRTK can achieve accuracy that meets the MLIT as-built control standards (grades) and is generally sufficient for typical civil engineering tasks. Note that satellite reception conditions can temporarily degrade accuracy, so for critical points it is recommended to observe multiple times to improve reliability.

Q. Can it be used in mountain areas or tunnels with no mobile reception? A. There are ways to use it in areas without mobile coverage. Some higher-end LRTK models or options support reception of the centimeter-class augmentation service (CLAS signal) provided by the domestic Michibiki quasi-zenith satellite. By swapping to a dedicated antenna, you can directly receive correction information from Michibiki satellites and continue RTK positioning even where mobile networks are unavailable. Therefore, under certain conditions, centimeter-level positioning is achievable in mountainous areas or tunnels without mobile coverage (though in completely indoor or deep underground locations satellite signals themselves may not reach). Having dual correction methods provides backup positioning in emergencies or communication outages.

Q. How are measured data shared and utilized? A. Data acquired with LRTK can be easily shared and utilized via cloud services. After a one-tap cloud sync from the app, the office PC can immediately view point clouds and photos, and you can show 3D data to external stakeholders by sending a URL link. A special viewer or high-performance PC is not required; you can intuitively rotate 3D views or measure distances in a browser. If you want to store and analyze data in-house, point-cloud data can be exported in LAS/PLY format and coordinate lists in CSV, for import into CAD software for comparison with design data or for producing report drawings. LRTK provides a rich environment for post-measurement data utilization—truly “measuring is just the beginning.”

Q. Will traditional surveying instruments and laser scanners become unnecessary? A. While LRTK can replace or complement conventional instruments in many scenarios, ideal practice is to use each tool appropriately. For control-point surveying requiring millimeter-level precision or monitoring minute displacements, high-precision TS and EDM instruments remain essential. LRTK is efficient and compact for as-built management, terrain surveying, and quantity calculations where centimeter accuracy suffices. For very large survey areas, drone aerial photography is suitable; LRTK complements drones by capturing under-tree areas or the undersides of structures. In practice, LRTK can greatly reduce the need for large equipment, allowing routine surveys to be centered on LRTK while using traditional instruments as needed. Tailoring tools to site needs is best; however, with LRTK enabling “anyone to measure immediately,” personnel and days previously dedicated to surveying can be drastically reduced, lowering dependence on conventional equipment.

Q. Can surveying really be completed by a single person? A. Yes, in most cases LRTK enables single-person surveying. Traditionally, a TS required an assistant to hold a prism, and transporting and setting heavy equipment involved multiple people. With a smartphone + LRTK, walking the site to acquire data and checking results on the smartphone screen can be completed by one person. Real-time position confirmation during measurement eliminates the need to coordinate with others for simultaneous tasks. In practice, after introducing LRTK some sites have switched to single-person survey patrols. However, safety rules remain: in hazardous areas always work with two or more people. LRTK maximizes personnel efficiency but does not replace safety measures. Compared to the past—when extra people and days were allocated solely for surveying—the ability to measure with the minimum necessary personnel when needed is highly significant.