The field changes with high-precision positioning! The secrets of cross-section creation enabled by LRTK

In recent years, centimeter-level high-precision positioning (half-inch level) technology has been dramatically changing civil engineering construction sites. Among these, the process of creating essential on-site cross-sectional drawings has been greatly streamlined and enhanced by the advent of LRTK. This article explains in detail the significance and roles of cross-section creation, the changes brought by high-precision positioning, the procedures and convenience of creating cross-sections using LRTK, the concrete operations for point-cloud scanning and section extraction and cloud processing, actual field use cases, applications to design comparison, inspection, and reporting through data sharing and AR utilization, and how promoting on-site DX helps eliminate dependence on individual skills and contributes to qualitative improvements in construction and inspection. Finally, we introduce the benefits you can gain by trying LRTK’s simple surveying function on site and provide tips for introduction.

Significance and role of cross-section creation

A cross-sectional drawing (cross-section) is a drawing that shows the shape of terrain or structures cut in the vertical direction. In the world of civil engineering and construction, cross-sections are widely used from the planning stage through construction and maintenance, and they play a very important role.

First, in the design stage, cross-sections are used to grasp longitudinal and cross-sectional shapes of terrain in plans for roads, bridges, and development sites. By understanding ground elevation differences and geological conditions from cross-sections, appropriate placement of structures, calculation of cut-and-fill volumes, and drainage planning become possible. Designers also use cross-sections to confirm the finished image and adjust design parameters such as slopes and thicknesses as needed.

Next, in the construction stage, cross-sections are used as instruction and inspection drawings to create the designated shapes on site. Construction personnel operate machinery based on the cross-sectional shapes shown in the design drawings (e.g., pavement thickness or slope of an embankment) to finish the soil and materials to the required heights and slopes. At this time, on-site transverse surveys are carried out as needed to measure the cross-sectional shape and confirm that the as-built shape matches the drawings. For example, in embankment works for levees, measurements verify whether the specified height and cross-sectional slope have been achieved; in roadworks, whether the pavement and gutter cross-sectional dimensions match the plan; and in buried pipe works, whether the burial depth and slope of pipes conform to instructions—these points are verified by on-site surveying. Cross-section creation is thus incorporated into site management as an inspection process to ensure construction quality.

Furthermore, in the maintenance stage, cross-sections are indispensable for assessing infrastructure soundness. For example, inspections of river levees and roadside slopes can compare cross-sections over time to determine whether repairs or reinforcement are necessary due to shape deformation or settlement from aging. Also, when records of cross-sections at the time of construction are available for buried objects, accurate burial positions and depths can be identified during later excavations, leading to safer and more efficient work.

The significance of cross-section creation lies in visualizing the site correctly at each stage—design, construction, and management—and supporting quality and safety. However, traditional methods of creating cross-sections involved much effort and challenges. In the next section, we look at the changes high-precision positioning technology brings while considering those challenges.

Changes brought by high-precision positioning (differences from total stations and leveling)

Traditionally, creating cross-sections on site mainly relied on manual surveying using total stations and optical levels. Experienced surveyors, often one or two people, had to measure heights and distances at key points of each cross-section from construction reference points and record them in paper field books. On large sites or complex terrain, the number of survey points could become enormous, and surveying and drafting each cross-section could take several days. Creating accurate cross-sections with limited personnel was a major burden for site managers. Also, because the number of points that could be measured manually is limited, if transverse surveys are conducted at fixed intervals there is a risk of overlooking terrain depressions or bulges between points. This could lead to failing to fully capture the actual shape and missing errors in the as-built shape. In addition, measurement results had to be manually transcribed and organized into drawings and reports, so preparing inspection materials involved a large amount of labor.

These problems were solved by high-precision positioning technologies using GNSS satellite positioning such as GPS. In particular, the spread of network RTK, which receives correction information over the internet and enables real-time centimeter-class positioning, has greatly changed on-site surveying. With a high-precision GNSS receiver (RTK rover) you can omit the setup equipment and post-processing formerly required and measure many points quickly by yourself. In places with a clear view of the sky, the device can start positioning within a few minutes after activation, and you can obtain successive 3D coordinates while walking with a single button operation. It has become realistic to cover areas that used to take half a day within 1–2 hours, achieving dramatic efficiency improvements. Because you don’t need to worry about establishing line-of-sight or setting targets, surveying can proceed nimbly even in areas with many obstacles. Also, since acquired data are immediately tagged with latitude, longitude, and elevation and saved electronically, there is no need to rely on paper field books, and the data can be directly used in CAD drawings or for preparing as-built inspection materials.

The benefits of high-precision positioning are not limited to labor savings. RTK-GNSS can stably provide height accuracy comparable to leveling (about ±2–3 cm (±0.8–1.2 in) in plan position, and about ±3–4 cm (±1.2–1.6 in) in elevation), ensuring sufficient accuracy for construction management. For example, if the allowable tolerance for as-built management is set at about ±5 cm (±2.0 in), it is desirable for the measuring instrument itself to have an accuracy of around ±1 cm (±0.4 in), and RTK can meet that requirement. Moreover, by dramatically increasing the number of measurement points, local excesses and deficiencies are less likely to be overlooked, potentially reducing variability in as-built quality. If many points are measured finely, differences from design lines can be checked in detail on cross-sections, improving the reliability of quality control. In this way, the introduction of high-precision positioning technology has enabled the combination of speed and accuracy in cross-section creation and has greatly improved the issues of traditional methods.

Procedures and convenience of creating cross-sections using LRTK

As a solution that revolutionizes on-site surveying, LRTK allows anyone to easily handle the high-precision positioning technologies described above on site. LRTK consists of a small RTK-GNSS receiver device that can be attached to a smartphone (e.g., iPhone) and a dedicated app, enabling positioning and measurement with accuracy comparable to traditional surveying equipment using only a pocket-sized device. So how do you create cross-sections using LRTK? Here are the basic steps.

• Survey preparation: Attach the LRTK device to your smartphone and launch the app. Connect to a network-type RTK correction service via the internet and configure the device to enable centimeter-level positioning (connection can be made with a single button). If necessary, localize the site’s coordinate system (such as plane rectangular coordinates) so that measured point data are handled in the same reference system as the design drawings.

• Field measurement: Measure the area you want to turn into cross-sections. There are two methods. (a) The continuous positioning mode, in which the surveyor moves along the section line and continuously records many points; and (b) the 3D scan mode, in which the smartphone’s built-in LiDAR sensor and camera are used to acquire point-cloud data of objects and terrain. The former quickly profiles the ground surface along the section centerline, while the latter scans the entire target area in detail and allows cross-sections to be extracted later at arbitrary positions. By choosing according to terrain and purpose, you can efficiently collect the necessary data. During measurement, acquired points are instantly plotted on the map with high-precision coordinate values and can be checked on the smartphone screen.

• Data saving and cloud sync: After measurement, the acquired positioning data (point clouds or point sets) are saved on the smartphone. With LRTK app’s sync function, data can be uploaded to a dedicated cloud platform (LRTK Cloud) with one tap. If there is no network, data are stored on the device and can be synced to the cloud later when connected. Centralizing data in the cloud enables real-time information sharing with colleagues in the office or design staff.

• Creating cross-sections: Perform cross-section creation processing on the cloud by using a web browser for the uploaded point-cloud or point data. It’s simple to use—just select the position where you want to view a cross-section from the map or 3D view on the screen. For example, you can specify two points and display a longitudinal profile (profile view) along that line. If point clouds have been obtained, the slice of the point cloud along the cross-section plane is rendered, reproducing the detailed actual cross-sectional shape of the ground and structures. Even if only measured points have been acquired, they can be interpolated to generate a smooth cross-section line. With the cross-section displayed, you can read elevation coordinates at arbitrary locations or measure differences from design values with a single click. Because these analysis functions are completed on the web without specialized CAD software or analysis tools, you can obtain the cross-section information needed on site immediately.

In this way, using LRTK makes the procedure for creating cross-sections extremely simple. With a small device and a single smartphone, surveying through drawing creation can be completed, and since no special equipment or advanced software skills are required, anyone can obtain accurate cross-sections in a short time. There is no need to take data back to the office for drafting as in traditional workflows, and the ability to immediately visualize and share on-site data speeds up construction decision-making and inspection planning.

Specific operations for point-cloud scanning and section extraction, and cloud processing

One major feature of LRTK is that it makes 3D point-cloud scanning easy. By combining the smartphone’s built-in LiDAR sensor with high-precision positioning, you can capture the site’s terrain and structures as detailed 3D data. For example, if you want to record the full shape of a slope or retaining wall surface, simply hold up the smartphone and move it slowly to acquire countless points (point cloud) that make up the surface with an accuracy of several centimeters (several inches). Each point is assigned accurate coordinates (X, Y, Z) by LRTK, so the entire scanned point cloud is immediately mapped to the real-world survey coordinate system. This greatly reduces the need for target setup and position-alignment post-processing that were previously required.

Cloud processing enables generation of high-precision point clouds that would be difficult to produce with the smartphone alone. The LRTK app also provides a photogrammetry shooting mode. When surveying wide areas or when a denser point cloud is needed, you can take multiple photos with a smartphone or drone and upload them to the cloud; the server then performs image analysis (SfM: Structure from Motion) to generate point-cloud data. Heavy computations are executed entirely in the cloud, so the field device is not burdened, and the user only needs to wait for the completed point cloud. The completed point cloud can be reviewed in the browser, and removal of unwanted points or integration of multiple data sets can also be handled in the cloud.

Extracting cross-sections from acquired point clouds is also intuitive. As mentioned above, in the LRTK Cloud viewer you specify two points as the section line and a sliced cross-section of the point cloud at that position is rendered. Point-cloud cross-sections reflect subtle irregularities of terrain and structures, enabling you to grasp details often missed on paper drawings. For example, slight bulges on part of a slope or the position of an exposed buried object within an excavation slope can be visually identified on a point-cloud section. If you upload design CAD data or BIM/CIM models to the cloud, you can overlay the point cloud with the design cross-section. Being able to compare measured values and the design section on the same screen makes it smooth to judge as-built conformity and identify areas that need rework.

Note that LRTK point-cloud scanning has a significant accuracy advantage over typical smartphone-only AR scans. While smartphone LiDAR is convenient, models could become distorted when scanning long distances due to accumulated positional error. LRTK continuously corrects the smartphone’s position by RTK positioning during scanning, so even when surveying a wide area at once, the shape distortion and positional offset are less likely to occur, maintaining high-precision point clouds. In this way, the fusion of point-cloud scanning and high-precision positioning enables anyone to easily generate precise 3D models on site and freely extract the necessary cross-sections.

Actual field use cases

High-precision cross-section creation using LRTK is powerful on all kinds of civil engineering and construction sites. Below are representative use scenarios.

• Slope (embankment face): In shaping slopes for roads and development sites, it is necessary to check whether the finished slope gradient matches the design. With LRTK, you can scan the slope surface to obtain a 3D model including fine undulations and check longitudinal and transverse sections at any location. Slope shapes that used to be partially grasped along a few survey lines can now be fully checked with point-cloud sections. Unevenness or local bulges become obvious on the cross-section, enabling early corrective action.

• Fill and excavation: In works such as dams, embankment construction, or roadbed works, as-built management is important to confirm whether soil has been built up to the prescribed cross-sectional shape. By measuring the post-construction fill cross-sections with LRTK, you can instantly determine whether each section matches design height and width. Based on point clouds you can calculate cross-sectional areas and compare them with design areas to check for missing fill—advanced analyses like this can be performed on site. Even for wide-area fills, one person can quickly obtain multiple cross-sections, dramatically improving as-built inspection efficiency for large-scale projects.

• Buried pipelines: In buried works such as water and sewer pipes or cable conduits, measurements are taken during trenching through backfilling to confirm appropriate slope and burial depth. Using LRTK, you can quickly measure the conduit positions inside open trenches and record them as cross-sections. For example, you can verify on site whether the cover depth over the pipe crown meets specifications and whether the pipe slope remains constant as designed. Scanning ground cross-sections before and after burial allows accurate understanding of burial depth and position in later excavation work, reducing the risk of third-party damage.

• Structures: Cross-sections are also effective for shape control of various structures such as bridge abutments and piers, retaining walls, box culverts, and tunnels. Scanning completed structures with LRTK lets you verify verticality of concrete walls or accuracy of arch shapes via cross-sections. For example, by measuring the tunnel inner surface as a point cloud and comparing it with the design shape, you can immediately determine whether the specified internal cross-section is secured. For aging surveys, periodically obtaining point-cloud sections of structures allows quantitative capture of deflection and displacement progression. Small changes that are difficult to record on paper are not missed with digital cross-sections.

• Exterior and site development: LRTK cross-sections are useful for exterior works around buildings and finishing inspections of development sites. Vertical gradients for parking lots and sidewalks, drainage slopes within residential lots, and elevation relationships across development sites can be measured across wide areas in a short time and compiled into cross-sections for evaluation. For example, you can quickly verify on site whether the development level within a lot is uniformly as designed and whether rainwater will not pond due to inadequate slope. Complex exterior shapes can be sectioned in any direction from point-cloud data, allowing precise checks where needed and early detection of construction errors.

Applications to design comparison, inspection, and reporting using data sharing and AR

The LRTK cloud platform and AR functions further promote sharing and utilization of acquired cross-section data. Survey data uploaded to the cloud can be viewed by all stakeholders via the internet. Designers and clients can check the latest point clouds and cross-sections from their office PCs without visiting the site. This greatly shortens the time lag of “measure on site, take data back, draft drawings, and report,” and smooths communication between the site and designers/supervisors. For example, if cross-sectional discrepancies are discovered during construction, the deviations from the design can be immediately shared on the cloud and corrective measures discussed promptly.

Also, with LRTK’s AR (augmented reality) function, you can intuitively overlay design data and on-site measured data. By compositing the design model or reference lines into the site view on a smartphone or tablet screen, you can confirm the finished image on the spot and use it for as-built comparisons and verification. For instance, AR-display of the planned structure model over the site point-cloud scan allows you to check before construction whether it will fit as designed or if there will be interferences. For cross-sections, projecting the design standard section line onto the ground with AR and comparing it to the current terrain lets you grasp cut-and-fill volumes on the spot. Visualizing design vs. existing differences—previously only compared numerically on drawings—is a major advantage.

Acquired cross-section data is also directly useful for creating inspection reports. You can print automatically generated cross-sections from point clouds or measured points for as-built inspection materials, or export measurement lists per section to CSV for inspection forms. The Ministry of Land, Infrastructure, Transport and Tourism has been formulating guidelines for as-built management using 3D measurement technology, and digital data-based as-built management is being recommended. Detailed cross-section data obtained with LRTK is far more objective and reproducible than traditional hand-measured records and serves as persuasive evidence to clients. When communicating with inspectors, viewing shared cross-sections in the cloud while explaining reduces misunderstandings and facilitates smooth approval. In this way, data sharing and AR/3D utilization maximize the impact of cross-section creation on site improvement.

Eliminating dependence on individuals and improving quality by promoting on-site DX

Cross-section creation using high-precision positioning and digital technology does more than simply improve work efficiency; it strongly supports DX (digital transformation) of construction sites. Traditionally, surveying and as-built management know-how tended to depend on experienced individuals, leading to so-called “dependence on specific people.” Equipment that only veterans could operate and complicated drawing creation were bottlenecks, and in some cases sites could not function due to labor shortages. By introducing intuitive surveying tools like LRTK, site measurement tasks are standardized and simplified, enabling operations that do not rely on specific individuals. Even newcomers can obtain high-accuracy cross-section data with intuitive smartphone operations, so teams can advance quality control without relying on veterans’ tacit knowledge. Because data are accumulated and shared in the cloud, judgments across the site are based on objective data rather than individual “experience-based intuition.” Digitizing and visualizing know-how also smooths knowledge transfer.

Promoting this DX is expected to qualitatively improve construction and inspection work. With detailed cross-section information available in real time, construction managers can check quality during work and immediately correct issues if found. Variability and omissions in as-built data are reduced, minimizing risks of rework and missed defects. At inspection stages, areas that were previously judged by planar records or partial spot checks can now be reliably evaluated based on 3D data, dramatically improving inspection accuracy. The labor saved can be redirected to other quality-improvement activities. Safety benefits are also notable: because surveying can be done with fewer people and in less time, entry into hazardous areas and prolonged roadside work are reduced, lowering worker risk. AR-enabled remote staking and measurement reduce the need for people to measure directly, benefiting both safety and productivity. Thus, LRTK’s cross-section creation solution that contributes to on-site DX helps address labor shortages and skill succession issues while elevating construction and inspection quality to a higher level.

Try LRTK’s simple surveying function on site

The best way to experience the benefits of high-precision positioning on site is to actually use it. LRTK provides an easy surveying mode designed for first-time users, allowing basic surveying and point-cloud measurement without complicated settings or expert knowledge. With only a smartphone and a small device, your usual site becomes a measurement field. For example, by experimentally scanning part of a slope and creating a cross-section, you will likely be surprised at the speed and accuracy that conventional methods could not achieve.

Why not bring the next-generation surveying experience to your site with LRTK’s simple surveying function? Even a small pilot application can produce changes in work efficiency and quality-check processes. Once you feel its effects firsthand, the rationale for full introduction of LRTK as a first step toward on-site DX will become clear. Please try the innovation in cross-section creation enabled by high-precision positioning at your company’s sites.