Innovative Cross-Section Measurement! High-Precision 3D Workflow Realized with LRTK and DXF

Table of Contents

• Introduction

• The Importance of Cross-Section Drawings

• Traditional Methods for Creating Cross-Sections and Their Challenges

• What is LRTK?

• Workflow for Creating Cross-Sections with LRTK

• Features and Benefits of LRTK

• Field Use Cases

• Conclusion

• Frequently Asked Questions

Introduction

In recent years, the emergence of 3D point cloud measurement technologies and high-precision positioning tools using smartphones has made it possible for anyone to easily acquire high-density 3D data. However, do you find it difficult to create the required cross-section drawings from that massive point cloud data and output them as DXF files that can be used in design drawings or CAD software? In fact, using the latest tools, extracting cross-sections from point clouds and exporting them in DXF format is surprisingly easy while maintaining high accuracy. This article explains how to realize a high-precision 3D workflow for creating cross-sections from point cloud data and exporting them in DXF format, comparing traditional methods and presenting examples of using the latest technologies. This is truly the innovation in cross-section measurement made possible by LRTK and DXF.

The Importance of Cross-Section Drawings

On construction and civil engineering sites, cross-section drawings are frequently created to verify the shape of completed terrain and structures. For example, in road construction, transverse cross-sections are required to show the finished road surface elevation and cross slope, and in rivers and dams, longitudinal sections are needed to record the internal shapes of embankments and revetments. Cross-section drawings are important documents for verifying whether construction was carried out according to the design by comparing the planned alignment at the design stage with the as-built alignment measured on site. Furthermore, cross-sections can be used to calculate earthwork volumes and evaluate structural stability, making them indispensable for construction quality control and proof of as-built condition.

Traditionally, obtaining such cross-sections required surveying staff to measure directly on site to collect data. However, with the spread of 3D point cloud scanning technology, it is now possible to digitally record a site in detail and afterwards cut cross-sections at arbitrary positions. Because point cloud data includes even the subtle undulations of the ground and structures, the extracted cross-sections faithfully reflect fine terrain changes. For this reason, creating cross-sections from point cloud scans, which can efficiently and comprehensively capture site geometry, is attracting attention now.

Traditional Methods for Creating Cross-Sections and Their Challenges

• Heavy manpower and time burden: Measuring a single cross-section required at least two people (a surveyor operating the instrument and an assistant), and for long-distance transverse surveys the work was very time-consuming because tripods and equipment had to be moved along the route. On large sites, cross-section surveying alone could take several days to several weeks.

• Dangerous working environments: Surveying on steep slopes or riverbanks often required entering hazardous areas, posing significant safety risks. Surveying in poor footing conditions carried the risk of falls and other occupational accidents.

• Limits in accuracy and coverage: Manual surveying could only obtain points at intervals of a few meters, possibly overlooking fine undulations between measurement points. Since drawings were made from only a few points, it was sometimes difficult for the cross-section line to fully reflect the reality of the site. In addition, general handheld GPS devices can have errors of 5–10 m, so they cannot be used to confirm accurate elevations; high-precision total station (TS) surveying was required.

• Time-consuming drafting: Writing down measured point values on site and then returning to the office to manually enter them into CAD software to draw lines was extremely tedious and a source of errors. Creating multiple cross-sections required repeating the same steps, consuming enormous effort even for experienced staff.

• Equipment and cost issues: To obtain higher-precision and more detailed cross-sections, it was necessary to introduce expensive 3D laser scanners or outsource to specialist contractors, which was often difficult on budget-constrained small to medium sites.

As shown above, traditional cross-section creation was time-consuming and labor-intensive and posed challenges in safety and accuracy. Although there has long been a need to create cross-sections more efficiently and accurately, a definitive solution did not emerge for a long time.

What is LRTK?

One solution to these challenges is LRTK, which combines a smartphone with high-precision GNSS. LRTK is a modern surveying system that makes centimeter-level positioning possible anywhere by attaching a palm-sized RTK-GNSS receiver to a smartphone or tablet. Developed by Refixia Inc., a venture from Tokyo Institute of Technology, this device enables high-precision surveying that previously required stationary instruments or specialized knowledge to be performed by a single person with just a smartphone. It is truly a revolutionary tool in the world of surveying.

LRTK supports the Real-Time Kinematic (RTK) method and, by using correction information provided by the Geospatial Information Authority of Japan (such as CLAS and the Continuously Operating Reference Station network), reduces the positioning error that was several meters with GPS alone to a few centimeters or less (a few cm or less). This gives the acquired point cloud data and measured points absolute coordinates aligned with the public coordinate system, allowing field measurements to be overlaid directly onto design drawings and maps. Operation is also intuitive: users simply press a button while checking their current position and accuracy on the smartphone screen to perform measurements. The ease of use means even beginners without special training can perform high-precision surveying and point cloud acquisition, which is a major advantage.

Workflow for Creating Cross-Sections with LRTK

With LRTK, the process of creating cross-sections from point clouds and exporting them in DXF format can be completed in just a few steps. The specific workflow is as follows:

• Point cloud data acquisition: By attaching an LRTK unit to a smartphone and walking around the site to scan, you can acquire high-density 3D point cloud data. As you move while the smartphone camera captures the surroundings, visible terrain and structures are recorded as a collection of countless points (a point cloud). Because LRTK GNSS assigns geographic coordinates to each point, the entire acquired point cloud exactly matches its real-world position.

• Automatic cloud processing: Once measurement is complete, the acquired data is uploaded in real time to LRTK’s cloud service (if there is no network at the site, data can be synchronized later). On the cloud, unnecessary points are removed, positions are corrected, and coloring is applied automatically, generating a 3D model of the entire site within minutes. The convenience of being able to view and manipulate point cloud data in a browser without needing a dedicated high-performance PC or special software is also attractive.

• Extracting cross-sections: In the cloud viewer, you can set cross-sections at arbitrary positions. By specifying two points on the point cloud model to indicate the line where you want a cross-section, a cross-section along that line is automatically generated. You can cut vertically through slopes for longitudinal sections or extract transverse sections perpendicular to roads—cross-sections can be taken at any angle and position. Fine undulations that would have been missed by traditional manual surveying are accurately represented in cross-sections derived from point clouds.

• Output in DXF format: The extracted cross-sections can not only be viewed on the screen but also downloaded as DXF CAD files with a single click. DXF is a standard format compatible with almost all CAD software, so the output files can be immediately incorporated into design drawings or attached to as-built documentation. Export to PDF or image formats is also supported, allowing saving of printable drawing data.

As described above, using LRTK enables the rapid creation of high-precision cross-sections from point cloud data obtained on site. Tasks that once took days can be completed on-site from surveying to drafting with LRTK, dramatically shortening lead times.

Features and Benefits of LRTK

LRTK offers many benefits beyond cross-section creation, across surveying and construction management. Below are the main features of LRTK compared with traditional methods.

• Ease of use with a smartphone: By simply attaching a small LRTK receiver to a smartphone or tablet, there is no need to carry large dedicated equipment. Intuitive app-based operation eliminates the need to transport heavy tripods or stationary laser scanners to the site. The compactness of the equipment, which fits in one hand, allows measurements to be started immediately when needed, which is a major advantage for fieldwork.

• Single-person operation: Survey tasks that used to require multiple people can be completed by one person with LRTK. By walking the site with a smartphone, one person can handle everything from terrain data acquisition to cross-section creation, reducing personnel coordination and costs. This enables rapid response even on sites with labor shortages and increases flexibility in work planning.

• Centimeter-level high accuracy: RTK-GNSS technology reduces positioning error to around a few centimeters (cm level accuracy (half-inch accuracy)). Because positional information can be obtained with smartphone-level convenience yet exceptional precision, elevations and distances reflected in cross-sections are highly reliable. Details that could not be captured by traditional manual surveying can be measured precisely, producing data that aligns closely with design drawings.

• Cloud integration and sharing: Point cloud data acquired on site is immediately synchronized to the cloud for secure storage and analysis. Data can be viewed from office PCs via a browser, and it is easy to share real-time status with stakeholders in remote locations. Since 3D point clouds can be manipulated without installing dedicated software, anyone can intuitively grasp the latest field information.

• AR visualization: Positioning-enabled point clouds and CAD drawings acquired with LRTK can be overlaid on the actual site using a smartphone's AR (augmented reality) functionality. For example, displaying a design-model structure on the finished terrain via AR allows on-the-spot confirmation of the final appearance. It is also possible to project previously scanned point cloud models of underground utilities in AR to visualize buried locations during later excavation work. With LRTK’s high-precision positioning, AR displays do not suffer misalignment between reality and virtual objects.

From the above features, LRTK can be described as an all-purpose surveying tool that enables “anyone, anywhere, with high precision” surveying and cross-section creation. Tasks that once depended on skilled technicians and extensive effort can be both simplified and upgraded by leveraging LRTK.

Field Use Cases

High-precision cross-section creation with LRTK is powerful in a variety of field scenarios. Below are representative use cases.

• Slope shape measurement and as-built inspection: For steep slope works, cross-sections are used to check finished slopes and quantities of cut and fill. Using LRTK, you can scan an entire slope from the ground without climbing dangerous heights, and even slopes with heights reaching several tens of meters (several tens of ft) can be measured in just a few minutes to obtain detailed point cloud data. You can extract transverse cross-sections at arbitrary positions and compare them with design sections, enabling early detection of improper fill or cut and helping prepare quality reports.

• Quality control of finished terrain: For infrastructure works such as rivers and roads, it is necessary to check as-built conditions with cross-sections and longitudinal/transverse profiles. By point-cloud-scanning finished revetments or roads with LRTK and overlaying the obtained cross-sections on design drawings, construction accuracy can be confirmed at a glance. Regular scanning during construction allows quantitative progress monitoring while performing quality control.

• Recording and visualization of buried utilities: For buried pipelines such as water, sewer, and gas, it is often difficult to know precise pipe locations after backfilling. LRTK can scan inside an open trench during excavation and digitally record the installed pipes. Even after backfilling, the acquired 3D data can be projected on the ground via AR to accurately visualize the buried pipe locations.

• Earthwork volume management for filling and excavation: For road construction, land development, and similar sites, accurate calculation of fill and excavation volumes is required. By point-cloud-scanning the terrain before and after filling and automatically calculating volumes from the differences, earthwork management that was previously done by hand is greatly streamlined. Creating arbitrary cross-sections and comparing as-built fill cross-sections with design plans makes it obvious where material is lacking or excessive. This information helps decisions on additional soil transport or disposal of surplus material, supporting both cost control and quality management.

By introducing LRTK to the field, measurement and drafting tasks that were previously difficult become dramatically more efficient. The ability to quickly output cross-sections from point cloud data as DXF provides a rapid means of obtaining drawing data that can be submitted as construction deliverables, and its application is expanding across various fields.

Conclusion

What once required skilled technicians and tremendous effort to create cross-sections can now be performed easily by anyone with the advent of LRTK. The ability to create cross-sections via point cloud scanning and output DXF data significantly advances the digital transformation (DX) of measurement tasks such as construction management and surveying. As exemplified by the Ministry of Land, Infrastructure, Transport and Tourism’s promotion of i-Construction, the importance of 3D measurement and digital as-built management is increasing, and efficient measurement methods that leverage the latest technologies are attracting attention across the construction industry. Being able to instantly convert detailed cross-section data obtained on site into drawings shortens lead times from quality checks to report preparation, directly improving productivity and accuracy.

LRTK is a platform that meets a wide range of simple surveying needs—not only cross-sections but also terrain surveying, as-built management, and AR-based site visualization. With just a smartphone, you can record the “now” of your site with high precision and quickly output the necessary drawings and data, enabling internalization of tasks that used to be outsourced and reducing costs. Why not bring efficiency and the wave of DX to your site with smart surveying using the latest technologies?

Frequently Asked Questions

Q1: What is a point cloud cross-section? A1: A point cloud cross-section is a 2D drawing created by extracting a specific section (a vertical cut) from 3D point cloud data. It is helpful to think of it as a transverse or longitudinal section that shows the internal shape of terrain or structures, generated from point cloud data.

Q2: What is the DXF format? A2: DXF is one of the standard file formats for CAD data and is compatible with a variety of design software. It is widely used when exchanging design data with other software or stakeholders; if you output a cross-section created from point clouds in DXF, it can be imported directly into many CAD programs for use.

Q3: Do I need specialized knowledge to operate LRTK? A3: No. LRTK is designed to be easy to use even for beginners without surveying expertise. You attach the device to a smartphone and follow the app instructions to perform measurements. The screen clearly displays current position and accuracy, so you do not need to worry about complicated settings. With a short training session, anyone can perform high-precision point cloud measurements.

Q4: Can I really create cross-sections alone? A4: Yes. With LRTK, one person can perform field measurements and output DXF cross-sections. Tasks that previously required multiple people can be completed simply by walking the site with a smartphone. Because the acquired data is automatically processed in the cloud, office-side manual work is also greatly reduced.

Q5: Can it be used in offline environments? A5: LRTK primarily uses cloud integration for data processing, but it can also be used where there is no internet connection. For sites outside network coverage, a local mode is available that allows point cloud processing on the smartphone itself and synchronization to the cloud later when a connection is available. This allows surveying in remote mountainous areas or underground spaces with poor connectivity.

Q6: Can I export formats other than DXF? A6: Yes. In addition to DXF, you can export in various formats such as CSV (coordinate lists), PDF, and PNG images depending on your needs. For example, use CSV for numerical data analysis and PDF or images for printing and distribution. However, if you intend to edit or use the data in CAD for design, DXF is the most convenient output format.

Q7: How can I learn more about LRTK? A7: The official LRTK website contains detailed product specifications, case studies, and the latest updates. If you are interested, please check the official website. If you have any questions, feel free to contact them via the inquiry form.