LRTK Makes It Possible! One-Click Output of DXF Cross-Sections from Drone Point Clouds

Table of Contents

• Introduction

• Basics of Drone Point Clouds and Cross-Sections

• Importance of Point Cloud Cross-Sections

• Traditional Methods for Creating Cross-Sections and Their Challenges

• What is LRTK?

• One-Click Cross-Section Output with LRTK

• Recommendations for Simple Surveying with LRTK

• FAQ

Introduction

Have you ever wanted to output the necessary cross-sections in DXF format from point cloud data acquired by a drone? In recent years, three-dimensional point cloud measurement technology has become more accessible, and anyone can obtain high-density terrain data over large areas using drones. However, do you think creating the necessary cross-sections from that enormous amount of point cloud data and exporting them as DXF files — a common CAD format — is a specialized and difficult task? In fact, with the latest tools, exporting point cloud cross-sections to DXF is surprisingly simple while maintaining high accuracy. This article explains how to create cross-sections from point cloud data acquired by drones and other means and export them in DXF format, comparing traditional methods and showcasing applications of the latest technologies.

Basics of Drone Point Clouds and Cross-Sections

First, let’s organize the basics of “point cloud data” and “cross-sections.” Point cloud data is a collection of many points acquired by laser scanners or photogrammetry. Each point contains three-dimensional coordinates (X, Y, Z) and color information, and the aggregation of points represents the shape of the object in three dimensions. Examples include point clouds obtained by scanning the interior of a building with lasers or terrain point clouds generated from photos taken by a drone. Recently, it has become possible to easily acquire surrounding point clouds using LiDAR built into smartphones.

On the other hand, a cross-section is a drawing that shows the internal profile of terrain or structures when they are vertically cut by a plane. In civil engineering, cross-sections of roads and longitudinal profiles of river embankments are widely used, and in architecture, building cross-sections are commonly used for design and construction. Creating cross-sections from point cloud data allows you to accurately convert the actual on-site shape into a 2D drawing, which is useful for comparing with design drawings and verifying as-built conditions.

Also, the DXF format (Drawing Exchange Format) is a standard drawing data exchange format supported by many CAD programs. If you output cross-sections as DXF files, the line data can be imported into various CAD and surveying software for use. In other words, DXF output serves as a bridge from “3D data from point clouds” to “2D drawing data that anyone can handle.”

Importance of Point Cloud Cross-Sections

Cross-sections are extremely important on construction and civil engineering sites for understanding and verifying the shapes of completed terrain and structures. For example, in road construction, cross-sections showing the finished road surface elevation and cross slope are required, and in river or dam works, longitudinal profiles showing the internal structure of embankments and revetments are needed. Cross-sections are fundamental documents for comparing the design alignment with field-measured actual alignments to verify whether the construction results match the design. Furthermore, cross-sections can be used to calculate earthwork volumes (cut and fill) and evaluate structural stability, making them indispensable for quality control and as-built verification.

Traditionally, obtaining such cross-sections required surveyors to perform direct measurements on-site to collect data. However, methods for acquiring three-dimensional point cloud data, such as aerial photogrammetry with drones, ground-based 3D scanners, and smartphone LiDAR measurements, have become widespread. Using these point cloud data, you can digitally record an entire site and later extract sections at arbitrary positions. Because point clouds include all information down to subtle surface undulations of the ground and structures, the extracted cross-sections faithfully reflect fine terrain changes. For these reasons, creating cross-sections from point cloud measurements, which can efficiently and comprehensively capture site shapes, is attracting attention today.

Traditional Methods for Creating Cross-Sections and Their Challenges

Traditional methods for creating cross-sections mainly involved manual field surveying and hand-drafting. Typically, a surveyor would use instruments such as a total station (TS) or level to measure points at regular intervals along the line where a cross-section is to be taken, and then produce CAD drawings in the office based on those elevation data. This approach had several challenges.

• Increased labor and time burden: Measuring a single cross-section typically requires at least two people (one to operate equipment and one to place staff), and for long cross-section surveys crews must move tripods and equipment, making the work very time-consuming. On large sites, cross-section surveys alone can take several days to several weeks.

• Dangerous work: Surveying on steep slopes or riverbanks requires workers to enter hazardous areas, increasing safety risks. Surveying in poor footing conditions can bring the risk of falls and other occupational accidents.

• Limits in accuracy and comprehensiveness: Manual surveying can only capture points at intervals of a few meters, so fine undulations between measured points may be missed. Because drawings are created from limited points, small field details may not be fully reflected in the cross-section. Also, general handheld GPS devices often have errors of about 5–10 m (16.4–32.8 ft), which is too large for elevation checks, so high-precision TS surveying was indispensable.

• Laborious drafting: The process of noting the values obtained in the field, returning to the office, and manually entering them into CAD software to draw lines is cumbersome and prone to errors. When creating multiple cross-sections, the same work must be repeated, requiring significant effort even from experienced technicians.

• Equipment cost issues: Obtaining higher-precision and more detailed cross-sections sometimes requires expensive 3D laser scanners or outsourcing to specialized contractors, which can be financially difficult for small to medium-sized sites.

As described above, traditional cross-section creation was time-consuming and labor-intensive and had issues with safety and accuracy. The need to “create cross-sections more efficiently and accurately” has existed for some time, but a decisive solution has been hard to find until now.

What is LRTK?

One solution to these challenges is LRTK, which combines a smartphone with a high-precision GNSS. LRTK is a surveying system that makes centimeter-level (half-inch accuracy) positioning possible anywhere by attaching a palm-sized RTK-GNSS receiver (GNSS refers to satellite-based positioning systems) to a smartphone or tablet. Because it links with the smartphone’s camera and LiDAR functions on a dedicated app, it can simultaneously capture not only position information but also surrounding 3D point cloud data, achieving a level of efficiency and convenience that was difficult with conventional surveying instruments.

One-Click Cross-Section Output with LRTK

So how can you create cross-sections from point clouds and generate DXF files using LRTK? Processes that used to require many steps can be completed in just a few steps with LRTK. Let’s look at the specific flow.

• Field data acquisition: Attach the LRTK receiver to a smartphone and simply walk around the site to scan and obtain high-density 3D point cloud data. As you move while taking photos with the smartphone camera, the terrain and structures are recorded as a collection of countless points (a point cloud). Because each point is assigned an accurate coordinate by LRTK’s high-precision GNSS, the overall point cloud precisely matches real-world positions.

• Automatic cloud processing: After measurement, the data is uploaded in real time to the LRTK cloud, where unnecessary points are automatically removed, alignment and coloring are applied, and other processing is performed. Without special high-performance PCs or complex software, a 3D model of the entire site can be generated in just a few minutes. If you are out of internet range, you can synchronize later, and you can review the data from an office PC via a browser.

• Section extraction: You can set cross-sections at arbitrary positions in the cloud-based 3D viewer. By clicking two points on the point cloud model on the screen to specify “I want to view the section here,” a cross-section along that line is automatically generated. You can extract sections at any angle and position, such as a slope cut vertically or a cross-section perpendicular to a road. Fine undulations that were easily missed with traditional methods are accurately depicted in sections derived from point clouds.

• Output as DXF data: The extracted cross-sections can not only be viewed on screen but also downloaded as DXF CAD data with one click. Since DXF is a standard format compatible with almost all CAD software, the output files can be immediately incorporated into design drawings and reports. Export to PDF or image formats is also supported for saving print-ready drawings.

Using LRTK in this way allows you to create high-precision cross-sections from point clouds acquired on site in a short time. Cross-section creation that used to take days to weeks can be completed on-site from surveying to drafting with LRTK, dramatically shortening lead times.

Recommendations for Simple Surveying with LRTK

Finally, here is an introduction to a new approach to “simple surveying on site” that you should know about in addition to creating cross-sections from point clouds. Traditionally, when checking a small dimension or elevation on-site, simple tools like tape measures or handheld GPS devices were often used, and one had to accept limited accuracy. Today, however, the solution called LRTK makes it possible to dramatically improve accuracy while maintaining ease of use.

LRTK is a state-of-the-art surveying tool that combines an ultra-compact high-precision GNSS receiver attachable to a smartphone with the smartphone’s built-in camera and LiDAR. Without special heavy machinery or large scanners, centimeter-level (half-inch accuracy) positioning and point cloud measurement can be performed with just a smartphone, greatly streamlining on-site simple surveying. For example, rather than laser-scanning a vast area to create a cross-section, you can use LRTK to directly measure the elevation or width at necessary points on-site and grasp the cross-section profile on the spot.

By introducing LRTK to the site, some tasks that previously required specialized survey departments or outsourcing can be carried out quickly by on-site staff themselves. Checks of cross-sectional shapes and elevations can be performed immediately without waiting for the survey team, smoothing construction progress management. Even in situations requiring high accuracy, LRTK can be trusted for simple surveying.

As high-precision positioning becomes easy for everyone to utilize, the “democratization of surveying” advances, including acquiring point cloud data and creating cross-sections. LRTK, which even beginners without専門知識 can handle, is truly a “surveying tool that fits in your pocket.” Combined with the digital data utilization skills cultivated through converting point clouds into drawings, try taking on the next-generation smart surveying. LRTK will be a reliable partner that strongly supports your site’s DX (digital transformation).

FAQ

Q: What is a point cloud cross-section? A: A point cloud cross-section is a two-dimensional drawing created by extracting a specific section (a slice by a plane cut vertically) from three-dimensional point cloud data. It is easy to understand if you think of it as cross-section drawings — transverse or longitudinal profiles — of terrain or structures created based on point cloud data.

Q: What is the DXF format? A: DXF is one of the standard file formats for CAD data, designed for exchanging drawing data between different software. Because of its high compatibility, it is widely used, and exporting cross-sections created from point clouds in DXF allows them to be imported and used directly in many CAD programs.

Q: Do I need expensive software to create cross-sections from point clouds? A: Not necessarily. You do not always need to purchase costly specialized software. Open-source point cloud processing software and some freeware can perform section extraction and DXF output. Recently, cloud services that process point cloud data and automatically generate cross-sections have also appeared. Paid professional software offers advanced features, but for beginners who need basic cross-sections, free tools are often sufficient.

Q: Can I obtain point cloud data without a laser scanner? A: Yes, you can acquire point cloud data without a laser scanner. A typical method is photogrammetry, which generates point clouds by analyzing many photos taken with a digital camera or drone using specialized software. Some smartphones now include LiDAR scanners, and apps can be used to easily scan the surroundings. Additionally, smartphone-linked surveying tools like LRTK make it easy to perform high-precision point cloud measurements yourself.

Q: Can an ordinary PC process cross-sections from large point cloud datasets? A: Point cloud datasets tend to be large because they contain vast numbers of points, but with some techniques you can extract sections on a general-purpose PC. The key is to handle only the necessary area. Trying to process an enormous point cloud all at once makes you need a high-performance machine, but the portion used for cross-sections is only a small part of the whole dataset. By loading only the point cloud near the target section in the software or thinning the data to reduce volume, a standard-spec PC can run smoothly. Using cloud services to process point clouds on servers and downloading only the resulting section data is also effective.

Q: Does operating LRTK require specialized knowledge? A: No, LRTK is designed to be easy to use even for those without surveying expertise. Attach the device to your smartphone and follow the on-screen instructions to perform precise measurements. Your current position and accuracy are displayed clearly in the app, so you don’t need to be concerned with complicated settings. With a short training session, anyone can perform centimeter-level (half-inch accuracy) point cloud measurements.

Q: Can I really create cross-sections all by myself? A: Yes. With LRTK, one person can perform on-site measurements and output cross-sections in DXF. Survey tasks that used to require multiple people can be completed simply by walking around the site with a smartphone. Because the acquired data is processed automatically in the cloud, drafting work after returning to the office is greatly reduced.

Q: Can LRTK be used at offline sites? A: LRTK primarily works in conjunction with the cloud for data processing, but it can be used without internet connection. For sites outside coverage, a local mode is available that performs point cloud processing on the smartphone itself, and data can be synchronized to the cloud later when connected. This enables reliable surveying even in mountainous areas or underground spaces where radio conditions are poor.

Q: Can cross-sections be exported in formats other than DXF? A: Yes. In addition to DXF, you can export in various formats such as CSV (coordinate data), PDF, and PNG images to suit your needs. For example, use CSV when you want numerical data for analysis, or save as PDF or images for distribution as paper drawings. However, if you want to edit or utilize the data for design in CAD, DXF export is the most convenient.

Q: How can I learn more about LRTK? A: The LRTK official site publishes detailed product specifications, case studies, and the latest update information. The LRTK series is also compatible with i-Construction promoted by the Ministry of Land, Infrastructure, Transport and Tourism and is an ideal solution for the construction industry’s DX (digitalization). If you are interested, please visit the [LRTK official site](https://lefixea.com). If you have any questions, feel free to contact us via the inquiry form. Why not update your site to the next stage by leveraging LRTK?