How to Speed Up Slope Surveying: Reduce Work Time with Smartphone Point Cloud Measurement

Slope surveying (norimen sokuryō) is an indispensable task for accurately understanding the shape of slopes along roads, development sites, and other areas. However, traditional methods require significant time and manpower for setting up surveying instruments and taking readings at each cross section, placing a heavy burden on site operations. Recently, leveraging point cloud measurement with smartphones has attracted attention for dramatically shortening the time required for slope surveying. This article organizes the necessity of slope surveying, the steps of conventional methods, and the causes of prolonged work time, then explains in detail the mechanism and benefits of [smartphone-based point cloud surveying](https://www.lrtk.lefixea.com/blog-js/p7). It also introduces the workflow from field measurement to cloud sharing and data output, and various uses of slope data, and finally touches on the advantages of adopting the latest smartphone point cloud measurement technology (LRTK).

The Need for Slope Surveying and Conventional Workflows

Slope surveying is conducted in various scenarios in civil engineering, such as investigations of slopes at risk of failure and verification of slope formations beside roads. The purpose is to understand slope angles, heights, and surface irregularities to aid safety measures and construction planning. Traditionally, measuring slope shapes commonly involved using a total station (TS) or a level and staff (rod). One surveyor places the staff on the slope while another reads the staff’s position and height with a TS set at a well-sighted point at the bottom or across the slope. In this way, coordinates of multiple points on the slope are obtained and connected to draw cross-sectional sketches to confirm slope gradients and shapes. If necessary, multiple cross sections along the longitudinal direction are measured to calculate overall earthwork volumes or to compare with the design shape.

However, with this conventional method, aiming and reading the instrument must be repeated for each measurement point, and depending on the scale of the slope, surveying alone could take from half a day to several days. For steep slopes, temporary scaffolding or safety harnesses may be required for surveyors to reach measurement points safely, which adds time for setup and teardown. Slope surveying has been labor-intensive on site and involved multi-step processes from preparation to post-processing of drawings.

Main Reasons Slope Surveying Takes So Long

Why do traditional surveying methods tend to take so much time? The main factors are summarized below.

• Human resources and the number of measurement points: To grasp the entire slope, many measurement points are required, and each point is measured by two or more people, consuming both manpower and time. For large slopes or surveys of multiple cross sections, it was not uncommon for an as-built measurement to take several days.

• Equipment preparation and setup: Transporting, installing, and calibrating surveying equipment such as TS or levels takes effort. Especially in mountainous areas or on steep slopes, simply carrying the equipment requires labor. High-precision equipment is also expensive, and if a company does not own it, outsourcing to a specialized contractor may be necessary.

• Securing scaffolding and safety measures: On steep slopes, temporary scaffolding or ladders may need to be installed and surveyors secured with safety harnesses to enter the area. The time required to prepare and remove these safety measures prolongs the overall work.

• Missed measurements and rework: Dangerous locations such as high places or unstable areas may require abandoning certain measurement points. Errors in handwritten notes or discovering points not captured on site that require re-measurement lead to duplicated work and further time consumption.

• Data organization and drafting: Post-processing, such as creating cross-sectional drawings from field measurements or inputting values into spreadsheets to calculate volumes, also takes time. Compiling survey results into reports and inspection documents is cumbersome and becomes a burden on engineers after site work.

Thus, conventional slope surveying often required large amounts of manpower and time while offering limited efficiency gains. Consequently, in recent years, efforts have been promoted to improve surveying and as-built management efficiency using digital technologies such as ICT construction and i-Construction. One technology attracting attention in this context is smartphone-based point cloud surveying.

Basics of Point Cloud Surveying and How Smartphone Measurement Works

Point cloud surveying is a surveying method that acquires the object surface as a collection of many points (point cloud data). Detailed surface data can be obtained in various ways: using a laser scanner to project laser onto a slope and collect reflected points as 3D coordinates, reconstructing shapes from images taken by a camera (photogrammetry), and so on. Because the entire slope can be measured as a surface in a short time, there is no longer a need to measure point by point as in conventional methods, greatly improving surveying efficiency.

Among these, smartphone-based point cloud measurement has gained attention in recent years. Modern smartphones are equipped with high-performance cameras and LiDAR sensors, and with a dedicated app you can 3D-scan the surrounding environment simply by holding up the phone and walking. LiDAR measures the distance to the slope using infrared lasers emitted continuously, acquiring hundreds of thousands of points per second to record the slope shape. This non-contact measurement allows capturing surface shapes from the ground without people climbing dangerous slopes.

Point cloud data obtained by the smartphone alone is based on the device’s internal coordinate system (local coordinates), so its absolute position and elevation on drawings are not immediately apparent. Also, slight distortions can occur in the data if the smartphone is moved during scanning. Coordinate correction therefore becomes important. By combining the smartphone’s GPS or a higher-precision RTK-GNSS receiver, the collected point cloud can be assigned accurate Earth-referenced coordinates. For example, if a small RTK positioning device (a device that corrects satellite positioning errors and can determine position with cm level accuracy (half-inch accuracy)) is attached to the smartphone, the device can continuously know its own position with high precision while scanning and assign absolute coordinates to each acquired point cloud in real time. As a result, even point cloud data easily captured by a smartphone can be used as measurement results with spatial coordinates reliable enough to match conventional surveying maps.

Convenience of Smartphone Point Cloud Data: Density, Cross Sections, Volume, Heat Maps

Point cloud data obtained with a smartphone contains high-density and three-dimensional information that is difficult to obtain with traditional manual surveying. Millions of points can cover the entire slope, allowing visual understanding of subtle depressions and bulges. The higher the density, the greater the freedom for analysis, making various downstream uses easier.

For example, once the entire slope’s point cloud is obtained, you can create cross-sectional drawings at arbitrary section lines in the data. Unlike the conventional method of measuring only major cross sections on site, you can later check cross-sectional shapes at any desired position or angle, reducing oversights and facilitating comparisons with design. Since point clouds represent the slope’s 3D shape, volume calculations for fills or cuts and surface area measurements can be performed instantly in software.

Furthermore, by overlaying the acquired point cloud data with the design model and calculating differences, you can visualize construction errors with heat maps. For example, coloring areas that match the design from blue to green and areas with large deviations from yellow to red allows immediate evaluation of slope workmanship. In this way, smartphone point cloud data is not just a set of coordinates but a rich information source that strongly supports downstream analysis and decision-making.

Workflow for Smartphone Point Cloud Measurement (Preparation to Sharing)

So how does smartphone point cloud measurement actually proceed? Here is an example of a typical workflow.

• Pre-preparation: Prepare the smartphone and auxiliary devices for measurement. Install the dedicated app on the smartphone and attach any necessary peripherals such as a high-precision GNSS receiver or pole. If there are control point coordinates or design data for the survey area, loading them into the app beforehand will make later comparisons smoother.

• On-site scanning: Walk around the lower and surrounding parts of the slope to be surveyed while holding up the smartphone to scan. Move so that the LiDAR covers the slope evenly and measure the surface from various angles to avoid omissions. Where it is safe to do so, move around to the upper and side parts of the slope to reduce blind spots and prevent point cloud gaps. Depending on the measurement range, moving the smartphone for a few minutes will capture the entire slope point cloud on site.

• Upload to the cloud: After scanning, upload the point cloud data from the smartphone to a cloud service. After uploading, automated processes such as point cloud alignment and noise removal are performed, and you can review the data in a 3D viewer on the cloud. If using high-precision GNSS, absolute coordinates may already be attached to the data immediately after upload, eliminating the need for additional control point adjustments.

• Data sharing and output: Point clouds on the cloud can be shared with stakeholders via the Internet. Even offices distant from the site can view the slope shape as a 3D model in a browser and measure distances and elevation differences. If necessary, point clouds can be overlaid with design CAD drawings or cross-sectional images can be exported as images. Ultimately, point clouds and cross sections can be output in DXF or PDF formats and saved or submitted as as-built measurement deliverables.

This workflow digitizes the entire process from field work to data organization and sharing. Smartphone measurement expands the range of tasks that can be completed on site, and since office tasks such as drawing creation and quantity calculation that were previously done back at the office are semi-automated, total work time is drastically reduced.

Wide Uses of Slope Data: As-built Verification, Pre- and Post-construction Comparison, Disaster Recovery

Detailed point cloud data of slopes acquired by smartphone can be used in various scenarios. Representative uses include:

• As-built verification of slopes: You can check whether the post-construction slope matches the design gradient and shape using point cloud data. By comparing the acquired point cloud with the design model, you can immediately see which areas deviate from the design. As-built inspections that were traditionally done by drawing cross sections manually and visually inspecting them can now be objectively evaluated based on digital data.

• Terrain comparison before and after construction: By scanning the original slope before construction and comparing it with the post-construction point cloud, you can accurately determine how much fill or cut was performed. For example, if the volume of a collapsed slope was measured beforehand, you can calculate the amount of soil actually added or removed during restoration by computing differences. Overlaying pre- and post-construction data also makes it easy to visually explain construction effects.

• Disaster recovery records: Even at sites where slopes have collapsed due to heavy rain or earthquakes, smartphone point cloud measurement can quickly record the damage. There is no need for prolonged work in dangerous areas; scanning from a distance can digitally record the collapse extent and soil volume. During subsequent restoration work, periodic point cloud measurements can precisely compare how the terrain changes before and after restoration. Disaster response requires speed and record preservation, and smartphone point cloud measurement contributes to both.

Responsiveness, Portability, and Labor Savings Unique to Smartphone Measurement

Introducing smartphone point cloud measurement dramatically improves site responsiveness and labor savings. Tasks that traditionally required scheduling surveying crews or arranging heavy equipment can now be started immediately with just one smartphone whenever the need arises. For example, if you suddenly need to check slope conditions, you can respond the same day without arranging heavy equipment. Even in light rain, you can seize a break in the weather and perform a short scan to minimize weather-related work interruptions.

Smartphones also offer high portability, allowing measurement anywhere a person can access, even in narrow sites or at height. Places that were difficult for large laser scanners to reach—such as under dense tree cover or behind bridges—can sometimes be flexibly approached with a handheld phone. In mountainous slope surveys where bringing in equipment is difficult, workers can move lightly and reduce their burden.

Another important point is that temporary scaffolding is no longer required. Because smartphone point cloud measurement is non-contact and can measure from a distance, there is no need to force entry onto dangerous slopes. If the entire slope can be scanned from the ground, traditional tasks such as climbing to high places to place a staff are eliminated along with fall risks. As a result, slope surveying can be completed safely by a small team, providing both labor savings and improved safety.

Conclusion: How Smartphone Point Cloud Measurement Is Transforming Site Work (Using LRTK)

Smartphone-based point cloud measurement technology is bringing revolutionary changes to slope surveying sites. The effects—shorter work times, reduced personnel and cost burdens, and improved safety—are significant. One high-precision smartphone point cloud measurement solution that realizes these benefits is [LRTK](https://www.lrtk.lefixea.com/lrtk-phone).

LRTK consists of a small RTK-GNSS receiver that attaches to a smartphone and a cloud service, enabling centimeter-level (half-inch accuracy) precision surveying that was difficult with the smartphone alone. For example, even on a large slope with a height difference of 30 m (98.4 ft), LRTK allows a 3D scan to be completed in about 1–2 minutes simply by walking while pointing the camera. The acquired point cloud data is assigned accurate coordinates from the start and can be used directly for as-built management deliverables. Because it can achieve accuracy that conforms to the Ministry of Land, Infrastructure, Transport and Tourism’s as-built management guidelines, you can confidently adopt it for operations.

By adopting such advanced smartphone surveying technology, slope surveying processes can be dramatically streamlined. Tasks that previously took expert technicians several days can be completed quickly by anyone, greatly improving site productivity. The ability to measure with a smartphone carried at all times means the current condition can be digitally recorded whenever needed, changing how construction management and maintenance are conducted. The use of smartphone point cloud measurement is becoming the standard for future slope management. Consider introducing it on your sites and experience the benefits for yourself.