How to Measure Differential Earthwork Volume: A Simple Guide from 3D Point Cloud Measurement to Volume Calculation with LRTK

Table of Contents

• What is differential earthwork volume?

• When differential earthwork volume is required

• Traditional earthwork measurement methods and their challenges

• Advantages of calculating differential earthwork volume using 3D point cloud data

• Easy differential earthwork measurement with LRTK

• Benefits of using LRTK

• Summary

• FAQ

What is differential earthwork volume?

Differential earthwork volume is the value that indicates how much the soil volume (volume) of the current land has increased or decreased compared to a reference terrain or structure shape. Simply put, it refers to the amount of soil added or removed — in other words, the *volume difference of earth and sand*. On construction sites, it is important to know the amount of soil removed by excavation and the amount of soil added by embankment. By accurately measuring this “differential earthwork volume,” you can quantitatively verify whether the shape matches the design or how far it deviates from the plan.

In civil engineering and construction, for example, when leveling land in development work, the amount cut from the initial ground (cut volume) or the amount filled into low areas (fill volume) is calculated as differential earthwork volume. The concept includes both cut volume (the volume of soil removed) and fill volume (the volume of soil added), and by offsetting the two, the final surplus or deficit of soil can be evaluated.

When differential earthwork volume is required

Measuring differential earthwork volume is indispensable in various situations in civil construction and infrastructure management. One representative case is as-built management. As-built management is the process of verifying whether the post-construction terrain or structures have been completed according to the design drawings, and public projects require submission of dimensions and quantities (volumes) of the as-built condition to the project owner. By understanding the differential earthwork volume, you can verify whether the construction result is within the design limits and, if deficient, decide on additional filling, or if excessive, decide on cutting for correction.

Differential earthwork volume is also important for final settlement of construction quantities. In excavation works and projects involving transport of soil, costs and schedules are managed according to the actual amount of soil moved. The soil volume calculated from the difference between the initial ground and the completed ground provides the basis for progress-based payments and settlement amounts under contracts. Objective soil volume data are necessary for contractors to receive appropriate compensation and for clients to confirm that the work quantities are within the planned scope.

Furthermore, differential earthwork volume is used for construction progress management. In long-term large-scale development or tunnel excavation, regularly measuring changes in on-site soil volume allows you to track whether excavation and filling progress is on schedule. For example, if you calculate the day’s excavation amount as the differential earthwork volume at the end of each workday, you can manage daily progress by quantity. Municipal infrastructure maintenance also uses terrain difference measurements before and after work to determine removed debris volumes or removed accumulated sediment after disasters.

Traditional earthwork measurement methods and their challenges

Traditionally, measurement of differential earthwork volume (cut and fill volumes) has often been carried out by manual cross-section surveys and volume calculations. Common methods include conducting transverse surveys of the terrain at regular intervals before and after work and calculating volumes using the average cross-section method from the resulting cross-section diagrams. Alternatively, the grid method, which divides the surface into a lattice and measures the elevation at each grid point, can be used to compute volumes. These methods require surveying staff and equipment such as laser levels and total stations to manually acquire elevation at each survey point.

However, manual-centric earthwork measurement has several challenges. The main issues are listed below.

• Time-consuming and labor-intensive: Measuring a large number of points requires multiple crews working long hours, imposing a significant burden on site personnel. Securing personnel with surveying expertise is also necessary, and in situations of labor shortage, it may be difficult to proceed with surveys as scheduled.

• Lack of coverage and risk of oversight: There is a limit to the number of points that can be measured manually, making it difficult to sufficiently cover the entire site. With only limited cross-sections or survey points, subtle undulations or errors between points may be overlooked. As a result, problems may only surface during as-built inspections when discrepancies with the design are pointed out, leading to additional remedial work.

• Safety concerns: Measuring on steep slopes or excavation areas may require workers to enter hazardous zones to take measurements. Standing on unstable soil involves risks such as slipping and is undesirable from a site safety management perspective.

• Workload for calculation and documentation: Plotting field measurements onto drawings to calculate cross-section volumes, preparing report charts, and creating photo logs are laborious. Site supervisors must perform extensive documentation alongside construction management tasks, increasing the possibility of human error and omitted records.

Thus, traditional earthwork measurement methods are limited in both accuracy and efficiency because they measure only at points and require substantial manpower and time. What is increasingly demanded is a new measurement method that can capture earthwork volumes more efficiently and with higher accuracy.

Advantages of calculating differential earthwork volume using 3D point cloud data

Recently, digital technology has been introduced into surveying and measurement, and earthwork calculations using 3D point cloud data have attracted attention. Point cloud data are collections of many measured points acquired by laser scanners or photogrammetry and represent terrain shapes as high-density 3D models. Unlike traditional cross-section surveys, which are point-based, point clouds capture the entire site as a surface, significantly improving the accuracy and efficiency of volume calculations.

The biggest advantage of using 3D point clouds is that they can measure large areas rapidly and as surfaces. For example, aerial photogrammetry with drones can capture the entire site from the air in tens of minutes, and terrestrial laser scanners can acquire precise point clouds consisting of millions of points in a short time. Point clouds reflect even fine ground undulations, so when used for volume calculations, they enable high-accuracy volume estimation that accounts for variations down to the centimeter level (half-inch accuracy). Small surpluses and deficits that were overlooked by manual surveys can be visualized in 3D data, greatly reducing the risk of missing as-built issues.

Non-contact measurement is another major advantage. Surveyors do not need to enter dangerous areas directly and can safely scan the entire site from a distance. Using drones or long-range laser measurement, data can be acquired from the air or at a distance even on steep slopes or collapsed terrain where people cannot enter. This allows for both improved worker safety and measurement efficiency.

Digital point cloud data are also easy to analyze and share. Dedicated software can automatically calculate fill and cut volumes from acquired point clouds, eliminating concerns about calculation errors. Results can be displayed as numeric data or color maps, making it easy to see at a glance where and how much soil needs to be added or removed. Because the data can be stored and shared electronically, stakeholders can immediately share information and make rapid decisions.

Although point cloud measurement offers great advantages, it has historically required expensive equipment and specialized technical skills, which posed an adoption barrier for small- to medium-sized sites. A solution that combines a smartphone with RTK-GNSS to obtain point clouds easily has emerged to address this. This is the simple surveying approach using LRTK introduced next.

Easy differential earthwork measurement with LRTK

LRTK is a surveying system composed of a small high-precision GNSS receiver that can be attached to a smartphone, a dedicated app, and a cloud service. By fusing the smartphone’s built-in LiDAR scanner (light detection and ranging) or camera with RTK positioning technology that provides centimeter-level accuracy (half-inch accuracy), anyone can easily perform 3D point cloud measurement and volume calculation. A major feature is that surveying work that used to require skilled personnel can now be performed by on-site technicians themselves with just a smartphone.

Here is the typical workflow for measuring differential earthwork volume using LRTK.

• Prepare surveying equipment: Attach the dedicated LRTK unit (GNSS receiver) to your handheld iPhone or iPad and connect it via Bluetooth or cable. Turn on the device outdoors and wait for several tens of seconds to acquire satellite signals and start RTK positioning. With correction information, positioning accuracy improves so that location can be measured with high precision of approximately ±2-3 cm (±0.8-1.2 in) in both horizontal and vertical dimensions.

• Prepare reference data: Prepare the reference model or reference surface to compare against. If you have design drawing data (e.g., terrain surface data in LandXML or SXF format), load it into the LRTK app to display the design surface model. If there is no design 3D model available, you can scan the pre-construction existing terrain once and save it as reference data, then re-scan the same area later to compare differences.

• Measure the current 3D point cloud: Scan the area you want to measure with your smartphone to acquire point cloud data. Switch the LRTK app to measurement mode and walk around the site with your smartphone; the built-in LiDAR captures surrounding terrain and generates a point cloud in real time. By combining RTK-GNSS position information, the acquired point cloud is assigned accurate coordinates (latitude, longitude, elevation). Move to cover the entire area of interest while scanning, and reduce blind spots by capturing the terrain from multiple viewpoints as needed. In a few minutes you can obtain tens of thousands to hundreds of thousands of 3D points, and the current terrain model will be reproduced on your smartphone.

• Automatic calculation of differential earthwork volume: After scanning is complete, the app calculates the differential volume between the acquired point cloud data and the reference data. The LRTK app can automatically compute fill and cut volumes with a single button. For example, if you have loaded the design model as the reference, pressing the “differential calculation” button will analyze the differences between the current point cloud and the design surface and instantly display the volume. Both the volume to be excavated (cut volume) and the volume to be filled (fill volume) are computed separately, so you can immediately see how much soil needs to be moved in or out.

• Review and use results: The calculated differential earthwork volumes can be checked as numbers on the smartphone screen and visualized with color maps. Color-coding parts higher than the reference surface in red and lower parts in blue makes it intuitive to see where to add or remove soil. Using AR mode, which overlays 3D data onto the smartphone camera view, you can visualize the virtual design surface on the actual site. This allows on-site decisions like “how many more centimeters to cut to reach the design surface” to be made instantly. Measurement results are saved to the cloud and can be shared with stakeholders or incorporated into reports.

With LRTK, the entire process from measurement to volume calculation and result review can be completed on site. There is no need for specialized equipment or complex CAD software, and the intuitive operation on a tablet or smartphone makes it accessible even to non-surveying specialists.

Benefits of using LRTK

LRTK, a new surveying method combining smartphones and RTK, offers several advantages over traditional methods. Below are the main benefits of using LRTK on site.

• Easy operation anyone can handle: Because the smartphone app guides you through the process, technicians without surveying expertise can start using it immediately. Complex equipment setup or surveying calculation knowledge is unnecessary, and intuitive operation yields accurate results.

• Immediate results in a short time: Since you can perform everything from point cloud scanning to differential volume calculation on site, measurement work is dramatically faster. Even on large sites, 3D measurement can be completed in a matter of minutes and volume results are available immediately, enabling real-time progress checks and rapid transition to subsequent tasks.

• Reduced personnel and cost: Tasks that previously required multiple people can be handled by one person with LRTK. There is less need to outsource to surveying companies or stop heavy equipment and wait, which reduces personnel costs and opportunity losses. Initial investment can be lower than purchasing dedicated high-cost equipment, and LRTK can be adopted as needed.

• Improved safety: Non-contact measurement with a smartphone means personnel do not need to enter hazardous areas, increasing site safety. For example, as-built measurements on steep slopes can be scanned remotely without workers climbing the slope, reducing risks of falls or collapses.

• High-accuracy measurement: RTK-GNSS provides coordinates tied to reference points, ensuring high reliability of measured data. LRTK allows all point clouds to have unified coordinates, making it possible to compare volumes across distant areas without error — something difficult to achieve with conventional methods. The positioning accuracy is sufficient to withstand as-built management standards.

• Easy data utilization and reporting: All measurement results are recorded as digital data and stored in the cloud. This makes it simple to compare with past measurements, use for electronic delivery, or repurpose data. The burden of pasting drawings into reports and organizing photos is reduced, streamlining preparation of as-built management documents.

By leveraging LRTK, earthwork measurement and as-built management can be greatly streamlined, enabling safe and reliable quality control. It is a powerful tool for promoting on-site DX (digital transformation) and achieving high-quality construction management with fewer personnel.

Summary

Differential earthwork volume is a critical quantity that affects construction quality and cost. Traditionally, measuring it relied on labor-intensive surveying and calculation, but the increasing use of 3D point cloud measurement is making it possible for anyone to quickly and accurately determine soil volumes. Solutions like LRTK, which combine smartphones and high-precision GNSS, allow on-site instantaneous calculation of differential earthwork volume and feedback into construction.

What used to take days with cross-section surveys can be completed on the same day using LRTK, and the results can immediately support construction management. This directly contributes to shortened schedules and improved quality, benefiting both clients and contractors. Measuring differential earthwork volume using a smartphone is becoming the new norm. If you currently face challenges in soil volume management or as-built measurement, consider trying simple surveying with LRTK. Adopting the latest technology on site can overturn past conventions and deliver efficiency and accuracy improvements.

FAQ

Q: Why measure differential earthwork volume? A: The purpose of measuring differential earthwork volume is to accurately grasp the amount of terrain change due to construction (excavation and fill). This allows verification that construction is performed according to design and enables appropriate cost settlement based on construction quantities. Differential earthwork volume data serve as evidence for as-built management and are important for quality assurance and contractual proof.

Q: What data are needed to calculate differential earthwork volume? A: Calculating differential earthwork volume requires two terrain datasets to compare. Generally, you prepare a “reference surface” and a “current surface” model and compute the volume difference. The reference surface can be the finished model from the design drawings or pre-construction original ground data. The current surface is measured data after (or during) construction. For example, in excavation work, comparing the pre-excavation terrain model and the post-excavation terrain model yields the actual moved soil volume.

Q: What preparation and equipment are required to use LRTK? A: To use LRTK, you need an iPhone or iPad equipped with a LiDAR sensor (e.g., iPhone 12 Pro or later), the LRTK high-precision GNSS receiver unit, and the dedicated app. Install the app on your smartphone and connect the LRTK unit. Then you can walk around the site with your smartphone to perform point cloud measurement. Because GNSS correction information is obtained via the Internet, a mobile communication environment (4G/5G) is required on site.

Q: How reliable is the measurement accuracy? A: LRTK uses RTK-GNSS to achieve approximately ±2-3 cm (±0.8-1.2 in) in the horizontal plane and a few centimeters in elevation. This is far more precise than conventional GPS and meets accuracy levels required for as-built management. However, accuracy can be affected by satellite reception conditions and the surrounding environment, so it is advisable to use it in open areas and allow sufficient measurement time. The smartphone LiDAR point cloud can capture shapes with several-centimeter (a few-inch) accuracy at close range. With proper measurement, practical accuracy sufficient for volume calculation can be ensured.

Q: Which is better, drone photogrammetry or smartphone+LRTK point cloud surveying? A: Drone photogrammetry and smartphone+LRTK point cloud surveying each have their strengths. Drones excel at quickly capturing large areas and are suitable for surveying areas that are difficult to access on foot, such as forests or large development sites. LRTK, on the other hand, is easy to use on site and provides immediate results without waiting for image processing. It can be used in urban areas with strict regulations or indoors, and is less affected by weather. Additionally, LRTK’s GNSS capability can be applied to control point surveying for drone photogrammetry to correct photogrammetry results to high accuracy. By choosing between drone and LRTK based on site scale and conditions, or using both complementarily, you can achieve more efficient and accurate earthwork management.