Table of Contents

• What is differential earthwork volume?

• Why grasping differential earthwork volume is important

• Traditional earthwork measurement methods and their challenges

• Advantages of calculating differential earthwork volume using point-cloud data

• Easy point-cloud surveying anyone can do with a smartphone

• Visualizing differential earthwork volumes with AR

• Improving site efficiency by instantly sharing point-cloud data

• Recommendation: simple surveying with LRTK

• FAQ

What is differential earthwork volume?

“Differential earthwork volume” refers to the difference in soil volume that arises when comparing a reference terrain dataset or design model with the current terrain data. For example, on an earthwork site you compare the design-grade elevations with the current ground surface to determine “how much more soil needs to be excavated” or “where fill is still lacking”—those quantities are the differential earthwork volumes. If you acquire terrain data before and after construction and compare them, you can also accurately calculate the actual volume of soil removed or brought in—i.e., the quantities of excavated material and backfill. In short, differential earthwork volume is an indicator that represents the difference in soil volume between two different times or models, and it is essential data on civil engineering and construction sites for managing cut-and-fill and verifying as-built quantities.

Why grasping differential earthwork volume is important

Accurately understanding differential earthwork volume on a construction site has many important implications. First, it is indispensable for construction cost and schedule management. If planned excavation or fill volumes differ from actual volumes, extra costs for residual soil disposal or additional procurement of fill can occur, creating unnecessary cost burdens. Conversely, if construction proceeds with insufficient soil, recovery later takes time and increases the risk of schedule delays. By always correctly tracking differential earthwork volumes, you can accurately plan the number of dump trucks and the schedule for soil transport, enabling efficient, waste-free scheduling.

From a quality control and as-built verification perspective, differential earthwork volume is also important. To verify that excavation and filling were performed to the designed elevations and shapes, overlaying the completed design model and the current terrain data and checking the differences is the most reliable method. If there are deviations from the specified lines, early corrective actions can be taken to prevent rework or corrective construction. With differential earthwork data, you can quantitatively show discrepancies between design and site, which helps in judging as-built compliance and assuring quality.

Moreover, differential earthwork information contributes to smooth communication among stakeholders. For clients, site supervisors, and heavy equipment operators to share a common understanding of soil volumes, combining numeric data with visual representations of the differences is effective. If you can show a concrete number like “we need to excavate another ○ cubic meters” along with where and how much soil remains, everyone can act toward the same goal more easily. Correctly identifying and sharing differential earthwork volumes smooths team communication and coordination on site and ultimately improves construction efficiency.

Traditional earthwork measurement methods and their challenges

There are several conventional methods for measuring earthwork volumes on site, including differential volumes, but each method has posed challenges in terms of ease of use and immediacy. Below are representative methods and their issues.

• Human-conducted cross-section surveying and volume calculation: A surveyor measures key terrain points with a total station or level, creates longitudinal and cross-sectional drawings, and calculates volumes using methods like the average cross-section method. While accuracy is high, this approach is very time-consuming and labor-intensive and requires skilled technicians. On large sites, it takes a long time to collect enough survey points, making frequent differential volume measurements impractical. Reading volumes from drawings also relies heavily on experience and judgment, introducing risks of human error and calculation mistakes.

• Rough estimates from equipment load volumes and dump truck counts: Sites sometimes estimate soil volumes roughly from the bucket capacity of excavators or the number of dump trucks. However, this is only an estimate and tends to have large errors. The soil moisture content and how it is loaded affect the per-truck volume, and differences from actual transport volumes can go unnoticed. Although convenient, this method lacks accuracy and is unsuitable for precise differential volume assessment.

• Drone photogrammetry: Recently, flying drones to take aerial photos and generating 3D models or point-cloud data to calculate volumes has become more common. This method can survey large areas in a short time, but it is constrained by aviation regulations and flight permissions and requires a skilled operator. It is also weather-dependent and cannot be flown in rain or strong wind. Image processing and point-cloud generation after shooting take time, so this method is not suitable when you need immediate on-site results.

• Terrestrial 3D laser scanners: Using high-precision ground-based laser scanners to obtain point-cloud data for volume calculations is another option. Millimeter-level precision is possible, but the equipment is very expensive and requires specialized knowledge to operate. Setting up the equipment is labor-intensive, and the resulting large data volumes are heavy to process, making everyday use by regular site staff difficult. As a result, even when such systems are introduced, they often go unused or are employed only in limited situations.

Thus, traditional earthwork measurement methods face issues such as variable accuracy, low operational efficiency, and difficulty in information sharing. In particular, the lack of real-time capability means a significant time lag between measurement and result, during which site conditions may change and responses fall behind. What has long been desired is a measurement method that anyone on site can easily use and that provides immediate results on the spot.

Advantages of calculating differential earthwork volume using point-cloud data

What is changing this situation dramatically is the use of 3D point-cloud data. Point-cloud data digitally record the surface shape of terrain and structures as a large collection of points (sets of XYZ coordinates). With recent improvements in PC and mobile device performance, point-cloud processing technologies have become more accessible, and point-cloud surveying is rapidly spreading on construction sites. Using point-cloud data dramatically improves the efficiency and accuracy of differential volume calculations.

Direct volume computation from point clouds: With point-cloud data, you do not need to estimate volumes from cross-sections as before; a computer can directly calculate the difference between two 3D models. Specifically, you overlay the “design model (or pre-construction original terrain data)” and the “latest as-built point-cloud data” and compute the volume difference between the two shapes with the press of a button. This allows cut and fill volumes to be determined accurately down to millimeters. By eliminating manual reading and calculation errors, you can obtain highly precise differential volumes in a short time.

Intuitive understanding through visual feedback: Point-cloud data also enable visually displaying differential volume results. The differences obtained by calculation can be presented not only as numbers (e.g., volume in cubic meters) but also as a colored heat map overlaid on the terrain. For example, areas that are higher than the design (excess fill) can be colored red and areas that are lower (still needing excavation) colored blue, making it immediately clear where on site soil is over- or under-supplied. Information that was hard to intuit from numbers or drawings becomes easy to understand when displayed in color on the point cloud. Site personnel can glance at a color map on a screen and instantly decide which locations to prioritize, reducing the risk of overlooking spots that need correction.

As described above, calculating differential earthwork volumes using point-cloud data far surpasses conventional methods in both accuracy and speed, and it also offers significant advantages in clarity and understandability.

Easy point-cloud surveying anyone can do with a smartphone

You may understand the usefulness of point-cloud data but wonder, “Don’t I need specialized surveying equipment or a drone to acquire point clouds?” This too has changed dramatically in recent years. It is now becoming possible to perform high-precision point-cloud scans using only a smartphone. Modern smartphones include high-performance cameras and various sensors, and mobile 3D measurement technologies that leverage these capabilities have emerged.

For example, some recent smartphones include a compact LiDAR (light detection and ranging) sensor that can generate point clouds in real time for several meters (several ft) around what the camera sees. On phones without LiDAR, photogrammetry using multiple photos or videos processed in the cloud can also create 3D models of larger areas. In other words, even without special surveying equipment, the smartphone in your hand can serve as a 3D scanner.

A notable development is solutions that combine smartphones with high-precision GNSS receivers (RTK-capable). While a smartphone alone can capture shapes with a camera or LiDAR, its built-in GPS typically has meter-level errors. By attaching a small GNSS receiver supporting RTK (real-time kinematic) corrections to the smartphone, you can reduce positioning errors to within a few centimeters (a few inches) horizontally and vertically. This allows the point-cloud data captured with a smartphone to be assigned highly accurate coordinates on the spot, producing accurate 3D survey data aligned with the site’s coordinate system.

With the smartphone + RTK-GNSS combination, high-precision point-cloud surveying is becoming possible with one-button simplicity, even for non-specialists. You attach a palm-sized device to your smartphone, walk around the site as if recording video while pointing the camera, and the surroundings are progressively turned into a point cloud. Time-consuming reference-point surveying and post-processing that were once required are minimized, and you can move from the freshly acquired 3D model straight to volume calculations. An era has begun in which anyone can perform 3D surveying on site “quickly, easily, and accurately.”

Smartphone-based point-cloud surveying offers many advantages not available with traditional methods. Key points are summarized below.

• Speed and immediacy: Walk around the site with a smartphone for a few minutes to scan, and you can get volume calculation results immediately afterward. For example, you can scan areas excavated that day in the evening and instantly grasp the day’s as-built volumes. Data processing is automated, greatly reducing the waiting time for results.

• Ease and labor savings: Measurement can be completed with just a smartphone and a small GNSS receiver, eliminating the need to transport heavy equipment or perform complex setups. Intuitive smartphone app operation allows anyone to measure, so workers without specialized training can handle it. This “take it out of your pocket and measure when needed” convenience makes it easy to incorporate into daily site operations.

• Improved safety: Even on hazardous slopes or large fills, you can scan from a safe distance by pointing a smartphone and capture detailed geometry, reducing the need for personnel to enter dangerous areas. Heights on steep faces that were difficult to measure manually can also be measured safely.

• Sufficient accuracy: The combination of high-precision GNSS corrections and point-cloud technology has been confirmed to meet the accuracy required for as-built management and volume calculations. It achieves accuracy comparable to traditional manual surveying while enabling coverage of wider areas, allowing reliable measurements. While fixed equipment may be needed for ultra-high-precision tasks, smartphone surveying accuracy is sufficient for most construction management use cases.

• Cost reduction: Smartphone-based measurement reduces the need to purchase expensive dedicated equipment or outsource surveying. You can start by using existing smartphones and adding a small receiver, minimizing initial investment. Because you can measure in-house whenever needed, outsourcing wait times are eliminated, providing excellent cost-effectiveness.

• Ease of continued use: Tools that are hard to operate or usable by only a few people do not become entrenched on site. Smartphone point-cloud surveying is easy for anyone to use anywhere, making it simple to incorporate into daily workflows. If your team routinely measures by themselves, site-wide data utilization will grow, shifting construction management from experience- and intuition-based to data-driven.

Thus, simple smartphone point-cloud surveying offers a compelling balance of speed, ease, safety, accuracy, and cost, making it highly practical for everyday site use. While drones may be more suitable for capturing very large areas at once, smartphones excel in detailed measurements and frequent progress tracking. By using drones and smartphones as appropriate, you can build a more efficient site measurement system.

Visualizing differential earthwork volume with AR

Once high-precision differential earthwork volumes can be calculated using point-cloud data and RTK positioning, it becomes important to present those results on site in a clear way. A promising approach that has attracted attention recently is using AR (augmented reality) technology. AR overlays digital information onto the real-time camera view on a smartphone or tablet. Using AR, you can overlay differential earthwork results directly onto the actual site scenery.

Concretely, you overlay difference results between the design model and the current point cloud (for example, the aforementioned heat maps or 3D fill/excavation models) onto the smartphone camera view. Areas that still need excavation can be shown with a translucent red fill model, and areas that are over-excavated or too low can be shown with blue tinted regions. When you look at the site through your smartphone, “excessly filled mounds” or “over-excavated depressions” that are not obvious to the naked eye appear color-coded and aligned with the actual terrain. Differences that were formerly confirmed only on drawings or through numbers can now be understood on site as if viewing the real object.

AR visualization dramatically improves on-site communication. For example, if a site supervisor points a smartphone and says, “Let’s excavate this red-shaded part by another 20 cm (7.9 in),” the heavy-equipment operator can immediately grasp the situation from the visual information on the screen. AR instructions are much easier to understand at a glance than showing paper drawings and saying “lower the ground here by ○ m (○ ft)…” When clients or managers inspect the site, you can show them the smartphone screen to let them instantly understand current progress and differences from the design. Explanations of as-built conditions that were difficult to convey through reports or drawings alone can be shared as if letting them see the site itself via AR, which facilitates smoother consensus-building.

Improving site efficiency by instantly sharing point-cloud data

Point-cloud data and differential volume results acquired with a smartphone become even more useful when integrated with cloud services. After measuring on site, a single tap can upload data to the cloud from the smartphone, enabling instant information sharing with engineers in the office or team members in remote locations. Site changes can be shared company-wide in real time, allowing rapid follow-up actions.

Uploading data to the cloud also allows viewing and checking 3D point clouds and measurement results in a web browser without heavy dedicated software. For example, automatically generated volume calculation results and cross-sections from point-cloud data can be viewed by all stakeholders on their PCs or tablets. By opening a URL, anyone can rotate and inspect the 3D model, enabling status checks and discussions without visiting the site.

Accumulating data in the cloud also enables history management and centralized information. If past point clouds and differential measurement results are stored chronologically, it becomes easy to verify “how much was excavated at the end of last month,” for example. Survey data that tended to be managed separately and scattered across sites can be organized in the cloud so all stakeholders access the same latest data. This prevents information gaps and drawing inconsistencies and promotes collaboration across site and office boundaries.

Combining smartphone-acquired point-cloud data with cloud services greatly streamlines the measurement cycle. Frequent scanning—weekly or even daily—with automatic differential volume calculation and sharing becomes practical, dramatically improving the speed and accuracy of progress management and as-built inspections.

Recommendation: simple surveying with LRTK

Using the advanced technologies introduced so far can greatly improve the efficiency of measuring and sharing differential earthwork volumes. However, some may feel that “high-precision GNSS, point clouds, and AR sound complicated.” This is where an all-in-one solution called LRTK deserves attention. LRTK is a surveying DX platform that combines a high-precision GNSS receiver, a smartphone app, and cloud services, developed as an easy surveying tool usable by non-specialists.

With LRTK, a small RTK-GNSS receiver attached to a smartphone provides centimeter-level accuracy (half-inch accuracy) positioning while the smartphone camera or LiDAR scans the site into point-cloud data, and the cloud performs the differential volume calculation and visualization in an integrated workflow. In other words, it is a one-stop package containing the functions needed for differential volume measurement. The UI is designed so site personnel can operate it from the smartphone they are already familiar with, and it is intended to be usable after a short initial training.

Introducing such tools on site allows formerly outsourced as-built surveys and volume calculations to be completed in-house, contributing to significant cost reductions. By leveraging the accumulated data, you can also advance the construction PDCA cycle. Most importantly, when site workers themselves can use digital surveying technologies, their work processes change and productivity improves. Even for simply checking differential earthwork volume, solutions like LRTK make it possible to build a system that lets you “know accurately right away” and “share on the spot.” This movement toward democratizing surveying technology is underway, making 3D surveying accessible to everyone. If you currently have challenges in site earthwork management or as-built measurements, consider introducing LRTK, a modern simple surveying solution using smartphones. Cutting-edge technology can dramatically improve site productivity and safety.

FAQ

Q: What data are required to calculate differential earthwork volume? A: Basically, you need two terrain datasets to compare. For example, point-cloud data of the “pre-construction ground model” and the “post-construction ground model,” or the “design completion model” and the “current point-cloud data.” Once you have the reference dataset and the current dataset, software can automatically calculate the volume difference between the two.

Q: What is smartphone RTK? Is the accuracy really sufficient? A: Smartphone RTK refers to a system that uses a high-precision GNSS receiver connected to a smartphone to perform real-time centimeter-level positioning. This enables smartphone positioning comparable to dedicated surveying equipment. Field validations have shown that smartphone point-cloud surveying can measure within a few centimeters (a few inches) horizontally and vertically, providing sufficient accuracy for typical civil engineering as-built checks and volume calculations.

Q: Compared with drone surveying, what are the advantages of smartphone point-cloud surveying? A: Drone photogrammetry can quickly survey wide areas but is more constrained by weather and flight permissions, and certain areas (under bridges or building facades) can be difficult to capture from the air. Smartphone point-cloud surveying can be performed on the ground even in rainy conditions and requires no preparation or permits, offering superior mobility. You can measure fine details from ground level that drones may miss. By choosing between drone and smartphone according to the task, you can take advantage of each method’s strengths for efficient measurement.

Q: Do I need special equipment for AR visualization of differences? A: No. In most cases, a commercially available smartphone or tablet is sufficient. AR visualization is done on the device’s screen, so you don’t need dedicated AR glasses. Install a compatible app on your existing device and you can experience AR-based differential displays immediately. If you want to share on a larger screen, using a tablet or mirroring the screen to a display is effective.

Q: Can I use this without internet connectivity on site? A: With LRTK, correction signals from the Quasi-Zenith Satellite System (e.g., QZSS/QLAS) can enable high-precision positioning even in mountainous areas with no cellular coverage. Measurement data can be synced to the cloud after moving to an area with reception, or you can store data on the smartphone offline and upload later. Therefore, surveying can be performed even when immediate network connectivity on site is not available.

Q: Can site staff use it? Is special knowledge or certification required? A: Yes, these systems are designed so site staff can operate them. Smartphone surveying apps are made to be intuitive, avoiding complicated technical terms and settings. With brief training or following a manual, users can start quickly. There are many cases where non-surveying construction managers have performed point-cloud measurements and differential checks with a smartphone and achieved operational improvements.

Q: How much does it cost to introduce? A: Compared to large traditional surveying equipment and dedicated software, smartphone RTK-based solutions are substantially less expensive. You can use existing smartphones and only need to procure small GNSS receivers, so initial investment is relatively small. In addition, by in-house handling of tasks previously outsourced, you can expect reduced running costs. Overall, it is a highly cost-effective approach.

Q: Point-cloud data files can be large—can smartphones and the cloud handle them? A: High-density point clouds can indeed become large, but smartphone point-cloud solutions automatically perform data compression and optimization. You can scan only the necessary areas to reduce redundant points, and data can be compressed in real time for cloud transfer so smartphone processing remains manageable. Detailed analysis is performed in the cloud and only the necessary results are sent back to the phone, preventing excessive storage or processing loads on the device. With sufficient network connectivity, even large 3D datasets can be handled smoothly via the cloud.