Table of Contents

• What is differential earthwork volume?

• Why understanding differential earthwork volume is important

• Traditional earthwork measurement methods and challenges

• Advantages of calculating earthwork differentials with point cloud data

• Simple point cloud surveying using smartphone RTK

• Visualizing differential earthwork with AR

• Improved site efficiency through immediate point cloud data sharing

• Recommendation for simple surveying with LRTK

• FAQ

What is differential earthwork volume?

Differential earthwork volume refers to the difference in soil volume between a reference terrain dataset or design model and the current terrain. For example, in site development works you can compare the design planned ground elevation with the current ground to determine “how much more soil needs to be excavated or filled.” By comparing pre- and post-construction terrain data, you can also calculate the actual volumes of soil moved (excavated material or imported fill). In short, differential earthwork volume is an indicator representing the volume difference of soil between two points in time or between different models, and it is indispensable on civil engineering and construction sites for managing cut-and-fill volumes and verifying as-built conditions. It is useful in every situation where soil is moved—such as slope shaping, confirming quantities of fill and cut, and managing earthwork in large-scale development projects.

Why understanding differential earthwork volume is important

Accurately grasping differential earthwork volume on construction sites has several important implications. First, it is essential for construction cost and schedule (progress) management. Misjudging the difference between planned excavation/fill quantities and actual amounts can lead to errors in disposal costs or procurement of backfill, directly resulting in extra costs or project delays. Constantly tracking differential volumes allows proper adjustment of the number of dump trucks to arrange and the soil transportation plan, enabling efficient construction planning. For progress management, regular volume measurements let you verify whether on-site work is proceeding as planned, preventing delays or rework in advance.

From a quality control (as-built verification) perspective, differential earthwork volumes are also critical. To verify that excavation and filling have reached the designed elevations and shapes, comparing the design model to the current condition and checking the differences is the most reliable method. If there is an excess or deficiency relative to the specified line, adjustments can be made and corrected on-site early. Correcting on the spot prevents later rework such as adding missing fill or cutting excess material, yielding better results in both quality and efficiency. Checking differential earthwork volume is therefore a vital process that can determine the overall quality of a project.

Additionally, differential earthwork volume data aids smooth communication among stakeholders. For owners, site supervisors, and heavy equipment operators to share a common understanding of earth volumes, visual sharing of differences is more effective than numbers alone. Accurately sharing quantitative information like “we need to remove X cubic meters more soil” makes it easier for everyone on site to move toward the same goal. Visualizing differential volumes clarifies on-site adjustment instructions and progress reports, strengthening team coordination.

Traditional earthwork measurement methods and challenges

Traditionally, earthwork on-site measurements have mainly relied on cross-section surveys performed by surveyors. Heights are measured at key points of the work area, longitudinal and cross-sectional drawings are produced, and cut/fill volumes are calculated from those sections. However, this method has several challenges.

• Dependence on manual work and skilled labor: Setting up surveying instruments (total stations or levels), taking measurements, drafting cross-sections on paper, and calculating volumes rely heavily on the expertise of experienced surveyors. It is difficult to ensure accuracy without skilled personnel. Because readings and calculations are done manually, human errors such as misreading or calculation mistakes tend to occur.

• Waste of time and manpower: Tasks such as setting survey points, recording measurements, drafting, and quantity calculations are labor-intensive and sometimes require temporarily halting site work. In large sites or areas with complex topography, obtaining sufficient points for accuracy can take a long time. Therefore frequent volume measurements were difficult, and missing timely checks risked delayed understanding of site conditions.

• Difficulty visualizing results: Survey results are reported as cross-section drawings and numerical tables, and it is not easy to intuitively understand “where and how much soil remains” from numbers on paper. Explaining to owners or construction managers often requires them to mentally overlay drawings onto the site, which can cause communication loss.

As described above, traditional methods suffer from variability in accuracy, low work efficiency, and difficulties in information sharing. A new approach gaining attention to solve these issues is the use of point cloud data and AR technologies, discussed next.

Advantages of calculating earthwork differentials with point cloud data

Rapidly spreading in recent years, 3D point cloud data is bringing major innovations to earthwork volume calculations. Point cloud data are digital datasets representing surfaces of terrain or structures as countless points (a collection of 3D coordinates). Because you can reconstruct detailed land shapes from these point clouds, they are highly effective for volume calculations.

Using point cloud data, you can directly calculate volumes from 3D models. There is no need to estimate volumes by individual sections as before; you can compare the entire current surface with the design surface at once. Specifically, you overlay the completed design model (or pre-construction original terrain data) and the latest current point cloud, then compute the differences. With software, you can calculate the differences between the two terrain models with the click of a button and compute the volumes of cut and fill down to the millimeter (1 mm (0.04 in)) with high precision. Manual calculation errors are eliminated, enabling rapid and precise understanding of differential earthwork volumes.

Another advantage of point cloud usage is the visual feedback. Differential results can be displayed not only numerically but also as a color map (heat map). For example, color-coding areas higher than the design (piled up) in red and areas lower than the design (excavated) in blue makes it immediately clear where excessive fill or unexcavated soil remains. Such point cloud heat map visualization allows site personnel to intuitively grasp the situation and instantly determine priority work areas.

Simple point cloud surveying using smartphone RTK

There are various methods to acquire point cloud data, such as laser scanners (LiDAR surveying) or drone photogrammetry, but smartphone-based point cloud surveying combined with RTK is attracting attention. RTK (real-time kinematic) is a technology that uses signals from GNSS (global navigation satellite systems) to obtain centimeter-level positioning accuracy in real time. Traditionally, RTK surveys required expensive dedicated GNSS equipment or setting up base stations. However, technological advances have produced small high-precision GNSS receivers that can connect to smartphones, making RTK positioning easily achievable.

With smartphone RTK, anyone can perform high-precision 3D surveying easily. By attaching a small dedicated RTK receiver device to a smartphone and launching an app, high-precision positioning starts in real time without complicated configuration. Holding up the phone’s camera or LiDAR sensor and walking around the site, you can sequentially capture surrounding terrain and structures as digital point cloud data. There is no need to carry heavy tripods to set up equipment or apply for drone flight permissions. By simply moving the smartphone while walking the site—almost like shooting a video—you can complete a high-precision point cloud scan with great ease.

Point clouds obtained with smartphone RTK have positioning errors corrected to within a few centimeters. Conventional built-in smartphone GPS had meter-level errors, but RTK precisely corrects both horizontal and vertical positions, so point cloud data acquired by a smartphone can be used for differential earthwork calculations with accuracy comparable to conventional laser scanner surveys. This enables site personnel to perform surveying themselves, preventing work stoppages while waiting for survey teams and avoiding increased outsourcing costs. Tasks that previously required a specialist team or external contractor, for example, can be completed by the site person alone with smartphone RTK.

Visualizing differential earthwork with AR

Even if you can compute high-precision differential earthwork with point clouds and RTK, it is important to convey the results on-site in an easily understandable way. This is where AR (augmented reality) technology is powerful. AR overlays digital information on top of the real-world image seen through a smartphone or tablet screen. Using AR, you can display differential earthwork results directly over the local scenery.

Specifically, the differences between the design model and the current point cloud (heat maps or 3D models) are displayed on the smartphone camera view. For example, you can overlay a semi-transparent red fill model on areas that still need excavation, and a semi-transparent blue region on spots that have been over-excavated and are too low. Looking at the actual site through the smartphone screen, you can see colored representations of soil mounds or depressions that would otherwise be invisible. Differences that were hard to intuit from drawings or numbers become visually understandable on the spot.

AR visualization dramatically smooths on-site communication. For instance, if a site supervisor points a smartphone and says, “Let’s excavate this red-shown area another 20 cm (7.9 in),” the heavy equipment operator can immediately grasp the situation from the visual on the screen. This makes instructions far easier to understand than spreading paper drawings and verbally saying “lower this ground by X m.” AR also allows owners and construction managers visiting the site to confirm progress and deviations from the design on the spot. As-built conditions previously explained with reports or drawings can now be shared as if seeing the actual thing through AR, greatly enhancing the persuasive power of explanations.

Improved site efficiency through immediate point cloud data sharing

Point cloud data obtained with smartphone RTK and the resulting differential earthwork calculations can be shared immediately via the cloud. Uploading data to the cloud right after measurement allows engineers in the office and other team members to view the latest information. This enables the entire organization to share site changes in real time and use them for rapid decision-making.

The benefits of data sharing are particularly apparent in speeding up construction management. For example, at one development site they performed a weekly smartphone point cloud scan of the current condition and had the cloud automatically calculate week-to-week volume changes. Sharing those results as heat maps during the morning meeting made it possible to instantly identify which areas required focused excavation or filling. A process that used to take a full day—waiting for the survey team to measure sections on-site, drawing in CAD, and calculating quantities at the office—was reduced to about 30 minutes by the site representative after introducing smartphone RTK. Faster data sharing allowed each trade to act quickly, reducing idle time and shortening the construction schedule.

Moreover, storing data in the cloud enables history management and data centralization. Past point cloud data and differential results are saved in a time series, making it easy to trace back and verify “how much was excavated at that time.” Survey data that tended to scatter across sites are organized on the cloud so all stakeholders can access the latest version on the same platform. This helps prevent problems like information leaks or using the wrong drawings.

Recommendation for simple surveying with LRTK

Using the advanced technologies described so far can dramatically improve efficiency in measuring and sharing differential earthwork volumes. However, some may feel that high-precision GNSS, point clouds, and AR sound difficult. That’s where LRTK (L-R-T-K) comes in as an all-in-one solution. LRTK is a surveying DX platform that combines a high-precision GNSS receiver, a smartphone app, and cloud services, developed as a simple surveying tool that anyone can use—even non-experts.

With LRTK, you can perform centimeter-level high-precision positioning with a small RTK receiver attached to your smartphone while scanning the site with the phone’s camera or LiDAR to create point clouds, and then calculate and visualize volume differentials in the cloud—all in one workflow. In other words, it’s a package containing all necessary functions for differential earthwork measurement. The UI/UX is designed so site personnel can easily operate it on their own smartphones, and even first-time users can learn within a short training session.

Introducing such tools lets companies complete as-built surveys and earthwork calculations in-house that they previously outsourced. As a result, costs are reduced and the accumulated data can be reused to enhance the construction PDCA cycle. Above all, when site workers themselves master digital technologies, the way work is done changes and productivity improves. Even for a single differential earthwork check, solutions like LRTK enable faster, more accurate understanding and on-site sharing. We are witnessing the democratization of surveying technology and an acceleration of site DX. If you have challenges in improving surveying efficiency or digitization, consider trying smartphone-based surveying systems.

FAQ

Q: What data are required to calculate differential earthwork volume? A: Basically, you need two terrain datasets to compare (or a “terrain dataset + design model”) to calculate differential volumes. For example, point cloud data of the terrain before and after construction, or a combination of the design finished model and the current point cloud. Overlaying these allows volume differences to be calculated.

Q: What is smartphone RTK? Is there any issue with accuracy? A: Smartphone RTK is a setup in which a high-precision GNSS receiver is connected to a smartphone, and RTK technology enables centimeter-level positioning on the smartphone. It provides positioning accuracy comparable to dedicated equipment, so point cloud surveys using a smartphone can maintain high accuracy. In many field cases, measurements with errors within a few centimeters have been confirmed (accuracy within a few centimeters (within a few cm (≈1-4 in)))).

Q: Compared to drone surveying, what are the advantages of smartphone point cloud surveying? A: Drone photogrammetry can survey wide areas in a short time but is subject to operational constraints like weather and no-fly zones. In contrast, smartphone point cloud surveying can be done on the ground even in rainy conditions and requires no setup or permits, giving it superior mobility. You can perform measurements yourself whenever needed. Because ground-level scanning captures details closely, it records features such as wall irregularities that drones may miss. Both methods have their use cases, but the convenience of completing the process with a single smartphone is highly attractive for site personnel.

Q: Is special equipment required to visualize differentials with AR? A: No. In principle, commercially available smartphones or tablets are sufficient. AR displays are viewed through the smartphone screen, so as long as a supporting app is available, special AR glasses are unnecessary. If you want a larger display or to share with multiple people, using a tablet or mirroring to a large display is a good option.

Q: Can on-site staff use these tools? Is specialized knowledge necessary? A: Yes. They are designed so on-site staff can handle them. Smartphone surveying apps feature intuitive UIs that avoid complex jargon. Even first-time users can master them quickly with simple training or manuals. In practice, there are increasing cases where construction management staff without surveying expertise conduct point cloud measurements and differential checks themselves and achieve efficiency gains.

Q: How much does it cost to implement? A: Compared to equipping large surveying instruments and dedicated software, solutions using smartphone RTK can be started at much lower cost. You can use an existing smartphone and only need a small GNSS receiver, greatly reducing initial investment. Considering that you can also bring previously outsourced surveying tasks in-house, overall cost-effectiveness is very high.

Q: Point cloud data files are large—can smartphones and the cloud handle them? A: High-density point cloud data can indeed become large, but smartphone point cloud surveying solutions automatically compress and optimize data or allow scanning only the necessary area to keep sizes manageable. Combined with cloud services, detailed processing is handled on the server side and only required information is transferred to the smartphone. Therefore operation on-site does not overly tax storage or processing power. With a suitable network environment, heavy 3D data can be handled smoothly via the cloud.