Visualize Differential Earthwork Volumes with Point Cloud Heatmaps! On-site Verification Made Easy with the Latest AR Technology

Table of Contents

• What differential earthwork volume is

• Why understanding differential earthwork volume is important

• Traditional earthwork measurement methods and challenges

• Advantages of calculating volume differences from point cloud data

• Simple point cloud surveying using smartphone RTK

• Visualizing differential earthwork volume with AR

• Improving on-site efficiency by instant sharing of point cloud data

• Recommendation for simple surveying with LRTK

• FAQ

What differential earthwork volume is

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 land development works you can compare the design planned ground elevation with the current ground to understand "how much more soil needs to be excavated or placed." By comparing terrain data before and after construction, it is also possible to calculate the actual volume of soil removed or brought in (the amounts of excavated soil or backfill). In short, differential earthwork volume is an indicator expressing the volumetric difference of soil between two points in time or between different models, and is indispensable on civil engineering and construction sites for managing cut-and-fill volumes and verifying as-built results. It is useful in all situations where soil is moved, such as slope shaping, checking the amounts of fill or cut work, and large-scale land development earthwork management.

Why understanding differential earthwork volume is important

Accurately understanding differential earthwork volume on site has several important implications. First, it is indispensable for construction cost and schedule (progress) management. Misjudging the difference between planned excavation or fill volumes and actual ones can lead to errors in disposal costs for surplus soil or in the amount of backfill procurement, directly resulting in extra costs or schedule delays. If differential earthwork volumes are constantly monitored, you can appropriately adjust the number of dump trucks and the plan for soil transport in and out, enabling an efficient construction plan without waste. For progress management, regular volume measurements make it possible to check whether work on site is proceeding according to plan, preventing delays and rework.

From a quality control (as-built verification) perspective, differential earthwork volume is also important. To verify whether excavation or filling has been performed to the design elevations and shapes, comparing the design model with the current condition and checking the differences is the most reliable method. If there is an excess or deficit relative to specified lines, adjustments and corrections can be made on site at an early stage. Correcting it on the spot prevents rework compared to filling shortages or re-cutting surplus later, resulting in better outcomes in both quality and efficiency. Checking differential earthwork volume is a crucial process that affects the overall quality of the project.

Furthermore, differential earthwork volume data helps facilitate smooth communication among stakeholders. For project owners, site supervisors, heavy equipment operators, and others with different roles to share a common understanding of soil volumes, visual sharing of differences in addition to numerical data is effective. Accurately sharing quantitative information such as "we need to remove another ○ cubic meters of soil" helps everyone on site move toward the same goal. Visualizing differential earthwork volume clarifies on-site adjustment instructions and progress reporting, strengthening team coordination.

Traditional earthwork measurement methods and challenges

Traditionally, earthwork on site has mainly been measured by surveyors performing sectional surveys. Heights are measured at key points of the work area, cross-sections are produced, and excavation and fill volumes are calculated from those. However, this method has several challenges.

• Dependence on manual work and craftsmanship: Setting up surveying instruments (total stations or levels), taking measurements, creating sectional drawings on paper, and calculating volumes rely heavily on the skills of experienced surveyors; ensuring accuracy is difficult without experienced personnel. Because humans read and calculate manually, misreading or calculation errors due to human error often occur.

• Waste of time and manpower: The series of tasks such as placing survey points, recording measurement points, drafting, and quantity calculation is very time-consuming and sometimes requires temporarily halting overall site work. On large or highly undulating sites, obtaining sufficient points for accuracy can take a long time. Therefore, frequent volume measurements have been difficult, and missing the right timing increases the risk of delayed situational awareness on site.

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

As described above, traditional methods exhibit issues such as variability in accuracy, low work efficiency, and difficulty in information sharing. Point cloud data and AR technologies, described next, are attracting attention as new approaches to solve these problems.

Advantages of calculating volume differences from point cloud data

Rapidly spreading in recent years, 3D point cloud data is bringing major innovation to on-site volume calculations. Point cloud data is digital data representing surfaces of terrain or structures as countless points (a set of 3D coordinates). Because detailed terrain shapes can be reconstructed from these point clouds, they are powerful for volume calculations.

Using point cloud data, volumes can be calculated directly from 3D models. There is no need to estimate volumes section by section as before; you can compare the entire current condition with the design surface. Specifically, you overlay the design model of the completed shape (or pre-construction original terrain data) and the latest current point cloud data and calculate the difference. With software, you can compute the difference between the two terrain models with the push of a button and accurately calculate the volumes of cut and fill down to the millimeter. Manual calculation errors are eliminated, allowing you to grasp precise differential earthwork volumes in a short time.

Another advantage of using point cloud data is the visual feedback it provides. The differential results can be displayed not only as numbers but as a color map (heatmap). For example, if areas higher than the design (excess fill) are colored red and areas lower than the design (excavated) are colored blue, it becomes immediately obvious where excess fill or unexcavated soil remains. This kind of differential visualization using point cloud heatmaps allows site personnel to intuitively understand the situation and instantly determine priority work areas.

Simple point cloud surveying using smartphone RTK

There are various methods to obtain point cloud data, such as laser scanning (LiDAR surveying) and drone photogrammetry, but smartphone combined with RTK for point cloud surveying has been attracting attention in recent years. RTK (real-time kinematic) is a technology that uses GNSS (global navigation satellite system) signals to achieve centimeter-level positioning accuracy in real time. Traditionally, performing RTK surveying required expensive dedicated GNSS equipment and setting up base stations. However, due to technological advances, small high-precision GNSS receivers that can connect to smartphones have emerged, making RTK positioning easy to realize.

Leveraging smartphone RTK, anyone can easily perform high-precision 3D surveying. By attaching a dedicated small RTK receiver device to a smartphone and launching an app, high-precision positioning begins in real time without complicated setup. While in this state, waving the smartphone’s camera or LiDAR sensor and walking around the site allows you to capture surrounding terrain and structures as digital point cloud data one after another. There is no need to carry heavy tripods or mount equipment, nor to file permission applications for drone flights. Simply moving the smartphone while walking the site completes a high-precision point cloud scan with the ease of shooting a video.

Point cloud data obtained with smartphone RTK is corrected so that positioning errors are within a few centimeters. Conventional built-in smartphone GPS had errors of several meters, but with RTK both horizontal and vertical positions are precisely corrected, so point cloud data acquired by smartphone can be used for differential earthwork calculations with accuracy comparable to conventional laser scanner surveys. It is now an era where site personnel can perform surveying themselves, preventing work interruptions while waiting for surveying and reducing outsourcing costs. For example, measurement work that used to be outsourced to specialist teams or external vendors can be completed by a single site person with smartphone RTK.

Visualizing differential earthwork volume with AR

Even if high-precision differential earthwork volumes are calculated using point clouds and RTK, it is important to convey the results clearly on site. This is where AR (augmented reality) technology proves powerful. AR is a technology that overlays digital information onto the real-world view displayed on a smartphone or tablet screen. Using this, you can display differential earthwork results directly over the actual scenery on site.

Specifically, the difference results between the design model and the current point cloud (heatmaps or 3D models) are displayed on the smartphone camera view. For example, areas that still need excavation can be shown as red semi-transparent mounds, while areas that have been over-excavated and are too low can be shown as blue semi-transparent zones over the live view. When you look at the real site through the smartphone screen, colored bumps and depressions that would otherwise be invisible appear to float in place. Differences that were hard to grasp from drawings or numbers become visually understandable on the spot.

AR visualization dramatically smooths on-site communication. For instance, if a site supervisor points the smartphone and instructs, "Let’s dig down 20 cm (7.9 in) in this red-displayed area," the heavy equipment operator can immediately understand the situation from the visual information on the screen. This allows clear instructions that are understood at a glance, rather than spreading paper drawings and verbally saying, "lower this ground elevation by ○ m (○ ft) …" Also, when a project owner or construction manager visits the site, they can confirm progress versus the design on the spot. As-built conditions that used to be explained via reports or drawings can be shared through AR in a way that gives the sense of seeing the real object on site, greatly increasing the persuasive power of explanations.

Improving on-site efficiency by instant sharing of point cloud data

Point cloud data acquired with smartphone RTK and the resulting differential earthwork data can be shared instantly via the cloud. If you upload the data to the cloud immediately after measurement, engineers or other team members in the office can view the latest information. This enables the entire company to share site changes in real time and use that for rapid decision-making.

The benefits of data sharing often show up as faster construction management. For example, at a certain land development site, the current condition was scanned with a smartphone once a week and weekly changes in earthwork volume were automatically calculated in the cloud. Sharing those results as heatmap charts at the morning site meeting made it possible to instantly determine "which areas should be prioritized for excavation or fill." Work that used to take more than a full day—survey teams measuring cross-sections on site and the office converting them to CAD and calculating quantities—has been completed in about 30 minutes by the site agent after introducing smartphone RTK. Because rapid data sharing allows each role to move quickly, waiting time is reduced and project schedules have been shortened.

Storing data in the cloud also enables history management and centralized information. Past point cloud data and differential results are saved in time series, making it easy to retrospectively verify "how much was excavated at that time." Survey data that tended to scatter across sites is organized in the cloud, and all stakeholders can access the latest version on the same platform. This helps prevent issues such as missing information or using incorrect drawings.

Recommendation for simple surveying with LRTK

By leveraging the advanced technologies described so far, measurement and sharing of differential earthwork volumes can be dramatically streamlined. However, some may feel that high-precision GNSS, point clouds, and AR sound complicated. This is where the all-in-one solution called LRTK is worth noting. LRTK is a surveying DX platform that combines high-precision GNSS receivers, a smartphone app, and cloud services, developed as a simple surveying tool that can be used even by non-experts.

With LRTK, you can perform centimeter-level positioning with a small RTK receiver attached to a smartphone while scanning the site with the phone’s camera or LiDAR to generate point cloud data, then calculate and visualize volume differences in the cloud—all in one seamless workflow. In other words, it is a package that includes all the functions needed for differential earthwork measurement. The UI/UX is designed so that site personnel can easily operate it with their own smartphones, and even first-time users can learn the operations with a short training period.

Introducing such tools allows companies to handle as-built surveys and volume calculations in-house instead of outsourcing them. As a result, costs are reduced and accumulated data can be leveraged 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 just checking differential earthwork volumes, solutions like LRTK enable a system where you can "understand more quickly and accurately and share it on the spot." A movement that could be called the democratization of surveying technology is underway now, accelerating on-site DX. If you feel challenges in streamlining or digitizing surveying tasks, you should consider trying a smartphone surveying workflow like this.

FAQ

Q: What data is needed to calculate differential earthwork volume? A: Basically, you need two terrain datasets you want to compare (or a terrain dataset plus a design model) to calculate differential earthwork volume. For example, point cloud data of "terrain before construction" and "terrain after construction," or a combination of the "design completed model" and the "current point cloud data." Overlaying these allows calculation of volumetric differences.

Q: What is smartphone RTK? Is there any problem with accuracy? A: Smartphone RTK refers to connecting a high-precision GNSS receiver to a smartphone and using RTK technology to enable centimeter-level positioning on the smartphone. It can achieve positioning accuracy comparable to dedicated equipment, so point cloud surveying with a smartphone maintains high accuracy. In many actual sites, measurements with errors within a few centimeters (within a few inches) have been confirmed.

Q: Compared to drone surveying, what are the advantages of smartphone point cloud surveying? A: Drone photogrammetry has the advantage of quickly surveying wide areas, but it is susceptible to operational constraints such as weather and no-fly zones. Smartphone point cloud surveying can be done on the ground even in rain and requires no preparation or permits, so it excels in mobility. You can measure immediately when needed by yourself. Also, because you scan from ground level, you can capture details such as wall irregularities that drones may have difficulty detecting. Both methods have their uses depending on the application, but the convenience of completing surveys with just a smartphone is a major attraction for site personnel.

Q: Do you need special equipment for AR-based differential visualization? A: No—basically, a commercially available smartphone or tablet is sufficient. AR display is performed through the smartphone screen, so as long as a compatible app is available, special AR glasses are not required. If you want to display and share on a larger screen, use a tablet or mirror the display to a large monitor when multiple people need to check.

Q: Can site staff use it effectively? Is specialized knowledge required? A: Yes—the systems are designed so that site staff can use them effectively. Smartphone surveying apps have intuitive UIs designed to be operated without worrying about difficult technical terms. Even first-timers can learn through simple training or manuals in a short time. There are increasing examples where construction management staff without surveying expertise conduct point cloud measurements and differential checks themselves, achieving efficiency gains.

Q: How much does implementation cost? A: Compared to purchasing conventional large surveying equipment and dedicated software, solutions using smartphone RTK can be started at significantly lower cost. You can use your existing smartphone, and the required equipment is usually just a small GNSS receiver, so initial investment is greatly reduced. Considering that surveying work previously outsourced can be handled in-house, the overall cost-effectiveness is very high.

Q: Point cloud data can be large—can it be handled by smartphones or the cloud? A: High-density point cloud data can indeed result in large file sizes. However, smartphone point cloud surveying solutions use techniques such as automatic compression/optimization and scanning only the necessary area to keep sizes manageable. By combining with cloud services, detailed processing is performed on servers while only necessary information is transferred to the smartphone. Therefore, it is possible to operate without overloading the smartphone’s storage or processing capacity. If the communication environment is adequate, heavy 3D data can be handled smoothly via the cloud, so you can confidently manage large-scale point cloud data.