Table of Contents

• What is earthwork volume calculation and why is it required in civil engineering?

• Traditional earthwork calculation methods and the advantages of using point clouds

• Use cases of point cloud data in civil engineering sites

• Smartphone-based point cloud measurement: photogrammetry and LiDAR scanning

• Improving smartphone surveying accuracy with RTK

• Steps to calculate earthwork volume from point cloud data

• Reducing on-site labor with simple 3D surveying using LRTK

• FAQ

What is earthwork volume calculation and why is it required in civil engineering?

"Earthwork volume calculation" is the process of computing the volume of soil, fill, or excavation handled in civil engineering works. On construction sites, accurate knowledge of earthwork volumes is indispensable for project planning and as-built management. Earthwork volume calculations are required in situations such as the following:

• Embankment (fill): For works that raise the ground level, the amount of fill material required to reach the specified elevation is estimated in advance, and the actual placed volume is checked.

• Cut (excavation): When excavating hills or ground to level a site, the volume of excavated and removed soil is measured and compared with the design quantities to verify there are no discrepancies.

• Slope shaping: When forming slopes created by cuts or fills (slope faces), the volume of soil to be removed or added to shape the slope to the design form is calculated.

• Land development: For site grading in residential or development projects, the volume of surplus soil or fill required for reclamation is calculated for planning and cost control.

Thus, earthwork volume calculations are necessary across many phases of civil engineering works, such as filling, cutting, slope shaping, and land development. By accurately computing earthwork volumes, you can properly arrange required soil materials and plan hauling schedules, enabling smooth project management. Volume calculations are also important for verifying the as-built shape; they provide objective quantity data for reporting to clients and for post-construction records.

Traditional earthwork calculation methods and the advantages of using point clouds

Traditional earthwork calculation typically involved creating cross-sectional drawings from survey data and using methods like the average-end-area method to compute volumes. For example, survey points measured at regular intervals on site are connected to draw cross sections, and volumes are calculated from the areas of those sections. However, this method has drawbacks:

• Many points must be measured manually on site, which requires a great deal of effort and time.

• Interpolation between survey points is based on assumptions, so small terrain undulations may not be captured, limiting accuracy.

• Calculation work is performed manually for each section, increasing the risk of errors and taking time to produce results.

In contrast, a recently notable method is earthwork calculation using 3D point cloud data. Surface models before and after construction or before and after filling/excavation are acquired as high-density point clouds, and the volume is computed from the difference between the two 3D datasets. The advantages of using point cloud data include:

• Improved accuracy: Point clouds are collections of many points that measure the surface thoroughly. They capture fine irregularities that manual surveys might miss, improving the accuracy of volume calculations. On-site verification has reported that volumes calculated from point clouds can have errors on the order of about 1% compared to traditional methods, showing comparable high accuracy.

• Efficiency: Once point cloud data are obtained, volumes can be automatically computed using mesh methods (e.g., comparing TIN models), so no additional field surveying or cumbersome manual calculations are necessary. If you need to recompute volumes for a different area, you can do so directly on the data. Field surveying itself can also be completed in a short time, significantly reducing the time from data acquisition to quantity calculation.

• Labor savings: Point cloud measurement can use specialized equipment or drones, but recently, as described below, it can be conveniently performed with a smartphone. In one case, work that previously required four people for one week (a total of 28 person-days) for volume measurement and calculation was completed by two people in one day (2 person-days) after switching to photogrammetry-based point cloud generation. This reduces required personnel while quickly producing volume estimates, enabling a faster PDCA cycle in construction management.

• Data reuse: Acquired point cloud data can be stored as evidence or used later for other analyses. For example, saving point clouds provides objective evidence for reconciling quantities with clients after construction, and past data can be referenced if design changes or additional work occur later. They are valuable as detailed 3D records that paper drawings or photos cannot provide.

Because point cloud-based earthwork calculation excels in both accuracy and efficiency, its importance has been growing. With trends like ICT-enabled construction and i-Construction promoted by the Ministry of Land, Infrastructure, Transport and Tourism, the adoption of 3D surveying and quantity calculation methods on sites is progressing.

Use cases of point cloud data in civil engineering sites

Point cloud-based earthwork calculation is used in various forms for actual construction site management. Here are some typical use cases.

● Monitoring as-built quantities before and after excavation or filling In civil works, terrain data are acquired before and after construction, and by comparing the design planned earthwork volumes with the actual constructed volumes, as-built management is conducted. For example, in excavation works, the design excavation volume calculated beforehand is compared with the actual excavated and removed volume obtained from point cloud data to verify whether the work was completed correctly. Using point cloud surveying provides a detailed surface model of the site in a short time, enabling on-the-spot verification of as-built volumes immediately after construction. If there is a shortage, additional backfill can be arranged promptly, and if there is a surplus, plans for disposal of remaining soil can be made quickly. Being able to determine quantities immediately after construction allows precise progress and cost control. Also, storing 3D point cloud data as evidence makes quantity reconciliation with the client smoother. Previously, after completion, it was common to re-measure heights at stake points or with surveying instruments and produce cross sections, but automatic calculation from point clouds greatly reduces the burden on site managers.

● Immediate volume measurement of small-scale soils Point cloud use is powerful not only for large earthworks but also for daily small measurement tasks. Examples include measuring the volume of a mound of remaining soil generated on site or the volume of stockpiles of crushed stone and other materials. Previously, these might have been roughly estimated with tape measures or surveying instruments, or measured later by a specialist, but point cloud measurement allows precise volumes to be quantified on site immediately. Recently, with smartphone LiDAR and mobile device 3D scanning, site supervisors themselves can scan a pile of remaining soil in minutes and instantly know its volume. Based on those results, they can adjust the number of operating machines or decide whether to arrange additional dump trucks—enabling real-time decision-making. The ability to revise construction schedules on the spot, which previously required returning with survey data, is a major advantage. Immediate volume assessment via point clouds improves daily construction management and as-built verification accuracy and speeds up on-site responses.

Smartphone-based point cloud measurement: photogrammetry and LiDAR scanning

Hearing that you can obtain high-density point cloud data may make you think "don't you need an expensive 3D laser scanner or a drone?" Indeed, specialized equipment and skills were traditionally required, but recently it has become possible to perform point cloud measurement with just a smartphone. There are two main approaches:

• Point cloud generation by photogrammetry This method generates 3D models or point clouds from multiple photos taken by a digital camera. With dedicated photogrammetry apps, simply walking around the site with a smartphone in hand will automatically capture multiple photos while a 3D model (point cloud) is built in the background. There is no need to set up a tripod or operate advanced equipment as in traditional surveying; the ease of obtaining precise point clouds simply by one person taking surrounding photos is attractive. Some solutions also automate post-processing in the cloud, allowing high-accuracy point clouds to be generated without specialist knowledge. However, photogrammetry requires taking a sufficient number of photos to cover wide areas and requires processing time for image processing afterward. Therefore, in terms of immediacy, it is inferior to the LiDAR scanning described below, but it has the advantage of covering large terrains and large fills or cuts with relatively inexpensive equipment. Aerial photogrammetry using drones is one such method, but it has regulatory and piloting hurdles. Smartphone photogrammetry requires no special qualifications and is safe to perform from the ground, making it very convenient for small-scale surveying tasks.

• Scanning with smartphone-mounted LiDAR Some of the latest smartphones and tablets include built-in LiDAR sensors (e.g., iPhone Pro series from iPhone 12 onwards, iPad Pro). Using LiDAR, you can directly scan surrounding shapes with laser light and generate point cloud data in real time. By launching a dedicated app and walking around the object with the smartphone in hand, you can acquire high-density point clouds consisting of millions of points in just tens of seconds to a few minutes. We are now in an era where "professional-grade 3D scanning from a device in your pocket" is possible, and construction technicians are beginning to incorporate smartphone point cloud measurement into their daily work. The advantages of smartphone LiDAR measurement are the immediacy of completing measurement and point cloud generation on the spot and the simplicity of operation. No complex preparation or equipment calibration is required, and anyone can easily perform high-precision measurement anytime. However, the measurable range at one time is limited, so you may need to scan sections of about tens of meters square and later merge them. Also, to obtain absolute coordinates (latitude/longitude or elevation), alignment with reference points is required. Even so, the mobilization to "measure immediately when needed" outweighs other methods, allowing agile on-site responses. Smartphone LiDAR scanning is particularly suitable for small-scale volume checks like those mentioned above.

Thus, smartphone-based point cloud measurement is realized by two methods—photogrammetry and smartphone LiDAR. Both share the feature that "they remove the need for costly equipment and specialist skills previously required and enable site staff to perform measurements themselves." Point clouds acquired solely by a smartphone are basically in local coordinates (an arbitrary coordinate system), but when combined with the RTK positioning described below, they can be aligned with survey coordinate systems and further improve accuracy.

Improving smartphone surveying accuracy with RTK

A key to making smartphone point cloud measurement practical on site is the use of RTK (real-time kinematic) positioning. Typical smartphone GPS accuracy is on the order of several meters, but RTK uses correction information from a base station to reduce positioning errors to a few centimeters. Previously, a high-performance GNSS receiver for surveying was required, but recently small RTK-capable antenna terminals that can be integrated with smartphones have appeared, enabling centimeter-class positioning easily.

Combining RTK high-accuracy coordinates with point cloud data obtained by a smartphone offers the following advantages:

• Attaching position coordinates: You can assign accurate world coordinates (latitude, longitude, elevation) on site to the point cloud acquired by a smartphone's LiDAR or camera. This allows point cloud data to be directly overlaid with design coordinate systems or public coordinate systems. Traditionally, manual comparison with control points or post-processing was necessary after measurement, but RTK-capable smartphone surveying provides data that are already position-aligned on site.

• Improved scale accuracy: Photogrammetry can sometimes introduce scale errors in parts of the model, but recording high-precision shooting positions with RTK helps maintain the correct overall scale of the model. For smartphone LiDAR measurements, applying RTK coordinate references to the obtained point cloud ensures measurement accuracy comparable to physical measurement with a tape measure. RTK is particularly useful for ensuring vertical (height) accuracy, and because height errors directly affect volume error in earthwork calculations, capturing elevation differences to within a few centimeters is important.

• Simplified control point surveying: Traditional as-built management required surveying many known points (benchmarks) installed on site and using their heights and positions as references. With an RTK-capable smartphone, you can obtain positioning results based on public coordinates instantly, which can eliminate the need for prior benchmark alignment or installing many known points. In other words, the smartphone itself becomes a mobile surveying instrument that can measure precise coordinates at any chosen location, allowing on-site surveying to be completed with minimal personnel.

• Integration with other data: Point clouds with high-accuracy position information are easy to integrate with other survey or design data. For example, you can compute difference volumes by comparing them with a design 3D model or point cloud data acquired at other times, or import measured point clouds into CAD drawings for direct as-built inspection. Improved data compatibility and versatility also streamline subsequent analysis and reporting.

Thus, the combination of smartphone and RTK is making high-precision surveying—previously requiring specialized equipment—accessible to anyone. On site, simply attaching a small GNSS antenna to a smartphone enables instant acquisition of high-precision position information without increasing workload, dramatically improving survey accuracy. The result is a new surveying workflow that achieves both speed/simplicity and accuracy.

Steps to calculate earthwork volume from point cloud data

How do you actually calculate earthwork volumes from acquired point cloud data? Here are the basic steps.

• Acquire the as-built point cloud data Capture point cloud data of the terrain or soil for the two states you want to compare, such as before and after construction. For excavation work, measure the terrain before and after excavation; for filling works, measure the ground before filling and the surface after filling. For standalone volume measurements (e.g., a pile of soil), acquire the surface point cloud of the pile and later define a reference surface. Point cloud acquisition methods include smartphone photogrammetry and LiDAR scanning, drone imagery, and terrestrial laser scanning; however, it is important to measure in the same coordinate system (either by using RTK to align to a survey coordinate system or by registering point clouds to each other later).

• Process and clean the point cloud data Import the acquired point clouds into dedicated software or cloud services. First remove unnecessary noise or points outside the measurement range so that only the points relevant to the volume calculation remain. If surrounding buildings, machinery, or trees are included and unrelated to the earthwork, remove or mask those point clouds. When handling multiple point clouds, perform alignment (registration) so they overlap in a common coordinate space. If RTK was used during measurement, they will generally already be aligned; otherwise, use common control points or feature points to integrate the point clouds.

• Create surface models To compute soil volumes from point clouds, you need to convert the point set into a surface (mesh). Generate triangular meshes (TIN: Triangular Irregular Network) or grid models from the terrain point clouds to create continuous surface models. Do the same for the comparison dataset. For single piles compared against a reference plane, set the ground as a horizontal plane (or an appropriate reference plane for sloping ground) and create a mesh model between that plane and the pile surface point cloud.

• Calculate volume Compute the volume difference between the two surface models. Common software calculates differential volume by summing prism volumes from height differences between mesh models, or by aggregating volumes from multiple cross-section comparisons. The result will yield figures such as "the volume is short of the design by ◯◯ cubic meters" or "the fill volume above the reference plane is ◯◯ m³." Point cloud processing software can also provide visual comparative displays of fills and cuts via color coding, making it easy to see where and how much material was removed or added.

• Use and verify results Use the calculated volumes for construction management. Submit them as as-built quantities to the client or reflect them in future schedule adjustments. Recalculation for different areas or conditions is easy. Because the point clouds are retained, you can extract a particular area and recalculate without new surveys. If results are questionable, you can re-scan on site for immediate verification. Rather than re-measuring afterward, additional measurements can be taken as needed and compared instantly, enabling a rapid PDCA cycle on site.

That is the basic workflow. Although it may seem complex, software and services that automate everything from measurement to volume calculation are increasingly available. Simply uploading smartphone-acquired point clouds to the cloud can produce reports like "fill volume ◯◯ m³, cut volume ◯◯ m³." As each step becomes more integrated, site personnel will soon be able to perform earthwork volume calculations with intuitive操作 without needing to handle each process separately.

Reducing on-site labor with simple 3D surveying using LRTK

One solution that further advances smartphone surveying and contributes to reducing on-site labor is LRTK. LRTK is a smartphone-integrated high-precision positioning system provided by Reflexia, consisting of a small RTK-GNSS antenna that can be attached to a smartphone called the "LRTK Phone," a dedicated surveying app, and cloud services. By attaching the LRTK device to an iPhone and launching the app, network RTK real-time positioning becomes possible, instantly improving the smartphone's position information to centimeter precision. The acquired position coordinates are linked to photo capture and point cloud scan functions, automatically assigning high-precision coordinates to data recorded by the smartphone’s built-in LiDAR or camera. A key feature is that high-precision 3D surveying can be completed with a single smartphone, enabling as-built measurements that previously required drone + GPS base stations or expensive laser scanners to be performed by a single field staff member using LRTK.

Using LRTK, on-site point cloud measurement and volume calculation can be performed in real time and with ease. For example, when scanning a fill or a pile of remaining soil with an LRTK-enabled smartphone app, the acquired 3D point cloud data are instantly used to compute volume, which is displayed on the smartphone screen. Because the point clouds have high-precision position information, the results can be compared with reference elevations or design models to accurately calculate fill and cut volumes on the spot. This dramatically shortens the workflow that previously required analyzing point clouds on a PC after acquisition, allowing site personnel to understand as-built quantities immediately after scanning—for example, determining on the same day whether additional soil removal is required or immediately checking backfill volumes to order shortages. By integrating with LRTK’s cloud service, point clouds and geotagged photos acquired on site are automatically saved and shared to the cloud. Colleagues in the office can share data in real time, and accumulated point cloud models over time can be compared and analyzed online, expanding the range of applications.

LRTK integrates easy measurement with high-precision positioning and data processing into one solution. Its user interface is accessible to anyone and requires no specialist knowledge, making it notable as a tool that enables surveying without relying on a dedicated surveying team—effectively ushering in an era where "one person, one device" can perform measurements. Workflows that formerly required many personnel for as-built measurement and quantity calculation can be remarkably streamlined and labor can be reduced with LRTK. As the civil engineering industry increasingly adopts 3D technologies, introducing smartphone surveying devices like LRTK will help you improve on-site productivity without falling behind. Take this opportunity to try new surveying methods using smartphones and LRTK: they can help you achieve maximum results with minimal effort and elevate construction site management to the next level.

FAQ

Q. What is point cloud earthwork volume calculation? A. Point cloud earthwork volume calculation is a method of determining soil volumes from 3D point cloud data (a collection of many coordinate points). Traditionally, manual surveying and cross-section-based volume calculations were common, but using point clouds allows you to capture the entire terrain in detail and calculate fill and cut volumes. It provides high accuracy and efficiency in computing as-built quantities, making it attractive for construction sites.

Q. Can volume calculation really be done with a smartphone? A. Yes, it is possible. Modern smartphones have high-performance cameras and LiDAR sensors, and with dedicated apps you can scan sites to obtain point cloud data. Volume calculation can be completed using the point clouds captured by a smartphone alone. For higher accuracy, using an RTK-capable antenna with the smartphone allows volume computation at precision comparable to surveying equipment.

Q. What is the difference between smartphone surveying and drone surveying? A. Drone (UAV) surveying captures aerial photogrammetry over a wide area at once, making it suitable for large sites or places only measurable from the air. However, drone flights require qualifications and flight permissions and are affected by weather. Smartphone surveying is performed from the ground by personnel walking the site; while it requires more effort, it is easy and faces fewer regulatory hurdles. Smartphones can measure in narrow areas or indoors where drones cannot fly. Accuracy depends on devices and methods, but smartphone + RTK can obtain point clouds with accuracy comparable to drone surveying. Choose between drone and smartphone based on site scale and use.

Q. Can surveying be done without RTK? A. Point cloud surveying is possible without RTK. Scanning with a smartphone’s camera or LiDAR can produce a 3D model. However, without RTK, the point cloud lacks absolute coordinates (latitude/longitude or elevation), which requires additional work to align to site-specific reference points. Also, lower GPS accuracy can cause small vertical errors that significantly affect volume calculations. RTK automates position alignment and error correction, dramatically improving surveying accuracy and efficiency. For strict earthwork control, using RTK is recommended.

Q. What is the accuracy and error range of point cloud surveying? A. It varies with conditions, but RTK-assisted photogrammetry and smartphone LiDAR measurements often achieve planar position accuracy within a few centimeters and vertical errors within a few centimeters to at most a few tens of centimeters. With proper measurement, volumes calculated from point clouds can match traditional manual survey results (errors within a few percent). However, insufficient photo coverage or gaps in wide-area scans will reduce accuracy, so adequate data acquisition and measurement planning are important. With on-site validation, practical earthwork management can be achieved at acceptable accuracy.

Q. Is the introduction cost lower than traditional methods? A. Generally, using smartphones for surveying has a lower initial cost compared to dedicated 3D laser scanners or drone systems. You can start by installing an app on an existing smartphone, and RTK-capable antennas are relatively compact and affordable for their performance. Labor costs can also be greatly reduced since tasks that previously required multiple people can be done by one person. However, depending on the surveying purpose and required accuracy, traditional equipment may still be necessary in some cases—so choose the optimal method according to each situation.