Point Cloud Earthworks Volume Calculation with a Smartphone: Labor Reduction on Site Using LRTK

Table of Contents

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

• Traditional methods for earthworks volume calculation and the benefits of using point clouds

• Use cases of point cloud data on civil engineering sites

• Point cloud measurement with a smartphone: photogrammetry and LiDAR scanning

• Improving smartphone surveying accuracy with RTK

• Procedure for calculating volume from point cloud data

• Labor reduction on site with simple 3D surveying using LRTK

• FAQ

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

“Earthworks volume calculation” means computing the volume of soil, fill, or excavated material handled in civil engineering works. On construction sites, accurate understanding of earthwork volumes is essential for planning and quality control. For example, earthworks volume calculation is required in the following situations:

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

• Cutting (excavation): When excavating hills or ground to level land, the amount of soil excavated and transported is measured and compared with the design quantities to verify there are no discrepancies.

• Slope finishing: When shaping slopes created by cutting or filling to the designed profile, the amount of soil to remove or add is calculated.

• Land development: For site preparation of housing or development land, the volume of spoil or fill required to level the overall terrain is calculated for planning and cost control.

Thus, earthworks volume calculations are needed in many phases of civil works such as filling, excavation, slope finishing, and land development. Accurately calculating volumes enables appropriate procurement of soil and scheduling of transport, allowing smooth project management. Volume calculations are also important for verifying as-built shapes, serving as objective quantitative data for reporting to clients and recording post-construction quantities.

Traditional methods for earthworks volume calculation and the benefits of using point clouds

Traditionally, earthworks volume calculations have been performed by creating cross-sections from topographic survey data and using methods such as the average-end-area method to compute volumes. For example, heights measured at surveyed points at regular intervals are connected to draw cross-sections, and the area of each section is used to compute volume. However, this method has these drawbacks:

• It requires many points to be measured manually on site, which involves significant effort and time.

• Interpolation between surveyed points is required, so fine terrain features may not be fully represented and accuracy is limited.

• The calculations are done manually per cross-section, increasing the risk of errors and delaying results.

In contrast, the recently popular method is to use 3D point cloud data for earthworks volume calculation. High-density point cloud surveys of surface conditions before and after construction, or before and after fill/excavation, are acquired and volume is computed from the differences between the two 3D datasets. Using point cloud data has the following advantages:

• Improved accuracy: Point clouds are collections of a large number of points that densely sample the surface. They capture fine undulations that manual surveys may miss, improving the accuracy of volume calculations. In site validations, reported errors of volumes calculated from point clouds are often around 1% compared to traditional methods, showing comparable high accuracy.

• Efficiency: Once point cloud data are obtained, volumes can be automatically calculated using mesh methods (e.g., comparing TIN models), so additional field surveys and tedious calculations are unnecessary. Recomputing volumes for a different area is just a matter of performing calculations on the existing data. Field surveys themselves can be completed quickly, drastically shortening the time from data acquisition to quantity calculation.

• Labor reduction: Although point cloud measurements can be done with dedicated equipment or drones, recently it has become possible to perform them with a smartphone (described later). For example, a task that previously required four people for one week (28 person-days total) was completed by two people in one day (2 person-days) after switching to photogrammetry-based point cloud creation. This reduces required personnel while enabling rapid volume calculation and allows faster PDCA cycles in construction management.

• Data reuse: Acquired point cloud data can be archived as evidence or reused for later analyses. Storing point clouds provides objective evidence when reconciling quantities with the client after construction, and past data can be referenced if design changes or additional works occur. Point clouds provide detailed 3D records that paper drawings or photos cannot.

Because point cloud-based earthworks volume calculation excels in both accuracy and efficiency, its importance has been increasing. With government-led promotion of ICT construction and i-Construction, adoption of 3D surveying and new quantity calculation methods on sites is progressing.

Use cases of point cloud data on civil engineering sites

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

● Quantity control before and after excavation or filling In civil works, terrain data are acquired before and after construction, and comparing the design volume with actual constructed volume enables as-built (quantity) control. For example, in excavation work, the design excavation volume and the actual excavated-and-removed volume can be compared from point cloud data to verify whether the work was carried out according to plan. 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 works. If there is a shortfall, additional backfill can be arranged quickly; if there is excess, a spoil disposal plan can be made immediately. Being able to know quantities right after construction helps accurate progress and cost control. Saving the 3D point cloud as verification also smooths quantity reconciliation with clients. Previously, confirming as-built quantities required re-surveying by setting out and measuring heights point by point, but automatic calculation from point clouds greatly reduces site managers’ workload.

● Immediate volume measurement of small soil piles Point cloud data are useful not only for large-scale earthwork but also for daily small measurements. Examples include measuring the volume of spoil piles generated during work or stockpiles of materials like crushed stone. Traditionally, one would measure dimensions with a tape or surveying instrument to estimate volume, or hire specialists to measure later. With point cloud surveying, you can get accurate volumes immediately on site. Nowadays, site supervisors can scan a spoil pile in minutes using smartphone LiDAR or mobile 3D scan features and obtain volume instantly. Based on the result, they can adjust the number of machines operating or decide whether to order additional dump trucks, enabling real-time decision-making. The ability to revise construction planning on the spot, rather than waiting to bring survey data back to the office, is a major advantage. Immediate volume measurement with point clouds improves daily construction and quality control accuracy and speeds up on-site responses.

Point cloud measurement with a smartphone: photogrammetry and LiDAR scanning

When you hear “high-density point cloud,” you might think expensive 3D laser scanners or drones are necessary. Indeed, specialized equipment and skills were required in the past, but recently it has become possible to perform point cloud measurements with just a smartphone. There are two main approaches.

• Photogrammetry for point cloud generation This method generates 3D models or point clouds from multiple photos taken with a digital camera. Using dedicated photogrammetry apps, you can walk around the site with a smartphone and the app will automatically take multiple photos while concurrently building a 3D model (point cloud) in the background. There is no need to set up tripods or operate advanced equipment; the ease of obtaining precise point clouds simply by taking surrounding photos alone is appealing. Some solutions automate post-processing in the cloud, allowing high-accuracy point cloud generation without specialized knowledge. However, photogrammetry requires taking a sufficient number of photos to cover wide areas and time for image processing afterward. So in terms of immediacy it is inferior to LiDAR scanning, but it can cover wide terrain and large fills or excavations with inexpensive equipment. Aerial photogrammetry using drones is a similar approach but has regulatory and piloting hurdles. Smartphone photogrammetry requires no special licenses and can be performed safely from the ground, making it very convenient for small surveying tasks.

• Smartphone-mounted LiDAR scanning Some recent smartphones and tablets include LiDAR sensors (e.g., iPhone Pro series from iPhone 12 onward, iPad Pro). Using LiDAR, the device directly scans surrounding shapes with laser light and produces point clouds in real time. By launching a dedicated app and walking around the object holding the phone, you can obtain a high-density point cloud of millions of points in just tens of seconds to a few minutes. We have entered an era where “professional-grade 3D scanning in your pocket” is possible, and construction technicians have begun adopting smartphone point cloud measurement in daily work. The advantages of smartphone LiDAR measurement are its immediacy—measurement through point cloud generation can be completed on site—and its simplicity of operation. No complex preparation or instrument calibration is needed, enabling “anytime, anyone, easily” high-precision measurement. However, the coverage per scan is limited; for example, you may need to partition an area of several tens of meters square (several tens of ft square) and perform multiple scans that are later merged. Also, obtaining absolute coordinates (latitude/longitude or elevation) requires alignment with reference points. Even so, the mobility to measure immediately when needed outperforms other methods, and smartphone LiDAR scanning is often the optimal solution for small-scale fill checks or spoil volume confirmation.

Thus, smartphone point cloud measurement is realized via photogrammetry and smartphone LiDAR. Both methods share the advantage of eliminating the previously necessary expensive equipment and specialized skills, enabling on-site staff to perform measurements themselves. Point clouds obtained solely with a smartphone are essentially in local coordinates (an arbitrary coordinate system), but by combining with RTK positioning (described later), alignment to surveying coordinate systems and further accuracy improvement can be achieved.

Improving smartphone surveying accuracy with RTK

A key to making smartphone point cloud measurement practical on site is using RTK (Real-Time Kinematic) positioning. The accuracy of a typical smartphone’s built-in GPS is on the order of several meters, but RTK uses correction information from base stations to reduce positioning errors to a few centimeters. Historically, high-performance GNSS receivers were required, but recently small RTK-capable antenna units that can be paired with smartphones have emerged, making centimeter-level positioning (half-inch accuracy) easily attainable.

Combining RTK-derived high-accuracy coordinates with point clouds acquired by a smartphone provides the following benefits:

• Adding georeferenced coordinates: You can attach accurate world coordinates (latitude, longitude, elevation) on site to point clouds obtained with the smartphone’s LiDAR or camera. This allows directly overlaying point cloud data on design coordinates or public coordinate systems. Previously, manual comparison with survey control points or post-processing was necessary, but RTK-enabled smartphone surveying provides data automatically aligned on site.

• Improved scale accuracy: Photogrammetry can produce scale errors in parts of the model, but recording high-precision camera positions with RTK preserves the correct scale of the entire model. For smartphone LiDAR, assigning RTK coordinate references to the resulting point cloud ensures dimensional accuracy comparable to direct physical measurement. RTK is particularly useful for ensuring vertical (height) accuracy; since elevation errors translate directly into volume errors in earthworks calculations, capturing elevation differences with centimeter accuracy (half-inch accuracy) is important.

• Simplified control point surveying: For as-built management, conventional practice involved setting benchmarks and surveying each point relative to their known positions. With an RTK-capable smartphone, you can obtain positioning results based on public coordinates immediately, potentially eliminating the need for pre-established benchmarks or multiple known points. In other words, the smartphone becomes a mobile surveying instrument capable of measuring precise coordinates at arbitrary locations, enabling surveying to be completed with the minimum necessary personnel.

• Integration with other data: High-accuracy georeferenced point clouds are easily integrated with other survey or design data. For example, you can compare with design 3D models or earlier-acquired point clouds to compute difference volumes, or import point clouds into CAD drawings for as-built checks. Improved data compatibility and versatility streamlines subsequent analysis and reporting.

In this way, the smartphone × RTK combination is making high-accuracy surveying—previously requiring specialist equipment—accessible to everyone. On site, simply attaching a small GNSS antenna to the smartphone provides instant high-precision positioning, greatly improving surveying accuracy without increasing workload. The result is a new surveying workflow that balances speed, simplicity, and accuracy.

Procedure for calculating volume from point cloud data

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

• Acquire as-built point cloud data Obtain point clouds for the terrain or soil of interest in the two states you want to compare (e.g., before and after construction). For excavation work, acquire the terrain before excavation and after excavation; for filling, acquire the ground before filling and the surface after filling. For standalone volume measurements (e.g., pile of excavated soil), acquire the surface point cloud of the pile and later set a reference plane. Point cloud acquisition methods include smartphone photogrammetry and LiDAR scanning, drone imaging, or terrestrial laser scanning, but it is important to measure in the same coordinate system (align to a survey coordinate system with RTK or later register the point clouds).

• Process and clean the point cloud data Import the acquired point clouds into dedicated software or cloud services. Remove unnecessary noise and points outside the measurement area so only the points relevant to the volume calculation remain. Mask or delete surrounding buildings, machines, trees, or other unrelated objects. If handling multiple point clouds, perform alignment (merging) so they overlap in a common coordinate space. If RTK was used, they will generally already be aligned; otherwise use common control points or recognizable features to register the point clouds.

• Create surface models To calculate volumes from point clouds, the point sets must be converted into surfaces (meshes). Generate triangular meshes (TIN: Triangular Irregular Network) or grid models from the terrain point clouds in the software to create continuous surface models. Do the same for the comparison dataset. For standalone piles, set a reference plane (horizontal plane or an appropriate slope plane for inclined ground) and create mesh models between that reference and the pile surface.

• Compute volumes Calculate the volume difference between the two surface models. Typical software computes differential volumes by integrating prism volumes from height differences between mesh models, or sums volumes from multiple cross-section comparisons. The output might be statements such as “There is a shortage of ◯◯ cubic meters compared to design” or “The volume of fill above the reference plane is ◯◯ m³.” Some point cloud softwares also provide visual comparison displays coloring cut/fill areas so you can immediately see where material was removed or added.

• Use and verification of results Use the computed 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 cloud data are retained; if you want the volume of a specific zone, you can extract that region and recalculate without new fieldwork. If there is doubt about results, you can rescan on site and immediately verify. Rather than re-measuring later, additional on-site scans allow prompt data comparison and accelerate the PDCA cycle.

That is the basic flow. Although it may seem complex, there are now many software and services that automate everything from measurement to volume calculation. By uploading smartphone-acquired point cloud data to the cloud, tools can generate a report like “fill volume XX m³, cut volume YY m³” automatically. With these tools, operators can perform volume calculations via intuitive operations without managing each step manually.

Labor reduction on site with simple 3D surveying using LRTK

One solution that furthers smartphone surveying and contributes to labor reduction on site is LRTK. LRTK is a smartphone-integrated high-precision positioning system provided by Reflexia, consisting of a small RTK-GNSS antenna attachable to a phone called “LRTK Phone,” a dedicated surveying app, and cloud services. Attaching the LRTK unit to an iPhone and launching the app enables network RTK real-time positioning, instantly upgrading the smartphone’s position information to centimeter-level accuracy. The obtained position coordinates integrate with photo capture and point cloud scan functions so that LiDAR or camera data recorded by the smartphone are automatically tagged with high-precision coordinates. A major feature is that high-accuracy 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 site staff member.

Using LRTK makes it possible to perform point cloud measurement and volume calculation in real time and simply. For example, when scanning a fill or spoil pile with an LRTK-enabled app, the captured 3D point cloud is used to calculate volume instantly and display it on the smartphone screen. Because the point cloud is georeferenced with high-precision coordinates, you can compare results to reference elevations or design models and accurately compute fill/cut volumes on the spot. This drastically shortens the workflow that once required analyzing point clouds on a PC after acquisition, allowing you to know as-built quantities immediately after scanning. This supports rapid site decisions such as “decide today whether additional spoil removal is required” or “confirm missing backfill volume and order additional soil right away.” LRTK’s cloud integration automatically saves and shares point clouds and geotagged photos captured on site. You can share data in real time with colleagues in the office and compare multiple point cloud models accumulated over time online, expanding possible uses.

LRTK integrates easy smartphone measurement, high-precision positioning, and data processing into a single solution. Its user interface is accessible to anyone without specialized knowledge, making it an attention-grabbing tool that enables measurement without relying on surveying specialists—truly “one device per person” surveying. Tasks that formerly required significant manpower for as-built measurement and quantity calculation can be dramatically streamlined and labor-reduced with LRTK. As 3D technologies are expected to become more widely used in the civil engineering industry, adopting smartphone surveying devices like LRTK will help you improve on-site productivity without missing the trend. Try this new surveying approach using a smartphone and LRTK: with minimal effort you can achieve maximum results and elevate construction site management to the next level.

FAQ

Q. What is point cloud earthworks volume calculation? A. Point cloud earthworks volume calculation is a method of computing soil volumes from 3D point cloud data (a collection of many coordinate points). Traditionally, manual surveying and cross-section-based volume calculation were common, but point clouds allow calculating fill and cut volumes while capturing the entire terrain in detail. Because it can compute as-built quantities with high accuracy and efficiency, it is gaining attention in civil engineering.

Q. Can you really calculate volumes with a smartphone? A. Yes. Modern smartphones have high-performance cameras and LiDAR sensors; using dedicated apps to scan a site yields point cloud data. From those point clouds, volumes can be computed, allowing the entire process to be completed with a smartphone. For higher accuracy, pairing the phone with an RTK-capable antenna enables volume computation at accuracies comparable to surveying instruments.

Q. What is the difference between smartphone surveying and drone surveying? A. Drone surveying captures aerial photos over wide areas at once, making it suitable for large sites or areas that can only be measured from above. Drones require licenses and flight permissions and are affected by weather. Smartphone surveying is performed by walking on the ground, which takes more effort, but is easier and faces fewer regulatory hurdles. Smartphones work well in narrow spaces, indoors, or areas where drone flight is difficult. Accuracy depends on devices and methods, but smartphone + RTK can achieve point clouds comparable in accuracy to drone surveys. Choose between drone and smartphone based on site scale and purpose.

Q. Can surveying be done without RTK? A. Yes, point cloud surveying is possible without RTK. Scanning with a standalone smartphone camera or LiDAR produces a 3D model. However, without RTK there is no absolute georeference (latitude/longitude/elevation), so you must align to local control points for each site. Also, low GPS accuracy can produce small elevation errors that significantly affect volume calculations. Using RTK automates alignment and error correction, dramatically improving surveying accuracy and efficiency. For strict earthworks quantity control, RTK combination is recommended.

Q. What are the accuracy and errors of point cloud surveying? A. It varies by conditions, but RTK-enabled photogrammetry or smartphone LiDAR often achieve planar position accuracies within a few centimeters and vertical errors typically within a few centimeters to at most a few tens of centimeters (a few inches to at most a few tens of inches). With proper measurement, volumes computed from point clouds can be almost equivalent to traditional manual survey results (errors within a few percent). However, insufficient photo coverage or overly broad scan areas with data gaps can reduce accuracy, so adequate data acquisition and measurement planning are important. If validated site by site, practical and acceptable accuracy for volume control is achievable.

Q. Are implementation costs lower than traditional methods? A. Generally, using smartphones for surveying tends to have lower initial costs compared to dedicated 3D laser scanners or drone survey systems. You can start by installing an app on an existing smartphone, and RTK-capable antennas are relatively compact and affordable given their performance. Labor costs also decline because tasks that previously required multiple people can be done by one person. However, depending on the surveying objectives and required accuracy, traditional equipment may still be necessary in some cases, so choose the optimal method case by case.