Thorough Guide to As-Built Volume Measurement! Easy, High-Precision Methods Using Point Cloud Scans

Table of Contents

• What is as-built volume measurement?

• Situations that require volume measurement

• Traditional volume measurement methods and their challenges

• Benefits of as-built volume measurement using point cloud scans

• Procedure for measuring volume with point cloud scans

• Comparison of instruments and methods used for point cloud measurement

• Conclusion: Recommendation for simple surveying with LRTK

• FAQ

What is as-built volume measurement?

As-built volume measurement is the process of measuring the volume of completed terrain or structures in civil engineering and construction to verify whether the as-built condition matches the design. Examples include embankments and excavations for roads, and fills for dams and levees—basically quantifying the amount of earth or materials produced by construction. In as-built management, dimensions and shapes such as width, thickness, and height are usually checked, but volume is also an important element. This is because as-built volume directly relates to the work quantity (amount of work completed), which is essential for cost calculation and quality verification.

In public works, it is necessary to prove conformity with the as-built management standards defined by the client, and volume measurement is part of that. For example, as-built volume measurement is performed to provide objective data showing whether the prescribed fill amount has been secured or whether excessive excavation has occurred. Traditionally, heights at limited points were measured by manual surveying and volumes were estimated by calculation. However, today, methods that utilize 3D point cloud data to more accurately and efficiently calculate the volume of the entire completed terrain are attracting attention. This article thoroughly explains the basics of as-built volume measurement and the latest measurement methods using point cloud scanning.

Situations that require volume measurement

Let’s identify the main situations in civil engineering and construction where volume measurement is needed. A representative case is earthworks. For embankments and cut-and-fill in roads and development sites, it is necessary to confirm whether earthwork has been placed or removed according to the planned volume. As-built inspections submit data such as “fill volume: ○○ m³” and verify whether there are discrepancies from contract quantities. Similarly, in dredging works for rivers or ports, measuring the volume of dredged material is important. These tasks are also related to progress/quantity management (verification of construction quantity) and form the basis for progress reports and billing to the client.

Volume measurement is also useful for managing residual soil and materials. Measuring the fill volumes of stockpiled soil or aggregate on site allows accurate estimation of the number of trucks needed for transport and better inventory management. Where previously volumes were roughly estimated by visual inspection or by measuring a few heights, 3D scanning now makes it easy to obtain accurate volumes. As-built volume measurement is thus indispensable across a wide range of scenarios, from quality control of construction to cost management.

Traditional volume measurement methods and challenges

First, let’s review the traditional volume measurement methods used before point cloud scanning. Typical methods were manual calculations using the average end-area method or the grid method. Heights and widths were measured at key points on site, cross-sections or grid elevation data were created, and volumes were calculated from those. For example, cross-section surveys might be conducted at 10 m (32.8 ft) intervals to determine the area of each section; the volume for each interval would be calculated by multiplying the average of adjacent section areas by the interval distance. This calculation has long been used as a basic earthwork quantity method.

However, several challenges with traditional methods have been pointed out. The first is the issue of coverage and accuracy. Manual surveying can only measure a limited number of points, so the amount of information obtained at once was very small. Even for wide embankments, only a few height points could be measured, and the overall volume had to be estimated by connecting those points. This can overlook subtle irregularities or local excesses/deficits. In practice, even if cross-sections at key points match the design, unexpected hollows or overfills between those sections can go unnoticed. The inability to capture surface and volumetric shapes was a limiting factor for accuracy.

Second is the issue of work efficiency. Traditional methods required surveyors and technicians to go to the site and measure point by point. When using a total station (TS) with a prism, relocating and setting up for each survey point on a wide site required enormous effort and time. Creating many cross-section drawings and calculating areas by hand was a major burden. In some cases, confirming as-built volumes could take several days, during which construction might be halted. It was common to “wait several days to confirm a few centimeters of discrepancy,” slowing overall project progress.

Third, safety concerns cannot be ignored. Tasks such as having people walk steep slopes to measure as-built shapes or stretching tapes near operating heavy machinery pose constant hazards. Measurements on heights, slopes, or deep excavations carry risks of falls and collapse. Traditional methods required personnel to enter these areas, making it difficult for site managers to quickly and safely ascertain volumes.

In summary, traditional as-built volume measurement had problems: “only point measurements,” “labor- and time-intensive,” and “unavoidable dangerous work.” A new solution that addresses these issues is the measurement method using point cloud scanning, described next.

Benefits of as-built volume measurement using point cloud scans

A point cloud scan is a technique that acquires objects or terrain as a collection of countless points (a point cloud) using laser measurement or photogrammetry. Recently, the use of point cloud data has dramatically advanced as-built management. Let’s look at the benefits of introducing point cloud scanning for as-built volume measurement.

• Higher accuracy through full-surface geometry capture: Point cloud data records the entire site as a 3D collection of points. Because it can measure the entire surface at high density, it can capture irregularities down to the millimeter level. Instead of estimating volume from a few height points, point clouds allow volume to be accurately calculated everywhere based on actual measurements. By comparing the acquired point cloud with the design model (3D data), you can evaluate across surfaces where and how much fill is missing or excess. Small errors that humans overlooked can be detected, and the accuracy of as-built management is dramatically improved.

• Improved efficiency and labor savings: Point cloud measurement can capture millions of points at once, enabling rapid surveying of wide areas. With drone photogrammetry, current point clouds of a large development site can be obtained in about half a day, and terrestrial laser scanning reduces measurements that used to take days to a matter of hours. Since volume calculations and cross-section generation can be automated from the acquired point cloud data, manual calculations and drawing creation are greatly reduced. As a result, the time required for as-built volume inspection is shortened, and results can often be obtained the same day without waiting for a survey team. In some cases, measurement can be completed by a single person, helping address labor shortages.

• Improved safety: Point cloud scanning is essentially non-contact surveying. Since data can be obtained from a safe distance using laser light or camera imaging, workers do not need to enter hazardous areas. Cliffs, steep slopes, and deep excavations can be captured by drone aerial photography or long-range laser scanning with zero risk. Scanning can be done from around the site without stopping operating machinery, reducing work interruptions. This lowers the risk of accidents during surveying and strengthens on-site safety management.

• Effective use of data and visualization: 3D data acquired as point clouds can be digitally stored, improving recordability. Uploading data to the cloud allows stakeholders to remotely check as-built conditions. For volume specifically, one useful application is visualizing differences between point clouds and design data as a heat map. Displaying areas matching the design in green, underfilled areas in blue, and overfilled areas in red gives an intuitive view of construction discrepancies across the site. Systems can also automatically calculate shortage and excess volumes and provide immediate answers to “how many cubic meters of fill are needed where” or “how many cubic meters should be removed from where.” Point cloud scanning has made as-built volume inspection quantitative and visual. Acquired data can also be reused for future maintenance or additional construction to analyze changes over time.

As described above, point cloud scanning for as-built volume measurement surpasses traditional methods in terms of accuracy, efficiency, safety, and data utilization. For these reasons, the Ministry of Land, Infrastructure, Transport and Tourism promotes the introduction of 3D surveying technologies as part of ICT construction and *i-Construction*, and guidelines such as the “Guidelines for As-Built Management Using 3D Measurement Technology (draft)” are being developed to formalize point cloud-based inspection methods. Validation tests have shown that volumes calculated from point clouds have high reliability, with errors of about 1% compared to results from traditional cross-section methods. In other words, volume measurement by point cloud scanning is not only accurate but is becoming the new standard due to its speed and comprehensiveness.

Procedure for measuring volume with point cloud scans

Next, we explain the general procedure for measuring as-built volume using point cloud scans. Even though this is modern technology, the basic flow is not difficult to grasp.

• Planning the measurement: First, plan which measurement method and equipment to use according to the target area and required accuracy. For a large development site, choose drone aerial photography; for detailed measurement of a structure, use a terrestrial laser scanner. If control points are needed, install them in advance. Also prepare design data (completed 3D model or drawings) if available.

• Acquiring point cloud data: Acquire point clouds on site according to the plan. For drone photogrammetry, take sufficient overlapping photos for later point cloud generation by software. For a laser scanner, set it on a tripod and scan, moving and scanning multiple times as needed to cover the whole area. When using a smartphone LiDAR scanner, hold the device and walk around the subject to scan. The important point is to cover the entire area with overlap so nothing is missed. Place targets or markers as needed so that multiple scans can be registered later.

• Processing point cloud data: Import the acquired point cloud data into PC software or cloud services. First remove unnecessary points (noise such as people or vehicles), then register multiple scans into a single coordinate system. For drone photogrammetry, photo-processing software will automatically generate point clouds and perform alignment. If control points were used, adjust the overall model to them. For smartphone scans, you may transform the point cloud later to align with known points. However, if RTK-capable equipment is used and the point cloud is acquired with absolute coordinates at capture, this processing can be simplified.

• Calculating volume: Calculate volume using point cloud processing software. There are mainly two methods. One is comparison with a reference surface. For example, for a fill, calculate the fill volume from the difference between the existing ground surface (or the planned design ground surface) and the completed fill point cloud. Overlay the point cloud and reference surface and integrate vertical differences to get volume. The other is comparison with the design model. If a completed 3D design model exists, compare it with the as-built point cloud to calculate differential volume. In either method, the software generates triangulated irregular networks (TIN) or mesh models from the point cloud and computes the volume difference between the two models. The result yields numbers such as “fill: ○○ m³” or “excavation: △△ m³” and “+▲% vs. design.”

• Verification and output of results: Verify that the calculated volume is reasonable. Compare with key cross-sectional volumes or known transport quantities as needed. If acceptable, output the results in reports and drawings. A point-cloud-specific output is the previously mentioned heat map used for as-built inspection. For example, overlay a color-coded map on the as-built plan to intuitively show local fill excesses and shortages—this is useful for explaining results to clients. Finally, storing the data in the cloud creates a record useful for future tracking or third-party verification.

That is the overall workflow. The parts that used to be measured and calculated manually for each cross-section are now largely automated and digitized with point clouds. Especially once a point cloud is captured, arbitrary cross-sections can be cut and recalculated later, avoiding the need to “return to the site because something was not measured.” If proper procedures are followed, point cloud scanning for volume measurement is a process that reliably yields results for anyone.

Comparison of instruments and methods used for point cloud measurement

There are several instruments and methods available to implement point cloud-based as-built measurement. Each has its characteristics and should be chosen according to site scale and purpose.

• Terrestrial 3D laser scanner: A device placed on a tripod that scans 360 degrees with a laser. It acquires high-density point clouds with millimeter-level precision. It is suitable for precisely recording the detailed shape of structures and slopes. However, the equipment is expensive, and covering large areas requires multiple relocations and advanced measurement planning. It is powerful for measuring as-built shapes of confined sites or structures.

• Drone photogrammetry: This method equips a camera on a drone and generates point clouds from many aerial photos. Its greatest advantage is rapid acquisition of large-area terrain, making it widely used for measuring volumes in development sites and quarries. Recently, high-resolution cameras and RTK-equipped drones have made it possible to acquire point clouds with centimeter-level accuracy (half-inch accuracy). However, aerial operations require compliance with aviation laws and pilot skills, and are affected by weather (wind and rain). Photo-based point cloud generation can also require significant computation time.

• UAV-mounted laser scanner: This method mounts a small laser scanner on a drone. Compared to photogrammetry, laser measurement can more easily capture terrain under vegetation and tends to offer more stable accuracy, but equipment costs are very high. This is geared toward large surveying companies and specialists; the barrier for direct adoption by typical construction sites is relatively high.

• Mobile mapping / vehicle-mounted LiDAR: A method that mounts laser scanners and cameras on a vehicle to acquire point clouds while driving. It is beginning to be used for as-built measurement and quantity management in roadworks. It can continuously measure large areas, but requires dedicated vehicles and equipment and involves substantial initial investment.

• Smartphone + GNSS (such as LRTK): A recently notable method uses the smartphone’s built-in LiDAR sensor. iPhone and iPad Pro models include LiDAR that can measure depth several meters ahead, enabling simple point cloud scanning. By itself, positioning accuracy is low and not suitable for professional work, but combining it with a high-precision GNSS RTK receiver makes it powerful. For example, the system called LRTK, which consists of a small RTK-GNSS device that attaches to a smartphone and a dedicated app, enables collection of precise 3D point cloud data with real-time position corrections simply by walking with a smartphone. This approach realizes RTK surveying and point cloud scanning in a palm-sized form, attracting attention for its low initial cost and ease of operation. The measurement range is limited to where a person can walk, but performance is sufficient for small- to medium-sized sites, detailed measurements, and routine progress management.

Each method has pros and cons, but the common trend is that the barrier to acquiring point clouds is lowering. 3D measurement that once required specialist contractors can now be performed with familiar tools like drones and smartphones. Particularly, smartphone-based systems like LRTK are designed to be user-friendly even for non-surveying construction managers, making “easy high-precision surveying for anyone” increasingly possible. By choosing the optimal method for the site scale and purpose, point cloud scanning for as-built volume measurement is by no means difficult.

Conclusion: Recommendation for simple surveying with LRTK

RTK-enabled point cloud scanning technology is transforming surveying and management practices at construction sites. The revolutionary style of a smartphone becoming a surveying instrument symbolizes on-site DX (digital transformation). The lowering of the threshold for as-built volume measurement—previously dependent on surveying specialists—to the point where site personnel can perform it routinely is significant, and is expected to strengthen quality control and improve productivity as a next-generation on-site tool.

In particular, RTK point cloud scanning with smartphone + LRTK provides new value to site management through the freedom to measure “anytime, anywhere, and alone.” There is no need to stop work to confirm as-built accuracy or to take unreasonable risks to perform manual measurements in dangerous areas; the PDCA cycle (plan-do-check-act) on site will accelerate. Fully utilizing the acquired 3D point cloud data to enhance on-site visualization can lead to early detection of previously unseen problems and smoother information sharing among stakeholders, yielding significant secondary benefits. Accurate positioning data also supports rapid decision-making for safety management and environmental measures, contributing to a safer and more secure construction system.

Given these advantages, the best way to understand point cloud scanning is to see it in action. Start by trying it on a familiar small scale. Introducing LRTK for small-scale fill volume measurements or during-construction as-built checks will let you experience its ease and usefulness. Adopting new technologies proactively will help your site evolve to the next stage. The “surveying with a smartphone” style enabled by LRTK has the potential to become the standard for surveying in the future. Take this opportunity to use cutting-edge simple surveying tools and experience increased efficiency and sophistication in as-built volume measurement and construction management. You will likely find significant changes in work processes and tangible benefits in both quality and productivity.

FAQ

Q. Can point cloud scanning really measure volume accurately? A. Yes—if planned and executed properly, high accuracy can be achieved. Point clouds from the latest laser scanners and photogrammetry can secure accuracy within a few centimeters when corrected with control points. Validation experiments report that volumes calculated from point clouds are nearly equivalent to those from traditional cross-section methods (errors around 1–2%). This level of accuracy meets the Ministry of Land, Infrastructure, Transport and Tourism’s as-built management standards and is suitable for official inspections and deliverables. However, to ensure accuracy it is advisable to take basic measures such as installing control points and performing repeated measurements for checks.

Q. Can non-experts perform volume measurement using point clouds? A. Yes. Dedicated analysis software and tools can automate everything from point cloud alignment to volume calculation. Systems such as LRTK are designed to be operable by non-surveying site staff; with a smartphone app, you can acquire point clouds and calculate volumes with the press of a button. There is no need to perform complex manual calculations—anyone who understands the basic workflow can learn it with short training. Vendors and service providers also offer support and training materials, so questions can be resolved quickly.

Q. What equipment and preparations are required to introduce point cloud scanning? A. Requirements depend on the acquisition method, but generally you need the measurement device and positioning equipment. For drone photogrammetry you need a drone and a high-precision GPS, photo-processing software, and targets for calibration as necessary. For terrestrial laser scanners you need the scanner, accompanying software, a tripod, and site targets. For smartphone + LRTK, you basically need a LiDAR-equipped smartphone and an LRTK receiver (iPhone or iPad Pro models are recommended). Additionally, RTK positioning requires subscribing to a GNSS correction service. These services provide correction data over the network and are offered by the Geospatial Information Authority of Japan, private companies, and mobile carriers. LRTK purchases often include guidance or trials for an appropriate correction service. Once initial setup is complete, you can power on at the site and start measurement, so the introduction hurdle is much lower than before.

Q. What about locations without radio or GPS coverage? A. Even in areas without communication or GNSS—such as indoors or tunnels—there are workarounds. One approach is to use terrestrial surveying equipment and known control points together. For example, in tunnels you can obtain coordinates of control points near the entrance and register scans from a laser scanner relatively. Higher-end LRTK models may support options that receive centimeter-class correction signals (CLAS) from Japan’s Quasi-Zenith Satellite System (QZSS), allowing direct reception of correction data from satellites even without cellular coverage. Post-processing kinematic (PPK) GPS, which does not require real-time communication, is another option for high-precision positioning. By selecting appropriate methods based on site conditions, you can gain the benefits of point cloud measurement even in mountainous or underground environments.

Q. I’m concerned about cost. Are there low-budget options for point cloud measurement? A. Large equipment does indeed cost more, but there are increasingly low-cost entry options. For example, drone photogrammetry can be introduced relatively inexpensively with just a drone and a camera, and photo-processing can be done using cloud services with pay-as-you-go pricing. Smartphone surveying with LRTK combines a high-precision GNSS receiver and a smartphone, but compared to conventional large instruments it is orders of magnitude cheaper and can be operated by site staff without a dedicated surveyor, yielding excellent cost performance. For point cloud processing, open-source free software and cloud-based measurement platforms are emerging, making 3D measurement accessible to small companies and sites. You can start with a minimal setup and expand gradually, so consider introducing it at an appropriate scale first.