Speed up volume calculations with point clouds! A new era of 3D surveying anyone can do

Table of contents

• Basic knowledge of 3D surveying and point cloud data

• Situations where volume measurement is required

• Traditional volume measurement methods and challenges

• Benefits of volume calculation using point clouds

• Procedure for deriving volume from point cloud data

• Comparison of instruments and methods used for point cloud measurement

• Summary: Recommendation for simple surveying with LRTK

• FAQ

In construction and civil engineering sites, volume calculation (earthwork quantity calculation) for embankment and excavation works is an essential task for progress control and measurement of work performed. Traditionally, terrain was measured with surveying instruments to create cross sections and volumes were calculated using methods such as the average cross-section method. However, in recent years, *3D surveying* using drones, laser scanners, and even smartphones has spread rapidly. By utilizing the *point cloud data* that can be obtained with these technologies, volumes can now be calculated more quickly and accurately within dedicated viewers and software. This article explains the basics of what point cloud data are, methods for calculating volumes using point clouds, and practical points for using them on site. Finally, we introduce the easy surveying solution using a smartphone, "LRTK", for simple surveys.

Basic knowledge of 3D surveying and point cloud data

First, let’s cover the basics of *3D surveying* and *point cloud data*. 3D surveying is a general term for methods that measure site terrain and structures in three dimensions and convert them into digital data. Representative methods are laser scanning (LiDAR) and photogrammetry. With a laser scanner, a device mounted on a tripod or vehicle emits laser light and acquires coordinates of many points based on the time or other parameters until the reflected light returns. A single scan can yield millions of high-density points, allowing shapes of terrain and structures to be recorded in detail down to the millimeter level (mm; ~0.04 in). On the other hand, photogrammetry captures many photos with a drone or camera and generates 3D models or point clouds by image analysis in software. It can rapidly capture wide areas of ground, and thanks to advances in software in recent years, high-accuracy point clouds can be created relatively easily.

The obtained *point cloud data* are a collection of innumerable measured points in space, with each point having three-dimensional X, Y, Z coordinate information. Points can also carry attribute information such as color or reflectance intensity. Simply put, a point cloud can be regarded as a 3D model representing an object’s shape with countless points. Whereas conventional surveying yielded only a few dozen to a few hundred points, point cloud surveying can obtain millions of points in a single measurement. Because the site’s shape can be measured densely and exhaustively, fine terrain undulations and minute surface irregularities of structures can be accurately reproduced. For this reason, the use of point clouds is encouraged in policies promoted by the Ministry of Land, Infrastructure, Transport and Tourism such as *i-Construction*, and the adoption of 3D surveying in the construction industry is progressing rapidly.

Situations where volume measurement is required

Next, let’s look at typical situations in civil engineering and construction sites where volume measurement is needed. The most typical case is earthwork in road construction and land development. For embankments and cuttings for roads, it is necessary to confirm whether the amount of soil placed matches the design, and in excavation to verify that the specified volume of soil has been removed. In as-built inspections, volumes are reported in forms like “embankment volume: ○○ m3” and differences from contract quantities are verified. Volume measurement is also important in dredging works for rivers and ports to determine how much sediment was removed. All of these tasks directly relate to progress management (verification of work quantity) and serve as the basis for reporting progress to the client and calculating construction costs, so accurate quantity grasp is required.

Furthermore, volume measurement is indispensable for managing excess soil and materials generated by construction. Measuring the volume of stockpiled soil or aggregate on site allows accurate estimation of the number of truckloads for removal or delivery and the required storage capacity. While these estimates were once made by visual inspection or by measuring only a few points, 3D scanning now enables direct measurement of actual values simply and with high precision. Thus, volume measurement is an important process spanning quality control of construction to cost management.

Traditional volume measurement methods and challenges

Now, let’s summarize the traditional volume measurement methods used before point cloud technology and the issues associated with them. Typical methods include manual calculations using the average cross-section method and the grid method. Heights and widths were measured at key locations on site to create cross-section drawings or grid measurement data and calculate volumes. For example, transverse surveys might be conducted at 10 m (32.8 ft) intervals to compute the area of each cross section, then multiply the average area of adjacent sections by the interval distance to obtain volume. Such calculation methods have long been the basis for earthwork quantity determination.

However, several challenges have been pointed out for traditional methods. The first is the problem of accuracy and coverage. Manual surveying limits the number of measurable points, so the information obtained in a single measurement was minimal. Even for wide embankments, only a few height points could be measured, and the overall volume had to be estimated by connecting those points. Naturally, there was a risk of overlooking small irregularities or localized depressions and bulges. In practice, there were cases where major cross sections matched the design, but unexpected depressions or excess fill occurred between them without being noticed. The inability to grasp shapes in areal and volumetric terms was a constraint on accuracy.

The second issue is work efficiency. Traditional methods required surveyors and technicians to measure the site point by point, often with multiple people. For example, when surveying with a total station (TS), on a large site the instrument often had to be moved and reference setups reestablished for each measurement point, requiring enormous effort and time. Creating numerous cross-section drawings and manually calculating areas and volumes imposed a heavy burden on site teams. In some cases it took days to confirm as-built volumes, forcing work to be paused during that period. “Waiting several days to confirm a few centimeters of discrepancy” was common and slowed the overall project schedule.

Third, the issue of safety is not to be overlooked. Tasks such as walking steep slopes to take measurements or using tapes to measure distances near operating heavy machinery always involve risk. Measurements at height or on unstable footing carry fall and accident risks, and the longer surveying takes, the more exposure workers have to danger. Consequently, traditional volume measurement faced various challenges in terms of accuracy, efficiency, and safety.

Benefits of volume calculation using point clouds

Volume calculation using point cloud scanning technology offers many benefits that can solve the issues of traditional methods described above. The greatest advantage is the dramatic improvement in work efficiency, reducing the time and effort required for earthwork quantity calculations. For example, on a large development site where a four-person survey team formerly spent one week (approximately 28 person-days) measuring and calculating as-built earthwork, switching to drone aerial imaging for point cloud generation and volume calculation in a point cloud viewer allowed the work to be completed by two people in one day (2 person-days). Tasks that took several days with manual surveying can often be completed within a day using point cloud technology. Significant reductions in work time create slack in project schedule management and lead to improved productivity.

Next, the advantage of data comprehensiveness and improved accuracy is substantial. Point cloud measurements generate highly dense, comprehensive point cloud data composed of millions of points covering the site thoroughly. While traditional methods estimated overall shapes from cross-section lines tens of meters apart or from limited measurement points, point clouds can record the actual terrain in detail. Therefore, volume calculations can reflect minute undulations and local over- or under-fill that were often overlooked by traditional methods, resulting in highly accurate quantity estimates. Actual validations often report that volumes calculated from point clouds differ little from values obtained by traditional methods, with errors often contained within about 1–2%. With proper measurement procedures, volume calculation from point clouds can achieve accuracy comparable to conventional surveying. Since wide areas can be measured finely and directly, the likelihood of overlooking localized features is reduced, producing more reliable quantity data.

Furthermore, the use of point cloud measurement can improve safety. Dangerous locations that are risky for personnel to enter can be surveyed by drone from the air or by remotely operated laser scanners, removing the need for workers to spend long periods in hazardous places. Shorter measurement durations also reduce on-site time and personnel exposure, contributing to risk reduction.

Thus, volume calculation with point clouds revolutionizes traditional methods in terms of efficiency, accuracy, and safety. It is a technology that can dramatically raise on-site productivity and surveying quality.

Procedure for deriving volume from point cloud data

Now, let’s look at an outline of the steps for calculating volume from point cloud data. The general flow is as follows.

• Acquiring point cloud data: First, acquire point cloud data of the terrain or embankment to be measured. As mentioned above, choose a suitable acquisition method depending on site scale and conditions: aerial photogrammetry using a drone-mounted camera, ground-based laser scanning with a terrestrial scanner, or scanning with a LiDAR-equipped smartphone. It is important to cover the measurement area completely and to include the ground plane that will serve as the reference for volume calculation. When comparing multiple measurement datasets, measuring in the same coordinate system makes later comparisons easier. For example, to calculate embankment volume by comparing pre- and post-construction point clouds, use common reference points or the same coordinate system in both measurements.

• Point cloud data processing and preparation: Import the acquired point cloud into dedicated software or a cloud service and prepare it for analysis and processing. For photogrammetry, point clouds are generated from captured photos through processing (SfM/MVS, etc.). Remove noise and unwanted elements from the obtained point cloud and extract only the area for which you want to calculate volume. For example, filter out unwanted points such as vehicles and people that are not part of the ground surface, and clip the target embankment area with a polygon as a preprocessing step. Many point cloud viewers include region clipping and noise removal features; use these to prepare data suitable for calculation.

• Performing volume calculation: Once the point cloud data are prepared, perform the volume calculation. In point cloud processing software, specify the calculation area and compute the volume as the difference from a reference surface. There are two main approaches. One is to calculate volume from differences between point clouds at multiple time points. Overlap point clouds from different times (e.g., before and after construction) and calculate fill or excavation volumes as the volumetric difference between the two terrain models. The other is to calculate volume from a single point cloud and a reference plane. For an isolated pile of soil, for example, you can enclose the base with a polygon and automatically calculate the volume between that polygonal reference plane and the point cloud surface. Recent point cloud viewers and surveying software have enhanced functions for volume calculation, and many allow you to obtain the volume of a specified area with almost one click. Previously, it was necessary to create a mesh model from the point cloud and calculate volumes in CAD, but now cloud services have emerged that automatically compute volumes simply by uploading point clouds and specifying an area. Even without difficult 3D CAD operations, intuitive point cloud viewers increasingly allow anyone to easily calculate earthwork quantities.

• Reviewing and utilizing results: Calculated volumes can be displayed immediately in the point cloud viewer or output as reports. Use those values for as-built management and progress reporting. If necessary, record calculation conditions (such as the reference plane used or which datasets were differenced) and point cloud accuracy verification results to facilitate later explanations and validation. Once point cloud data are acquired, you can readily compute volumes for additional areas later. For example, if terrain changes after heavy rain, you can extract and re-calculate the relevant area from existing point cloud data without re-surveying the entire site.

Comparison of instruments and methods used for point cloud measurement

There are various instruments and measurement methods for acquiring point cloud data. Each has different characteristics, so choose the appropriate method according to site scale, required accuracy, and cost. Below is a comparison of representative methods and their features.

• Drone (photogrammetry): Captures wide areas from the air in a short time and generates point clouds and terrain models from large numbers of photos. Suitable for open wide sites and measuring stockpiled earth volumes. Flight safety management and flight permits are required to operate drones, but when used effectively they can efficiently survey areas that are unsafe or inaccessible on foot. The accuracy of the resulting point cloud depends on flight altitude, camera performance, and accuracy of control points (ground reference points), but with proper procedures it is possible to estimate earthwork volumes with errors on the order of a few centimeters (a few inches).

• Terrestrial laser scanner: Includes tripod-mounted stationary LiDAR instruments and vehicle- or pedestrian-mounted mobile mapping scanners. Because laser light directly measures dense point clouds, a single scan can obtain very detailed data. Effective for measuring fine details of structures and complex terrain. However, the equipment is expensive, and operation and data integration require expertise. Also, scanning from one direction can create shadows where point clouds cannot be acquired, so scanning from multiple positions and registering the data may be necessary. It is a high-precision method but involves time and cost.

• Smartphone/tablet (LiDAR-equipped): Some modern smart devices include compact LiDAR sensors, enabling easy 3D scans. Measurement range is limited to a few meters (a few ft), but they are useful for capturing shapes of small embankments or structures. Dedicated apps can acquire point clouds on site and in some cases perform simple volume calculations. While a smartphone alone can capture relative shapes, higher accuracy needs can be met by combining the device with an RTK-capable external GNSS receiver (for example, an LRTK device), enabling centimeter-level positioning accuracy (cm level accuracy (half-inch accuracy)) with affordable equipment. By attaching a small device weighing a few hundred grams to a smartphone, anyone can obtain high-precision 3D point clouds with a pocket-sized surveying setup.

• Ground photogrammetry: Without using a drone, take many photos from the ground with a digital camera or smartphone and generate point clouds by software analysis. Useful for urban areas where aerial flight is not possible or for indoor spaces. Because the photographer can only capture within walking range, it is not suitable for large-scale surveys, but for small sites you can build 3D models with careful shooting. Although processing time increases with the number of photos, sufficiently practical accuracy can be achieved by properly placing control points. In short, depending on site conditions you can choose an optimal measurement method and obtain point cloud data even without expensive dedicated equipment, and then calculate volumes from that data.

Summary: Recommendation for simple surveying with LRTK

As we have seen, volume calculation using point clouds is bringing major changes to civil surveying. Tasks that used to require experienced technicians several days to perform can now be done by anyone in a short time using drones or smartphones. Point cloud technology is becoming more sophisticated while evolving to be more familiar and user-friendly. The era of “3D surveying anyone can do” is truly upon us.

If you feel “I’d like to try 3D surveying at my site,” a practical way to start is with simple surveying using a smartphone and LRTK. LRTK is a solution consisting of a compact GNSS receiver for smartphones and a dedicated app that turns your everyday smartphone into a high-precision surveying instrument. It is designed to be operable without complicated procedures or special qualifications and aims to be a revolutionary “one-device-per-person universal surveying instrument.” Its reasonable pricing has already led to widespread on-site adoption, changing how surveying is done. Using LRTK, anyone can easily acquire point cloud data with centimeter-accuracy position information (cm level accuracy (half-inch accuracy)), share that data in the cloud, and use it for volume calculations. Adopt the latest tools wisely and experience the benefits of 3D surveying on your site.

FAQ

Q1. Can I calculate volumes from point clouds without drones or expensive 3D scanners? A. Yes, it’s possible. High-performance laser scanners and drones are convenient for large-scale surveys, but there are ways to leverage point cloud technology without them. For example, LiDAR-equipped smartphones and tablets can easily acquire point cloud data for small objects. If high-accuracy positioning is required, combining a smartphone with a GNSS device such as LRTK enables centimeter-level point cloud surveying with affordable equipment. There is also ground-based photogrammetry that builds 3D models from photos without drones. In short, with appropriate methods suited to site scale and purpose, you can obtain practical point cloud data and perform volume calculations even without expensive gear.

Q2. Are point cloud viewers and surveying software difficult to operate? Can beginners handle them? A. Modern point cloud viewers and 3D surveying software have become user-friendly, and basic viewing and measurement are not very difficult for beginners. Depending on the software, intuitive operations such as dragging the mouse to change the viewpoint and selecting “distance measurement” or “volume measurement” from a menu and clicking are common. Cloud-based point cloud viewers are particularly designed to minimize complex settings. Of course, advanced analysis requires corresponding skill, but for volume calculation you can generally get the hang of it after a few trials. Many software and services provide tutorials and support materials, so start with small datasets and gradually gain experience.

Q3. Can I trust the accuracy of volumes calculated from point clouds? How do they compare to traditional surveying errors? A. Volumes calculated from properly acquired point clouds can achieve accuracy comparable to traditional surveying. In practice, earthwork quantities derived from drone photogrammetry or terrestrial laser scan point clouds are often within about 1–2% of values obtained by conventional cross-section methods. That means values comparable to carefully performed traditional surveys can be obtained. However, ensuring that accuracy requires proper procedures such as calibration of survey control points and accurate registration between point clouds. Noise and missing data in point clouds can introduce errors, so post-processing such as removing unwanted points and data completion is important. Under suitable conditions, volume calculation from point clouds is a reliable method for quantity estimation.

Q4. Doesn’t it take a long time to calculate volumes from 3D point clouds? Don’t data processing and computation require enormous time? A. The time from point cloud generation to volume calculation can be dramatically shortened depending on the chosen method. In the past, post-processing of laser scans required advanced specialist software and time, but automated systems from measurement to calculation are increasingly widespread. For example, using a drone, aerial imaging for a wide area can often be completed in about 15 minutes, and uploading photos to a cloud service can generate point cloud models and orthophotos within a few hours. Smartphone LiDAR scans can acquire point clouds by walking around for tens of seconds to a few minutes, and some apps display volume results instantly. Point cloud viewers have optimized processing, and typical earthwork calculations are computed almost in real time by a computer. Overall, the total work time is much shorter than manual calculations. Even for large data volumes, cloud services can process data on servers so your local PC is not burdened.

Q5. Are volumes measured and calculated from point clouds accepted as official progress quantities? A. There is not yet a single nationwide uniform operational rule, but point cloud surveying for progress management is increasingly being adopted officially. For national and municipal projects, *i-Construction* initiatives have led to documents such as “3D As-built Management Guidelines,” and the use of quantities derived from point clouds in inspections and quantity confirmation is growing. However, to be officially accepted, procedures that demonstrate surveying reliability are required. For photogrammetry, this may include placing known ground control points and performing accuracy verification; for laser scanning, equipment calibration and error checks against existing terrain may be required. When submitting to clients or authorities, it will be necessary to prepare documentation showing point cloud measurement accuracy and calculation methods. As technical standards are established, results from properly conducted point cloud surveys are increasingly recognized as official records and means of quantity determination. There are already sites where quantities measured by point clouds were accepted in inspections, and it is expected that reporting progress quantities from point clouds will become a new standard alongside traditional methods. It is advisable to actively utilize the benefits of the new method while combining it with conventional approaches where appropriate.