The New Normal for As-Built Volume Measurement: Visualizing Sites with Smartphones × AR

Table of Contents

• What is as-built volume measurement and why is it important?

• Easy 3D as-built measurement with iPhone and smartphones

• Visualizing sites with AR: overlaying design data and point clouds

• Pass/fail determination and report generation through automatic point cloud analysis

• Possibilities expanded by LRTK for simple surveying

• FAQ

What is as-built volume measurement and why is it important?

"As-built volume measurement" is part of the process in civil engineering and construction where the shape and dimensions of the terrain or structures after construction are measured to verify whether they match the design drawings. In earthworks such as embankments and excavations, it is particularly necessary to accurately measure whether the specified amount of soil (volume) has been placed or removed. In as-built management, the completed shape—referred to as the as-built (as-built shape)—is checked to determine whether it conforms to specifications, in other words, whether "the work was carried out according to the drawings," and corrective action is taken if problems are found to ensure quality. The results directly affect inspection pass/fail decisions and handover to the client, so as-built volume measurement is a critical process in construction quality control. For example, if embankment fill is insufficient, additional work is required; if it is excessive, rework will be necessary. Because as-built volumes influence construction progress measurements and payments, it is not an exaggeration to say that the quality of these measurements can determine a project’s fairness and economics.

Traditionally, as-built volumes were measured by manually surveying the ground before and after works using surveying instruments such as total stations (TS) and levels, and calculating volume differences from the elevation differences of the obtained points. Specifically, surveyors measured heights at regular intervals on site to draw cross-sections, and manually calculated the embankment or excavation volumes from the cross-sectional areas and extents before and after construction. However, this method easily overlooks undulations or leftover material between measured points, and errors can accumulate due to the coarse sampling at discrete points. The larger the site, the more limited manual surveying becomes: it requires time and manpower, so there has been demand for more efficient and higher-precision methods for as-built volume measurement. In fact, preparing for as-built inspections and the surveying work itself have long required substantial labor and time, imposing a significant burden on site personnel.

Easy 3D as-built measurement with iPhone and smartphones

In recent years, smartphone-based 3D measurement has attracted attention as a solution to this problem. Particularly notable is the site scanning using the LiDAR sensor built into Apple’s *iPhone*. LiDAR is a technology that measures distance to targets at high speed using infrared lasers, and models from the iPhone 12 Pro onward include a LiDAR depth sensor that can measure up to approximately 5 m (16.4 ft). With dedicated apps, this sensor together with the camera can instantly record surrounding terrain as point cloud data. Point cloud data is a 3D dataset composed of many points’ coordinates (X, Y, Z) in space, representing the shape of the object as a high-density collection of points. Being able to measure an entire terrain in a surface-like manner with a single smartphone and digitally copy the whole site is revolutionary.

For smartphones without LiDAR or when more detailed measurement over a wider area is required, photogrammetry is also used. Photogrammetry is a technique that reconstructs three-dimensional models from multiple photographs taken with a smartphone camera, applying the same principles as drone aerial photogrammetry or DSLR-based photographic surveying on a phone. By recording video of the site with a dedicated app and analyzing that footage in the cloud to generate point clouds, 3D data can be obtained even in areas beyond LiDAR’s reach. LiDAR scanning is attractive for its on-the-spot, real-time point cloud generation, but it is limited in measurement distance and range. Photogrammetry, while requiring longer processing time, has the advantage of covering vast areas and capturing complex details. By choosing between LiDAR and photogrammetry according to site conditions, the potential of as-built measurement data obtainable from a single smartphone is greatly expanded.

Moreover, if high-precision positioning information (GNSS positioning coordinates) is added to point cloud data acquired by a smartphone, the measurement results can be directly overlaid onto the design coordinate system. Typically, raw iPhone scans do not include absolute latitude, longitude, and elevation, so aligning with control points used to require extra work. However, recently small RTK-GNSS receivers (real-time kinematic high-precision GPS) attachable to smartphones can feed centimeter-level positioning into the phone in real time. For example, attaching an RTK-capable positioning device to a smartphone allows accurate world coordinates to be added to acquired point clouds and photos, enabling as-built recording with precision comparable to surveying instruments. This makes it possible to perform strict comparisons with design data and calculate volumes using only a smartphone, without expensive dedicated surveying equipment.

In one case, a site survey that used to take half a day was completed in just a few dozen minutes simply by having a site manager walk around a newly created site while scanning with an iPhone. By using 3D scanning in this way, an entire site that previously could only be captured as fragmented points can now be digitized in a short time.

Because smartphones are familiar tools used by many people in daily life, these new measurement techniques can be introduced on site without special training or equipment.

Visualizing sites with AR: overlaying design data and point clouds

Another innovation enabled by smartphones is site visualization through AR (augmented reality) display. With AR technology, 3D models of design data and reference lines can be overlaid on the live site image on a smartphone or tablet screen. For example, in road embankment work, the designed finished-model can be displayed as AR on site and compared with the current terrain. When viewing the site through the phone, the virtual design model or lines appear superimposed over the real scene. This makes subtle deviations that are hard to grasp from drawings alone immediately obvious, allowing intuitive assessment of whether the as-built conforms to the design.

Furthermore, displaying a heat map that color-codes differences between acquired point cloud data and the design model enables instant recognition of areas of excess or deficiency. In embankment or paving inspections, areas that are higher than the design or conversely lacking will be shown in colors such as red or blue on the AR display, allowing quick identification. This visualization enables discovery of defects before the formal as-built inspection and immediate correction on site. For example, additional soil can be added in areas lacking fill, and excess fill can be cut on the spot—such rapid corrective measures help secure quality toward passing inspections. Traditionally, evaluation of the current state had to wait until measurement results were compiled into drawings or tables, but AR can make this process real-time and enable quick decision-making.

AR visualization is also powerful for explanations to clients and supervisors. Being able to show the finished form directly on site makes it easier to share construction results that are hard to convey with words or drawings alone, increasing stakeholders’ confidence and understanding.

Pass/fail determination and report generation through automatic point cloud analysis

Point cloud data of as-built conditions acquired by smartphone can be automatically analyzed by cloud-based systems or in-app measurement functions. By overlaying design data and measured data for comparison, deviations in as-built geometry and volume differences from embankment or excavation are computed instantly. Soil quantity tabulation that used to be performed manually back at the office can now be calculated automatically simply by uploading data to the cloud from the field, yielding results in a short time. Even for large embankment projects handling tens of thousands of cubic meters of soil, computers—rather than manual labor—perform the analysis, enabling objective and rapid as-built evaluation.

Analysis results can be used immediately as numerical data or heat maps. For example, information such as "the proportion of areas within ±○ cm of design" or "how many cubic meters are in deficit or excess" can be automatically turned into reports, providing the evidence needed for as-built pass/fail determinations. These data can be shared with stakeholders via the cloud so that supervisors or clients in remote offices can check the latest site conditions from their desks. Instead of carrying paper drawings or photos and rushing to explain, everyone can access the same digital "site truth."

Additionally, this digital process ties measurement through to report generation seamlessly. Point clouds and analysis results are stored electronically, significantly reducing the manual transcription work into photo ledgers and as-built management tables. With dedicated software, as-built management reports can even be generated automatically from survey photos and measurement data captured on site. For example, inspection forms and reports with 3D models for as-built inspections can be output at the push of a button, reducing the workload on staff. This also prevents human errors in documentation, improving the reliability of quality control. Accumulated 3D point cloud data also serves as a digital record of the completed product for maintenance management. These initiatives align with the government-promoted ICT modernization of construction sites (*i-Construction*), and in the future, storing and utilizing as-built data as digital twins could contribute to advanced post-construction maintenance and progress management. By leveraging smartphones × AR and point cloud technology, the entire flow from surveying to analysis and reporting can be streamlined, dramatically improving site productivity and transparency.

Possibilities expanded by LRTK for simple surveying

Smartphone- and AR-based new as-built volume measurement solutions are already entering practical use on sites. A representative example is the solution called LRTK. LRTK consists of a high-precision GNSS unit that can be attached to a smartphone, a dedicated app, and cloud services, and is designed so that anyone can perform simple surveying on site with ease. By combining an iPhone with a receiver weighing only a few hundred grams, centimeter-level positioning is possible without complex initial setup or specialist equipment. Using the LRTK app, the aforementioned point cloud scanning and AR overlay of the design model, as well as guidance to stake positions and photo-attached survey logs, can be performed in an all-in-one workflow—tasks that previously required specialists or expensive equipment. It is fair to say that an era in which surveying through to as-built inspection can be completed with a single smartphone has arrived. Because existing smartphones can be used, initial deployment hurdles are low, and the ease of introducing it on site without special qualifications or permits is also an advantage.

In practice, local governments and construction companies have begun smartphone surveying using LRTK, achieving results in disaster recovery site surveys and infrastructure as-built management. There are reports where surveying work that used to take several people several days was completed by one person in a short time using LRTK. The efficiency gains from smartphones × AR can be a significant help in the construction industry, which faces severe labor shortages. As site digitization progresses, advanced analyses based on survey data and AI-driven optimization of construction management are also expected to emerge.

Smartphone- and AR-based as-built volume measurement is becoming the new normal in future site management. As smartphone and data analysis technologies continue to advance, the accuracy and efficiency of as-built measurement will only improve further. As a first step, it is well worth trying cutting-edge tools like LRTK. For more details, please also refer to the [LRTK official site](https://lefixea.com).

FAQ

Q. What is as-built volume measurement? A. It is the measurement of the volume of completed structures or terrain to verify that construction was carried out according to the design. In civil engineering, as part of as-built management, it checks whether embankments and excavations meet the planned soil quantities. In short, it refers to quantitatively confirming whether the as-built shape matches the planned values shown in the drawings.

Q. Can smartphones really achieve accurate surveying? A. Yes, with the latest smartphone measurement technologies. iPhone LiDAR scanning enables high-precision 3D measurement at short ranges, and combining it with an RTK-GNSS receiver can achieve positioning errors on the order of several centimeters. Under favorable conditions, planar positioning accuracy of 2-3 cm (0.8-1.2 in) and vertical accuracy within about 5 cm (2.0 in) can be expected. With proper calibration and good measurement conditions, smartphone surveying can measure as-built conditions with accuracy comparable to traditional surveying instruments. In fact, smartphone-based as-built measurement methods meet the accuracy standards specified in the Ministry of Land, Infrastructure, Transport and Tourism’s “As-Built Management Guidelines (draft)” and are robust enough for official inspections.

Q. What are the advantages compared to traditional methods? A. Smartphone × AR as-built measurement offers many advantages not found in conventional methods. First, speed is significantly improved: measurement through analysis can be completed on site, accelerating inspections and progress-based payment calculations. Second, it reduces manpower and cost: a single person can measure with a handheld smartphone without arranging specialist surveying teams or heavy equipment. Safety is also enhanced: detailed measurement on hazardous slopes can be avoided by measuring from a distance, reducing worker risk. There are also large benefits in quality and communication: objective evaluation based on data and AR-enabled visual sharing reduce misunderstandings with clients and prevent rework.

Q. Can it be used without specialized knowledge? A. Smartphone surveying tools are designed for intuitive operation, and with basic training they can be used by non-specialists. For example, LRTK allows point cloud scanning and AR display simply by moving the smartphone according to on-screen instructions, so first-time users can handle it after short training. However, understanding basic surveying principles and how to interpret data helps achieve more accurate results. Compared to traditional surveying instruments, there are fewer settings and it is simpler overall, and the greatest appeal is that site personnel themselves can autonomously perform measurements.

Q. What is needed to start as-built measurement with a smartphone? A. Basically, a compatible smartphone and a dedicated measurement app are sufficient to start. A smartphone with LiDAR is ideal, but non-LiDAR models can also be used with photogrammetry apps. For accurate alignment, an RTK-GNSS receiver (high-precision GPS unit) is desirable, as it reduces the effort required to align acquired point clouds and models to design coordinates. Having the design data to compare against (3D models or drawing information) is also effective. For example, by introducing LRTK, attaching a small GNSS to a smartphone and launching the app allows measurements to begin immediately, enabling site staff without surveying expertise to use it right away.

Q. How does smartphone measurement differ from drone photogrammetry? A. Drone-based photogrammetry (aerial surveys) has the advantage of being able to capture wide areas from above and is effective for large sites. However, drones have flight restrictions and regulatory requirements for operation and are more susceptible to weather. In contrast, smartphone measurement can be carried out easily from the ground and can be used in confined spaces or urban areas without restrictions. Drone data often require office-based processing after capture, whereas smartphones can generate point clouds and perform analysis in real time on site. Drone deployment and operation often require expensive equipment and specialist skills, while smartphone measurement can begin simply by installing an app on an existing device, making it superior in terms of cost and convenience. Of course, for some sites it is useful to combine drone and smartphone data—capturing from both the air and ground to complement each other. The best method depends on the situation, but for routine as-built measurement the smartphone × AR approach offers exceptional ease and immediacy.