Instant As-Built Volume Measurement You Can Do Now! Easy Centimeter Accuracy (cm level accuracy, half-inch accuracy) for Anyone with LRTK

Table of Contents

• The importance of as-built management and volume measurement

• Traditional volume measurement methods and their challenges

• 3D scanning technology using smartphones

• Achieving centimeter accuracy in smartphone measurements with RTK-GNSS

• As-built volume measurement anyone can do with LRTK

• Summary

• FAQ

What if you could accurately measure the volume of embankments or excavations at a construction site with just a single smartphone?

Soil volume measurement for as-built management is an essential process for tracking construction progress and verifying quality, but for a long time it required specialized surveying teams and expensive equipment. Now, by combining smartphones with the latest technologies, an era has arrived in which anyone can quickly and accurately compute volumes on site.

This article explains, step by step, the importance of volume measurement in as-built management, the challenges of traditional methods, solutions offered by the latest 3D scanning technology, and simplified surveying enabled by the RTK-GNSS solution “LRTK.”

The importance of as-built management and volume measurement

In civil engineering and construction, there is a process called “as-built management” for checking and recording whether finished structures and terrain conform to the shapes and dimensions in the design drawings. It is an important task that proves, with measurement data, that the actual finish falls within the tolerances set by the client, and it is indispensable for quality assurance of the work. Especially on public infrastructure sites such as roadworks and land development, as-built management results can determine inspection approval and handover conditions, so strict measurement and recordkeeping are required.

Calculating soil quantities (volumes) in as-built management also plays a vital role. For embankments and excavations, it is necessary to accurately measure whether the prescribed amount of soil has been placed or removed. Volume values directly affect progress management (work quantity tracking), pass/fail judgments in as-built inspections, and construction payments, so their accuracy greatly impacts the fairness and economics of a project. For example, embankment or excavation volumes were traditionally measured by surveying the ground before and after construction and calculating the difference, or by hand-calculating using cross-sectional areas and lengths on drawings with the average cross-section method. However, methods that measure only a few discrete points tend to miss local depressions or bulges, resulting in overlooked overfills or under-excavations and the risk of rework later. This is especially true for large-scale earthworks, where manual measurement has limits, and there has been demand for new measurement methods that can measure volumes efficiently and comprehensively.

Traditional volume measurement methods and challenges

Conventional volume measurement typically involves leveling surveys or total stations to measure key points of the terrain and then calculating areas and volumes on drawings. Specifically, the elevation differences between the as-built and design or post-construction terrain are measured at various locations, cross-sections and longitudinal sections are created, and volumes are then calculated. This method has the following issues:

• Labor and time: Large sites require many survey points, and surveying, drafting, and calculations take a long time.

• Errors from point data: Measurable locations are limited to discrete points or section lines, so surface irregularities or local depressions and bulges may be missed. Consequently, errors can accumulate in calculated volumes.

• Human limitations: Surveying on steep slopes or poor footing is hazardous, and some locations cannot be approached closely for detailed measurement. It is difficult to comprehensively cover a large earthwork site with manpower alone.

• Rework risk: If overlooked overfills or under-excavations between survey points are discovered at inspection, rework may be required, affecting schedules and costs.

Because of these limitations in efficiency and accuracy, the field has needed solutions that can measure volumes more quickly and comprehensively.

3D scanning technology using smartphones

To meet these needs, 3D scanning technology using smartphones has attracted attention in recent years. In particular, iPhone models from the iPhone 12 Pro onward are equipped with a LiDAR sensor, enabling easy high-precision 3D measurement. LiDAR is a technology that measures distance to objects using infrared lasers, and the iPhone’s LiDAR can acquire distance data to about 5 m (16.4 ft). Working in conjunction with the smartphone’s camera, it records the surrounding shape as a collection of many points (point cloud data). A point cloud represents the site’s shape with countless coordinate points and can reproduce space as a realistic 3D model similar to a photograph.

For smartphones without LiDAR, or when you want to measure a wider area in detail, photogrammetry is also useful. Photogrammetry reconstructs three-dimensional shapes from multiple images of a site taken with a smartphone camera. The same principles used in drone aerial photogrammetry or DSLR-based photogrammetry can be realized on a smartphone; by recording video with a dedicated app and analyzing it in the cloud (processing takes several minutes to tens of minutes), you can create 3D models including areas beyond LiDAR’s reach. LiDAR has the advantage in real-time capability, while photogrammetry can cover wide areas and fine details at high density if time is available. Depending on site scale and required accuracy, you can choose between these smartphone scanning methods to efficiently acquire point cloud data.

Using point cloud data obtained by smartphone allows you to capture terrain as surfaces rather than just points, dramatically improving the accuracy and reliability of volume calculations. The number of points obtainable vastly exceeds what can be recorded by manual point measurements, enabling small irregularities in embankments and excavations to be fully digitized. For example, if you scan an entire embankment and overlay the resulting point cloud on the design 3D model, you can intuitively check elevation differences with a color-coded heat map. Visualizing irregularities and errors makes it easy to correct insufficient fills or excessive areas before inspection. The acquired 3D data can be stored and shared in the cloud as-is, providing compelling evidence for as-built records. Quantity calculations from point clouds are more objective than traditional cross-section computations and serve well as explanatory materials for clients. Sharing point cloud data via the cloud also allows remote stakeholders to review the site’s 3D model, helping to prevent disputes caused by misunderstandings.

Additionally, at excavation sites, scanning before and after construction and calculating the difference between the two point clouds can automatically compute removed soil volume (excavation quantity). You can grasp work progress on site in just a few minutes, eliminating the need to bring data back to the office to calculate volumes as in the past.

However, one challenge remains for standalone smartphone 3D scanning. The point cloud data obtained are not linked to absolute geographic coordinates (latitude, longitude, elevation). Point clouds recorded on a smartphone are only models in the device’s internal virtual coordinate system, so manual alignment was necessary when comparing them with design drawings or other survey data. Recently, technologies have emerged to solve this problem.

Achieving centimeter accuracy in smartphone measurements with RTK-GNSS

The key to further improving smartphone scanning accuracy is RTK-GNSS (Real-Time Kinematic GNSS). RTK-GNSS is a method that corrects satellite positioning (GPS, etc.) errors in real time, enabling positioning measurements with centimeter-level accuracy. Traditionally, achieving such positioning precision required expensive surveying GNSS receivers and base stations. However, miniaturization and cost reductions have progressed in recent years, and small RTK-capable receivers can now be easily connected to smartphones.

Combining RTK-GNSS with smartphone 3D scanning allows you to assign precise latitude, longitude, and elevation to each point in the point cloud data. In other words, scanned 3D models can be recorded in the actual surveying coordinate system (plan coordinates and elevation datum). This eliminates misalignment when comparing measurement data with design drawings and removes the need for additional manual alignment. For example, previously, aligning a 3D scan with design CAD data required on-site measurements of known reference points to match both datasets. With RTK-enabled smartphone measurement, point clouds are acquired in correct coordinates from the start, so you can immediately analyze differences from the design without such tedious adjustments. Moreover, point clouds acquired at multiple times will share a common coordinate system, making time-series comparisons of change amounts smooth.

With high-precision positioning information, smartphones can be used as professional surveying instruments. In addition to point cloud-based volume calculations, you can measure coordinates of arbitrary points for drafting or check heights using only a smartphone and a small GNSS receiver. Measurements that used to require a specialized surveyor can increasingly be performed by site staff on the spot. Quick feedback prevents rework and contributes to improved quality control. It is becoming a reality that simply carrying a smartphone per person enables completion of necessary measurements.

As-built volume measurement anyone can do with LRTK

A solution that easily realizes the high-precision 3D measurement described above using a smartphone + RTK-GNSS is LRTK. LRTK provides RTK-GNSS positioning accuracy and 3D scanning capabilities comparable to large conventional instruments by attaching a pocket-sized RTK-GNSS receiver to a smartphone (iPhone/iPad) and measuring with a dedicated app.

By simply walking around the site with a smartphone, you can obtain high-precision point cloud data and calculate the required soil volumes on the spot. For example, if you want to measure the volume of a stockpile on site, simply walking around and scanning with a smartphone equipped with LRTK will let you measure embankments of several hundred cubic meters in a matter of minutes. After scanning, the volume (in cubic meters) is immediately displayed on the smartphone screen, and if a planned design volume is available, you can see the difference on the spot.

Acquired point clouds are integrated with cloud services so that uploading automatically overlays them with design data for difference analysis, visualizes elevation differences as heat maps, and generates volume reports. Because you can intuitively compute required quantities via the app and cloud without relying on specialized CAD software, the system is easy to use even for those without surveying expertise.

LRTK’s emergence has greatly lowered the barrier to as-built volume measurement. Below are the advantages of simple surveying using LRTK:

• Ease of use: All you need is a smartphone and a small receiver. There’s no need to carry heavy tripods or surveying instruments, and you can measure whenever needed.

• Speed: Scanning to volume calculation on site can be completed in as little as a few minutes. With cloud integration, you can immediately confirm and share results without returning to the office.

• High accuracy: RTK-GNSS provides positional accuracy within a few centimeters or less (a few centimeters or less). You can obtain much more precise as-built data than with conventional methods, reducing rework caused by errors.

• Safety: You can record shapes remotely even on hazardous slopes or poor footing. Minimizing site entry helps ensure worker safety.

• Versatility: Beyond soil volume calculation, LRTK can be used for distance and area measurements, as-built pass/fail checks, and as-built management with AR overlays of design data. For example, using AR to overlay 3D design models on site video allows you to transparently confirm the location of buried structures or instantly detect deviations between excavation surfaces and design grade lines. One device can meet a wide range of surveying needs, so the benefits can outweigh the introduction cost.

By using LRTK, surveying and measurement tasks that previously had to be left to specialists can be performed by anyone on site as part of daily work. Free from expensive equipment and complicated procedures, being able to check as-built volumes whenever necessary will dramatically improve construction efficiency and quality control.

Summary

Volume measurement in as-built management used to require time and experience, but the fusion of smartphone 3D scanning technology and RTK-GNSS has made it possible for anyone to implement it right away. Using point cloud data enables accurate coverage of wide areas, dramatically improving the accuracy of soil quantity calculations and making it easier to ensure fairness and quality in construction. Instead of estimating from limited survey points as in the past, digitally measuring the entire site and preserving solid evidence provides great reassurance to both clients and contractors.

The adoption of new technologies is changing construction management practices. The Ministry of Land, Infrastructure, Transport and Tourism has drafted guidelines for as-built management using 3D measurement technology and is promoting ICT-based as-built and progress management. In this trend, easy-to-use, high-precision measurement tools like LRTK strongly support on-site digital transformation (DX). In fact, high-precision measurements using smartphone + RTK are already being adopted at construction sites nationwide, with reports of significant efficiency and labor savings compared to traditional methods. As a new tool that can transform how site work is done, its spread is expected to increase. If you’ve only tried traditional methods so far, try smartphone surveying once—you’ll likely be surprised by the combination of efficiency and accuracy.

FAQ

Q: Can I accurately measure as-built volumes with only a smartphone? A: By combining a smartphone’s LiDAR scan with RTK-GNSS positioning, you can calculate volumes with an accuracy on the order of a few centimeters (cm level accuracy, half-inch accuracy). Because positioning precision comparable to conventional GPS surveying can be achieved, high-accuracy soil quantity calculations from point clouds obtained by 3D scanning are possible. Verification has shown errors within about 1-2 cm (0.4-0.8 in), yielding results comparable to typical field surveying (a smartphone’s LiDAR scan alone can produce errors on the order of tens of centimeters (tens of inches), but RTK correction dramatically improves positioning accuracy).

Q: How does this differ from measurements by drone or laser scanner? A: Drone aerial surveys and terrestrial laser scanners (TLS) excel at measuring wide areas but may require specialized operators, flight permits, and large equipment. The strength of smartphone + LRTK measurement is the convenience of using equipment you always have at hand. Depending on site conditions, smartphone scanning can sufficiently cover up to several hundred square meters, and in combination with drones you can efficiently 3D-model an entire site. Smartphones are also effective in areas where drones cannot enter, such as indoor spaces, under bridges, or inside tunnels. Portability and the ability to operate solo in confined spaces are major differences.

Q: Can people without surveying knowledge or qualifications use it? A: Yes. Basic operations are designed to be intuitive, and site personnel can use the system after a short training or by consulting a manual. The system automates specialized settings and complex calculations, so users simply follow on-screen prompts to scan and measure. However, basic surveying knowledge will make understanding and applying the results easier.

Q: Is it acceptable to use this method for as-built management in public works? A: Yes. The Ministry of Land, Infrastructure, Transport and Tourism has begun recommending 3D as-built management methods as a new standard in the Reiwa era, and methods for calculating volume from point clouds are specified in guidelines. Cases of submitting point cloud survey results as electronic deliverables and as-built management documents are increasing. Data acquired with LRTK can conform to required coordinate systems and accuracy control, and when properly managed, can be treated as equivalent to conventional measurement results.

Q: What is needed to use LRTK? A: Basically, you need an iPhone or iPad, the LRTK device, and a communication environment for RTK positioning to start using LRTK. Communication environment refers to an internet connection or communication device to receive GNSS correction information (such as a VRS correction service). For more stable measurements, an optional monopod to stabilize the smartphone can be used, though it is not mandatory. Because the necessary equipment is compact, preparation and transportation are much easier than with conventional surveying sets.

Q: How are measurement data saved and utilized? A: Point clouds and positioning data acquired with the LRTK app are automatically saved in the cloud and securely backed up. Point cloud data can be downloaded in standard formats such as LAS or XYZ as needed. Comparison results with design data and volume calculation reports can be exported as PDFs, allowing you to incorporate them into drawings and reports like conventional surveying deliverables.