Slope as-built management is changing: Instant assessment of slope unevenness with AR heat maps

Table of contents

• Traditional challenges in slope as-built management

• What is an AR heat map

• Reducing work burden

• Immediate assessment and rapid feedback

• Improved safety

• What is needed to introduce AR heat maps

• Simple surveying with LRTK

• FAQ

Traditional challenges in slope as-built management

Slope as-built management is the important process of confirming whether a slope has been constructed to the designed shape and dimensions to ensure quality and safety. Especially for slopes along roads and on development sites, it is necessary to check whether the gradient and surface irregularities deviate from design standards to prevent collapse or construction defects. However, traditional as-built management methods have had many challenges.

• Measurements are labor- and time-intensive: Traditionally, manual surveying using tape measures, staffs, and levels was the norm, and checking a wide slope often required multiple people and could take a full day or more. Key cross-sections were sampled and measured, but selecting measurement points and setting up access also took effort.

• Difficult to measure accurately on steep ground: On steep or curved slopes, it is not easy to press a scale against the surface to measure thickness or slope. Capturing small surface irregularities in detail is difficult, inevitably causing errors or missed measurements.

• Cannot cover the entire area, so oversights occur: The number of points that can be measured manually is limited, making comprehensive inspection of every area difficult. Even if sampled cross-sections show no problems, there may still be sections between them that deviate from the design. Traditional methods thus carried the risk of overlooking subtle bumps or inadequate thickness.

• High workload with safety concerns: Surveying on slopes is heavy labor and places a large burden on workers. Working in unstable postures at height increases the risk of falls and is inherently dangerous.

As described above, traditional slope as-built management faced numerous problems in terms of accuracy, efficiency, and safety. A key solution attracting attention in recent years is using three-dimensional point cloud data for as-built management. By performing point cloud surveying with laser scanners or photogrammetry, the entire slope shape can be recorded in detail as a collection of countless points (point cloud). This enables digital understanding of the entire slope’s as-built condition and allows confirmation of surface irregularities that could not be obtained from conventional cross-section measurements. In fact, the Ministry of Land, Infrastructure, Transport and Tourism promotes ICT use in construction sites (such as i-Construction), and draft as-built management guidelines include the use of 3D survey data. With this tailwind, point-cloud-based as-built management is likely to become increasingly mainstream.

What is an AR heat map

By comparing a 3D model of the current condition obtained from point cloud data with the designed 3D model (or pre-construction terrain), the elevation difference (amount of deviation) between them can be calculated. Visualizing this difference by color-coding is called a heat map. It shows at a glance which parts of the slope are higher (bulging) or lower (excavated) than the design. For example, if protruding high areas above the design surface are shown in red and recessed low areas in blue, parts that deviate from the design become immediately intuitive.

Furthermore, using AR (augmented reality) technology to overlay this heat map directly onto the actual slope on site is what we call an “AR heat map.” When viewing the slope through a tablet or smartphone camera, the color-coded heat map appears superimposed on the real view. Because red and blue highlights seem to float on the actual slope, you can intuitively point out on the spot which areas meet the design and which deviate from the standard.

With this AR heat map, construction personnel and clients (inspectors) can share the same visual information on site. Judgment of as-built quality, which used to be hard to explain with drawings and numerical data alone, becomes immediately clear when shown overlaid on the real object in AR. Communication is simplified, reducing rework and disputes caused by misunderstandings. Also, by using AR display during intermediate stages of construction, you can virtually project the completed design onto an unfinished slope and share construction targets on site. Although point cloud heat maps can be reviewed on a PC, the revolutionary value of AR is being able to directly compare them with the real object on site. Being able to immediately grasp the as-built state at the construction site dramatically increases the speed and reliability of as-built management.

AR heat maps are a new technology that can revolutionize slope as-built management. Next, let’s look in detail at the specific benefits this technology can provide.

Reducing work burden

Introducing AR heat maps significantly reduces the workload and effort involved in slope as-built management. Because point cloud scanning can capture the entire slope in a short time, measurement work that formerly took a full day by manual labor becomes far more efficient. In fact, a survey by the Ministry of Land, Infrastructure, Transport and Tourism reported that introducing ICT such as 3D surveying reduced earthwork labor hours by about 30% on average. Using AR heat maps allows you to quickly execute the entire flow from measurement to as-built confirmation, so the burden on site personnel is dramatically reduced.

There are also more tools now that non-specialists can use, enabling measurement with fewer people. For example, many recent smartphones are equipped with small LiDAR sensors, and with a dedicated app a single smartphone can acquire high-density point clouds. This avoids situations where multiple veteran surveyors must be stationed on site and contributes to measures against labor shortages. Once acquired, point cloud data can be reused for difference analysis against the design or for drawing generation, reducing the need for re-measurement and administrative work, and improving overall productivity.

Moreover, reducing surveying work and rework leads to lower labor costs and shorter construction schedules, producing cost benefits as well. Freed-up time and personnel can be allocated to other tasks, contributing to the overall efficiency of the site.

Immediate assessment and rapid feedback

With AR heat maps, you can judge as-built quality on the spot, instantly. Traditionally, after surveying at the site, it took time to return to the office, compare with drawings, and compile reports. However, advances in point cloud surveying and cloud technology now make it possible to process data on site immediately after construction and generate and verify a heat map the same day. In other words, you can determine right after completion whether the work matches the design or requires correction, and if necessary start remedial work that same day. This enables early detection and rapid response to issues, preventing schedule extensions due to rework.

For example, in slope greening work, performing point cloud surveying immediately after applying seed or topsoil will make areas with insufficient spray thickness obvious on the heat map. You can identify where additional application is needed on the spot and address it early, minimizing the risk of quality defects.

Because the heat map covers the entire slope, even fine unevenness or insufficient thickness will not be overlooked. Color coding in red or blue makes deviations instantly obvious, enabling inspectors to make confident pass/fail judgments. For clients (inspection side), being able to visually confirm results of as-built inspection on site is a major advantage. It can reduce the number of times inspectors need to visit the site later, and for remote sites online sharing enables remote inspection, contributing to faster inspection processes.

Improved safety

Using AR heat maps also contributes to improved on-site safety. Point cloud scanning is essentially non-contact, so workers do not need to spend long periods in hazardous steep areas. For example, a smartphone with LiDAR or a lightweight 3D scanner can complete measurements by scanning the slope from a safe location. Drones can also be used when necessary to acquire data remotely. This reduces the need to carry heavy surveying equipment while walking the slope, lowering the risk of falls and heatstroke associated with working at height.

Furthermore, AR heat maps create leeway in on-site work, which can help reduce human error. Previously, taking measurements in awkward postures or rushing to compile inspection results could lead to mistakes or accidents. With AR heat maps, measurement through to checking can be done calmly, improving not only the physical safety of the work environment but also the safety of work quality (error prevention). This is useful for on-site safety management and greatly contributes to reducing worker burden and preventing accidents. In construction sites where safety is paramount, reducing dangerous tasks in this way is highly significant.

What is needed to introduce AR heat maps

Although AR heat maps offer many advantages, what equipment and technology are required to put them into practice on site? The basic workflow follows the steps “3D measurement” → “create differential heat map” → “AR display.”

First is high-precision 3D surveying. You need to acquire the current condition of the target slope as point cloud data. This can be done with terrestrial laser scanners, drone photogrammetry, or smartphone-mounted LiDAR scanners. Recently, smartphones and small laser scanners can acquire point clouds with several-centimeter accuracy (cm level accuracy (half-inch accuracy)), so large-scale surveying equipment is not always necessary. For example, built-in smartphone LiDAR is suitable for close-range (a few meters (a few m (several ft))) measurements, whereas for large-area slopes you can combine drone photogrammetry. By combining multiple methods you can acquire high-density 3D data for any terrain.

Next is comparison with design data. Overlay the measured point cloud with the design surface data and calculate the elevation differences. Use dedicated software or cloud services to analyze the point cloud and generate the heat map. The difference calculation itself can be automated, but you need to prepare the underlying 3D model or reference surface data of the design.

Finally, AR display. To view the generated heat map on site, you need an AR-capable application. Typically a tablet or smartphone app overlays the heat map on the camera image. Accurate overlay requires correctly aligning the device’s position and orientation. For high-precision overlay, there is a method to measure the device’s position using RTK-GNSS to centimeter-level positioning (to position devices to centimeter-level accuracy (cm level accuracy (half-inch accuracy))). Another method is to place reference markers on site beforehand and have the camera recognize them for accurate alignment. The positioning and alignment mechanisms differ by system, but in all cases the goal is to match the real-world coordinate system with the digital data coordinate system.

As described above, to integrate the previously separate steps of measurement, analysis, and verification into a single workflow, each step must be linked. When performing each step with separate devices and software, specialized operation and data conversion were required. However, recently one-stop solutions that integrate these steps have appeared.

Simple surveying with LRTK

One solution that makes it easy to use AR heat maps on site is LRTK. LRTK is an all-in-one surveying system using a smartphone that handles everything from point cloud measurement to differential heat map analysis and AR display for as-built checks. By combining a dedicated app with cloud services, it eliminates the need to use multiple devices and software and is designed for intuitive use by anyone. It also includes functions to automatically calculate volumes of fill or excavation from acquired point clouds, contributing not only to as-built management but also to quantity management.

Specifically, with LRTK you can acquire high-precision 3D point clouds with just a smartphone, and differences from design data are automatically calculated. Because you can check heat maps immediately on site, you can judge as-built quality on the spot. Acquired data can be uploaded to the cloud and shared with stakeholders, making it easy to report survey results in real time. True to its name as a tool for simple surveying, it dramatically simplifies the formerly complex work process.

By leveraging modern tools like LRTK, the efficiency, accuracy, and safety of slope as-built management will improve dramatically. If you feel that surveying takes too long or as-built checks are burdensome in your current site, adopting such solutions may lead to surprisingly smooth operational improvements. Actively integrating advanced technologies can achieve both quality assurance and operational efficiency, accelerating DX (digital transformation) on site.

FAQ

Q: What is an AR heat map? A: An AR heat map is a method that color-codes the differences between measured point cloud data of a slope and the design data, and visualizes that color coding by overlaying it on the real slope using AR technology. It allows intuitive and rapid as-built management by showing at a glance which parts of the slope match the design and which parts deviate.

Q: What equipment or software is required to use AR heat maps? A: Basically you need 3D measurement equipment (laser scanner, drone, or LiDAR-equipped smartphone), software or cloud services to compare the point cloud with the design and compute differences, and an AR-capable device (tablet or smartphone) and app for AR display. Integrated systems also exist; for example, with LRTK you can complete surveying through AR display with just a smartphone.

Q: Can the measurement results obtained with AR heat maps be trusted for accuracy? A: Yes—if the source point cloud data are accurate, verification via heat maps is very reliable. Point clouds obtained by laser scanning or high-resolution photogrammetry typically have errors within several centimeters. AR display accuracy depends on the device alignment, but using dedicated equipment or RTK-GNSS makes it possible to overlay the digital data on the real object with centimeter-level positioning. Therefore, if measured appropriately, AR heat maps can provide practical, reliable accuracy.

Q: Is an AR heat map useful for clients (inspection personnel)? A: Yes, AR heat maps are an effective tool for client-side as-built inspections. When inspectors see color-coded results on the actual slope on site, they can intuitively understand as-built quality without lengthy explanations. The government is promoting the use of 3D data through initiatives like i-Construction, and new technologies like AR heat maps are expected to be widely adopted in inspection processes. For remote sites, cloud-based data sharing enables remote verification, making it an efficient communication tool between clients and contractors.

Q: How can I try an AR heat map? A: A simple way to try is to introduce a surveying system that supports AR heat maps. For example, smartphone surveying solutions like LRTK let you experience point cloud measurement through AR display without specialized equipment. Trying it on your own site will let you feel the benefits in reduced work time and improved quality. Start with a small site or a pilot project to verify the effects before full-scale adoption.

Q: Do I need special skills or certifications to operate it? A: No—once you learn the basic operation of the equipment, you can generally use it without advanced specialized skills. Modern smartphone apps and measurement devices are user-friendly and most site personnel can master them with short training. However, to perform accurate as-built evaluation, basic knowledge of surveying and design drawings is required.