Accelerate On-site DX! Start Smart As-built Management with AR Heat Maps

Table of Contents

• What is an AR heat map?

• Benefits of AR heat maps

• Steps to create an AR heat map

• Real-time verification of construction status with AR display

• Summary

• FAQ

What is an AR heat map?

On construction sites, "as-built management" — measuring and recording whether pavement, embankments, land development, structures, etc., have been finished according to design drawings — is indispensable. In recent years, a new 3D visualization method called a heat map has appeared in as-built management, and when combined with AR (augmented reality) technology it has become possible to intuitively check construction accuracy on site. An AR heat map overlays a heat map that color-codes the differences between the actual finished terrain or structure (as-built) and the design data onto the real world using AR. In other words, by projecting digital pass/fail information onto the actual view, it becomes a next-generation as-built management tool that makes quality instantly understandable.

Heat maps show the error at each location with colors. For example, areas that are higher than the design are shown in red or warm colors, while areas that are lower than the design such as unremoved material are shown in blue or cool colors, and areas with small errors within acceptable range are shown in green (note: color examples). By glancing at it, you can intuitively tell which locations are higher or lower than the standard and whether the finish is acceptable. Subtle irregularities or trends that are easy to miss on paper drawings or numeric lists can be readily discovered with colored 3D visuals. This as-built heat map is a "visualization" tool for as-built management and is becoming a new standard in the era of on-site DX (digital transformation). In fact, the Ministry of Land, Infrastructure, Transport and Tourism is promoting 3D measurement and surface as-built evaluation through initiatives like *i-Construction*, and in the FY2025 draft as-built management guidelines the use of "on-site as-built verification using AR and other digital technologies" is included, indicating that as-built management using heat maps and AR is beginning to be adopted as an official method.

Benefits of AR heat maps

Using AR heat maps brings many advantages to the field that conventional methods could not provide. Here are the main benefits.

• Intuitive quality assessment: Because the magnitude of errors is shown by color, anyone from site workers to clients can understand construction accuracy at a glance. It is far easier to interpret than reports consisting only of numbers or text, and it makes it easier for the whole team to share where corrections are needed. For example, the finish of pavement work is visually communicated to craftsmen and machine operators through colorized unevenness on a heat map.

• Prevention of measurement omissions and oversights: High-density 3D measurements such as point cloud data allow evaluation of the entire construction area, so local defects or small bumps that tend to be missed by spot checks can be detected. A heat map that covers a wide area can comprehensively identify quality inconsistencies. Even for embankments and land development, every corner can be checked, reducing human error.

• Rapid feedback: If you scan during construction and convert to a heat map, you can check the as-built status immediately at that point. Early discovery of problem areas and on-the-spot rework minimizes rework. With AR display, the location of defects can be identified instantly, eliminating the need to view a heat map and then take layout marks on site as before. This contributes significantly to shorter schedules and quality assurance.

• Improved records and traceability: Heat maps and original point cloud data can be stored in the cloud as digital records. You can save detailed construction histories that could not be preserved on paper drawings, making it easy to perform root cause analysis by comparing past as-built data during future maintenance. Integrating as-built data into BIM/CIM models for asset management also turns the data into a valuable resource after completion.

• Labor-saving and improved safety: Point cloud measurement and automated analysis that can measure large areas with high precision greatly reduce the manpower and time required for measurement tasks. Dangerous areas such as heights and slopes can be scanned remotely, contributing to worker safety. As-built checks in places that were previously difficult become easy with heat maps, resulting in labor savings and enhanced safety for inspection tasks.

Thus, AR heat maps greatly contribute to improving the accuracy and efficiency of quality control. So how do you actually create and use such heat maps? Next, we will look at the basic workflow.

Steps to create an AR heat map

Here is a step-by-step explanation of the general procedure for creating an AR heat map (as-built heat map). From preparing the necessary data to generating and using the heat map, proceed with the following steps.

• Prepare the design data: First, prepare the 3D design data that will serve as the basis for comparison. For earthworks or land development, this means the design ground model (TIN data or design surface); for pavement, the design surface elevation data; for structures, 3D design models such as BIM/CIM. The point is to clearly define in data what the ideal shape (target) is. In as-built management, this design model is the standard for pass/fail judgments.

• 3D measurement of the as-built condition: Next, measure the actual finished shape in 3D. Point cloud measurement using laser scanners or drone photogrammetry has become mainstream for scanning the entire site to obtain high-density measurement data. Recently, there has also been an increase in cases where point clouds are obtained easily using smartphones equipped with LiDAR sensors. For example, some recent iPhone and iPad models have built-in LiDAR; if you combine these with an RTK-GNSS receiver, you can perform point cloud surveying with centimeter-level accuracy (half-inch accuracy) using a smartphone. The important point is to measure the as-built condition thoroughly and acquire data with sufficient accuracy. By utilizing point cloud measurement that can scan large areas in a short time, you can obtain a digital as-built model that includes the details of terrain and structures.

• Georeferencing the data: Align the design data and the acquired as-built data in the same coordinate system. If measurements were taken from the start using public coordinates or other absolute coordinates, the datasets will automatically align and little effort is needed. For example, if point clouds were acquired with RTK-capable equipment, the acquired data already has accurate world coordinates, so you can overlay the design model as-is. If measurements were taken in a local coordinate system or there are slight offsets, adjust both datasets to known control points. If the positions are not correctly aligned here, subsequent heat map results cannot be trusted, so check carefully.

• Generate the heat map: Compare the prepared design model with the as-built point cloud data to generate an as-built heat map. Using dedicated analysis software or cloud services, run functions such as "difference analysis" or "create heat map" and the height error at each point will be calculated and a color-coded heat map will be generated in a short time. Typical color schemes show small errors in green, areas higher than the design in yellow to red warm colors, and areas lower than the design in blue to purple cool colors. If you set threshold values for allowable errors in advance, you can display areas within that range in green and emphasize out-of-range areas in red or blue. Some tools allow you to adjust the heat map mesh (grid) size and color range. Automatic comparison processing by computer is very fast, so you can get results in a short time even for datasets of several hundred thousand points.

• Review and analyze results: Review the generated heat map on a PC or in the cloud and analyze the construction quality. By looking at the color distribution, you can intuitively read where and by how much areas are higher or lower. For example, you might identify "the center of area ◯◯ is overfilled by +5 cm (±? in) relative to design" or "area △△ is -3 cm lower than design." Displaying numeric errors at points on the heat map as needed, analyze overall trends (for example, whether the site is generally slightly high or only some parts are low). Because heat maps are visual, they are easy for on-site craftsmen and heavy equipment operators to understand directly, making them an effective communication tool for sharing areas that require correction. Also, if you upload the data to the cloud, stakeholders in remote offices can view the same 3D heat map via a web browser. You can share information with remote supervisors and clients in real time to obtain accurate instructions and approvals.

• Corrective work and record: If defective areas are identified on the heat map, perform the necessary rework on site (such as re-compaction of embankments or trimming of overfilled areas). After correction, perform 3D measurement again and confirm the finish with a heat map in the same way. Once you confirm that the issues are resolved, output the final as-built heat map and inspection results as an as-built management report. Recently, systems that automatically generate heat map reports with one click have appeared, allowing you to quickly create submission materials by combining photos and traditional drawings. Because it can be completed with digital data, report preparation workload is greatly reduced. Store the obtained heat maps and point cloud data within the company to use for future project planning and knowledge sharing among engineers.

That is the basic flow for creating an AR heat map. The key points are to acquire high-accuracy as-built data, perform proper georeferencing, and leverage automated tools to efficiently analyze and visualize. Next, we will explain AR display as a way to use this heat map on site to check construction status in real time.

Real-time verification of construction status with AR display

Once an as-built heat map has been created, displaying it on site with AR lets you overlay digital information on the real object to verify construction status. AR-capable apps or systems load the heat map data onto mobile devices (smartphones or tablets) and overlay a virtual heat map onto the camera view. Because you can view the pass/fail of the as-built indicated in color composited into the actual site scene, you can intuitively understand on the spot "how much and where to correct."

The basic AR display procedure is to transfer the heat map data generated on the cloud or PC (a colored 3D point cloud model, etc.) to a mobile device. Then on site, point the smartphone or tablet camera at the actual structure or terrain in the screen and overlay the heat map. The device's tilt and orientation are detected by gyroscope sensors and the virtual heat map viewpoint is synchronized, but accurate overlay requires improving the positional information of the device. Smartphone GPS accuracy (on the order of several meters (several ft)) may cause the heat map to be misaligned, so for more accurate AR overlay take measures such as the following.

• Improve device positioning with high-precision positioning: Use RTK-GNSS or network RTK services to correct the smartphone's position to centimeter-level accuracy (half-inch accuracy). For example, place a base station on site or use public GNSS correction services (Ntrip, etc.), and connect an RTK receiver to the smartphone for high-precision positioning, which minimizes the mismatch between digital data and real space.

• Align using reference markers: Place known points or markers (targets) on site and fix the virtual heat map to those points in the AR system. For example, place a marker on the ground and match that position to the corresponding point on the heat map to reliably align the virtual display with the real object.

With compatible systems, these methods allow precise determination of the smartphone's pose and enable the heat map to be overlaid exactly on site. With centimeter-level AR (half-inch accuracy), you can accurately identify which real-world spot corresponds to the color indicated on the heat map and immediately proceed with on-site corrections. Introducing AR heat maps brings the digital pass/fail judgment of as-built conditions into the real environment, enabling real-time construction management. It evolves from a mere inspection record to a practical on-site quality improvement tool.

Summary

This article introduced AR heat maps, a new technology for as-built management, covering their overview, benefits, creation steps, and on-site usage. Compared to conventional survey-centered as-built management, the heat map + AR approach can check large areas quickly and with high accuracy, and its visual nature makes results easy to understand, dramatically improving construction management efficiency and quality. The adoption of digital technology enables thorough inspection with small teams and smooth information sharing between site and office. As part of on-site DX, adoption is expected to continue growing.

That said, some may feel that advanced 3D scanning and analysis are difficult to handle in-house. However, user-friendly simplified surveying systems have recently appeared, allowing point cloud measurement and heat map creation without specialized surveying skills. For example, using a system like LRTK that mounts a small RTK-GNSS receiver on a smartphone turns the phone into a high-precision 3D scanner, and cloud services can automatically generate as-built heat maps from on-site scans. Furthermore, those heat maps can be displayed on the smartphone in AR for one-stop on-site verification. By leveraging all-in-one solutions that minimize dedicated equipment and complex manual work, even first-time users can easily practice cutting-edge smart as-built management. Take this opportunity to introduce digital technology on site and improve quality control and operational efficiency.

FAQ

Q: What is an AR heat map? A: An AR heat map is an as-built heat map that visualizes with colors the differences between the actual finished shape and the design shape after construction, overlaid onto the real world using AR technology. It compares acquired point cloud data or other as-built data with design models; areas with small errors appear green, significantly raised areas appear red, and excavated areas appear blue, enabling a visual as-built management tool that lets you judge construction accuracy at a glance.

Q: What equipment and software are needed to create a heat map? A: Basically, you need equipment to perform 3D measurements on site and software (or a cloud service) to process that data. For example, obtain point cloud data with a terrestrial 3D laser scanner, a drone (photogrammetry), or a LiDAR-equipped smartphone, and use dedicated PC software or a cloud system to compare with the design data and generate heat maps. Recently, platforms have appeared that automatically create heat maps simply by uploading point clouds and design models to the cloud.

Q: Can I create as-built heat maps with only a smartphone? A: Yes, it is possible. Some modern smartphones (e.g., certain iPhone Pro models) have LiDAR sensors; by combining these with a dedicated RTK-GNSS receiver, you can use a smartphone as a high-precision 3D scanner. By scanning point clouds with a dedicated app and uploading them to the cloud, services can automatically generate heat maps. Using smartphone surveying systems like LRTK, even those without surveying expertise can complete point cloud measurement, heat map creation, and AR-based on-site verification using only a smartphone.

Q: What is required to overlay a heat map on site with AR? A: AR display requires an AR-capable smartphone or tablet and a dedicated app that loads and shows heat map data. The virtual model is overlaid onto the device's camera view, but accurate overlay requires precise detection of the device's position and orientation. For higher accuracy, device coordinates can be improved via RTK-GNSS position correction, or markers (targets) may be placed on site for reference alignment. With compatible systems, centimeter-level positioning without relying on the phone's built-in GPS is possible, enabling accurate, non-shifted heat map display on site.

Q: Are as-built heat maps accepted as official as-built management documents? A: In recent years, as-built heat maps have gradually been recognized as one official as-built management method. The Ministry of Land, Infrastructure, Transport and Tourism has incorporated 3D measurement techniques for surface as-built management, and heat map evaluations are being trialed and introduced in earnest. For some earthworks projects, comprehensive as-built measurement and heat map evaluation are becoming mandatory. Therefore, it is possible to submit 3D as-built data including heat maps as inspection documents, and they are actively used in modern ICT construction sites. However, follow the guidelines of each contracting authority and, if required, submit printed heat map drawings or electronic data as instructed.