Table of Contents

• What is an AR heat map?

• How AR heat maps work and their benefits

• Reduce rework with real-time quality checks

• Labor savings and safety improvements through remote sharing

• Steps and precautions for introducing AR heat maps

• Adoption trends in local governments

• Simple surveying anyone can use: Start AR heat maps with LRTK

• FAQ

What is an AR heat map?

In construction and civil engineering sites, confirming and recording whether work has been completed according to the drawings—known as as-built management—is indispensable. A relatively new method for this as-built management is the heat map. By combining this with AR (augmented reality) technology, it has become possible to intuitively check construction acceptability on site. An AR heat map is a three-dimensional colored visualization of the differences between measured data of a completed structure or terrain and the design data. For example, areas that are higher than the design are shown in reddish tones, areas that are lower because insufficient material was removed are shown in bluish tones, and areas that conform to the design are shown in green; the color indicates the magnitude of the error. At a glance, you can intuitively understand “which points are higher or lower than the standard” and “whether the finish is acceptable or not.”

Subtle bumps and depressions that are easily overlooked in flat drawings or numeric lists can be readily discovered with a colored 3D visual. In other words, an AR heat map is a visualization tool for as-built management. The Ministry of Land, Infrastructure, Transport and Tourism is also promoting three-dimensional measurement and surface as-built evaluation through initiatives like *i-Construction*, and heat-map-based as-built management is beginning to be incorporated into official guidelines. As a new standard suited to the era of on-site DX (digital transformation), AR heat maps are spreading.

How AR heat maps work and their benefits

AR heat maps are created by comparing high-density 3D survey data such as point clouds obtained on site with the 3D model from the design stage. By overlaying the surveyed current-state data on the design model and automatically calculating the height error at each point, color-coding according to the error magnitude becomes possible. The typical color rule is a gradient where areas with small errors are green–blue tones, areas that are raised above the design and too high are warm colors (yellow–red), and areas that are too low are cool colors (blue–purple). If threshold values for allowable ranges are pre-set, conforming areas are shown in green while exceedances are clearly emphasized in red or blue. The resulting heat map data can be transferred to a mobile device and overlaid on the camera view to create an AR heat map. By superimposing errors as color information, anyone can intuitively evaluate quality.

The main benefits of using AR heat maps include:

• Intuitive quality judgment: Because the magnitude of errors is shown by color, anyone from site workers to clients can understand construction accuracy at a glance. It’s easier to understand than numeric or written reports, and corrective locations can be shared with the whole team.

• Prevention of measurement omissions: Because surface evaluations can be made with data that covers wide areas like point clouds, localized defects that would be missed by conventional spot checks can be detected. This exhaustively reveals quality irregularities and prevents oversights.

• Rapid feedback: If you scan and generate heat maps during construction, you can immediately check as-built conditions on the spot. Early detection and correction of problem areas reduce large-scale rework later, shortening schedules and ensuring quality.

• Recordkeeping and traceability: Heat maps and point cloud data can be stored in the cloud as digital records. This preserves detailed “construction history” that paper drawings could not retain, making future maintenance comparisons and root-cause analysis easier. Integrating as-built data into BIM/CIM models also makes it a valuable information resource after completion.

• Labor savings and improved safety: Point cloud scanning and automated analysis that can measure wide areas in a short time greatly reduce the manpower and time required for measurement tasks. Data can be obtained from a distance even for high or hazardous locations, reducing the frequency with which workers need to enter dangerous areas and improving safety. Places that were difficult to inspect before can be easily checked with heat maps, reducing human error.

Because of these advantages, AR heat maps are attracting attention as a method that dramatically improves the accuracy and efficiency of quality control. Next, let’s look in detail at how this technology can be used on-site.

Reduce rework with real-time quality checks

A major strength of AR heat maps is that they allow construction quality to be checked in real time. Traditionally, surveys were conducted after completion to check as-built conditions, and any deficiencies would be corrected at a later date. With AR heat maps, however, you can scan the current state at each stage of construction and evaluate quality immediately. Errors are color-displayed on the spot, enabling immediate identification of defects and prompt corrective work. This minimizes rework discovered later.

For example, in paving work, you can scan the surface after compaction to instantly check for areas with insufficient thickness. If areas appear blue on the heat map (indicating insufficient thickness), you can immediately add pavement to meet the standard. Previously, thickness insufficiencies were often discovered after completion by coring tests, requiring rework with machines brought back onto the site; real-time checks prevent such waste. Site supervisors and heavy equipment operators can also immediately understand their construction accuracy through AR on a tablet, making it clear “where and how much to fix.” As a result, early detection and correction of quality issues lead to shortened schedules and improved quality.

Labor savings and safety improvements through remote sharing

Because AR heat maps record site conditions as digital data, they are also easy to share and verify remotely. If a heat map uploaded to the cloud is shared with office PCs or staff at other sites, clients or supervisors located elsewhere can discuss while viewing the same visual information. This reduces the frequency of on-site inspections, cutting travel time and personnel costs (labor savings).

Nowadays, video conferencing systems and systems for remote site attendance (online attendance) are becoming more established, and they pair exceptionally well with AR heat maps. In one local government trial, a contractor’s as-built heat map was shared via the cloud with the client, and the person in charge checked the site heat map on a tablet from the office. By viewing color-coded surface as-built data, they could understand quality conditions at a glance without the need to inspect numerous points on site as before. They also implemented remote inspections in which the office gave instructions via video call, requested additional measurements at points of uncertainty, and had the on-site workers immediately measure those points and send results back.

AR heat map use also contributes to improved safety. For example, in confined sites or high-place work where large on-site gatherings for inspection posed risks, remote sharing allows verification by a minimal number of people. In hazardous areas, workers can check AR displays from a distance via tablet without approaching directly, helping ensure safety. In this way, digital data sharing and AR display make it possible to perform quality verification efficiently and safely with a small number of people.

Steps and precautions for introducing AR heat maps

Here are general steps and key points to consider when introducing AR heat maps. Even without advanced expertise, you can operate them if you understand the basic workflow.

• Design data preparation: First, prepare the 3D design data that will serve as the standard. In civil engineering, this includes ground surfaces and structural design models (TIN data, BIM/CIM models, etc.). Clearly define in digital data which shape is the target.

• Current-state 3D measurement: Next, measure the actual post-construction shape in 3D. Point cloud surveying is the mainstream approach, scanning the entire site with terrestrial 3D laser scanners or drone photogrammetry. Recently, methods that use LiDAR-equipped smartphones to easily acquire point clouds have become more common. The important point is to measure the current state without omissions and obtain data with as high positioning accuracy as possible. Using equipment that can measure large areas quickly will yield accurate current-state models that include fine details of terrain and structures.

• Data alignment: Align the design data (ideal shape) and the current-state data in the same coordinate system. If you measured using an absolute survey coordinate system (such as the world geodetic system) from the start, the two datasets will automatically align with minimal positional offset. For example, if point clouds are acquired with RTK-GNSS–compatible equipment, the acquired data itself will have high-precision coordinates and will overlap precisely with the design model. If measurements were taken in a local coordinate system or small offsets exist, you will need to perform a fitting adjustment to align both datasets to known reference points. Because inaccurate alignment will undermine the credibility of the subsequent heat map results, this step should be carried out carefully.

• Heat map generation: Compare the prepared design data and the current-state point cloud data and generate the heat map via automatic analysis. Running a “create as-built heat map” function in dedicated analysis software or on a cloud service will calculate height differences at each point and produce a 3D model with color-coded differences. By adjusting mesh (grid) size and color range settings, you can create an easy-to-read heat map. The generated results can be reviewed on a PC or in the cloud, and, if needed, exported as images or saved as model data.

• Overlay and display on site with AR: Load the finished heat map data into a tablet or smartphone and overlay it on the site imagery. Use a dedicated AR app to project the virtual heat map model onto the camera view. To overlay accurately, the device’s position and orientation must be precisely known, so use high-accuracy positioning methods where possible. For example, equipping the device with RTK-GNSS provides centimeter-level position correction (half-inch accuracy), minimizing misalignment between the heat map and the actual site. Alternatively, preparing markers or known reference points on site and fixing the virtual model to them is also effective. With high-precision alignment, the heat map will remain correctly positioned even as you walk around with the device.

The above is the basic flow, but there are several precautions when introducing the system. First is the accuracy of acquired data. If the point cloud or photogrammetry results are low in accuracy, the reliability of the heat map will decrease. Perform equipment calibration and sufficient surveying preparation in advance to obtain the most accurate current-state data possible. Second, consider the AR display environment on site. In places where GPS does not reach (indoors or mountainous areas), RTK-GNSS cannot be used, so measures such as installing physical markers are necessary. Also pay attention to tablet screen brightness and battery levels when viewing through a device. Finally, establishing internal operational rules is important. Define when to perform heat map measurements, data sharing procedures, and how to use the results in reports so that AR heat map adoption becomes a routine part of on-site operations.

Adoption trends in local governments

AR heat maps are spreading not only among major construction companies but also to local governments and public works sites. The Ministry of Land, Infrastructure, Transport and Tourism itself has been conducting on-site demonstrations, and in 2024 a road construction project under the Kanto Regional Development Bureau publicly demonstrated AR as-built management. The tablet displayed the 3D design data and site survey data differences as a heat map, and a demonstration intentionally created a 25 cm (9.8 in) raised area using styrofoam boards, which showed up red. The office staff responsible for the site said, “Being able to confirm by surface during remote attendance is revolutionary,” and they valued the advantage of being able to judge as-built acceptability from a remote office.

There have also been reports of inspections using AR heat maps at the municipal level. In one prefectural river project, the contractor’s as-built heat map was checked simultaneously by the prefectural office and the site, and remote attendance via online meetings enabled instruction and correction. In this case, the heat map shared on the cloud was viewed while the person in charge specified additional points they wanted measured; on-site workers immediately measured those points and sent the results, confirming that everything was within standards. Participants commented, “It’s much easier to understand by checking a color-coded heat map surface than by chasing paper drawings and large volumes of numbers.”

In this way, attention to AR heat map technology is growing among local governments, and adoption is progressing from the perspectives of DX promotion and workstyle reform. Clients can expect shorter inspection engagement times and more efficient remote supervision, while contractors benefit from smaller on-site teams and improved safety; both sides are beginning to recognize the advantages. With support from the national i-Construction initiatives, more municipalities and public projects are likely to adopt AR heat maps in the future.

Simple surveying anyone can use: Start AR heat maps with LRTK

Up to this point we’ve examined the mechanisms and effects of AR heat maps, and some readers may think, “Advanced 3D scanning and analysis sounds difficult for our company” or “Don’t we need specialized surveyors?” However, recently simple surveying systems that anyone can handle have appeared, making it possible to perform point cloud measurements and heat map creation easily without special skills. A representative example is smartphone-based LRTK.

LRTK is a solution that turns a smartphone into a centimeter-level accuracy (half-inch accuracy) universal surveying instrument by attaching a compact RTK-GNSS receiver to the phone and linking it with dedicated apps and cloud services. The smartphone camera or LiDAR sensor scans the site, and the acquired point cloud data is automatically uploaded to the cloud. The cloud compares it with the design data and generates an as-built heat map with a single click. The generated results can be downloaded back to the smartphone for AR display, so surveying through quality checking with heat maps is completed in one stop.

Using such all-in-one tools minimizes the need for expensive specialized equipment and complicated data processing, enabling even first-time sites to practice as-built management with AR heat maps easily. If LRTK-based simple surveying spreads, not only specialists but also municipal staff and site technicians will be able to use high-precision AR technology in daily work. This aligns with the i-Construction initiatives promoted by the Ministry of Land, Infrastructure, Transport and Tourism, and such tools can become strong partners supporting on-site DX. Take this opportunity to adopt these latest technologies on site to improve quality control and streamline operations.

FAQ

Q: What is an AR heat map? A: It is a visualization that color-codes the differences between measured values of a completed structure or terrain and the design model. Current-state measurement results such as point clouds are compared with design data, and areas with small errors are shown in green, prominent raised areas in red, and excavated areas in blue. It is an as-built management tool that enables immediate judgment of construction accuracy at a glance.

Q: What is needed to create and display AR heat maps? A: Basically, you need equipment to measure the site in three dimensions and software (or a cloud service) to process data and display AR. Acquire point cloud data with a 3D laser scanner, drone, LiDAR-equipped smartphone, etc., then use dedicated software on a PC or a cloud system to compare with the design model and generate the heat map. After that, load the generated heat map into a smartphone or tablet AR app to overlay it on the real-world view.

Q: Can a smartphone alone handle heat map measurement through AR display? A: Yes, it is possible. Recent smartphones (for example, iPhone Pro series models) come with LiDAR sensors, and by combining them with a small RTK-GNSS receiver, a smartphone can become a high-precision 3D scanner. If you use a dedicated app to acquire point clouds from the smartphone and upload them to the cloud, heat maps can be generated automatically. Systems like smartphone-based LRTK allow smartphone-only workflows from heat map creation to AR display without specialized surveying knowledge.

Q: How can I achieve high-accuracy AR overlay? A: To accurately overlay a heat map on site in AR, you need to know the device’s position and attitude precisely. Built-in GPS in smartphones or tablets has large errors, so, if possible, use RTK-GNSS for positioning augmentation to correct device position to centimeter-level position correction (half-inch accuracy). Installing known reference markers on site to fix the virtual model can further reduce misalignment. With compatible systems, common AR issues such as positional offset and drift are eliminated, allowing heat maps to remain correctly positioned across large sites.

Q: Are as-built heat maps accepted as official as-built management documents? A: In recent years, as-built heat maps have increasingly been recognized as one of the official as-built management methods. Revisions to the Ministry of Land, Infrastructure, Transport and Tourism guidelines explicitly state that “as-built evaluation based on comparison of point cloud data and design data, with results shown by heat maps, etc.” is permitted. In other words, color-coded heat map diagrams can be submitted as inspection documents. However, the final handling depends on the client’s instructions, so it is advisable to consult beforehand and confirm how they will be treated as formal records.