The Key to Smart Construction! Visualize Site Data with AR Heat Maps

Table of Contents

• What is an AR heat map?

• Benefits of AR heat maps

• How to create an AR heat map

• Real-time confirmation of construction status with AR display

• What is simple surveying with LRTK?

• FAQ

On construction sites, measuring and recording whether the finished work matches the drawings—known as quality control—is indispensable. In recent years, a new method called the heat map has emerged for this quality control, and by combining it with AR (augmented reality) technology, site conditions can be intuitively checked on the spot. An AR heat map is a decisive technology for realizing smart construction, dramatically improving efficiency and quality in construction management. This article explains what an AR heat map is, its benefits, and the concrete steps to create one. We also introduce how to project a heat map into real space with AR and check construction accuracy in real time. Learn next-generation quality control methods using the latest digital technologies to help drive DX (digital transformation) on your site.

What is an AR heat map?

An AR heat map is three-dimensional visualization data that compares the shape of a completed structure or terrain (as-built) to the design data and color-codes the differences. Point cloud data or 3D surveying data acquired after construction are overlaid with the 3D model from the design phase (design surface data), and the error at each location is indicated by color. For example, areas that are higher than the design are shown in red or warm colors, areas that are lower because insufficient material was removed are shown in blue or cool colors, and areas that conform to the design are shown in green. At a glance, you can intuitively see which points on site are higher or lower than the standard and whether they are acceptable or not.

Such as-built heat maps can be described as visualization tools for quality control. Subtle undulations and overall trends that are hard to notice on flat drawings or numeric lists are easily discovered with colorized 3D visuals. In recent years, the Ministry of Land, Infrastructure, Transport and Tourism has promoted 3D measurement and surface-based as-built evaluation (heat map display) through initiatives such as *i-Construction*, and heat map–based quality control is beginning to be incorporated into technical guidelines. In other words, as-built management using AR heat maps is becoming a new standard in the DX era of construction.

Benefits of AR heat maps

AR heat maps provide many advantages that traditional methods could not. The main benefits include:

• 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 easier to comprehend than reports composed only of numbers or text, and it becomes simple to share the points that need correction with the entire team.

• Prevention of missed measurements: Because surface evaluation can be performed with high-density data like point clouds, localized defects that sampling inspections might miss can be detected. A heat map covering a wide area can uncover variations in quality without omission.

• Rapid feedback: If you scan and convert to a heat map during construction, you can check the as-built status immediately. Early detection and rework of problem areas minimize rework, leading to shorter schedules and improved quality.

• Record keeping and traceability: Heat maps and point cloud data can be stored in the cloud as digital records. This preserves detailed “construction history” that could not be kept on paper drawings, making it easy to compare with past data for cause analysis during future maintenance. As-built data can also be integrated into BIM/CIM models for use in facility management, providing valuable information even after completion.

• Labor savings and improved safety: High-coverage point cloud scanning and automated analysis significantly reduce the manpower and time required for measurement tasks. Because high or hazardous areas can be scanned remotely, this contributes to worker safety. Heat maps make it easy to check as-built conditions in areas that were previously difficult to access, reducing human error.

In this way, AR heat maps greatly contribute to improving accuracy and efficiency in construction quality. So, what steps should you take to actually create such a heat map? The next section covers the concrete process.

How to create an AR heat map

Below is a step-by-step explanation of the typical workflow for creating an AR heat map, from preparing the necessary data to generating the heat map.

• Prepare the design data: First, prepare the 3D design data that will serve as the comparison baseline. For earthwork, this would be the ground model at the design stage (TIN data or design surface data); for structures, it would be a BIM/CIM 3D design model. In short, this step clarifies in data form “which shape is considered ideal (target).” This design model becomes the pass/fail criterion for the as-built evaluation.

• 3D measurement of the current condition: Next, measure the actual post-construction shape in 3D. Point cloud measurement has become mainstream, and scanning the entire site using terrestrial 3D laser scanners or drone photogrammetry is commonly used. Recently, cases of easily acquiring point clouds using LiDAR-equipped smartphones have increased. For example, by combining a high-performance smartphone (e.g., a tablet equipped with a LiDAR sensor) with an RTK-GNSS receiver, point cloud surveying with centimeter-level accuracy (half-inch accuracy) is possible even with a smartphone. Regardless of the method, the important point is to measure the current condition thoroughly and obtain data with as high positioning accuracy as possible. Point cloud scanning, which can cover wide areas in a short time, yields a digital as-built model that includes detailed terrain and structural features.

• Align the data: Overlay the measured as-built data and the design data in the same coordinate system. If measurements were taken in survey coordinates (such as public coordinate systems), both datasets will automatically align, so minimal effort is needed for alignment. For example, if a point cloud is acquired with RTK-capable equipment, the acquired data itself has high-accuracy coordinate values, so you can simply overlay the design model. If measurements were taken in a local coordinate system or there are slight offsets, perform a fitting adjustment using known points on site to align the two datasets. If alignment is not correct here, the reliability of subsequent heat map results will be compromised, so verify carefully.

• Generate the heat map: Compare the prepared design data with the acquired as-built data to create an as-built heat map. Running the “create heat map” function in dedicated analysis software or a cloud service automatically calculates the height difference at each point and generates a color-coded heat map of those differences. Typical color schemes show small errors in green, areas higher than the design in yellow to red, and areas lower than the design in blue to purple. If you set tolerance thresholds in advance, you can customize the display so that values within tolerance appear green and exceedances are emphasized in red or blue. Some tools allow adjustment of the heat map mesh (grid) size and color ranges. Because the comparison process is computer-accelerated, results can be obtained quickly even for datasets on the order of hundreds of thousands of points.

• Review and analyze results: Review the generated heat map on screen and analyze construction quality. From the color distribution you can intuitively read “which locations are how much higher or lower.” For example, you can identify that “the center of Area ○○ is overfilled by +5 cm (2.0 in)” or “Section △△ has −3 cm (−1.2 in) of leftover material compared to the design.” You can also inspect numerical errors at individual points on the heat map and analyze overall trends (e.g., generally a bit high or only specific spots low). As a visual tool, heat maps are easy for site workers and heavy equipment operators to understand, making them effective for communicating areas requiring correction. Uploading data to the cloud allows stakeholders in remote offices to view the same 3D heat map via a web browser. This enables real-time sharing with supervisors and clients for precise instructions or rapid approvals.

• Correction work and record: If defects identified by the heat map require corrective work (such as regrading or additional fill), perform the necessary rework on site. Then remeasure in 3D and confirm the final condition with another heat map. Once the problem is resolved, output the final as-built heat map and inspection results as an as-built management chart (report). Many modern systems can automatically generate reports with heat maps, allowing you to create submission materials combining photos and drawings with one click. Since everything is digital, the effort to prepare reports is greatly reduced. Store the resulting heat maps and point cloud data in-house for reference for future projects and for knowledge sharing among engineers.

That is the basic flow for creating AR heat maps. The key points are acquiring high-accuracy as-built data, proper alignment, and utilizing software or cloud automation tools. Next, we explain AR display as a method to use the heat map for real-time on-site confirmation.

Real-time confirmation of construction status with AR display

Once an as-built heat map has been created, displaying it on site with AR allows you to overlay digital information onto the real object and check construction status. The heat map data is loaded into a mobile device via a dedicated AR-enabled app or system, and a virtual heat map is overlaid on the camera view. Because the pass/fail of as-built conditions is shown in color composited with the real scene, you can intuitively understand “which location needs how much correction” on the spot.

The AR display procedure begins by transferring the heat map data (colorized 3D model or point cloud) to a mobile device. Then, hold up a smartphone or tablet camera on site and overlay the heat map onto the actual structure or terrain shown on the screen. For accurate alignment, it is effective to use the device’s GPS and gyro sensors as well as high-precision positioning or reference markers. For example, using RTK-GNSS to correct the device position to centimeter-class (half-inch accuracy) or fixing virtual objects to known points on site minimizes misalignment between the heat map and the field. Supported systems achieve high-precision AR with these corrections so that the virtual heat map stays correctly positioned even while walking around with the device.

AR on-site confirmation offers many benefits. First, identifying problem locations becomes dramatically faster. Since red or blue areas displayed on the screen clearly indicate which actual points correspond, you can mark the ground on the spot or directly instruct the heavy equipment operator, “Please cut another ◯ cm (◯ in) here.” Previously, you had to use inspection documents and a surveying instrument to locate the corresponding site points, but that effort is no longer required. AR also contributes to streamlining site inspections. Presenting heat map AR on a tablet during on-site inspections with clients or supervisors lets you share pass/fail status immediately. Because you can visually show “which range was corrected by how much,” explanations and consensus building become smoother. There is also the effect of reducing remeasurement effort. If high-precision point cloud data were collected when creating the heat map, you can pinpoint locations on AR without having to remeasure many points for inspections. From a safety perspective, confirming hazardous areas remotely via AR without sending personnel into them reduces risk.

By displaying as-built heat maps in AR, you bring digital pass/fail evaluation into the real world and enable real-time construction management. The combination of heat maps and AR is not merely a record for inspection but a quality improvement tool that can be used immediately on site.

As AR heat map usage expands toward realizing smart construction, you may think, “Advanced 3D scanning and analysis seem difficult for our company…” If so, rest assured. Democratization of technology has advanced, and simple surveying systems that anyone can operate are now available. Even without specialized surveying skills, people can now easily perform point cloud measurement and heat map creation. The next section introduces simple surveying using LRTK as a representative example.

What is simple surveying with LRTK?

When you hear about advanced technology for as-built management, you may think, “Do I need expensive 3D scanners and specialized skills?” In reality, centimeter-class (half-inch accuracy) high-precision surveying is possible simply by combining a smartphone with a compact GNSS receiver. A representative example is the new surveying system “LRTK” provided by Reflexia Corporation.

LRTK consists of a small RTK-GNSS device that mounts to a smartphone, a dedicated app, and a cloud service. By scanning with the smartphone’s built-in LiDAR while applying RTK position corrections, anyone can obtain high-precision as-built point clouds with one touch. The acquired data is automatically recorded in alignment with known coordinates such as public coordinate systems, eliminating complicated post-processing. Uploading point cloud data to the LRTK cloud enables immediate browser-based measurements of distances and areas, calculation of volume differences, and heat map comparison analysis with design data. Without installing dedicated analysis software on a PC, you can review and share as-built data from the field using only a tablet. LRTK also includes a function to display acquired heat maps in AR on site, allowing you to give precise repair instructions on the spot.

By leveraging LRTK, 3D surveying and as-built inspection that once required specialized contractors and expensive equipment can be carried out surprisingly easily. Work time can be greatly reduced, and a dramatic improvement in productivity can be expected. LRTK also supports the Ministry of Land, Infrastructure, Transport and Tourism’s *i-Construction* initiatives, making it a powerful solution to promote site digitization. For more details, refer to LRTK’s official site and other resources. Why not adopt cutting-edge LRTK and evolve your site to the next stage?

FAQ

Q: What is an AR heat map? A: An AR heat map visualizes the difference between the actual shape after construction and the design shape by color. It compares as-built 3D measurement data such as point clouds with the design model, showing areas with small errors in green, areas that are significantly overfilled in red, and excavated areas in blue, allowing intuitive assessment of quality. It is a tool for immediate judgment of construction accuracy.

Q: What equipment and software are required to create a heat map? A: Basically, you need equipment for on-site 3D measurement and software (or a cloud service) for data processing. Acquire as-built point cloud data with a 3D laser scanner, drone, or LiDAR-equipped smartphone, then compare it with the design data using dedicated software on a PC or a cloud system to generate a heat map. Recently, platforms have emerged that automatically create heat maps with one click by matching uploaded point clouds and 3D design models on the cloud.

Q: Can I create an AR heat map with only a smartphone? A: Yes. By combining a modern smartphone (e.g., a high-end model equipped with a LiDAR sensor) with a compact RTK-GNSS receiver, you can use the smartphone as a high-precision 3D scanner. Some services allow you to scan point clouds with a dedicated app on the phone and upload them to the cloud to automatically generate heat maps. Using a smartphone surveying system like LRTK, even those without surveying expertise can complete high-precision point cloud acquisition and heat map creation with just a mobile device.

Q: What is needed to overlay a heat map on site with AR? A: AR display requires an AR-capable smartphone or tablet and a dedicated app (or a compatible cloud service) that can load heat map data. The device’s camera feed and sensors are used to overlay the virtual model on real space, but accurate overlay requires precise knowledge of the device’s position and orientation. For higher accuracy, use RTK-GNSS to correct device position or place markers (targets) on site for reference alignment. With compatible systems, centimeter-class (half-inch accuracy) alignment can be achieved without relying on the phone’s standard GPS, so heat maps remain stable and properly aligned on site.

Q: Are AR heat maps accepted as official as-built management documents? A: In recent years, 3D as-built management using heat maps has been increasingly recognized as an official method. The Ministry of Land, Infrastructure, Transport and Tourism’s guidelines include surface-based as-built management using 3D measurement technologies, and heat map evaluation is being trialed and adopted. In some earthwork projects, comprehensive as-built measurement and heat map evaluation are becoming mandatory. Therefore, submitting 3D as-built data including heat maps as inspection documents is possible and is actively used in advanced ICT construction sites. However, follow the instructions of the contracting authority and submit printed heat map charts or electronic data as required.

Q: In what types of sites is heat map–based visualization effective? A: Heat map visualization is widely effective where shape and dimensional quality control are important: earthwork managing cut/fill volumes, slope finishing checks in erosion control and road works, verifying pavement flatness and pavement thickness in paving works, and shape checks for structures such as tunnels and dams. Heat maps can be used for progress management during construction, final as-built inspections, and long-term displacement monitoring. Applications in maintenance, such as detecting bridge deflection over time or deformation of concrete structures, are also increasing.

Q: Aren’t large point cloud datasets difficult to handle? A: It’s true that 3D point clouds can reach millions to tens of millions of points, making file sizes very large. However, modern software and cloud services are designed to handle large datasets efficiently. Functions exist to thin out unnecessary regions or focus display on areas of interest, so performance concerns on a PC can be mitigated. Cloud-based rendering and browser display services allow site tablets to view 3D data without heavy load. With the right tools, the size of point cloud data does not pose an insurmountable obstacle.

Q: Is there a cost-benefit to adopting new 3D surveying technologies? A: Purchasing a dedicated 3D laser scanner can require an investment on the order of millions of yen, but methods using a smartphone and compact GNSS are relatively low-cost. By using AR heat maps to catch defects early, reduce rework, and lower labor through fewer personnel, the expected benefits can outweigh the investment. In short, the latest point cloud measurement and heat map technologies can deliver productivity gains and quality assurance that justify the initial cost.