No specialized equipment needed! Easy as-built management with LRTK + AR heat maps

Table of contents

• What is an as-built heat map?

• Benefits of as-built heat maps

• How to create an as-built heat map

• Real-time construction checks with AR heat maps

• Summary

• FAQ

On construction sites, “as-built management”—measuring and recording whether the work matches the design after construction—is indispensable. Recently, a new method called the as-built heat map has emerged for this management, and by combining it with AR (augmented reality) technology, it has become possible to intuitively check the construction status on site. This article explains what an as-built heat map is, its benefits, and concrete steps for creating one. It also introduces how to project the created heat map into the real world using AR to check construction accuracy in real time. Learn this modern as-built management method using digital technology to improve quality control efficiency.

What is an as-built heat map?

An as-built heat map is a 3D visualization that compares the completed structure or terrain (the as-built condition) with the design data and color-codes the differences. Point cloud data or 3D survey data acquired after construction are overlaid with the 3D model from the design stage (design surface), and the error at each location is shown with colors. For example, areas that are higher than the design are shown in red or warm colors, areas that were not excavated enough and are lower are shown in blue tones, and areas that match the design are shown in green. The feature is that you can instantly and intuitively see which locations are higher or lower than the standard and whether they pass or fail.

An as-built heat map can be seen as a visualization tool for as-built management. Subtle undulations or trends that are hard to notice in flat drawings or lists of numbers can be easily found with colorized 3D visuals. In recent years, the Ministry of Land, Infrastructure, Transport and Tourism has been promoting 3D measurement and surface-based as-built evaluation through initiatives like i-Construction, and heat-map-based as-built management has begun to be incorporated into official guidelines. In other words, as-built heat maps are becoming a new standard in the era of on-site DX.

Benefits of as-built heat maps

Using as-built heat maps yields many benefits that were hard to obtain with conventional methods. Here are the main advantages.

• Intuitive quality assessment: Because the magnitude of errors is shown in color, anyone from on-site workers to clients can understand construction accuracy at a glance. It is far easier to understand than reports consisting only of numbers or text, and it becomes easier for the whole team to share the points that need correction.

• Prevention of measurement omissions: Because the entire surface can be evaluated using high-density data such as point clouds, local irregularities or defects that sampling measurements might miss can be detected. A heat map that covers a wide area can comprehensively reveal quality variations.

• Rapid feedback: If you scan and generate heat maps during construction, you can check as-built conditions immediately. Finding and reworking problem areas early minimizes rework, shortens schedules, and helps ensure quality.

• Record keeping and traceability: Heat maps and point cloud data can be stored as digital records in the cloud. You can save a detailed “history of construction” that could not be recorded on paper drawings, making it easy to compare past data during future maintenance for root-cause analysis. Also, integrating as-built data into BIM/CIM models for asset management makes the data valuable even after completion.

• Labor savings and improved safety: Point-cloud measurement that covers large areas at once and automated analysis can greatly reduce the manpower and time for measurement tasks. High or dangerous locations can be scanned remotely, contributing to worker safety. As-built confirmation of places that were previously difficult becomes easy with heat maps, reducing human error.

As described, as-built heat maps greatly contribute to improving the accuracy and efficiency of quality control. So how exactly do you create such a heat map? The next section walks through the concrete steps.

How to create an as-built heat map

Below is a step-by-step explanation of the typical flow for creating an as-built heat map. Proceed from preparing the necessary data to generating the heat map as follows.

• Preparation of design data: First, prepare 3D design data to serve as the comparison standard. For earthworks, this would be the design ground model (TIN data or design surface); for structures, the BIM/CIM 3D design model, etc. The point is to clearly define in data which shape is considered the ideal (target). In as-built management, this design model becomes the basis for pass/fail judgment.

• 3D measurement of the actual condition: Next, measure the actual shape after construction in 3D. Point-cloud measurement is the mainstream method these days; terrestrial 3D laser scanners or drone photogrammetry are commonly used to scan the entire site. Lately, cases of easily acquiring point clouds with LiDAR-equipped smartphones have also increased. For example, combining an iPhone Pro model’s built-in LiDAR sensor with an RTK-GNSS receiver makes it possible to perform point-cloud surveying with centimeter-level accuracy (half-inch accuracy) even using a smartphone. Whatever method you use, the important thing is to measure the site comprehensively and acquire data with as high positioning accuracy as possible. Point-cloud scans that can cover wide areas quickly allow you to obtain a digital as-built model that includes fine details of terrain and structures.

• Georeferencing the data: Align the design data and the acquired as-built data on the same coordinate system. If you measured in a survey coordinate system from the start (such as a global geodetic coordinate system), the two will be consistent automatically, so little effort is required for alignment. For example, when point clouds are obtained with RTK-capable equipment, the acquired data already has high-accuracy coordinates, so you can overlay the design model directly. If measurements were made in a local coordinate system or there is some offset, perform a fitting adjustment using known control points to align the datasets. If the positions are not correctly aligned here, subsequent heat maps cannot be trusted, so verify carefully.

• Generating the heat map: Compare the prepared design data with the as-built point cloud data to create the 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. In typical color schemes, areas with small errors are green; regions that are higher than the design are warm colors (yellow to red); areas lower than the design are cool colors (blue to purple). If you set tolerance thresholds in advance, values within tolerance appear green while exceeding areas are emphasized in red or blue, making it easy to identify nonconforming spots at a glance. Some tools let you adjust the heat map mesh (grid) size and color range arbitrarily. Comparison processing is done quickly by computers, so even hundreds of thousands of points can be processed in a short time.

• Reviewing and analyzing results: Check the generated heat map on screen and analyze the construction quality. By observing color distribution, you can intuitively read “which locations are how much higher or lower.” For example, you might identify “the center of area ◯◯ is overfilled by design +5 cm (2.0 in)” or “part △△ has a -3 cm (-1.2 in) leftover excavation.” You can also inspect numerical errors at individual points on the heat map as needed and analyze overall trends (whether the whole surface is slightly high or only specific spots are low). Because heat maps are visual, they are easy for on-site workers and heavy equipment operators to understand, making them an effective communication tool for sharing correction points. Additionally, uploading data to the cloud enables remote stakeholders in an office to view the same 3D heat map in a web browser. You can share information in real time with distant supervisors or clients and solicit accurate instructions or approvals.

• Correction work and documentation: If defective areas identified by the heat map exist, perform the necessary corrective work on site (such as regrading or additional fill). After correction, re-measure in 3D and similarly verify the finish with a heat map. Once you confirm the issue is resolved, output the final as-built heat map and survey results as as-built management charts (forms). Modern systems can automatically generate reports with heat maps and may create submission-ready materials with photos and drawings in one click. Because the workflow can be completed with digital data, the time required to prepare reports is greatly reduced. Store the acquired heat maps and point cloud data internally to serve as references for future projects and for sharing technical knowledge among engineers.

That covers the basic workflow for creating as-built heat maps. The key points are to acquire high-accuracy as-built data, perform proper alignment, and leverage automation tools. Next, we explain how to use AR displays to check construction status in real time using these heat maps.

Real-time construction checks with AR heat maps

Once you have created an as-built heat map, displaying it on site with AR (augmented reality) allows you to overlay the real object with digital information to check construction status. The heat map data is loaded onto a mobile device through a dedicated AR-enabled app or system, and a virtual heat map is overlaid on the camera view. This lets you view color-coded pass/fail information composited with the real scene, enabling you to intuitively grasp “which locations and by how much they need to be corrected” on the spot.

The procedure for AR display starts by transferring the heat map data (colorized 3D model or point cloud) to a mobile device. On site, point the smartphone or tablet camera at the actual structure or terrain shown on the screen and overlay the heat map on it. For accurate alignment, in addition to the device’s GPS and gyro sensors, using high-precision positioning or reference markers is effective. For example, you can correct the device position to centimeter level (half-inch accuracy) with RTK-GNSS or fix a virtual object to a known on-site control point to minimize mismatch between the heat map and the site. Supporting systems implement such corrections to realize high-precision AR, so the virtual heat map stays correctly positioned even while walking around with the device.

AR-based site checks provide many advantages. First, identifying problem areas becomes rapid. Since red or blue spots on the screen clearly indicate the corresponding real locations, you can mark the ground there or directly instruct an equipment operator, “Cut this by ◯◯ cm.” Previously, one had to use a surveying instrument with heat map reports to find the corresponding on-site positions, but that effort becomes unnecessary. Second, it improves the efficiency of joint inspections. During on-site inspections with clients or inspectors, showing the AR heat map on a tablet allows immediate sharing of pass/fail conditions. Because you can visualize “how much of what area has been corrected,” explanations and consensus-building become smoother. There is also a reduction in remeasurement effort: if high-accuracy point-cloud measurements were completed when creating the heat map, AR can identify positions without the need to remeasure numerous points for inspection. From a safety perspective, checking remotely with AR without entering hazardous areas lowers risk.

Thus, displaying as-built heat maps with AR brings digital pass/fail judgments into the real world and enables real-time construction management. The combination of heat maps and AR is not merely an inspection record but a practical tool for on-site quality improvement.

Summary

This article introduced how to create as-built heat maps and how to utilize them with AR. Compared to traditional survey-centered as-built management, the heat map + AR method allows rapid, high-accuracy checks over wide areas and provides visually clear results, dramatically improving construction management efficiency and quality. The adoption of digital technology enables thorough inspection with small teams and smoother information sharing between site and office. As part of on-site DX (digital transformation), this approach will likely become increasingly widespread.

That said, some may feel that advanced 3D scanning and analysis are difficult to implement in-house. However, simple surveying systems that anyone can use have recently appeared, enabling easy point-cloud measurement and heat map creation without specialized surveying skills. For example, LRTK, a compact RTK-GNSS receiver you attach to a smartphone, transforms a phone into a centimeter-level accuracy (half-inch accuracy) 3D scanner and automatically generates as-built heat maps in the cloud from scanned data. Furthermore, those heat maps can be displayed in AR on the smartphone, enabling one-stop on-site verification. By using an all-in-one solution that minimizes dedicated equipment and complex manual work, even beginners can easily implement modern as-built management. Take this opportunity to introduce digital technology on site to raise quality control levels and improve operational efficiency.

FAQ

Q: What is an as-built heat map? A: It is a visualization that color-codes the differences between the actual shape after construction and the design shape. Acquired point cloud data are compared with the design model; areas with small errors are green, significantly overfilled areas are red, and excavated areas are blue, etc., so quality is indicated intuitively by color. It is an as-built management tool that allows quick judgment of construction accuracy.

Q: What equipment and software are needed to create heat maps? A: Basically, you need equipment to perform 3D on-site measurement and software (or a cloud service) to process the data. Obtain point cloud data with 3D laser scanners, drones, or LiDAR-equipped smartphones, and use dedicated software or cloud systems to compare them with the design data to generate heat maps. Recently, platforms that automatically create heat maps by matching point clouds and design models in the cloud have appeared.

Q: Can you create as-built heat maps with a smartphone? A: Yes. Modern smartphones (e.g., iPhone Pro series) have built-in LiDAR sensors, and by combining them with a dedicated RTK-GNSS receiver, you can use the phone as a high-precision 3D scanner. With a dedicated app to acquire point clouds and upload them to the cloud, services that automatically generate heat maps are available. Using a smartphone surveying system like LRTK, even those without surveying expertise can complete the process on a smartphone.

Q: What is required to overlay a heat map on the site with AR? A: AR display requires an AR-capable smartphone or tablet and a dedicated app that loads the heat map data. The device’s camera and sensors are used to overlay the virtual model on the real space, but to align it accurately you must know the device’s position and orientation precisely. For higher accuracy, correct the device position with RTK-GNSS or place on-site markers (targets) for alignment. With the right system, you can achieve centimeter-level alignment without relying solely on smartphone GPS, allowing on-site heat maps to be displayed without shifting.

Q: Are as-built heat maps accepted as official as-built management documentation? A: In recent years, as-built heat maps have been increasingly recognized as an official as-built management method. The Ministry of Land, Infrastructure, Transport and Tourism’s guidelines include surface-based as-built management using 3D measurement technology, and heat-map-based evaluation is being trialed and adopted. In some earthwork cases, comprehensive as-built measurement and heat-map evaluation have become 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-driven construction sites. However, follow the client agency’s guidelines and submit printed heat-map charts or electronic data as required.