Streamline As‑Built Management for Pavement Work! Instantly Check Thickness with AR Heat Maps

Table of Contents

• What is an as-built heat map?

• Benefits of using AR heat maps

• Procedure to check pavement thickness with an AR heat map

• How to use AR heat maps on site

• Recommendation: Simple surveying with LRTK

• FAQ

In construction sites, especially in road paving works, as‑built management to verify that thickness and elevation match the design is indispensable. If pavement thickness is insufficient, durability decreases and early damage may occur; conversely, excessive thickness leads to material waste and higher costs. Ensuring the design thickness and minimizing variability are important for both quality assurance and economy. Traditionally, thickness checks have been done by spot inspections (core sampling for thickness measurement) or cross‑section elevation surveys, but these methods can only measure limited locations and are time‑consuming. In recent years, a new as‑built management method called a heat map has emerged, and when combined with AR (augmented reality) technology, it has become possible to intuitively check pavement thickness on site. This article explains what an as‑built heat map is, its benefits, and how to create one. It also introduces how to use AR heat maps to immediately check thickness on site and explores points that help streamline quality control in paving works.

What is an as-built heat map?

An as‑built heat map is 3D data that visualizes, with color coding, the differences between measured data of the completed pavement or terrain and the design data. For example, areas paved thicker than designed and therefore raised are shown in warm red tones, while areas that are low due to insufficient thickness are shown in cool blue tones. Areas that fall within the design tolerance appear green, allowing an intuitive grasp at a glance of where the pavement is thicker or thinner than the specification and whether the finish is acceptable.

An as‑built heat map can be called a visualization tool for as‑built management. Subtle thickness variations or trends that are hard to notice from flat drawings or lists of numbers can be easily discovered with colored 3D visuals. Traditionally, thickness or elevation at key points was measured by sampling and the errors from design values were confirmed numerically. However, using a heat map allows a comprehensive, area‑based overview of the entire site, making differences of a few centimeters (a few inches) less likely to be missed. Recently, the Ministry of Land, Infrastructure, Transport and Tourism has been promoting area‑based as‑built management using 3D measurement through initiatives like i‑Construction, and heat‑map evaluation is beginning to be included in guidelines. In the paving field as well, quality control using heat maps is becoming a new standard.

Benefits of using AR heat maps

When as‑built heat maps are used on site, many benefits that could not be obtained with conventional methods arise. The main advantages are summarized below.

• Intuitive quality assessment: Because the magnitude of errors is shown by color, anyone from on‑site workers to the client can understand construction accuracy at a glance. It is easier to understand than reports with only numbers or text, and makes it easier for the whole team to share points that need correction. Visual explanations also facilitate consensus building with stakeholders who have limited technical knowledge.

• Prevention of missed inspections: Because the entire pavement can be evaluated with high‑density 3D measurement data like point clouds, locally thin areas that spot checks may miss can be detected. Heat maps that cover wide areas can exhaustively uncover quality variability. This reduces missed inspections due to measurement omissions and leads to reliable quality confirmation.

• Rapid feedback: If you scan and generate a heat map during construction or immediately after finishing, you can check the as‑built status on the spot. Early discovery and rework of problem areas reduces the need for major repairs later, shortening schedules and ensuring quality. Because acquired data can be shared instantly via the cloud, reporting to clients and internal stakeholders can be done quickly. In fact, there are reported cases where as‑built inspections that used to take two days were completed in half a day after introducing point cloud scanning and heat maps.

• Efficiency and labor savings in inspection work: Heat map analysis, which can measure wide areas at once, greatly reduces the manpower and time required for measurement work. Automatic processing of measurement results smooths the creation of reporting drawings and forms. High or hazardous areas can be measured remotely and safely, contributing to reduced worker burden and improved safety.

• Digital records and traceability: As‑built data such as heat maps and point clouds can be stored in the cloud, preserving detailed construction histories that paper drawings cannot. These data can be useful for future maintenance by enabling cause analysis through comparison with past data, and can be integrated into models like BIM/CIM. Some systems can automatically output as‑built management tables with heat maps, significantly streamlining the creation of inspection documents. The accumulated data remain valuable after completion and contribute to long‑term quality control and maintenance.

• Simplified acceptance inspections: If you display the heat map in AR, you can verify construction results on the spot during client acceptance inspections. This reduces the need to remeasure while checking paper drawings or numbers, and facilitates smooth pointing out of nonconforming areas and agreement on corrective actions. Because the heat map is based on point cloud data with assured accuracy, there is no need to remeasure all locations as before (the conventional workflow of locating corresponding points on site with a total station or GNSS while looking at forms can be reduced), and the inspection proceeds faster.

As shown, using AR heat maps greatly contributes to improved construction accuracy, faster inspections, reduced effort in acceptance inspections, and overall work efficiency.

Procedure to check pavement thickness with an AR heat map

So, what steps should you take to actually check pavement thickness with an AR heat map? The basic workflow is explained step by step below.

• Prepare design data: First prepare the 3D design data to serve as the reference (the finished design model or surface elevation information). For road pavement, prepare the reference elevations and a 3D model of the finished surface from the design drawings. If you have pre‑paving subgrade data (pre‑construction ground elevation), you can directly calculate the actual pavement thickness by taking the difference between that and the post‑construction data. In any case, ensure that the reference data used for comparison are organized in a unified coordinate system.

• 3D measurement of the pavement surface: Next, 3D‑scan the completed pavement surface to acquire as‑built data (point cloud). Terrestrial 3D laser scanners or drone photogrammetry can measure wide areas in a short time. Recently, LiDAR‑equipped smartphones also allow easy pavement scanning. For example, by using an RTK‑capable smartphone combined with a high‑precision GNSS unit, you can acquire as‑built point clouds with centimeter‑level accuracy (half‑inch accuracy). Even if the smartphone lacks LiDAR, you can use photogrammetry apps that process multiple photos in the cloud to create 3D point clouds. The key point is to measure the entire pavement without gaps and to record data with high positioning accuracy.

• Difference processing and heat map generation: Compare the measured point cloud with the design data, calculate the elevation (thickness) differences, and create a heat map. Using dedicated software or comparison functions in cloud services, you can overlay the uploaded design model and point cloud and automatically compute differences. If the measurement data include survey coordinates (such as the World Geodetic System), there is little effort required for alignment. With a few clicks, a heat map is generated showing in color how many centimeters each point is higher or lower than the design. Adjust the grid size of the heat map and the color thresholds (tolerance ranges) as needed, and configure the display so that pass/fail is easy to determine according to site standards.

• On‑site confirmation with AR display: Load the completed heat map data onto a tablet or smartphone and overlay it onto the camera view for AR display. Through the device screen, the color distribution of the heat map is projected onto the actual pavement surface. To overlay accurately, the device’s position and orientation must be identified precisely; using an RTK‑GNSS‑compatible system makes it possible to align virtual and real worlds with centimeter‑level accuracy (half‑inch accuracy). This allows you to bring the office‑created heat map to the site and confirm thickness excesses or shortages on the spot.

How to use AR heat maps on site

AR heat map verification transforms the on‑site quality confirmation process. By projecting a heat map on site, you can verify the finish immediately after paving and start any necessary corrective work right away.

For example, in paving works you can measure immediately after finishing, create a heat map on site, and check for any thin areas. If the heat map reveals areas thinner than the tolerance, you can instantly locate them and perform additional paving or surface correction. There are reports that AR display of heat maps on tablets allowed machine operators, who had difficulty interpreting paper drawings, to intuitively understand problem locations. Moreover, if no nonconforming areas are found on the heat map, you can approve the inspection on the spot and proceed to the next process without interruption. Traditionally, one would take data back to the office, identify defective areas on drawings, return to site to mark them, and then repair later, causing time lag. With AR heat maps, the cycle of “measure → compare → fix” can be completed on the same day. Being able to correct thickness variability the same day prevents variations in construction accuracy from affecting subsequent processes and minimizes schedule loss.

During client acceptance inspections, sharing a tablet screen with an AR heat map enables smooth pass/fail judgments and corrective instructions. Because the colored data displayed on the heat map are tied to actual site locations, you can point out “which point is short of the standard by how many cm (in)” on the spot. Visual data are easier for clients to understand than mere numerical reports and enable more convincing explanations. Since the verification is based on highly accurate point cloud data, there is no need to remeasure in detail with conventional instruments during the inspection. This shortens the time required for acceptance inspections and reduces the burden on both site and inspectors.

Recommendation: Simple surveying with LRTK

As described so far, AR heat maps are highly effective for as‑built management in paving works. Intuitive, data‑driven thickness checks enable improved construction accuracy, faster inspections, simplified acceptance procedures, and overall efficiency improvements. Introducing these digital technologies to the site can be expected to raise quality control levels and productivity.

That said, some may feel that “3D measurement and AR sound difficult.” However, solutions are now available that allow easy, high‑accuracy as‑built measurement using smartphones. For example, by using LRTK (a system that turns a smartphone into a high‑precision surveying instrument), you can attach an RTK‑GNSS receiver to an iPhone or other smartphone to transform it into an all‑purpose surveying device. This lets you scan pavement surfaces, automatically generate heat maps in the cloud, and display them in AR on the smartphone in a one‑stop workflow. As an all‑in‑one system, the introduction cost is far lower than conventional expensive surveying equipment, making it easy for small‑ to medium‑scale sites to adopt. In addition, after a short training period, even those without surveying expertise can start using it, enabling site staff to readily practice modern as‑built management. Allowing site staff to perform measurement and inspection without relying on veteran surveyors helps alleviate labor shortages and reduce dependency on specific individuals. Utilize simple surveying with LRTK and consider introducing AR heat map–based efficient thickness management to your paving sites.

FAQ

Q: What is an as‑built heat map? A: It visualizes, with color coding, the difference between the actual post‑construction shape data and the design shape. By comparing acquired point cloud data with the design model, areas with small errors appear green, areas raised due to excess thickness appear red, and areas low due to insufficient thickness appear blue. It is an as‑built management tool that lets you judge pavement thickness excesses or shortages at a glance.

Q: What types of works can AR heat maps be used for? A: In addition to paving, they can be used for earthworks such as embankments and cuts, as‑built inspection of concrete structures, and terrain management for rivers or land development—basically any situation where shape is measured and quality is checked. Where work types have specifications for elevation or thickness, as‑built evaluation with a heat map is generally applicable. For example, road improvement works can check subgrade and pavement flatness, slope works can check gradient as‑built, and concrete placement works can verify thickness filling—applications are numerous. Because the method visualizes discrepancies between design and measured data with color, the applicable range is very wide.

Q: What equipment and software are needed to create a heat map? A: Essentially, you need equipment for on‑site 3D measurement and software (or a cloud service) to process the acquired data into a heat map. For example, acquire point cloud data of the pavement surface using terrestrial laser scanners, drones, or LiDAR‑equipped smartphones, then upload that data to dedicated desktop software or a cloud system to compare with design data and generate a heat map. Recently, services have appeared that automatically create heat maps simply by uploading point clouds and design models to the cloud.

Q: Can I create an as‑built heat map with a smartphone? A: Yes. With modern smartphones (e.g., LiDAR‑equipped iPhones) and dedicated surveying apps, you can scan surrounding structures or terrain to obtain point clouds. By combining an RTK‑GNSS receiver to improve positioning accuracy, you can use a smartphone as a high‑precision 3D scanner. Systems like LRTK enable end‑to‑end workflows from measurement to heat map creation on a smartphone without surveying expertise. Field adoption of smartphone + receiver as‑built measurement has already begun.

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 can load heat map data. The device uses its camera and sensors to overlay the virtual heat map onto the real world, but accurate alignment requires precise knowledge of the device’s position and orientation. For high accuracy, device positioning can be corrected with RTK‑GNSS or site markers can be used for alignment. Using compatible systems allows centimeter‑level alignment (half‑inch accuracy) rather than relying solely on the device’s built‑in GPS, so the heat map stays correctly placed on site.

Q: Can AR heat maps be used for small‑scale projects? A: Yes, absolutely. 3D as‑built management was once limited to large projects with dedicated survey teams, but smartphone‑based measurement methods now make it easy to perform thickness checks for everyday small repairs or partial works. They meet needs like “measure quickly and check immediately,” directly improving on‑site efficiency. Even for small projects, the ability to detect and address problems early provides significant value regardless of scale. Also, smartphone measurement requires a small initial investment, making adoption feasible even for small jobs.

Q: Are as‑built heat maps recognized as official as‑built management documents? A: In recent years, as‑built heat maps have been increasingly recognized as one as‑built management method. The ministry’s draft guidelines include area‑based as‑built management using 3D measurement, and examples of heat‑map evaluation moving from trials to full adoption are increasing. In some earthworks projects, comprehensive as‑built measurement and heat‑map evaluation are now required. Therefore, submitting 3D as‑built data including heat maps as inspection documents is possible, and they are actively used in advanced ICT construction sites. However, follow the client’s instructions and submit heat map images or electronic data in the required formats as needed. Heat map figures and 3D as‑built data can often be exported in electronic delivery standard formats (for example LandXML or PDF drawings), making digital deliverables easier to prepare.