New Essential Tool for ICT Construction: The Cutting Edge of AR Heat Map Utilization

Table of Contents

• Challenges of traditional as-built control

• What is an AR heat map?

• Benefits of AR heat maps

• Use cases for AR heat maps

• Steps to introduce AR heat maps

• Conclusion

• FAQ

On construction sites, as-built control—confirming and documenting that the finished work matches the design—is indispensable. However, with traditional methods it is not easy to grasp accuracy on site or to intuitively share as-built status with all stakeholders. Recently, a new approach using heat maps for as-built control has emerged to address these issues, and by combining it with AR (augmented reality) technology it has become possible to visualize construction accuracy on the spot. This article explains what an AR heat map is, its background and benefits, and concrete ways to use it. Learn how to apply the latest AR techniques in ICT construction to improve on-site quality control and efficiency.

Challenges of traditional as-built control

On civil engineering sites, as-built measurement is often conducted to confirm whether the completed terrain or structures fall within design specifications. Traditionally, survey staff measured depths and heights at regular intervals and checked deviations from the design using drawings and numerical data. However, this approach has several challenges.

First, point-by-point measurements cannot cover the whole area, so subtle undulations or localized defects may be missed. Spot checks cannot fully capture variability across large surfaces, and it has sometimes turned out later that only some areas were out of tolerance. Also, the results are not intuitively easy to understand. Measurement results are summarized as numbers on drawings or in tables, which are hard for site workers and clients to interpret, causing delays in sharing problem areas. For example, explaining on paper “which area needs to be cut by how much” does not make it easy to indicate the exact location on site. As a result, corrective work can be delayed and consensus building can take time.

Furthermore, the measurement and verification process itself requires significant effort and time. Grasping as-built conditions over a wide area requires measuring many points, taking manpower and days. Measurements at heights or on steep slopes require special attention to safety. In short, traditional as-built control has issues in coverage, visibility, and efficiency, and better methods have been sought.

What is an AR heat map?

A promising digital technique to solve these problems is the as-built heat map. An as-built heat map is a 3D dataset that visualizes the magnitude of deviations by color after comparing post-construction measured data with design data. Specifically, point clouds or 3D models (as-built) obtained by scanning the site are overlaid with the 3D design model (design surface), and vertical differences and offsets at each location are represented by color. For example, areas that are higher than the design (overbuilt) are shown in red or warm colors, areas that are lower due to insufficient cutting are shown in blue tones, and areas nearly matching the design with negligible error are shown in green—allowing instant recognition. The color gradient intuitively shows which locations are higher or lower than the standard and whether they are acceptable or not.

This as-built heat map is truly a “visualization” tool for as-built control. Tiny bumps hard to notice on flat drawings or numeric lists and overall trends are easy to detect on a color-mapped 3D visualization. The Ministry of Land, Infrastructure, Transport and Tourism is promoting the use of 3D measurement and surface as-built evaluation (heat maps) through initiatives like *i-Construction*, and heat-map-based evaluation methods are being incorporated into recent as-built control guidelines. In other words, heat maps are beginning to become a new standard in the DX era for construction sites.

An AR heat map is the display of this heat-map data overlaid onto real space using AR technology. By overlaying the colored 3D data onto live images of the actual site seen through the camera of a tablet or smartphone, you can visualize the digital heat map as if it were pasted onto the real site. With an AR-capable mobile device, you can display the as-built heat map over the completed structure or terrain and check it against the actual object.

To accurately align an AR heat map on site, the device’s current position and orientation must be known with high accuracy. Standard smartphone GPS has errors of several meters (several ft), so the heat map display would be misaligned if used as-is. RTK-GNSS (real-time kinematic positioning) is effective here. By combining an RTK-capable GNSS receiver with a smartphone, position information can be corrected to centimeter-level (half-inch accuracy), minimizing the gap between virtual data and real space. If there are known control points on site, you can calibrate by fixing the virtual model to those points, or place fiducial markers for alignment—various techniques improve overlay accuracy. Recently, smartphones come standard with advanced AR capabilities (ARKit, ARCore, etc.), and anyone can easily experience AR display with a compatible app. Thanks to these technological foundations, AR heat maps for on-site overlay and verification have reached practical maturity.

Benefits of AR heat maps

Introducing AR heat maps brings many benefits to sites that traditional as-built control could not provide. Key advantages include:

• Intuitive quality assessment: Since error magnitudes are shown by color, anyone from site workers to clients can instantly understand construction accuracy. Visual information is easier to grasp than reports of numbers or text, making it simpler for the team to share points that need correction.

• Prevention of missed measurements: High-density point cloud data from drones or laser scanners allows evaluation of entire surfaces, so irregularities or localized defects that spot checks might miss can be detected. Heat maps covering wide areas expose quality variability without omission.

• Rapid feedback: If you scan and generate heat maps during construction, you can immediately check as-built status. Early detection and rework of problem areas minimize rework and contribute to shorter schedules and ensured quality.

• Records and traceability: Heat maps and point cloud data can be stored digitally in the cloud. You can preserve detailed construction histories that paper drawings could not capture, making future maintenance comparisons and root-cause analysis easier. Integrating as-built data into BIM/CIM models for asset management turns these records into valuable post-completion resources.

• Labor savings and improved safety: Point cloud measurement and automated analysis drastically reduce manpower and time for measurements. High or hazardous areas can be scanned remotely, enhancing worker safety. As-built checks in previously difficult locations become easy with heat maps, reducing human error.

Thus, AR heat maps are an innovative tool that significantly contribute to improved quality control and operational efficiency. They have the potential to change on-site “business as usual,” and their use is expected to expand.

Use cases for AR heat maps

How do AR heat maps perform on actual sites? A typical use case is as-built verification for earthworks. For example, in roadworks or embankment projects, the finished surface is measured with a 3D scanner or drone to create a heat map. Displaying that on a tablet in AR makes areas that are overfilled (too high) or undercut (too low) appear color-coded on the ground. Workers and site supervisors can precisely identify problem areas on the spot and give concrete instructions to machine operators, such as “lower this area by ○ cm.” Viewing red areas on the heat map while performing corrections reduces missed rework and miscommunication, allowing corrective operations to proceed smoothly.

AR heat maps also shine in acceptance inspections with clients (inspectors). Previously, explanations at the site involved carrying as-built reports and drawings and, if necessary, re-measuring with total stations—time-consuming work. If the heat map is projected on site via AR, all parties share the same visual information, preventing misunderstandings and enabling swift inspection. If the point cloud data used for scanning was properly accuracy-controlled with survey instruments, simply confirming the colored AR model provides sufficient evidence and reduces the need to remeasure many points. Field trials of AR heat maps report positive feedback such as “we no longer get confused about which point is being referenced on site” and “we can accurately point out out-of-spec areas and easily issue corrective instructions.” Because AR greatly simplifies location identification, consensus building among stakeholders can be completed more quickly.

AR heat maps can be applied to many other as-built control scenarios, from concrete structure checks to tunnel lining shape verification. For example, in tunnel projects, measuring the internal cross-section by point cloud and generating a heat map of deviations from the design, then projecting it onto the tunnel wall in AR, allows efficient detection of overbuilds or shortages in the placed concrete. Three-dimensional deviations that are hard to understand from plan views or numbers can be visually confirmed on site, ensuring effective correction. In this way AR heat maps are applicable from ground to structures and contribute to on-site productivity improvements.

Steps to introduce AR heat maps

To use AR heat maps on site, data measurement and preparation are required in advance. The general introduction steps are summarized below.

• Preparation of design data: First prepare a reference 3D design model. For earthworks this might be the design ground surface data or the target TIN model; for structures it might be a BIM/CIM 3D model. In short, define the “target as-built shape” clearly in data form. This design model serves as the quality assessment standard for as-built control.

• 3D measurement of the current condition: Next, 3D-scan the actual post-construction shape. Laser scanners for point cloud measurement and drone photogrammetry (SfM) are commonly used today to obtain detailed terrain data for the whole site. For small sites, smartphone-integrated LiDAR scanners can also be utilized. These methods measure wide areas quickly and capture the current condition with a large number of points and high accuracy.

• Heat map generation: Compare the design data with the acquired as-built data to generate a heat map. Import the point cloud data into dedicated software or cloud services, which automatically calculate height differences at each point and create colorized 3D meshes or colored point clouds. In some cases, volume differences for fills and excavations are calculated simultaneously. Generated heat map data can be rotated and zoomed on a PC and exported as images for reporting and sharing.

• Prepare for AR display: Then prepare to display the heat map data on a mobile device. Install an AR-capable surveying app on a tablet or smartphone and transfer/load the generated 3D heat map data to the device. Supported data formats vary by app, but typically colorized 3D meshes, point clouds, or proprietary formats containing as-built evaluation results are imported.

• On-site alignment: Take the device to the site and overlay the heat map on the camera image. To align accurately, in addition to the device’s built-in GPS and gyroscopes, perform high-precision reference alignment. Using an RTK-GNSS receiver (for example, a smartphone-mountable LRTK device) to correct the device’s coordinates can align the virtual model and the real object to centimeter-level (half-inch accuracy). If necessary, fix AR objects to known control points or place markers to improve alignment precision.

• On-site verification and recording: Once the heat map is perfectly overlaid on the site, you can check as-built conditions. While viewing the color distribution, mark out-of-spec areas and determine where repairs are needed. When corrective measures are clear, immediately provide feedback to the construction team. Recording AR-displayed screens as photos or videos creates materials for stakeholder explanation and meeting records.

These are the basic steps. Although the workflow may seem long at first glance, recent solutions provide one-stop workflows from measurement to AR display. Systems that seamlessly connect point cloud measurement, heat map generation, and AR viewers enable even first-time users to implement modern as-built control without difficult operations. Even without specialized knowledge in data creation, simple apps can guide you to hold up a phone and automatically colorize height differences. Actively adopting digital technologies on site will raise your quality control level and improve operational efficiency.

Conclusion

In the era of ICT construction, AR heat maps are now an indispensable new tool. Site verifications that once relied on experience and intuition are shifting to objective, data-driven visual checks. Surface-based as-built evaluation using heat maps is becoming part of ministry guidelines and an industry standard, and combining it with intuitive on-site AR usage greatly advances construction management.

With fewer experienced workers and workstyle reforms progressing, mastering DX tools like AR heat maps directly links to both productivity gains and quality assurance. If everyone can “see” and judge data on site, communication losses decrease and rework is avoided. Accumulating digital records also creates valuable assets for future maintenance. This is truly a shift from “measure and finish” to “measure and utilize.”

Introducing AR heat maps may seem daunting at first, but nowadays a smartphone combined with a compact GNSS device enables easy, high-precision simple surveying. Necessary equipment and software are compact, making AR heat maps a realistic option even for small- to mid-sized sites. The important thing is to try it once on site. You will likely find it hard to go back to the old ways. With AR heat maps on your side, why not take your site to the next stage?

FAQ

Q: What is required to use AR heat maps on site? A: AR display requires an AR-capable smartphone or tablet and a dedicated app that can load heat map data. The device’s camera and sensors overlay the virtual model, but for high-precision display it is desirable to correct device positioning using RTK-GNSS. Specifically, a smartphone-mountable RTK-capable GNSS receiver (e.g., an LRTK device) and internet connectivity (or an environment to receive the Quasi-Zenith Satellite System’s CLAS corrections) are ideal. Also prepare the design data and the measured point cloud data to be converted into a heat map and loaded into the app in advance.

Q: How accurate is the displayed position? Is it comparable to traditional surveying instruments? A: Using RTK-GNSS can achieve an accuracy on the order of a few centimeters (a few in). This is comparable to traditional total stations and dedicated GNSS surveying instruments. Environmental and satellite reception conditions can introduce slight errors, but for confirming as-built acceptability or marking pile-driving positions it is sufficiently accurate. For tasks requiring millimeter-level precision or when extra assurance is needed, you can selectively recheck critical points with conventional instruments.

Q: Isn’t the introduction cost and equipment substantial? A: No. Recently, compact and affordable equipment has become widespread, so large investments are not as necessary as before. For example, RTK-GNSS receivers used to require large, expensive dedicated units, but now palm-sized smartphone-compatible devices are available. Being able to use existing smartphones or tablets also reduces cost. Drone and 3D laser scanning measurement can be outsourced or rented, so purchase is not mandatory. You can keep initial costs low while expecting a strong return on investment through efficiency gains.

Q: Are the operations and settings difficult? A: Operations are simple. Attach the GNSS receiver (such as an LRTK device) to the smartphone, start the app, and follow on-screen instructions for measurement and AR display. Initial setup mainly involves configuring GNSS correction service reception and connecting to the smartphone; once done, there are few special procedures. Those familiar with surveying or ICT tools will find it intuitive. New users can become proficient with brief training or reviewing the manual.

Q: What if GNSS cannot be used at the site? A: GNSS positioning using satellite signals works best where the sky is open. In dense forests or urban areas with many high-rise buildings, satellite signals may be blocked or reflected, reducing accuracy. Underground or indoor locations are generally unsuitable for satellite positioning. In such environments, calibrating by aligning to local known control points or combining AR methods with conventional surveying is recommended. That said, systems such as Japan’s Quasi-Zenith Satellite System have improved urban positioning stability, and many outdoor environments can achieve practical accuracy—so try it on site first.

Q: Will smartphone-based simple surveying make conventional instruments unnecessary? A: Smartphone + RTK can already substitute for many uses such as as-built checks and temporary stake setting. However, traditional surveying instruments are not completely obsolete. For example, placing control points that require millimeter-level precision or indoor measurements where GNSS is unusable still call for total stations or optical instruments. That said, smartphone AR surveying will increasingly cover general as-built management and pile position marking. A pragmatic approach is to use each method according to the purpose and gradually replace tasks that can be made more efficient with AR.

Accelerate site DX with simple surveying using LRTK

The LRTK series is a simple surveying solution that leverages smartphones. It enables centimeter-level GNSS positioning, shortens work time, and significantly improves productivity for construction, civil engineering, and surveying sites. Compatible with the Ministry of Land, Infrastructure, Transport and Tourism’s *i-Construction*, it is an optimal tool to strongly support on-site digitalization (DX).

For details about LRTK, please refer to the links below.

• [What is LRTK｜LRTK Official Site](https://www.lrtk.lefixea.com)

• [LRTK Series｜Device List Page](https://www.lrtk.lefixea.com/lrtk-series)

For product inquiries, quotations, or consultations about introduction, please feel free to contact us via the [inquiry form](https://www.lrtk.lefixea.com/contactlrtk). Let LRTK take your site to the next stage.