Immediate Response from On-site Inspection to Rework! Shorten the PDCA Cycle with AR Heat Maps

Table of Contents

• PDCA cycle and on-site inspections

• Traditional on-site inspections and their challenges

• What is an AR heat map?

• Immediate as-built confirmation with AR heat maps

• How AR heat maps shorten the PDCA cycle

• Information sharing via cloud integration

• Promoting simple surveying with LRTK

• FAQ

PDCA cycle and on-site inspections

In construction sites, the PDCA cycle (Plan-Do-Check-Act) is widely used as a method for quality and schedule management. In the Plan phase you create design drawings and construction plans; in Do you carry out the actual work; in Check you verify the as-built condition (the finished state of the work) and quality; and in Act you perform necessary rework or improvements. By repeating this flow, quality and efficiency at the site are improved. Especially at the Check stage, discovering defects early and responding quickly in the Act stage can determine the success of the entire project. If problems are missed during on-site inspections or responses are delayed, significant rework can occur in later stages, leading to increased costs and schedule delays. Conversely, if inspection through rework can be handled immediately on site, problems can be corrected while still minimal, preventing rework and shortening the overall PDCA cycle to keep the project running smoothly. In other words, being able to run the PDCA cycle immediately on site is the key to preventing unresolved quality issues and improving productivity.

Traditional on-site inspections and their challenges

Traditionally, post-construction as-built inspections and surveying work have been performed mainly by experienced surveyors using equipment such as total stations (TS) and levels. For example, in road construction, experienced surveyors meticulously measure subgrade elevation and slope gradients based on control points and compare them with the design values on drawings to verify construction accuracy. However, this conventional method has several noted challenges.

• Heavy reliance on advanced skills and experience: Accurate surveying and as-built verification require specialized knowledge and extensive experience, and achieving sufficient accuracy without skilled personnel has been difficult. Many processes—selecting survey points, operating equipment, error correction, and reading drawings—depend on artisanal skills, introducing the risk of human error.

• Time-consuming and labor-intensive work: Measuring numerous points on site and comparing them to drawings is very time-consuming. On large sites, measurements alone can take an entire day, making frequent inspections difficult. As a result, problems tend to be discovered late, and timely corrective action becomes hard.

• Results are not intuitively shareable or interpretable: Measurement results are often reported as paper drawings or numerical data, making it hard to intuitively grasp “where and how large the errors are.” When explaining to site workers or clients, you must have them mentally overlay the numbers on the drawings onto the actual site, which consumes time and can lead to misunderstandings.

• Shortage of skilled personnel and outsourcing costs: In recent years, the aging and shortage of personnel responsible for surveying and inspections has become serious. It has become difficult to always secure skilled surveyors on site, and more cases require outsourcing as-built measurements to specialized external contractors. This increases costs and scheduling burdens, slowing down site responsiveness.

As described above, the traditional approach has limits in ensuring accuracy, operational efficiency, and information sharing, all of which impair on-site responsiveness.

What is an AR heat map?

One promising solution to these challenges is as-built verification using AR heat maps. AR (Augmented Reality) technology overlays digital information onto real-world imagery to visualize construction deviations. A heat map represents the magnitude of differences with a color gradient—for example, areas matching the design are shown in blue or green, while areas below or above the reference are shown in red or orange. By viewing the site through a smartphone or tablet screen, it becomes immediately clear which areas are overfilled relative to the design and which have been over-excavated and are too low. Without even looking at a table of numbers, the color-coded display on the screen lets you intuitively identify “places that require rework.”

To realize an AR heat map, design data must be compared with current survey data. A 3D design model or reference surface data for the construction target is preloaded into the device, and differences are calculated by automatically aligning on-site point cloud data (three-dimensional measurement data of current conditions) with that model; the result is displayed as a heat map. Recent smartphones are equipped with high-performance cameras and LiDAR sensors, and dedicated apps using these features make precise on-site point cloud measurement and AR display possible. Previously, special AR equipment and extensive setup were required, but with improved device performance and industry-wide digital transformation initiatives such as the Ministry of Land, Infrastructure, Transport and Tourism–led [i-Construction](https://www.mlit.go.jp/tec/i-construction/) policy, AR heat maps are becoming a practical solution that “anyone can operate with just a smartphone.”

Immediate as-built confirmation with AR heat maps

Using AR heat maps, you can perform prompt as-built inspections immediately after construction. Whereas conventional workflows required taking survey data back to the office to identify problem areas, AR heat maps allow you to detect differences on site in real time and take immediate action. Here’s the specific flow.

• Construction completion scan: As soon as construction is finished, a responsible person (even a less experienced junior staff member) attaches a small RTK-GNSS receiver (for example, an LRTK device) to a smartphone such as an iPhone and walks the site. The smartphone’s built-in LiDAR sensor scans the surroundings, acquiring the post-construction terrain as high-density point cloud data in a matter of minutes. Because it captures shapes without gaps even over wide areas, local irregularities are not missed.

• On-site AR comparison of the as-built: Once measurement is complete, the app on the smartphone automatically aligns the acquired point cloud data with the preloaded 3D design model and immediately calculates the as-built differences. Switching the phone to AR mode overlays the heat map onto the actual pavement or structure. Areas within the specified elevation are shown in green or blue; areas lower than the design (insufficient) are highlighted in red; areas that are too high are highlighted in orange. By simply looking at the site through the phone screen, you can instantly confirm whether quality standards are met.

• Immediate rework and rechecking of defects: If areas shown in red on the AR heat map indicate insufficiency, you can immediately perform corrective work on site—add fill, recompact, or trim, for example. After reworking, rescanning the affected area with the smartphone will show the heat map turn green, confirming the elevation now matches the design. In this way, the sequence of construction → inspection → rework can be completed without leaving the site.

• Sharing and recording result data: The measured point cloud data and heat map images are uploaded to the cloud for storage and sharing. Supervisors or clients not on site can review the as-built results online the same day. When preparing inspection reports later, referring to the data accumulated in the cloud allows accurate and efficient compilation of documents.

By implementing immediate as-built confirmation with AR heat maps, the on-site inspection through rework can be completed within a single cycle. Because site personnel themselves can perform quick as-built checks and corrections with a smartphone, the waiting time for surveying and losses from rework that were previously necessary are greatly reduced.

How AR heat maps shorten the PDCA cycle

When the above flow is realized, the PDCA cycle at construction sites speeds up dramatically. Because Check and Act can be executed on site in real time, the time lag that used to occur after Plan→Do is eliminated. Conventionally, the process required analyzing survey results to identify defects, performing rework at a later date, and then reconfirming—during which work would be interrupted and, in some cases, additional costs and scheduling losses would occur from reorganizing personnel or equipment. After introducing AR heat maps, these feedback steps can be completed within minutes to tens of minutes after construction, minimizing rework. Early correction of problems eliminates the risk of leaving quality defects unaddressed and allows subsequent stages to proceed with confidence.

Furthermore, being able to run the PDCA cycle immediately on site contributes to shortened schedules and cost reductions. Reduced rework eliminates unnecessary material and labor costs, and reduces idle time for machines and personnel caused by awaiting inspections. By ensuring quality at each process before moving forward, accidents where many defects are discovered at the final stage are prevented, smoothing the progress of the entire project.

Also, because data is recorded and shared digitally, communication among stakeholders is invigorated. If issues discovered on site are shared to the cloud on the spot, remote supervisors and clients can grasp the situation in real time. This reduces discrepancies in understanding of inspection results and facilitates smooth agreement on corrective policies. Analyzing accumulated as-built data can feed back into future planning to revise quality standards, thereby enhancing the PDCA cycle itself. The use of AR heat maps not only increases on-site responsiveness but also has great value in promoting data-driven continuous improvement.

Information sharing via cloud integration

Data obtained from AR heat maps can be shared immediately with stakeholders via the cloud. For example, point cloud data and heat map images uploaded from a site smartphone can be viewed on office PCs or tablets, enabling seamless information sharing that connects the site and remote locations. This allows construction results to be checked and instructions issued the same day, even without attending the site. Because the same visual information is shared on the cloud, there is no need to send drawings by email or explain by phone, which speeds decision-making and reduces communication losses.

In addition, accumulated 3D data in the cloud is useful for long-term site records and reuse. If you scan as-built conditions after each construction stage, you can easily track changes in as-built conditions over time according to daily progress. Because daily point cloud data are unified in world coordinates, overlaying them later allows accurate comparison of construction progress. This is extremely useful as quality control records and in as-built reports. Moreover, when planning similar projects in the future, referring to past data can improve construction procedures, and in the event of problems, causes can be investigated from the data—leading to secondary use of accumulated data. Cloud integration enables real-time, systematic management of site information and contributes to promoting site DX (digital transformation) and improving productivity.

Promoting simple surveying with LRTK

Using the advanced technologies described above greatly improves the efficiency of as-built inspection and feedback and contributes to shortening the PDCA cycle. However, some may feel uneasy—thinking “high-precision GNSS, point cloud measurement, and AR sound difficult” or “can we really operate this ourselves?” This is where the all-in-one solution LRTK is attracting attention. LRTK is a surveying DX platform that combines high-precision GNSS receivers, smartphone apps, and cloud services, and it was developed as an easy surveying tool that can be operated even by non-specialists.

With LRTK, a small RTK-GNSS receiver attached to a smartphone enables centimeter-level high-precision positioning (cm level accuracy (half-inch accuracy)) while the phone’s camera or LiDAR scanner scans the site to generate point cloud data. The platform then calculates and visualizes volume and shape differences on the cloud, all in a one-stop workflow. In other words, it is a package that contains all functions required for the PDCA of on-site inspection: as-built measurement, difference heat map display, and data sharing. The UI/UX is designed so that site personnel can operate it on their own smartphones, and even first-time users can learn to operate it quickly through short training.

By introducing such tools, as-built surveying and earthwork volume calculations that were previously outsourced can be completed in-house. This contributes to cost reduction and, with the effective reuse of accumulated data, the advancement of the construction PDCA cycle. Above all, when on-site staff themselves become proficient in digital technologies, their ways of working change and productivity improves. For example, even a single finish check can be carried out “more quickly and accurately and shared on the spot” by using a smartphone surveying solution like LRTK. Indeed, a movement toward the democratization of surveying technology is beginning, accelerating on-site DX. If you feel there are issues in your current surveying or inspection workflow, consider trying this kind of simple as-built check using smartphone surveying.

FAQ

Q: What data is required to use AR heat maps? A: Basically, you need two types of data to compare (or “design data + current condition data”). That is, a 3D model from the design stage or reference surface data and as-built data such as point clouds measured on site. By overlaying these, differences are calculated and displayed as a heat map.

Q: What is smartphone RTK, and is its accuracy adequate? A: Smartphone RTK refers to a setup in which a high-precision GNSS receiver is connected to a smartphone, and RTK (real-time kinematic) technology enables centimeter-level positioning on the smartphone. Because positioning accuracy comparable to dedicated high-precision GPS equipment can be achieved, point cloud surveying with a smartphone is highly reliable. In practice, many sites have confirmed measurement accuracy within a few centimeters (within a few inches).

Q: Compared with drone surveying, what are the advantages of smartphone-based as-built confirmation? A: Drone photogrammetry can survey wide areas quickly, but it is susceptible to operational constraints such as weather and flight restrictions. In contrast, smartphone-based site measurement can be conducted on the ground even in rain and requires no prior preparation or permits, offering superior mobility. The ease of immediately performing measurements yourself when needed is a major advantage. Also, ground scanning can record details such as wall surface irregularities that drones may have difficulty capturing. Both methods have their use cases, but the convenience of completing tasks with a single smartphone is highly attractive to site personnel.

Q: Do AR visualizations of differences require special equipment? A: No—generally, commercially available smartphones or tablets are sufficient. Since AR display is viewed through a phone or tablet screen, you only need a compatible dedicated app; there is no need to provide special AR goggles. If multiple people want to check together, displaying on a tablet’s large screen or mirroring the screen to a TV can be useful.

Q: Can site staff use it? Is specialized knowledge required? A: Yes—these systems are designed so that site staff can use them. Smartphone surveying apps are intuitive; following on-screen prompts is enough to perform measurements and display differences. Even beginners can master the system in a short time with simple training or a manual. There are increasing examples of construction management staff without surveying expertise conducting point cloud measurements and AR heat map checks themselves and achieving improved efficiency.

Q: How much does implementation cost? A: Compared with acquiring large conventional surveying instruments and dedicated software, solutions using smartphone RTK and AR apps can be implemented at much lower cost. By leveraging existing smartphones or tablets and relatively inexpensive small GNSS receivers, initial investment can be greatly reduced. Considering that surveying work previously outsourced can be brought in-house, overall cost-effectiveness is very high.

Q: I’ve heard point cloud data can be large—can smartphones and the cloud handle it? A: While high-density point clouds tend to produce large file sizes, smartphone point cloud surveying solutions include automatic compression and optimization to keep data at manageable sizes. You can also limit scans to the required area to avoid unnecessary data. In addition, by integrating with cloud services, detailed processing is performed on servers, and only necessary information is transferred to the smartphone to reduce load. Therefore, you can operate on-site smartphones without worrying about storage shortages or processing delays. Provided that the communication environment is adequate, heavy 3D data is designed to be handled smoothly via the cloud.