AR Heatmap Introduction – High-Precision As-Built Management Using a Smartphone

Table of Contents

• What is an AR heatmap?

• How to create an AR heatmap

• On-site uses of AR heatmaps

• Benefits of as-built management using a smartphone

• Recommendation for simple surveying with LRTK

• FAQ

What is an AR heatmap?

An AR heatmap is a drawing that intuitively visualizes with a color gradient whether the as-built (finished shape) of completed structures or terrain in civil engineering and construction is finished according to design. Also called an as-built heatmap, it compares the difference between the design 3D model (or the design surface height) and the actual as-built data measured after construction, and expresses that deviation by color. Areas with small deviations are shown in colors such as blue or green, while areas that are higher than the design or lower than the design are highlighted in red or orange, allowing you to grasp the quality of construction accuracy at a glance.

In conventional as-built management, it was common to measure finished heights at many points (points) for roads or land development and record numeric values to compare with design values. However, such point measurements carry the risk of overlooking unevenness in places that were not measured. A heatmap allows you to understand the height conditions of the entire construction area as a surface, and slight height differences are revealed by color, helping to prevent oversights. Another reason heatmaps are emphasized is that it is too late if you discover “it was not built according to the design” after the work is completed. For reliable quality assurance, it is ideal to check as-built conditions immediately after construction and, if there are problem areas, to rework them early—but traditional methods required significant effort and time to measure wide areas. It was also necessary to take measurement results back to the office to compare with drawings and locate defects, making immediate on-site response difficult.

AR heatmaps emerged as a solution to these challenges. By using heatmaps that show differences in color, you can verify the finish on the spot immediately after construction and prevent overlooking quality defects. Because you can visualize construction accuracy on site and take countermeasures immediately if necessary, rework can be minimized.

How to create an AR heatmap

Thanks to recent advances in smartphone technology and ICT, creating an AR heatmap can be accomplished without special surveying equipment. The basic flow is as follows.

• Prepare the design data: First, prepare the design data that will serve as the reference. For roads and land development, this corresponds to the 3D model created at design time or the reference height data for as-built. Even if only paper drawings are available, digitize the reference sections and design height information from the drawings to create the reference surface. What is important here is to prepare data that matches the design coordinate system (the reference coordinate system) for later comparison.

• Measure the as-built on site with a smartphone: Next, measure the terrain or shape of the structure after actual construction with a smartphone. Recent smartphones are equipped with high-performance cameras and LiDAR sensors, and by scanning the surrounding terrain with a dedicated app you can acquire the current shape as countless points (point cloud data). Even if the smartphone does not have LiDAR, you can generate a point cloud model using photogrammetry by taking multiple photos with the smartphone camera and processing them in the cloud. Also, by combining the smartphone with a high-precision GNSS unit and performing RTK positioning (real-time kinematic positioning), you can assign accurate latitude, longitude, and height coordinate values to the acquired point cloud and each measurement point in real time. This enables you to measure the as-built on site in world coordinates (absolute coordinates) without special reference-setting work.

• Compare with design data and generate the heatmap: Compare the point cloud data of the as-built acquired with the smartphone against the design data on a cloud service or dedicated software, calculate the differences, and generate the heatmap. By overlaying the uploaded design model and the on-site point cloud and automatically computing the height difference at each point, a heatmap is automatically created that color-codes areas that are higher or lower than the design. If the point cloud data is RTK-enabled and the coordinates match, cumbersome alignment is unnecessary and the comparison can be completed with a click. The generated heatmap visually indicates how many centimeters each location is higher or lower than the design, allowing you to understand the overall as-built accuracy visually. Generally, blue or green indicate within tolerance (pass), areas higher than the reference are red, and low areas are yellow; this coloring allows you to distinguish pass and fail areas at a glance.

• Adjust heatmap display: Adjust heatmap display settings as needed. For example, you can change the heatmap grid (mesh) size to adjust the coarseness/fineness of the display. It is also important to set the color thresholds, i.e., the range of allowable error, according to site standards. For example, if the allowable error is ±3 cm (±1.2 in), set the threshold so the color changes at that value to obtain a heatmap that judges pass/fail more strictly. Conversely, if you want a rough understanding, you can loosen the threshold. Flexibly adjust the color scale according to site needs.

Using the above steps, you can create an AR heatmap from point cloud data measured with a smartphone. Even without expensive specialized software, cloud services and apps that provide one-stop workflows from surveying to point cloud processing and heatmap generation have become more common. The important point is to compare the design data and the as-built data in the same coordinate system. In this respect, RTK-enabled smartphone surveying allows reliable comparison without the trouble of aligning coordinates. The era in which a single smartphone can complete on-site as-built inspection and heatmap creation is becoming a reality.

On-site uses of AR heatmaps

An AR heatmap you worked to create demonstrates its true value when fully utilized on site. Incorporating heatmaps into site construction management operations dramatically improves the speed and accuracy of quality control. Here are some concrete examples of use.

• Immediate pass/fail judgment and rework: With a heatmap, you can judge pass/fail (pass/fail) of the finish on the spot immediately after construction. For example, in paving work, you can quickly measure with a smartphone right after finishing, create a heatmap, and immediately check for any areas where height is insufficient compared to the design (areas shown in red on the heatmap). If nonconforming areas are found, you can precisely locate them on the spot and proceed to additional paving or cut away excess fill immediately. Previously, one would return to the office, identify defective areas on drawings, then mark them on site later for rework. Compared with that, a heatmap that enables the cycle measure → compare → fix to be completed on site the same day is an astonishing efficiency tool. This rapid on-site response minimizes rework and enables early correction of defects.

• On-site visualization with AR: The created heatmap can not only be viewed on a smartphone or tablet screen but also displayed over the actual scenery using AR (augmented reality) functionality. Modern smartphones have advanced AR capabilities; by loading high-precision heatmap data into the device and viewing through the camera, you can superimpose a colored heatmap onto field structures. For example, when you look at the ground through the smartphone screen, you can see, in colors matched to the scenery, how much higher or lower the spot you are standing on is compared to the design (an image of “site view + heatmap” overlapped). This allows pinpoint visual identification of defects without squinting at drawings or numbers or relying on experience and intuition. If you work while looking at the smartphone screen, you can give intuitive instructions such as “remove a little more from this red area.” Because AR is displayed with centimeter-level accuracy (half-inch accuracy), steps that previously required marking can be omitted, speeding up construction management.

• Measurement and safety management in difficult areas: Smartphone-based AR heatmaps also excel in safety. For example, when confirming the as-built condition of a steep slope, previously a surveyor had to climb the slippery slope to measure heights, which involved danger. By using a smartphone and heatmap, you can scan the entire slope from a safe distance, acquire point cloud data, and evaluate the finish using the generated heatmap. Even in areas with poor footing or where heavy machinery is operating, you can inspect the as-built non-contact without entering the area, contributing to reduced occupational hazard risk. You can also use heatmaps to check that materials are not protruding outside the construction area and that fill does not exceed the prescribed area. Heatmaps can thus serve as both as-built management and safety patrol tools.

• Data sharing and report creation: Heatmap tools that can connect to the cloud make it easy to share an as-built heatmap created on site with the office and stakeholders immediately. For example, if you send point cloud data and a heatmap for areas worked on in the morning to head office via the cloud, managers can perform quality checks from the office the same day and issue corrective instructions to the site if necessary. Previously, aggregating inspection results could take days and corrective meetings were often delayed, but heatmaps enable a PDCA cycle for construction that operates at near real-time speed. Moreover, heatmaps and point cloud data are stored on the cloud in time series, becoming a digital ledger of daily as-built management. This eliminates the need for handwritten field notebooks and pasted photo albums with later transcription to Excel, reducing human error by automatically accumulating data. Functions that automatically generate inspection reports (heatmap images, cross-sections, coordinate lists of measurement points, etc.) with one click have also appeared, greatly shortening the time required to create inspection documents. In the future, it may be possible to automatically compile a full set of deliverables for submission to inspectors from data acquired on site. In this way, AR heatmaps are a revolutionary method that not only visualizes quality on site immediately but can consistently use that data for recording, sharing, and reporting.

Benefits of as-built management using a smartphone

As described above, the use of AR heatmaps enables quality checks with unprecedented speed and accuracy, and it is the use of smartphones that brings this power to the fullest. Finally, let us summarize the main benefits that as-built management using smartphones plus the latest technologies brings to the site.

• Major labor and time savings: With smartphone surveying and point cloud scanning, one person can measure wide areas of as-built in a short time. Measurements that previously required multiple people and hours can be completed in just a few minutes, minimizing construction interruptions. Daily small-scale as-built checks can also be carried out easily, directly contributing to shorter construction schedules.

• Prevention of oversights through surface measurement: Conventional point measurement methods risk missing subtle unevenness in areas not measured. Smartphone point cloud scanning can measure the entire ground surface as a surface, enabling complete digital capture of the current status. Slight depressions or bumps in intermediate areas are revealed on the heatmap, greatly reducing omissions and oversights like “only this spot differed from the design” after inspection.

• Real-time feedback: Smartphone-based as-built management allows measurement and judgment on the spot, providing overwhelmingly fast feedback. If defects are found and corrected with a heatmap on the day of construction, the risk of failing later inspections is reduced. Cloud connectivity also enables real-time sharing with stakeholders, allowing the PDCA cycle for construction quality to run at high speed.

• No specialized skills required; elimination of dependence on individuals: Because familiar smartphones and intuitive app operations can be used for surveying, site staff can handle tasks without advanced surveying qualifications or expert skills. As-built management that relied on veteran surveyors can be shared across the team, alleviating staffing shortages and dependence on a single skilled person (knowledge silo). With short training, young employees and heavy equipment operators can master the tools, contributing to DX across the site.

• Low-cost introduction: Solutions using smartphones require far lower initial investment compared to conventional large surveying equipment. As high-precision GNSS and point cloud processing services have become available and devices have been miniaturized, they can be introduced with relatively inexpensive equipment and software combinations, making them accessible even for small- to medium-scale sites. Subscription-based services also allow use for only the necessary period without large upfront purchases.

• Digital records and efficient document creation: Point cloud coordinate lists, heatmap images, site photos, and all information related to as-built management are automatically stored as digital data. There is no worry about loss or deterioration as with paper field books or photo albums, and data can be searched and referenced immediately when needed. Automatic report functions allow inspection documents to be prepared with one click. Time previously spent on report creation can instead be devoted to core construction management tasks.

In these ways, as-built management using smartphones brings advantages in efficiency, accuracy, safety, and economy that surpass traditional methods. Especially for routine small-scale surveying and partial as-built checks, the ability to “measure immediately and know immediately” provides great value on site. Of course, for assessing very large areas or when sub-millimeter accuracy is required, it is effective to use conventional equipment appropriately; however, as a tool supporting daily construction management, smartphone + heatmap is becoming indispensable.

Recommendation for simple surveying with LRTK

So far, we have looked at how to create and utilize AR heatmaps with a smartphone and the benefits. Finally, as one concrete solution that underpins this foundation, we introduce LRTK. LRTK is an innovative system that transforms a smartphone into a “surveying instrument anyone can use,” consisting of the high-precision GNSS receiver device “LRTK Phone” and a dedicated smartphone app and cloud service.

Usage is simple: attach the LRTK device to the smartphone and perform the initial settings in the app. With just this, a smartphone’s built-in GPS, which normally has errors of several meters (several ft), can measure positions with ± several centimeters (± several in) accuracy. This is achieved by utilizing satellite positioning correction technology called RTK-GNSS, enabling positioning accuracy comparable to expensive stationary surveying instruments in a palm-sized device. The device connects to the smartphone via Bluetooth or USB, and by using correction information received over the internet (for example, national or commercial VRS services), real-time high-precision positioning is available in outdoor environments with clear sight lines. In short, with a smartphone + LRTK, anyone can stably perform centimeter-class surveying.

A major feature of LRTK is its low introduction barrier and ease of use. Device costs are lower compared to dedicated surveying equipment, making it possible for each worker to have a high-precision GNSS device that was once prohibitively expensive. Because it attaches to the smartphone or tablet you already use, there is no need to purchase multiple large specialized machines. For those who want to try on a small budget, monthly plans that include cloud services are available, allowing minimal initial investment and short-term introduction. Operationally, the LRTK device is very small and lightweight, easy to carry to the site, and the app operations are intuitive and simple. Those without surveying expertise can start using it after short training. It truly enables each site worker to carry a “personal surveying instrument” in their pocket and measure whenever they need to. For example, where teams previously waited to use a single surveying instrument, with LRTK each person can measure immediately, dramatically improving overall site productivity. Its compact size also makes surveying at heights and in narrow locations easier, reaching points that were previously inaccessible. Acquired data syncs automatically to the cloud, eliminating worries about backups and internal sharing for each measurement.

Thus, LRTK is a low-cost, easy-to-introduce and simple-to-operate smartphone surveying solution. The effects obtainable with small investment—large time savings in surveying, prevention of rework by reducing human error, and cost savings from improved quality—are substantial, and payback periods are often short. The LRTK concept of “anyone can easily perform high-precision surveying with a smartphone” aligns with construction DX initiatives promoted by the Ministry of Land, Infrastructure, Transport and Tourism such as *i-Construction*, and has been welcomed on sites. Because it can be used by not only experienced surveyors but also young staff and heavy equipment operators, organizational digitization advances, and one-person surveying enables labor savings and speed improvements. Smartphone + LRTK truly stands as an innovative partner for future on-site construction management.

If voices in your field raise requests like “I want to make as-built management more efficient” or “I want to try easy surveying with a smartphone,” consider introducing simple surveying with LRTK. Just by taking a smartphone and a small device in hand, surveying and as-built verification tasks that previously required manpower and time can be dramatically streamlined. By raising on-site quality management levels through digital visualization tools such as heatmaps, you can also improve workstyles and safety management. LRTK should serve as a powerful tool to accelerate your site’s DX and will surely be useful at your construction sites.

FAQ

Q1: Is the accuracy of as-built measurements taken with a smartphone really reliable? A: Using high-precision GNSS (RTK), smartphones can achieve measurement accuracy of ± several centimeters (± several in) in planimetric position and several centimeters in height. Compared to conventional smartphone built-in GPS errors of several meters (several ft), this is a dramatic improvement in accuracy. However, to fully realize this high precision, a good reception of satellite signals is required. Use in outdoor areas with clear sight lines and ensure a communication environment that can stably receive correction data.

Q2: What preparations and equipment are required to create an AR heatmap? A: Basically, prepare design data, a smartphone + surveying app, and, if possible, a high-precision GNSS unit (RTK-capable device). First, prepare the design model or reference height data for comparison. On the smartphone side, use an app capable of point cloud scanning and, if necessary, attach an external RTK-GNSS receiver (for example, an LRTK device). RTK positioning requires correction information from a reference station, so connect to a service that can receive correction data over the internet (for example, a VRS service via Ntrip). Once these preparations are complete, you can perform high-precision on-site measurement with only a smartphone and generate heatmaps from that data.

Q3: Can any smartphone be used? A: Smartphone surveying devices like LRTK support major iOS (iPhone and iPad) and Android models. Modern-generation smartphones generally meet the specifications. If the device has a LiDAR scanner, direct point cloud scanning is possible in-app, but even LiDAR-less phones can use photogrammetry by taking multiple photos to generate a point cloud model, so they are supported. The required conditions are the ability to connect to external GNSS receivers via Bluetooth or USB and that the dedicated app supports the OS version in use. In principle, most commercially available smartphones and tablets are usable.

Q4: How large an area can a smartphone LiDAR scan measure? A: The effective range of smartphone-built-in LiDAR is typically a radius of several meters (several ft) up to about 10 m (32.8 ft / 33 ft). Therefore, when scanning a wide site at once, divide the area into several blocks and walk around to scan them sequentially. On the other hand, using photogrammetry mode, cloud processing of many taken photos can generate point cloud models for much wider areas. However, photogrammetry takes time to produce results, so when immediacy is required, it is recommended to use LiDAR for quick overview and supplement detailed 3D models with photo mode as needed. With some ingenuity, a single smartphone can flexibly handle areas from small to large.

Q5: Compared to drone surveying or terrestrial laser scanners, what are the benefits of smartphone surveying? A: The greatest benefits are ease and immediacy. Drones and high-performance 3D scanners can measure large areas at once, but the equipment is very expensive, requires specialized skills, and has higher hurdles such as prior flight permission applications, placement of control points, and data processing time. In contrast, a smartphone + LRTK can be taken out and used by anyone on site immediately, and results can be confirmed on the spot, offering great ease of use. Smartphone surveying is particularly suitable for small-scale as-built checks and routine inspections during construction. Conversely, for cases where you want an aerial overview of a very large area, use a drone; for millimeter-level ultra-high-precision measurement, use a stationary laser scanner—using conventional technologies appropriately together with smartphone surveying is effective. The ideal is to combine surveying methods according to the scale and purpose of the site.

Q6: Can as-built data acquired with a smartphone be submitted as official inspection documents? A: Yes. As-built data acquired with smartphone RTK + point clouds can be compiled in formats that conform to the Ministry of Land, Infrastructure, Transport and Tourism’s as-built management guidelines (provisional). For example, LRTK saves measurement point coordinate data and point cloud data in coordinate systems and accuracies that meet electronic delivery standards, so they can be used directly as deliverables for inspection. It is possible to output records that meet the accuracy requirements specified in the “as-built management guidelines (earthwork)” using RTK-GNSS, and to export 3D data in LandXML format and heatmap diagrams as PDFs for submission to inspectors. Documents that were previously submitted as paper drawings or Excel sheets are increasingly being accepted as digital data. As-built management using smartphones and ICT has reached a level sufficient for official inspections.

Q7: I’m worried about the cost of new introduction and operating expenses—does it provide good cost performance? A: Introducing smartphone RTK and as-built management apps is vastly lower cost compared to conventional surveying equipment. Even including dedicated devices, you can start from several hundred thousand yen range, and using subscription plans allows you to operate with monthly expenses without large initial outlays. Device management is also easy with just a smartphone and compact device, and no specialized operator is required. Considering effects such as reduced labor costs, shorter construction schedules, and avoidance of rework through early correction of defects, payback is often achieved in a relatively short period. Reports from sites indicate labor reduction from “one person completing as-built measurement” and quality improvement from “correcting defects on the spot.” These benefits greatly improve total productivity, making it an investment with reasonable cost performance.