Table of Contents

• What is an as-built heat map?

• How to create an as-built heat map

• On-site uses for as-built heat maps

• Benefits of as-built management using a smartphone

• Recommendation: simple surveying with LRTK

• FAQ

What is an as-built heat map?

An as-built heat map is a drawing that intuitively visualizes, using color coding, whether completed structures or terrain in civil and construction works match the design. Concretely, it compares the difference between the design 3D model (or the design surface elevations) and the as-built data measured on site, and represents that difference with a color gradient. Areas with no deviation are shown in blue or green, while areas that are too high or too low compared to the design are highlighted in red or orange, so construction accuracy can be judged at a glance. Traditionally, as-built management meant recording elevations at key points numerically for inspection. However, using a color-coded heat map makes it possible to understand the entire site surface-wise and not miss small elevation differences.

As-built heat maps are important because if someone later points out that the finished work differs from the design drawings, it can cause rework or disputes. For solid quality assurance, it is ideal to verify the as-built immediately after construction and correct any problem areas early. Traditional as-built measurement used tapes, rods, levels, total stations, etc., measuring one point at a time, so covering wide areas required a great deal of effort and time. On top of that, inspection results had to be taken back to the office and compared with drawings to identify defects, making immediate on-site response difficult. The as-built heat map emerged as a solution to these challenges. A heat map that shows differences with color allows immediate verification of the finish on site and prevents overlooking quality defects.

How to create an as-built heat map

So how is an as-built heat map actually created? In recent years, with the development of smartphones and ICT technologies, it has become possible to easily create as-built heat maps with a smartphone without special surveying equipment. The basic creation steps are as follows.

• Design data preparation: First, prepare the reference design data. For roadworks or land development as-builts, this corresponds to the 3D model from design or the reference elevations. Even if you only have paper drawings, you can input the reference cross-sections or design elevation information into software to generate a reference surface. The key is to prepare data that matches the design coordinate system for later comparison.

• Measure the as-built on site with a smartphone: Next, measure the completed site shape with a smartphone. Modern smartphones are equipped with high-performance cameras and LiDAR sensors, and using a dedicated app to scan the surrounding terrain you can capture the current shape as countless points (point cloud data). Even on devices without LiDAR, you can generate point clouds via photogrammetry features that process multiple photos in the cloud. Furthermore, if you combine the smartphone with a high-precision GNSS unit and perform RTK positioning, you can attach accurate Earth coordinates (latitude, longitude, elevation) to the captured point cloud or measurement points in real time. This enables measuring the as-built in absolute coordinates without special reference setup.

• Compare with design data and generate the heat map: Compare the point cloud data captured by the smartphone with the design data to create a heat map. For example, cloud services with comparison functions let you overlay an uploaded design model and the site point cloud with a few clicks and compute the differences. If the point cloud is RTK-capable and coordinates match, positioning adjustments are unnecessary and numeric comparison is automated. The result is an automatically generated heat map that color-codes excesses and shortages in elevation. The map shows by color how many centimeters higher or lower each point is relative to the design, allowing a visual grasp of overall as-built accuracy. Typically, blue or green indicate within tolerance, higher-than-design areas are set to red, and lower areas to yellow, so OK and NG areas are apparent at a glance.

• Adjust heat map display: Adjust the heat map display settings as needed. You can change the grid (mesh) size for coarser or finer heat maps, or set color thresholds (tolerance ranges) to match site standards. For example, if the allowable tolerance is ±3 cm (±1.2 in), set the thresholds so colors change at that value to create a stricter pass/fail judgment map. Conversely, if a rough overview is the goal, you can set wider thresholds. Flexibly configure the color scale according to site needs.

With the above process, you can create an as-built heat map from point cloud data measured by a smartphone. Even without special analysis software, many recent cloud services and apps provide an end-to-end workflow from measurement to automatic calculation and heat map display. The important point is to compare design and current data in a common coordinate system. RTK-capable smartphone surveying takes care of this. The era when a single smartphone completes on-site as-built inspection and heat map creation is becoming a reality.

On-site uses for as-built heat maps

As-built heat maps demonstrate their true value when used directly on site. Incorporating heat map-based as-built checks into site operations dramatically increases the speed and accuracy of quality control.

● Immediate pass/fail judgment and rework: With an as-built heat map, you can determine pass/fail of the finish on the spot immediately after construction. For example, in paving work, you can measure with a smartphone immediately after finishing, generate a heat map, and instantly check whether there are any areas lacking elevation compared to the design (shown in red). If a nonconforming area is identified on the heat map, you can locate it and perform additional paving or trimming as rework right there. Considering the traditional process—returning to the office to find the defective area on drawings and later marking it on site for rework—this is an astonishing efficiency improvement. Because the cycle of “measure → compare → fix” can be completed on the same day, rework is minimized and early correction of defects is realized.

● AR visualization on site: The created heat map can be viewed not only on smartphones or tablets, but also overlaid on the real scene. Modern smartphones have advanced AR (augmented reality) features; if you load high-precision heat map data into the device and view it through the camera, you can superimpose color displays onto site structures. For example, holding a smartphone showing the heat map over the ground will reveal how much higher or lower that location is compared to the design [site view + heat map]. This lets you pinpoint defects without referring to drawings or numbers and without relying on intuition or experience. Looking at the smartphone screen while wearing a helmet, you can give intuitive on-site instructions such as “the red area runs from here to here, so shave a little more off.” Thanks to centimeter-class AR display (cm level accuracy (half-inch accuracy)), tasks like setting out are reduced and construction management speeds up.

● Measurement and safety management in difficult areas: Smartphone-based as-built heat maps also support safety. Traditionally, checking the as-built of steep slopes required surveyors to climb the slope to measure heights, which carried risks. By using a smartphone and heat map, you can scan the entire slope from a distance and evaluate the finish from a safe location. In areas with poor footing or where heavy machinery is operating, you can inspect the as-built non-contact from outside the area, contributing to improved occupational safety. Watching the heat map, you can also check for overspread materials or embankment beyond the work area, so heat maps can serve simultaneously as a safety patrol tool.

● Data sharing and report generation: With cloud-enabled heat map tools, it’s easy to share that day’s as-built heat map with the office or stakeholders immediately. For example, if you send the point cloud and heat map for the morning’s work to headquarters via the cloud, managers can perform a quality check from the office in the afternoon and issue instructions to the site if corrections are needed. Where compiling inspection results used to take days and delay countermeasure meetings, you can now run construction PDCA at near-real-time speed. Heat maps and point cloud data are stored in the cloud time-series, accumulating as daily as-built records. This eliminates the need to handwrite measurements in field books and later transcribe them into Excel; digital data is automatically accumulated, reducing errors. Functions now exist that automatically output as-built management reports (heat map images, cross-sections, lists of measured point coordinates, etc.) at the push of a button, greatly shortening document preparation time. In the future, it will likely become possible to automatically assemble all deliverables required by inspectors from on-site data. In this way, as-built heat maps are a groundbreaking method that visualizes quality on site instantly while enabling consistent use of that data for recordkeeping, sharing, and reporting.

Benefits of as-built management using a smartphone

As described above, as-built heat maps enable quality checks with unprecedented speed and accuracy, and the factor that maximizes that power is smartphone utilization. Finally, let’s summarize the main benefits that smartphone + modern technology brings to on-site as-built management.

• Significant labor and time savings: With smartphone surveying and point cloud scanning, one person can measure a broad area’s as-built in a short time. Measurements that previously took multiple people hours can be completed in just a few minutes, minimizing construction interruptions. Routine small as-built checks can be performed easily, directly shortening project schedules.

• Prevention of oversight through surface-based measurement: Traditional point measurements risked missing unevenness away from measured points, but smartphone point cloud scans measure the ground surface comprehensively. Because data captures every corner, slight bumps in intermediate areas are revealed by the heat map. This greatly reduces omissions where “only this part differed from the design” after inspection.

• Real-time feedback: Smartphone-based as-built management lets you perform measurement through judgment on site, delivering overwhelmingly fast feedback. Finding and correcting defects with a heat map on the construction day reduces the risk of later rejection in inspections. Cloud integration enables real-time sharing with stakeholders, accelerating the construction quality PDCA cycle.

• No specialist skills required; reduction of person-dependency: Because surveying can be done with a familiar smartphone and intuitive app operations, field staff can handle it without advanced surveying qualifications. As-built management that once relied heavily on veteran surveyors can be distributed across the team, alleviating labor shortages and reducing person-dependency. After a short training, younger staff or operators can use it, contributing to DX on site.

• Low-cost introduction: Smartphone-based solutions require much lower initial investment than traditional large surveying equipment. As high-precision GNSS and point cloud processing have been service-ized and devices miniaturized, you can introduce them with relatively inexpensive equipment and software combinations, making them accessible even for small to mid-size sites. Subscription-based services allow adoption for only the necessary period without large one-time purchases.

• Digital records and streamlined documentation: Measurement coordinate lists, heat map images, field photos—everything related to as-built management is stored digitally. There’s no worry about losing or degrading paper notebooks or photo albums, and data can be searched and referenced immediately. Automated report features let you produce inspection documents with one click, freeing time for core construction management tasks.

Smartphone-based as-built management provides advantages over traditional methods in efficiency, accuracy, safety, and economics. The ability to “measure now and know now” is especially valuable for routine small surveys and partial as-built checks. For very large-area overviews or millimeter-level ultra-precise measurements, conventional equipment remains effective, but for daily construction management, smartphone + heat map is becoming indispensable.

Recommendation: simple surveying with LRTK

So far we’ve discussed how to create and use as-built heat maps with smartphones and the benefits. Finally, we introduce one concrete solution that supports this workflow: LRTK. LRTK is an innovative system that turns smartphones into an “easy-to-use all-purpose surveying instrument.” It consists of the high-precision GNSS receiver device “LRTK Phone” and a dedicated app and cloud service.

Attaching the LRTK device to a smartphone and performing a simple setup lets a smartphone GPS, which normally has errors of several meters (several feet), measure positions with ± several centimeters (± a few inches) of accuracy. This is realized by using RTK-GNSS correction technology and makes surveying-level positioning accuracy comparable to expensive fixed surveying machines possible with a palm-sized device. The device connects to the smartphone via Bluetooth or USB and uses correction information received over the Internet (for example, government or private VRS services) to perform real-time high-precision positioning. In an outdoor environment with good sky visibility, smartphone surveying using LRTK enables anyone to perform stable centimeter-class measurements (cm level accuracy (half-inch accuracy)).

A major feature of LRTK is its low introduction barrier and ease of use. Device costs are lower than dedicated machines, making it possible for each worker to carry a high-precision GNSS device that used to cost hundreds of thousands of yen per unit. Because it is attached to the smartphone or tablet you already use, you don’t need to purchase many special machines. For those who want to start with low initial investment, monthly subscription plans that include cloud services are available, allowing adoption as an operational expense for only the required period. Operationally, LRTK is very compact and lightweight, easy to carry on site, and the app is intuitive and simple. People without surveying expertise can start using it after short training. Imagine each worker having their own pocket surveying device—LRTK’s strength is that you can measure whenever you need to. For example, where one team used to wait to use a single device, with LRTK each person can measure on their own, dramatically improving site productivity. Its compactness also makes surveying at heights or in tight spaces easier, allowing access to previously unreachable points. Measured data syncs automatically to the cloud, removing worries about backing up or sharing measurements.

LRTK is thus a low-cost, easy-to-introduce, and simple-to-operate smartphone surveying solution. The benefits obtained from relatively small investment—time savings in surveying, reduction of human errors and rework, and fewer reworks due to improved quality—are significant, and payback periods are often short. LRTK’s concept of “easy high-precision surveying with a smartphone” aligns with construction DX initiatives such as the Ministry of Land, Infrastructure, Transport and Tourism’s i-Construction, and is highly welcomed on sites. Because it can be used by not only experienced surveyors but also younger staff and machine operators, organizational digitization advances and single-person surveying enables labor reductions and speed improvements. Smartphone + LRTK is truly an innovative partner for future on-site construction management.

If your site is looking to streamline as-built management or try easy smartphone surveying, consider adopting LRTK for simple surveying. With a smartphone and a small device in hand, surveying and as-built verification tasks that used to require manpower and time are dramatically streamlined. Using digital visualization tools such as heat maps raises the level of quality control on site and contributes to work style reform and improved safety management. LRTK can strongly support site DX and will surely be useful at your construction sites.

FAQ

Q1: Is the accuracy of as-builts measured with a smartphone really sufficient? A: Yes. Using high-precision GNSS (RTK), smartphones can achieve horizontal positioning accuracy of ± several centimeters (± a few inches) and vertical accuracy on the order of a few centimeters (a few inches). This is tens of times more accurate than the meter-level errors of conventional built-in smartphone GPS. However, to achieve high precision you need an environment where satellites can be received well. Use in outdoor areas with good visibility and ensure a communication environment that can stably receive correction information.

Q2: What preparation and equipment are required to create an as-built heat map? A: Basically, you need design data, a smartphone + surveying app, and ideally a high-precision GNSS unit (RTK-capable). First prepare the design model or reference elevation data for comparison. On the smartphone, use an app that can perform point cloud scanning and, if needed, attach an external RTK-GNSS receiver (for example, an LRTK device). RTK positioning requires correction data from a base station, so connect to an internet-accessible service that provides such corrections (for example, Ntrip VRS services). With these preparations, you can perform high-precision field measurements with only a smartphone and generate heat maps from the data.

Q3: Can any smartphone be used? A: Devices like LRTK are compatible with major iOS (iPhone and iPad) and Android models. Most modern smartphones meet the specifications required. Devices with built-in LiDAR can perform point cloud scanning directly in-app, but even non-LiDAR phones can generate point cloud models via photogrammetry from photos, so they are still usable. Requirements include the ability to connect to an external GNSS receiver via Bluetooth or USB and that the dedicated app supports the device’s OS version. In general, common commercial smartphones and tablets are compatible.

Q4: How large an area can be measured with a smartphone LiDAR scan? A: Smartphone LiDAR effective distance is roughly a radius of several meters to up to 10 m (32.8 ft). Therefore, to scan a wide site at once you typically divide it into blocks and measure by walking around them sequentially. Using photogrammetry mode, many photos can be cloud-processed to generate point cloud models for wider areas. However, photogrammetry takes time to produce results, so if immediacy is required you can use LiDAR for a quick overview and supplement detailed models with photo mode. In this way, a single smartphone can flexibly handle small to large scales with some planning.

Q5: Compared with drone surveying or terrestrial laser scanners, what are the advantages of smartphone surveying? A: The greatest advantages are ease of use and immediacy. Drones and high-performance 3D scanners can measure large areas at once but are expensive, require specialized skills, and often involve permits, control point setup, and time-consuming data processing. By contrast, smartphone + LRTK can be taken out by anyone on site for immediate measurement and on-the-spot result confirmation. Smartphone surveying is particularly well-suited for small as-built checks during construction and routine inspections. For very large-area overviews or where aerial perspective is needed, drones are useful; for millimeter-level ultra-precise measurements, fixed laser scanners are appropriate. Ideally, use smartphone surveying together with other methods as appropriate for the site’s scale and goals.

Q6: Can as-built data acquired with a smartphone be submitted as official inspection documents? A: Yes. As-built data obtained with smartphone RTK + point clouds can be compiled in formats compliant with the Ministry of Land, Infrastructure, Transport and Tourism’s as-built management guidelines (draft). For example, LRTK saves measured point coordinates and point cloud data in coordinate systems and accuracies that meet electronic submission standards, so the data can be used as inspection deliverables. It is possible to output records that meet the accuracy requirements in “As-built management using RTK-GNSS (earthworks)” and to export 3D data in LandXML and heat map figures as PDF for submission to inspectors. Where as-built reports and forms were traditionally submitted on paper or Excel, digital submissions are increasingly being accepted. Smartphone + ICT-based as-built management has reached a level that can sufficiently support official inspections.

Q7: I’m worried about the cost of new equipment and operational expenses. Is it cost-effective? A: Introducing smartphone RTK and as-built management apps is overwhelmingly lower cost than traditional surveying equipment. Even including dedicated devices, you can start from tens of thousands of yen, and subscription plans let you operate with low initial expense and pay monthly. Device management is simpler with just a smartphone and a small terminal, and specialized operators are not required. Considering savings from reduced labor costs, shortened schedules, prevention of rework, and fewer reworks due to improved quality, payback is often achieved in a relatively short period. Reports from sites indicate productivity improvements from “one person completing as-built measurement” and quality improvements from “correcting defects on the spot.” Overall productivity increases substantially, so it is generally a cost-effective investment.