No drawings needed? Achieve on-site visualization with AR heat maps

Table of contents

• What is an AR heat map?

• Benefits of AR heat maps

• Use cases for AR heat maps

• How to create an AR heat map

• Real-time verification of construction status with AR display

• Summary

• Simple surveying with LRTK

• FAQ

On construction and civil engineering sites, it is routine to check current construction status against the finished form while referring to design drawings and plans. However, it is not easy to map a flat drawing onto the site in your mind, and unless you are experienced, it is difficult to accurately read the finished shape from numbers and lines. “How many cm (in) more do we need to excavate here?” “Which parts have been overfilled?” — such judgments have required comparing drawings and the site and imagining the 3D differences in your head. In recent years, the shortage of experienced survey technicians has become more serious, and a new system is needed that enables even less experienced members to accurately understand the site. What if, without special skills or years of intuition, you could simply hold up your smartphone and instantly see the differences between the site and the design? In fact, by leveraging the latest digital technologies, that is becoming possible. The keyword is AR heat map. This technology overlays colored differences onto the real landscape, enabling such intuitive site visualization that one could say “drawings aren’t needed.” This article explains what AR heat maps are, their benefits, use cases, and concrete creation methods. At the end of the article, we also introduce LRTK, a solution that lets anyone easily start AR-enabled surveying.

What is an AR heat map?

An AR heat map is a 3D visualization method that color-codes the differences between the finished terrain or structures (as-built) and the design data. Point cloud data or 3D survey data acquired on site are overlaid with the 3D model from the design phase (design surfaces or BIM/CIM models), and the errors at each point are expressed by color differences. For example, areas that are built higher than the design are colored in red tones, whereas areas that have not been cut enough and are low are colored in blue tones, and areas finished according to design are shown in green. At a glance, you can intuitively understand which locations are higher or lower than the specification and whether they are acceptable or not. In short, an AR heat map makes subtle undulations that were hard to grasp from drawings or lists of numbers visible on a colored 3D map. The Ministry of Land, Infrastructure, Transport and Tourism has also been promoting the use of 3D measurement and surface-based as-built management through policies such as ICT construction and *i-Construction*, and heat map–based as-built evaluation has begun to be incorporated into official guidelines. AR heat maps are becoming a new standard in the era of on-site DX.

Benefits of AR heat maps

Using AR heat maps brings many advantages that conventional planar inspection methods could not achieve. Here are the main benefits.

• Intuitive quality assessment: Because the magnitude of errors is indicated by color, anyone from site workers to clients can understand construction accuracy at a glance. It is easier to understand than reports consisting only of numbers or text, and it makes it easier for the whole team to share points that need correction.

• Prevention of missed measurements: By evaluating the entire surface with high-density 3D data such as point clouds, you can detect unevenness (fine bumps and dips) and localized defects that are easily missed by spot checks. A heat map that covers a wide area can exhaustively uncover variations in quality.

• Fast feedback: If you scan and convert to a heat map at any time during construction, you can immediately check the as-built condition at that time. Detecting problem areas early and reworking them prevents large-scale rework later, contributing to shorter schedules and maintained quality.

• Records and traceability: Heat maps and point cloud data can be stored in the cloud as digital records. You can save detailed construction histories that paper drawings could not preserve, making it easy to perform cause analysis by comparing with past data during future maintenance. After completion, as-built data can be integrated into BIM/CIM models for maintenance management, becoming valuable informational assets.

• Labor savings and improved safety: Point cloud measurement and analysis that can automatically measure large areas at once significantly reduce manpower and time for measurement tasks. Dangerous or high places can be scanned remotely, reducing the risk to workers. Heat maps make it easy to check as-built conditions in places that were previously difficult to inspect, helping reduce human error.

Thus, as-built heat maps greatly contribute to improving precision and efficiency in quality control.

Use cases for AR heat maps

AR heat maps are expected to be useful in various civil engineering and construction scenarios. They are especially effective in the following situations.

• Earthworks and land development: In land development and earthworks, comparing the design ground elevations with the current state lets you know “how much more soil should be excavated or placed.” Since AR heat maps show surface elevation differences in color, overfilled areas or incomplete excavation spots are visible at a glance, enabling efficient soil quantity management.

• Road paving: For paving works, heat maps can be used to confirm final pavement elevation and smoothness. Comparing the design longitudinal and cross profiles with measured data highlights areas with insufficient pavement thickness or bumps in color, allowing even slight unevenness to be detected and corrected for a smooth surface.

• Slope shaping: The slopes formed by embankment or cutting can be checked for gradient and shape using AR heat maps. By comparing the design model with the as-built, you can identify parts that protrude more than planned or parts that were overcut and are hollowed out. Even on dangerous steep slopes, you can grasp the situation by scanning from a distance, enabling safe and reliable slope management.

• As-built of structures: For tunnels, bridges, concrete structures, and the like, comparing the design shape and the as-built after construction lets you detect insufficient concrete thickness or protrusions via heat maps. Differences of a few centimeters that are hard to notice with the human eye are visualized by color-coding, making quality inspection and as-built management of structures more precise.

How to create an AR heat map

To actually create an AR heat map, follow steps like the ones below.

• Preparation of design data: Prepare the 3D design data that will be the basis for comparison. For earthworks, this would be the design ground model (TIN data or design surface data); for structures, it would be the 3D design model of BIM/CIM. In other words, first prepare the “ideal shape (target shape) data.”

• 3D measurement of the current condition: Next, measure the actual shape after or during construction in 3D. Point cloud measurement has become mainstream recently, and methods include terrestrial laser scanners, drone photogrammetry, and LiDAR-equipped smartphones to scan the entire site. A particularly notable method is combining a compact RTK receiver with a smartphone to collect point clouds while walking. This does not require heavy tripod equipment or drone flight permission, and anyone can acquire high-accuracy point cloud data as if recording video. Obtain current data using methods appropriate to the scale, from wide-area terrain to structural details.

• Differential calculation and heat map generation: Overlay the acquired current-data and design-data in dedicated software or cloud services, and compute the differences. Calculate the elevation differences or displacement amounts at each point and generate a color-coded heat map representing the results. A single button can automatically create a colored difference map, preventing human calculation errors.

Real-time verification of construction status with AR display

Once a differential heat map is created, use AR display to present it clearly on site. By overlaying the heat map or difference model onto the camera view of a smartphone or tablet, a colored virtual model appears in the real landscape. For example, overlay a translucent red fill model on areas that still need excavation and a translucent blue region on areas that have been overcut and are too low. By viewing the site through the screen, soil buildups and depressions that are not normally visible are indicated by color, allowing you to understand the situation at a glance. Rather than spreading paper drawings and verbally saying “lower this ground elevation by ○ m (○ ft)…”, you can point to the screen and say, “Let’s dig down this red area by 20 cm (7.9 in),” enabling the machine operator to intuitively grasp the amount of work. When clients or site supervisors visit, they can also check the current progress and differences from the design on the spot via their smartphones. As-built information that was previously explained with reports and drawings can be shared as a visual part of the scene through AR, greatly improving the persuasiveness of explanations. In this way, AR visualization dramatically smooths on-site communication and creates an environment where everyone can share the same understanding and respond quickly.

In practice, at one land development site, the team performs a point cloud scan of the current state with a smartphone once a week, automatically calculates soil volume changes from the previous week in the cloud to generate a heat map, and shares it at morning meetings. As a result, the whole site immediately understood which areas should be prioritized for excavation or filling. Tasks that previously took the surveying team a whole day or more to measure cross sections, create CAD drawings, and calculate soil volumes are now completed by the site representative in about 30 minutes after introducing smartphone RTK. Faster feedback and information sharing have reduced waiting times and contributed to schedule compression.

Summary

Visualizing sites with AR heat maps has the potential to greatly change construction management and quality control. By overlaying information that was hard to grasp from paper drawings and numbers onto the actual scene, even less experienced technicians can accurately understand the current state and make appropriate decisions. Combined with cloud technologies, real-time data sharing between site and office becomes possible, aligning with the construction DX that *i-Construction* aims for and enabling smarter site operations. It does not mean drawings are never used, but using AR heat maps significantly reduces the need to spread drawings during site work and decreases communication loss. Technology can complement areas that relied on the intuition and tacit knowledge of veterans, bringing an era in which everyone can achieve high-quality construction within reach. AR heat maps are becoming a new standard in the on-site DX era; consider actively adopting them. In the future, it will be common to rely on digital information rather than paper drawings. Using such advanced technologies can be a major solution to labor shortages and skills succession issues. For improved operational efficiency and quality, try introducing AR heat maps on your site.

Simple surveying with LRTK

Even if you have seen how AR heat maps and high-accuracy positioning and point cloud measurement work, you may feel that putting them into practice yourself seems advanced and difficult. That’s where the all-in-one solution LRTK is worth noting. LRTK is a surveying DX platform that combines a high-precision GNSS receiver, a smartphone app, and cloud services, and it has been developed as a simple surveying tool that can be used even by non-specialists.

With LRTK, a palm-sized RTK-GNSS receiver attached to a smartphone provides centimeter-level (half-inch accuracy) high-precision positioning while the smartphone camera or LiDAR scans the site to generate point cloud data, and the cloud performs soil volume differential calculations and heat map visualization in a one-stop workflow. In other words, it is a package that includes all the functions necessary to create AR heat maps. The UI is designed so that site personnel can easily operate it on their own smartphones, and even first-time users can learn to operate it with short training.

By introducing such a tool, tasks that were previously outsourced—such as as-built surveying and soil volume calculation—can be completed by in-house site staff. This contributes to cost reduction and, through the utilization of accumulated data, can enhance the construction PDCA cycle. Above all, when site staff themselves master digital technologies, the way work is done changes and productivity improves dramatically. Even for a single as-built check using AR heat maps, solutions like LRTK enable a system where you can “grasp more quickly and accurately and share on the spot.” A democratization of surveying technology is beginning, and site DX is accelerating. If you feel challenges in survey or construction management efficiency and digitalization, try a smartphone surveying system once.

FAQ

Q: What data is needed to create an AR heat map? A: Basically, if you have the two 3D datasets you want to compare, you can generate a differential heat map. For example, a combination of “the model data at the design stage” and “the point cloud data measured after construction” works. Overlaying datasets such as terrain point clouds before and after construction or a design model and as-built point cloud allows you to visualize differences at each point (cut-and-fill amounts or displacements) with color.

Q: Do I need special equipment or software for AR display? A: No, a commercially available smartphone or tablet is usually sufficient. AR display is performed through a mobile device’s screen, so as long as a compatible app is available, dedicated AR glasses are not required. If you want to share with a large number of people on site, consider using a tablet’s large screen or mirroring to a TV screen.

Q: Can accuracy be ensured with smartphone surveying? A: Yes, modern smartphone surveying technology can achieve high accuracy within a few centimeters (a few inches). In particular, using RTK-GNSS can provide positional accuracy comparable to traditional total station surveying. Positioning accuracy depends on satellite reception conditions, but with Japan’s augmentation satellite services and the spread of networked RTK, stable centimeter-level accuracy outdoors is increasingly achievable. In many actual sites, smartphone + RTK has enabled as-built measurement within a few centimeters (within a few inches).

Q: Can site staff use it? Is specialist knowledge required? A: Yes, it is designed so that site staff can use it. Smartphone app UIs are intuitive and do not use difficult technical terms, so anyone can follow on-screen instructions. With short training or a manual, beginners can learn quickly. There are growing examples of construction management staff without surveying expertise conducting point cloud measurement and differential checks themselves and improving efficiency.

Q: What are the advantages compared to drone surveying? A: Drone aerial surveying can measure large areas quickly, but it has operational constraints such as weather and no-fly zones. Smartphone surveying can be done on the ground even in rain and requires no special permits, so it has superior mobility. The ease of measuring on demand is a great advantage. Also, ground-level scanning captures details such as wall surface irregularities that drones may have difficulty capturing. Each method has its strengths, but the convenience of completing tasks with just a smartphone is a powerful asset on site.

Q: Is the introduction cost high? A: Compared to assembling a full set of large surveying instruments and dedicated software, solutions using smartphone RTK can be started at a significantly lower cost. You can use your existing smartphone and only need a small GNSS receiver and a subscription service, greatly reducing initial investment. Considering that surveying tasks previously outsourced can be in-sourced, the total cost-effectiveness is very high.

Q: Even if you say “no drawings needed,” can you really do without drawings? A: AR heat maps greatly reduce the need to refer to drawings on site, but the design drawings themselves are not rendered unnecessary. They are an auxiliary tool to visualize the site based on data, and official inspection records and pass/fail judgments will still use drawings and numerical records as before. However, because AR displays allow everyone to visually confirm differences at the same location, on-site consensus building and reporting/explanations become much easier. In other words, drawings remain necessary as final verification, but you can achieve a “no-drawing” effect in the sense that you no longer need to constantly compare drawings during on-site work.