Smartphone turns into a surveying instrument: Next-generation construction management realized by LRTK and AR heat maps

The evolution of smartphones and AR (augmented reality) technology is creating a new wave in surveying and construction management on construction sites. A small device that attaches to a smartphone, LRTK, now enables centimeter-level high-precision positioning and 3D scanning on a single smartphone—functions that previously required dedicated surveying instruments—so smartphones are literally transforming into “surveying instruments.” In addition, the on-site ability to overlay design data with as-built conditions and display differences in color through an AR heat map makes it possible to intuitively check workmanship on the spot and immediately issue corrective instructions.

This article explains the next-generation construction management enabled by LRTK and AR heat maps, describing the challenges of conventional methods and how the new technologies solve them, the benefits they bring to sites, and concrete use cases. It is intended for those involved in civil engineering and construction management or surveying, municipal staff who inspect infrastructure works, and anyone interested in on-site digital transformation, presenting the new possibilities for surveying and as-built management opened by smartphones.

Table of contents

• Problems with conventional surveying and as-built management

• How smartphones and AR change the site: What is an AR heat map

• How LRTK turns a smartphone into a surveying instrument

• Benefits brought by smartphone × AR construction management

• Use cases of AR heat maps

• Conclusion: Toward simplified surveying with LRTK

• Frequently Asked Questions (FAQ)

Problems with conventional surveying and as-built management

On construction sites, measuring and inspecting the as-built shape of finished structures and ground to confirm they match the design is indispensable. However, traditional methods have many inefficiencies. Using total stations (TS) or optical levels to measure heights and thicknesses point by point, recording the numbers, then taking those notes back to the office to compare with drawings is a time- and labor-intensive process. As a result, it is not uncommon for as-built inspections to take several days to complete. These tasks also tend to rely on experienced technicians, and with staffing shortages and an aging workforce, it has become difficult to secure sufficient surveying personnel for each site. In some cases, surveying work must be done by two-person teams, which increases labor costs and complicates scheduling. Furthermore, high-precision measurements require dedicated instruments such as a TS or RTK-GNSS receiver, which typically demand initial investments on the order of several million yen, posing a high barrier for small and medium-sized firms. The ongoing costs of maintenance and management and the risk of theft are additional burdens that cannot be ignored.

Manual-centered conventional surveying also has latent human error in measurement values. Mistakes can occur when transcribing numbers recorded on site or through cumulative errors from repeated measurements, creating the risk of rework based on incorrect data. In addition, organizing measurement results and creating reports or as-built drawings is a major burden for site personnel. It takes time to digitize paper records and translate them into drawings, and during that time subsequent work often proceeds on site, so problems are frequently discovered late. For example, even if pavement thickness falls below specifications or the slope of embankment is insufficient, traditional methods make it difficult to notice on the spot, and such issues may only become apparent after drafting the drawings later. By the time problems are discovered, concrete may already have hardened or heavy equipment may have been removed, leading to extra costs and man-hours for remedial work.

Thus, conventional construction management and as-built inspection have lacked immediacy and imposed significant personnel and cost burdens. Valuable site data that is collected is often underutilized, serving only as attachments to reports. To solve these problems, a new approach that allows accurate and intuitive grasping of as-built conditions in real time on site was required.

How smartphones and AR change the site: What is an AR heat map

AR (Augmented Reality) technology has recently attracted attention as a trump card to solve these issues. AR is a technology that overlays three-dimensional digital information onto camera images from smartphones and other devices; while it once felt like an experimental cutting-edge technology, improvements in mobile device performance have made it practical for everyday construction management. The latest iPhones and iPads include high-performance cameras and LiDAR sensors, and with dedicated apps it is now possible to intuitively check as-built conditions on site. Industry DX initiatives such as the Ministry of Land, Infrastructure, Transport and Tourism’s “i-Construction” also support this trend, and AR is increasingly expected as a powerful solution that enhances both site efficiency and quality.

How does smartphone AR actually help on site? Turning checks that used to be done on drawings into on-site “visualization” of digital information enables direct, immediate checks and brings various benefits. Below are some typical use cases.

• AR display of design models: 3D design data of buildings and civil structures (BIM/CIM models, etc.) can be overlaid onto the site scenery so that placement and dimensions can be intuitively confirmed on the spot. For example, before construction, the planned building model can be displayed in AR on the ground for layout/setting out, or during construction you can compare through the camera whether columns or walls have shifted from design positions. Discrepancies between the design image and the actual finished appearance that are hard to grasp from drawings or traditional surveying instruments can be immediately perceived in the real space with AR.

• AR heat map display of as-built differences: Initiatives are underway to compare three-dimensional as-built data (point clouds or survey data) acquired after construction with design data in the cloud and present deviations as a color-coded heat map for on-site confirmation. If a heat map automatically generated in the cloud is downloaded to a smartphone and overlaid on the camera image, it becomes immediately clear which areas are higher or lower than the design. For example, you can evaluate the finished height of embankments or development sites, or the pavement thickness and slope of roads, in a planar manner and instantly correct defective areas, accelerating the PDCA cycle of construction management. Previously, even if numbers or drawings were used to create a heat map, locating the problem spot on site required re-setting out or marking; however, high-accuracy AR allows the heat map to be overlaid directly onto the real scenery so mismatched areas are obvious at a glance and corrective work can begin immediately. The baseline values for the heat map colors and the grid spacing displayed can be adjusted, allowing results to be visualized in a readable format tailored to the application.

• AR透視 of buried assets: The positions of pipes and structures buried underground can be displayed as if seen through the surface even after paving hides them. For example, in sewer pipe works, scanning the pipe with a smartphone before backfilling and saving that scan as a point cloud with centimeter-level position coordinates in the cloud makes it possible for anyone to determine the pipe alignment and depth simply by pointing a smartphone at the site after backfilling. Compared to the traditional method of consulting drawings or searching for marked positions on the road, being able to instantly find buried assets on site helps prevent construction errors and improves safety.

• Other applications: AR is expected to be used in a variety of other on-site tasks. For heavy equipment operation, AR can visualize work areas and excavation depth criteria to assist guidance; concrete placement locations can be virtually marked in advance and shared; and for training, AR reproductions of real sites are being used for safety drills and procedure familiarization. The applications continue to expand, but especially noteworthy is the combination of as-built management and AR—i.e., AR heat maps—for immediate on-site checks, which is a use case that yields tangible benefits right away.

How LRTK turns a smartphone into a surveying instrument

A key technology that makes the AR applications described above easy to realize on site is the innovative solution called LRTK. LRTK refers to attaching a compact high-precision GNSS receiver (antenna) to a smartphone, turning the smartphone into a surveying device with centimeter-level accuracy. Traditionally, the accuracy of built-in smartphone GPS has been limited to errors of several meters, which is insufficient for AR alignment. Earlier general AR systems also required placing markers on each site and calibrating the camera, which is unrealistic across wide construction areas. LRTK uses RTK-GNSS (real-time kinematic positioning), applying correction information from a base station in real time to reduce positional measurement errors to the centimeter level. While RTK has long been used in surveying, miniaturization of receivers in recent years has made RTK-capable GNSS devices that can be attached to smartphones available. Combining a smartphone with such a device allows the terminal’s position to be measured on Earth coordinates to the centimeter, enabling marker-less accurate placement of virtual design models and heat maps in the real world.

LRTK hardware integrates a high-sensitivity GNSS antenna, receiver, and battery into a palm-sized compact design and connects to smartphones via Bluetooth or Wi‑Fi (compatible with both iPhone and Android). By installing a dedicated LRTK app on the smartphone and pairing with the device, satellite signal reception and RTK correction acquisition begin immediately, and high-precision positioning within a few centimeters can start without special setup. It also supports Japan’s Quasi-Zenith Satellite System “Michibiki” and its centimeter-level augmentation service (CLAS), so as long as Michibiki signals can be received, centimeter-level positioning can be maintained even in mountainous areas or disaster sites with no communication coverage. LRTK Phone has been introduced on the Cabinet Office’s official site as a Michibiki-compatible product, and its technological capability has drawn official attention.

Moreover, LRTK links with cloud services to enable on-the-spot upload of acquired positioning data and photos. For example, photos taken with a smartphone can automatically have centimeter-precision latitude/longitude and elevation plus time and notes attached and be saved and shared in the cloud instantly. This enables real-time construction management such as checking as-built data collected on site from the office. With LRTK optimized in both hardware and software, anyone can easily perform centimeter-level surveying and record as-built conditions without being a specialized surveyor.

LRTK comes in several product lines according to use, and a representative one is the smartphone-attachable device LRTK Phone. The main functions and features achievable with this device are summarized below.

• Centimeter-level high-precision positioning: Although using a smartphone, RTK-GNSS dramatically improves positioning accuracy so errors are kept to a few centimeters (at best about 8 mm (0.31 in)). In addition, support for Michibiki’s CLAS signal ensures stable centimeter-level accuracy even in mountainous or communication-outage sites.

• 3D point cloud measurement and earthwork volume calculation completed on the smartphone: By utilizing the LiDAR scanner and cameras built into iPhone and iPad Pro, large point cloud data can be easily acquired simply by scanning the surroundings. From the acquired point cloud, volume and area calculations can be performed instantly, so you can immediately compute earthwork volumes for embankment or excavation on site. This can be applied to as-built checks for machine earthwork or measuring the burial depth of pipes; tasks that used to rely on dedicated software can now be completed with a single smartphone.

• Overlaying design data via AR projection: Using the high-precision positioning information obtained by LRTK and the device’s orientation/pose data, elements on design drawings or 3D models can be accurately overlaid onto real space (AR projection). Because you can compare design data and as-built conditions on the smartphone screen and confirm immediately, you can judge in real time whether construction is proceeding according to design and issue corrective instructions on the spot if discrepancies are found.

• Automatic recording and sharing of positioning data: Coordinates of measured points and photos/notes taken are all recorded on the smartphone with position and time information and can be shared instantly within the team via the cloud. This eliminates the need to re-enter site-collected as-built data in the office, and development is underway for features that generate reports with one click (to be provided in the future).

• Point cloud data with position coordinates at centimeter-level accuracy (cm level accuracy (half-inch accuracy)): For example, scanned pipes saved as point clouds include centimeter-level coordinate information, enabling post-backfill visualization and verification on site.

Benefits brought by smartphone × AR construction management

Combining smartphones, LRTK, and AR technology as a next-generation construction management method delivers the following benefits on site.

• Real-time measurement and rapid response: Since surveying and as-built checks can be performed immediately on site, accept/reject judgments and corrective instructions that previously had to wait until the next day or later can be made in real time. Detecting issues instantly and correcting them immediately after construction minimizes rework and prevents schedule delays.

• Reduced work time and increased efficiency: Because the flow from measurement to verification is digitalized and completed on site, substantial time savings are achieved. There is no need to wait for the surveying crew to arrive or for drawing checks in the office; the responsible person can measure and verify whenever needed, reducing unproductive waiting time.

• Labor savings and response to technician shortages: With surveying and as-built checks possible using a single smartphone, tasks that originally required two people can be handled by one. Even with a shortage of experienced surveyors, less-experienced personnel can perform a certain level of surveying and checks by following intuitive AR displays. Dependence on specialized skills decreases, enabling limited personnel to manage sites.

• Cost reduction and reduced capital investment: You can substitute expensive total stations and GNSS equipment with a combination of a smartphone and an LRTK device, reducing the initial equipment investment burden. If work previously outsourced to external surveyors can be handled in-house with simple means, those outsourcing costs are also reduced. Preventing rework also significantly reduces unnecessary construction expenses, leading to overall construction cost compression. This makes particular economic sense for small and medium-sized contractors and organizations managing many sites.

• Improved accuracy and quality assurance: Strict GNSS position corrections and 3D scanning dramatically improve the accuracy and reliability of on-site measurement data. Human errors and oversights are reduced, making it easier to ensure construction quality per the design. Because AR heat maps allow planar quality checks, subtle height differences and slope defects that were previously hard to detect can now be identified, raising overall construction precision.

• Utilization of digital records and information sharing: Because point cloud data and geotagged photos and other information acquired on site are all digitally recorded and stored, additional measurements needed later can be reproduced from the data. The tedious process of transcribing paper records is eliminated, and report creation is streamlined, significantly reducing the time required to prepare documentation. With cloud-based sharing between site and office and among stakeholders, progress and quality can be checked remotely, and 3D models can be reviewed together in meetings to reach consensus—facilitating smooth communication. Reducing information transmission lag enables the entire team to make quick and accurate decisions.

Use cases of AR heat maps

The combination of smartphone surveying and AR heat maps can be applied widely: on-site checks of thickness and slope in road pavement works, control of ground elevation in embankment and land development, verification of dimensions and positions in bridge and building works, and recording and visualization of buried utilities such as water and sewer pipes. Its utility spans all aspects of civil construction, making it a practical simple-measurement and inspection tool not only for contractors but also for municipal staff responsible for infrastructure maintenance.

Conclusion: Toward simplified surveying with LRTK

Smartphones combined with LRTK and AR heat maps are beginning to permeate sites with a next-generation construction management approach that overturns conventional wisdom. The many benefits described in this article—shorter time for surveying and as-built confirmation, labor savings, and quality improvement—are already being demonstrated, representing a strong tailwind for the civil engineering and construction industries facing manpower shortages and the need for greater efficiency.

LRTK dramatically lowers the barrier to surveying, and the era of simplified surveying—where anyone with a smartphone can easily perform high-precision measurements—has become a reality. This is an opportunity to move beyond management based on experience and intuition toward data-driven smart site operations. By proactively adopting this new technology that transforms smartphones into surveying instruments, why not realize construction management reforms on your sites that balance efficiency and quality?

Frequently Asked Questions (FAQ)

Q1. What is an AR heat map? A. An AR heat map is a technique that visualizes the deviations between as-built measurement data and design data using color coding and overlays that visualization on the smartphone’s camera image. It lets you intuitively grasp height differences and areas with insufficient thickness so you can immediately check quality on site and make corrective decisions.

Q2. Is surveying with a smartphone accurate enough? A. With LRTK-based smartphone surveying, RTK-GNSS corrections reduce errors to the order of a few centimeters. The accuracy is comparable to that of conventional expensive surveying instruments and is sufficiently practical for many civil and construction surveying tasks. Field verification has confirmed centimeter-level precision, so you can use it with confidence.

Q3. Do I need specialized knowledge or qualifications to use LRTK? A. No special qualifications are required. LRTK is designed for anyone to use: simply attach the device to your smartphone and launch the app to start high-precision positioning. Even without expertise in surveying or AR, you can perform measurements and checks intuitively by following on-screen guidance. While basic surveying knowledge makes it easier to get the most out of the system, LRTK’s ease of use means it can be operated without veteran-level skills.

Q4. What kinds of sites and works can it be used for? A. It can be used widely—from roads, land development and earthworks, and bridge/building construction to buried utility works like water and sewerage, and even post-completion maintenance. It is useful for pre-construction surveys and setting reference points, setting out and machine guidance during construction, post-construction as-built inspections, and infrastructure inspections after handover. It is applicable to outdoor large sites as well as indoor construction (such as verifying equipment installation positions).

Q5. Are there cost benefits to introducing smartphone surveying? A. Yes, the cost benefits are significant. Previously, achieving centimeter-level surveying required initial investments in instruments on the order of several million yen, but a combination of an LRTK device and a smartphone can be introduced at a vastly lower cost. Reducing the need to hire external surveyors and lowering rework rates also yields indirect cost savings. With affordable equipment that improves in-house work efficiency, smartphone-based solutions offer substantial economic advantages, especially for small and medium-sized contractors and organizations managing many sites.