The On-site Revolution Begins! Absolute-Coordinate AR Opens Up the Future of 3D Drawing Visualization

Table of Contents

⒈ Challenges of Conventional AR Technologies ⒉ High-Precision Positioning with Absolute-Coordinate AR Enabled by RTK ⒊ Use Cases for Overlaying 3D Drawings in AR ⒋ The Future of Absolute-Coordinate AR Accelerating On-Site DX ⒌ Starting On-Site AR with Simple Surveying Using LRTK ⒍ FAQ

In recent years, the technology to overlay 3D drawings with AR on construction and civil engineering sites has rapidly gained attention. AR (augmented reality) is a technology that overlays digital information onto real-world scenes through smartphones or tablets. Because it allows completed images that were previously only viewable as drawings or 3D CAD models to be intuitively grasped by overlaying them onto the actual site scenery, many benefits are expected, including prevention of construction errors, smoother consensus-building among stakeholders, and improved work efficiency. In particular, if three-dimensional design data (BIM/CIM models, etc.) can be displayed on site as-is, they can be used widely—from pre-construction planning simulations to on-site progress checks during construction and post-completion verification—and therefore are attracting significant attention from people in all roles involved in surveying work, such as civil construction managers, design personnel, survey technicians, and municipal staff.

However, conventional AR technologies have issues with alignment accuracy and the amount of effort required, creating a barrier to full-scale use in the construction sector where precision is demanded. In this article, we organize those conventional AR challenges and explain how RTK-GNSS-based absolute-coordinate AR can transform work on site as a solution. We also describe concrete use cases for AR overlays and future prospects, and finally introduce the solution LRTK-based simple surveying that allows anyone to easily deploy high-precision AR in the field.

Challenges Faced by Conventional AR Technologies

Many AR apps for smartphones and tablets currently in use display virtual objects by capturing the surroundings with the device's camera and sensors while tracking the device's movement. However, this conventional AR had several issues when used on construction sites.

• Manual alignment required: When overlaying a 3D model onto the real world, initial calibration work was required, such as placing and scanning QR code markers at each site or manually positioning the model to match known reference points. The effort of performing alignment at every site is a major burden.

• Model drift: The location accuracy of ordinary smartphone GPS is only on the order of a few meters, and AR apps render virtual models based on the device’s relative movement (relative coordinates), so as you move across a wide area small errors accumulate and the displayed position drifts. A model that was initially placed correctly tended to diverge from the real object over time or with walking.

• Insufficient accuracy: On civil engineering and construction sites, positional errors of even a few centimeters can be problematic. However, typical AR has difficulty achieving that level of high accuracy, and there was the issue that it is essentially unusable in situations requiring millimeter-level precision.

As described above, conventional AR technology alone can sometimes fail to sufficiently meet the accuracy and stability required on construction sites, and even when 3D models are overlaid they can only be used as a rough guide. In response to this, a new approach called absolute-coordinate AR has emerged and will be introduced next.

RTK-enabled absolute-coordinate AR for high-precision alignment

Absolute Coordinate AR is an AR technology that places virtual models based on absolute positional information such as geodetic coordinates used in surveying or the coordinates of known reference points. The key to achieving this is high-precision positioning using RTK-GNSS (real-time kinematic satellite positioning).

Using RTK-GNSS, the typical GPS positioning error of several meters (several ft) can be reduced to a very small range of just a few centimeters (a few in). By using dedicated high-precision GNSS receivers and correction signals from a base station, centimeter-level positioning (cm level accuracy (half-inch accuracy)) becomes possible even on smartphones. By incorporating RTK-derived position information into AR apps, the displayed position of 3D models can be aligned with the absolute coordinates specified in the design drawings.

As a result, no prior calibration is required. Once the model's position in absolute coordinates has been set, you can bring a device to the site and immediately display the virtual model in place. You can start overlaying 3D drawings without the tedious reference-alignment work. Also, because the model is fixed to real-world coordinates, the model remains in the correct place even when the user moves. For example, if you approach the installation location of a bridge pier, a full-scale bridge pier model will appear to rise from the bare ground at the exact position and height; in this way, the real and the virtual align perfectly with no offset.

Using absolute-coordinate AR in this way, you can overlay 3D models with high accuracy even across wide areas. What was previously difficult—the accurate projection of 3D models across an entire site—becomes a reality, enabling dramatic efficiency improvements in construction management and surveying. The main advantages are summarized as follows.

• Eliminating positional drift: High-precision GNSS minimizes positional errors, so models won't move on their own or gradually drift. Even with long-duration or long-distance use, the AR display remains stable and does not deviate from the initial position.

• Anyone can place models accurately: Because it is based on absolute coordinates, workers no longer need to make manual fine adjustments. No special marker placement or expertise is required, and as long as they have a device, anyone can make the model appear in the correct position.

• Reduction of on-site rework: Because work can proceed with virtual models placed at the design-specified positions, you can prevent mistakes discovered later like "the position was wrong." As a result, this leads to reduced rework (backtracking) and improved quality.

Use cases for overlaying 3D drawings in AR

Now, let's look at several representative scenarios to see how "overlaying 3D drawings" with absolute-coordinate AR can actually be useful on-site.

Pre-construction Planning Simulations and Design Checks

Before construction, you can display the design-stage 3D model on site with AR and simulate the plan, using it for preliminary checks. For example, in road construction you can overlay 3D models of the planned road and bridge onto the site's terrain to verify whether they fit as designed. Because it allows you to intuitively grasp terrain clashes or inconsistencies with the surrounding environment that drawings might not reveal, it is effective for identifying risks before construction.

Also, while meetings were traditionally held with stakeholders using two-dimensional drawings, AR allows the client and on-site staff to review the finished image together on site. Since everyone can see the same expected outcome while discussing, it also helps eliminate discrepancies in understanding and streamline consensus-building.

• Prevention of construction errors: By detecting discrepancies between the design and site conditions at an early stage, it reduces the risk of proceeding with work in the wrong location.

• Sharing among stakeholders: By sharing a life-size model of the completed work on site, it aligns the client’s and contractor’s expectations and smooths the explanation and approval processes.

• Consideration of plan revisions: By viewing the model in AR, if problems are found, design changes or countermeasures can be considered before construction. This contributes to planning with less rework.

Progress monitoring and quality control during construction

Even during construction, overlaying 3D drawings with AR proves powerful. You can compare the design model on-site with in-progress structures and temporary installations, and verify progress and accuracy in real time.

For example, before pouring concrete, you can display the as-designed final model in AR over the assembled rebar and formwork. This allows you to tell at a glance whether the rebar positions and the formwork heights match the design model. If there is any misalignment, it can be corrected before pouring. This lets you address mistakes such as "the height was wrong" or "the position was off" much earlier than noticing them after pouring, thereby reducing rework.

Similarly, even at a stage where construction has progressed to some extent, you can overlay the completed model on top of the structure being built to check the as-built condition. You can verify on-site via AR whether the as-built (finished product) matches the design in dimensions and position, and ensure quality by immediately correcting any deficiencies. Because supervisors and inspectors can view the AR imagery together while pointing out issues and confirming, this prevents on-site communication loss and facilitates smooth consensus on corrective actions.

• Early detection of construction errors: Discrepancies that used to be discovered only after completion or after waiting for survey results can now be detected instantly during work with AR displays.

• Immediate quality verification: Because the finished work can be compared to the model as the work progresses, you can verify in real time whether it meets quality standards.

• Efficient supervision and inspection: It reduces the time spent comparing drawings and the actual work, and because everyone on site can share the same AR information, communicating issues and confirming corrections is more efficient.

Post-Completion Verification and Infrastructure Maintenance and Management

Overlays using absolute-coordinate AR can also be applied to inspections after construction completion and to the maintenance and management of infrastructure facilities. For example, at project completion, if you display the as-designed 3D model in AR over the finished structure and perform as-built verification, you can intuitively check whether the final deliverable matches the design. Inspections of critical structures still require detailed measurements, but by using AR to get an overall view you can carry out verification tasks more efficiently.

During routine infrastructure inspections, by overlaying past inspection data and design drawings onto the current structure using AR, you can visually grasp changes over time. For example, in bridge inspections, projecting previous crack locations with AR and comparing them to the present makes it easy to confirm crack progression. Also, in road excavation work, displaying maps of buried pipes and cables on site with AR and visualizing invisible underground buried objects can prevent accidents that inadvertently damage lifelines.

• Quick confirmation of as-built condition: At completion, you can use AR to survey the entire site and check differences from the design, streamlining inspection tasks.

• Visualization of long-term changes: By overlaying inspection histories onto the actual asset, the progression of deterioration and repair histories becomes immediately apparent, helping appropriate maintenance management.

• Locating underground buried objects: Pipes, cables and other utilities that are normally invisible can be located using AR displays, contributing to safer construction and maintenance.

Improving Efficiency and Reducing Labor in Surveying Operations

AR overlay of 3D drawings also streamlines on-site surveying and measurement work. This is because, with high-precision absolute-coordinate AR, simple surveying and dimensional checks can be performed on the spot without using dedicated surveying equipment.

For example, at a construction site, when you want to check whether the elevation at a given point matches the design, traditionally you had to set up surveying instruments such as a level or total station to take measurements. However, by using an RTK-enabled AR app, you can simply hold up a smartphone and compare the design model’s elevation reference with the current ground or structures. By combining the device’s tilt sensor and LiDAR functionality, you can also measure elevation differences from the ground surface, so you can instantly measure heights and positions with a certain degree of accuracy. This reduces the number of times you need to call a surveying team for minor checks and expands the range of verifications that site personnel can perform themselves.

Furthermore, by using the design positions displayed in AR as a reference when driving stakes and marking, the simplification of surveying (setting-out) work can also be expected. Even inexperienced workers only need to mark the positions indicated in AR, allowing survey points to be set quickly while avoiding reliance on individual expertise.

• On-site dimension verification: By using the overlaid model as a ruler to visually measure differences from the current conditions, users can perform quick self-checks.

• Reduced surveying workload: In situations where simple measurements suffice, expensive surveying instruments are not required, saving personnel and time.

• Layout positioning support: By referencing the positions indicated by AR, even non-experts can carry out highly accurate layout positioning tasks, leading to improved overall productivity.

The Future of Absolute-Coordinate AR to Accelerate On-Site DX

Overlaying 3D drawings using absolute-coordinate AR is thus bringing about a change that could rightly be called "on-site revolution". Even within the momentum of *i-Construction* and construction DX promoted by the Japanese government, high-precision construction management and surveying methods that leverage AR+RTK are beginning to become the new standard. So how will on-site AR utilization evolve going forward?

First, a technical challenge is dealing with environments where GNSS (satellite positioning) is difficult to use. Under elevated structures, inside tunnels, or in dense urban areas surrounded by tall buildings, satellite signals can be blocked or reflected, causing high-precision positioning using RTK to be unstable. To maintain AR accuracy in such environments, measures like pre-calibrating at known points on site or supplementing with local positioning systems (total stations or simple beacons, etc.) will be challenges going forward.

There are also device-related issues when using smartphones outdoors. For example, in strong sunlight the screen can be hard to see, and the device can become overheated and operate unstably. These problems are also points that must be resolved to enable wide deployment in the field.

On the other hand, these challenges are gradually being resolved thanks to technological advances. In particular, on the device side, companies are progressing in the development of AR glasses and MR headsets. In the future, rather than handheld smartphones, people will wear helmet-integrated smart glasses and be able to use AR displays with both hands free. Workability should further improve, for example allowing workers to check projected 3D drawings even while carrying heavy loads. GNSS is also improving year by year as the number of satellites increases and augmentation signals are enhanced. In Japan, a centimeter-level augmentation service via the Quasi-Zenith Satellite System has been commercialized, and high-precision positioning in mountainous areas and urban areas has become more stable than before (centimeter-level augmentation service (cm level accuracy (half-inch accuracy))). Furthermore, with the spread of 5G and the development of cloud services, we can expect a future where multiple people can share position data and video captured on-site in real time, and synchronize the same AR space with experts at remote locations to confirm work.

The future of 3D drawing display brought by absolute-coordinate AR is not merely a story about a novel gadget; it holds the potential to transform on-site work itself. As drawings and surveying become digitized, this technology brings scientific backing and efficiency to site management that has until now relied on human intuition and experience. If hardware and software are further developed, new work styles such as paperless construction, eliminating the need to carry drawings, and remote construction management, allowing sites to be monitored and directed from afar, will become increasingly realistic.

On-site AR Starting with Simple Surveying Using LRTK

Finally, as a solution for easily leveraging these absolute-coordinate AR technologies in the field, we introduce LRTK. LRTK is a smartphone-compatible absolute-coordinate AR system that utilizes high-precision RTK-GNSS. By attaching a dedicated compact GNSS receiver to a smartphone and simply launching the corresponding app, anyone can instantly perform AR displays with centimeter-level accuracy (cm level accuracy, half-inch accuracy). No complex configuration or tedious initial calibration is required; when you arrive on site, you can immediately overlay the design model in place.

With this LRTK, high-precision on-site verification that previously required relying on specialist surveying teams can be performed on the spot by construction managers and designers themselves. It can be used for a wide range of applications such as construction management, surveying, and infrastructure inspection, and supports data sharing via the cloud, making it easy to review information recorded on site while in the office. The LRTK series also supports the Ministry of Land, Infrastructure, Transport and Tourism’s i-Construction initiative, making it a practical solution that strongly supports DX (digital transformation) in the construction industry.

LRTK is already being introduced at a variety of sites, from major construction companies to local governments. Experience for yourself the absolute-coordinate AR — a "revolution on the jobsite" — at your workplace. What used to be cumbersome surveying and as-built inspections becomes remarkably simple, letting you take site management to the next stage.

FAQ

Q: What do you need to overlay 3D drawings in AR? A: Basically, you need the 3D design data and a smartphone or tablet that can run a compatible AR app. To achieve construction-grade accuracy, it's ideal to have GPS correction equipment or an RTK-capable GNSS receiver. For example, using a high-precision positioning device such as an LRTK that can be attached to a smartphone will allow you to display models with an accuracy of a few centimeters (a few in).

Q: What is the positioning accuracy of absolute-coordinate AR? A: When using RTK-GNSS, theoretically the error is within about 1–2 cm (0.4–0.8 in). However, because it depends on satellite reception and the environment, in practical use you should assume accuracy on the order of several cm to several tens of cm (several in to several tens of in). Even so, this is far more accurate than conventional GPS (errors of several meters (several to several tens of ft)) and is at a level that can be used without problems in many construction management and surveying tasks.

Q: Can people without specialized knowledge use AR overlay technology? A: Yes. The operation of AR apps is intuitive, and by following the on-screen guidance while looking at a smartphone display users can bring up models. Even with absolute-coordinate AR, the cumbersome calibration that was previously required is no longer necessary, so there is less trouble with initial equipment setup. It is designed so on-site staff can start using it after a short training session.

Q: What happens in places where GNSS cannot be used, such as inside tunnels or in densely built-up urban areas? A: Unfortunately, in environments where positioning information from satellites cannot be obtained, the accuracy of absolute-coordinate AR also degrades. In such cases, auxiliary measures are required, such as performing manual corrections using local control points on site or aligning models by using nearby landmark structures. Recent technologies are advancing research into integration with local positioning systems that work indoors and into estimating positions by matching pre-scanned point cloud data, so it is expected that AR overlays will become possible in a wider range of environments in the future.

Q: Do you need expensive specialized equipment to display 3D drawings in AR? A: No. Previously, special hardware or headsets were required in some cases, but now high-precision AR can be achieved with a combination of consumer smartphones and compact GNSS receivers. For example, LRTK is one solution that works with such everyday devices. Because you can start with a handheld device instead of a special head-mounted display, the initial barrier to adoption has been greatly reduced.