Will AR Misalignment Cause Construction Errors? The Latest Countermeasures with LRTK!

Table of Contents

• Increasing AR Use on Construction Sites

• Construction Errors Caused by AR Misalignment

• Main Causes of AR Misalignment

• Conventional Measures to Prevent AR Position Drift

• “Non-shifting AR” Realized by High-precision Positioning

• Simple Surveying and AR Use with LRTK

• FAQ

Increasing AR Use on Construction Sites

In recent years, the construction industry has increasingly adopted AR (augmented reality) technology, and initiatives to overlay drawings and 3D models directly on site are growing. By simply pointing a smartphone or tablet, you can project the finished image and design intent onto the actual scene, allowing intuitive sharing of spatial awareness and expected finishes that are hard to convey with drawings alone. Because everyone—from site supervisors to craftsmen and owners—can view the same AR imagery to confirm the finished appearance, AR is expected to help prevent mistakes caused by “differences in perception.” For example, previously a small positional difference on a paper drawing might be overlooked, resulting in a completed structure protruding a few centimeters from the boundary. With AR, however, you can visualize boundary lines and building positions through your phone before foundation work, notice even a few centimeters (a few in) of deviation, and correct it in advance. In this way, AR use is expected to significantly contribute to preventing construction errors.

Construction Errors Caused by AR Misalignment

On the other hand, if AR displays are themselves misaligned with the real-world positions, the technology could introduce new construction errors. Workers may trust the AR digital information and proceed, only to find the displayed positions were incorrect, leading later to “re-marking” or “rework.” Some site personnel may have experienced concerns like “I tried the phone’s AR, but the display was slightly off and I couldn’t trust it.” If AR display misalignment is left unaddressed, AR—originally intended to prevent mistakes—can instead become the cause of mistakes. Below are representative examples of errors that can occur due to AR misalignment.

• Boundary misidentification: If the AR boundary line is displayed offset from its actual position, building placement may be misjudged, potentially resulting in structures being built outside the site boundary.

• Damage to buried utilities: When visualizing underground pipes or cables with AR, an offset display may lead to digging in unsafe locations and accidentally damaging existing infrastructure.

• Positioning mistakes: When AR indicates bolt hole locations or equipment mounting points, an offset of even tens of centimeters (tens of in) can cause work to be done in places that do not match the required dimensions, leading to rework.

As shown above, AR display position misalignment can lead to serious trouble if ignored. To use AR reliably on site, it is crucial to minimize display misalignment.

Main Causes of AR Misalignment

So why does AR misalignment occur? The main factors are as follows.

• Positioning errors: Smartphone GPS accuracy is generally said to be on the order of several meters (several ft), which leads to overall AR display misalignment. On large outdoor sites, errors of several meters (several ft) mean that even if design data is overlaid, AR models will not match the real world. Vertical errors are also significant, causing models that should be projected onto the ground to appear to float or sink below ground.

• Limits of environment recognition: AR apps use SLAM technology to estimate device pose from camera image features. However, in environments with few landmarks—such as bare lots—it's difficult to maintain accurate positioning using only the camera, and as a user moves the model may gradually drift, so what was initially aligned will slowly become misaligned.

• Heading sensor errors: Smartphone and tablet electronic compasses (magnetic sensors) can be distorted by nearby metal objects or high-voltage lines. Construction sites often contain heavy machinery and rebar that disturb magnetic fields, causing device heading errors that affect AR object orientation and position.

• Imprecise initial registration: When overlaying drawing data onto the site, it is necessary to perform position alignment (registration) between the virtual model’s coordinate system and the real survey coordinates. Many AR apps use markers (e.g., QR codes) placed on site as a reference to adjust model position, but even a small error in marker placement leaves residual error. Manual visual alignment also has limits, and with such methods it’s difficult to achieve perfect registration.

Conventional Measures to Prevent AR Position Drift

To address the causes above, the following measures have been used on sites.

• Marker-based registration: Place markers such as QR codes at positions corresponding to reference points on drawings, and have the AR app read them to correct model display positions. This is an easy initial alignment method, but it requires effort to attach markers, and if a marker is off by a few centimeters (a few in), the display will carry the same error. There is also the risk of markers shifting or peeling off due to wind or people passing by, so reliability can be lacking.

• Manual calibration at known points: Compare known reference points on site (such as survey-verified stakes) with the AR model and have users manually move/rotate the model on the device to align it. Fine-tuning at multiple points can improve accuracy to some extent, but it requires skill and it is difficult to achieve perfect alignment. Visual alignment by eye introduces subjectivity, so the same level of accuracy cannot be guaranteed regardless of the person performing it.

• Use in combination with surveying equipment: Perform critical layout tasks with conventional total stations or laser measuring devices, and use AR strictly as an auxiliary confirmation tool. While survey machines provide precise reference points and elevation, AR is used for overall visualization and interim checks. However, since AR alone cannot complete the work, this increases effort and time and can discourage AR adoption.

These conventional methods have helped minimize AR drift, but they all involve site labor and cost and are not fundamental solutions. To make AR truly accessible to anyone, a more reliable and easy-to-use “drift prevention” mechanism was needed.

“Non-shifting AR” Realized by High-precision Positioning

An approach that has gained attention recently is combining high-precision positioning technologies to realize “non-shifting AR.” A representative technology is RTK-GNSS (real-time kinematic positioning), which adds correction data to satellite positioning to reduce measurement errors to within a few centimeters (centimeter-level accuracy (half-inch accuracy)). While typical smartphone GPS can have errors of several meters (several ft), RTK-GNSS can achieve the roughly centimeter-level accuracy needed for civil engineering and construction management.

One solution developed to make RTK practical on site is LRTK. By attaching a dedicated compact antenna to a smartphone or tablet and receiving correction data (such as VRS) from a base station via the Internet, users can continuously measure their position with centimeter-level accuracy. Feeding this high-precision position information into an AR app allows automatic and accurate registration between virtual design data and the real world.

The biggest benefit of introducing high-precision positioning is that it eliminates the need for complex on-site registration work. For example, conventional workflows required aligning instruments to drawing reference points, driving stakes, and using markers for initial setup—but with LRTK you simply stand on the site with a smartphone. Because design models are projected exactly to their intended positions based on the global geodetic coordinate system, fine initial adjustments are almost unnecessary.

Moreover, centimeter-level positioning with LRTK dramatically improves AR display stability. Even when walking around a large site, models remain fixed at the correct positions without drifting or floating. With conventional AR, model positions can slowly shift as the user moves, but high-precision GNSS corrections act as the “eyes” of AR, keeping models accurately anchored. This makes AR reliable for tasks such as surveying across multiple locations and wide-area quality checks.

High-precision positioning is also effective for vertical alignment. RTK-GNSS can precisely measure elevation, so the height basis for AR-displayed models is accurate. Whether displaying the depth of underground utilities in AR or verifying embankment heights in earthworks, the displayed positions will match actual elevation relationships, improving trustworthiness.

Simple Surveying and AR Use with LRTK

LRTK serves as a platform that simply realizes high-precision positioning and the use of digital design data, supporting on-site DX (digital transformation). With only a compact antenna attached to a smartphone, you can handle everything from uploading drawing data to position correction, AR-based on-site checks, and even as-built verification using 3D scanning.

For example, upload construction drawings (CAD data or BIM models) to LRTK’s cloud in advance, start the smartphone app on site, and you can immediately display the drawings in AR for position checks. No complex equipment setup or special skills are required—intuitive operation lets you start simple surveying. Marking stake positions can be done accurately even by novices by following on-screen guides. Combined with LiDAR scanners in modern smartphones and tablets, you can instantly capture 3D point clouds of work areas to aid as-built checks and earthwork quantity calculations.

By leveraging LRTK, tasks that previously required specialized personnel for on-site surveying and checks become accessible to anyone. Visualizing drawings, boundaries, and buried utilities with AR helps prevent construction errors, while simple surveying balances site management efficiency and accuracy. If you face challenges in pre-construction position checks or error prevention, consider updating your site workflow with an AR solution using LRTK.

FAQ

Q: Do I need special equipment or expensive devices to use AR? A: No. Basic AR functions can be used with modern smartphones and tablets without additional hardware. You can start by installing a compatible app on your current device even without dedicated AR glasses. If you want to improve accuracy seriously, attaching a small GNSS antenna (for example, LRTK’s antenna) to enhance positioning accuracy will enable more reliable AR displays.

Q: Is a phone’s GPS alone sufficient for AR display of drawing data? A: For simple checks, a phone’s built-in GPS can display AR, but its accuracy is limited to around several meters (several ft). To achieve the precision required for construction, a system that corrects positions to the centimeter level—such as RTK-GNSS—is essential. For example, ordinary GPS positioning can cause wall or column locations to deviate by tens of centimeters (tens of in) from drawing positions. For important position checks, we recommend combining AR with high-precision positioning technology.

Q: How should I prepare drawing data for AR display? A: Prepare digital design files such as CAD data, BIM models, or image files. While 3D data is ideal, 2D drawings can also be displayed in AR by placing them on the ground or converting them to line data. If you upload drawing files to LRTK’s cloud, you can easily call them up on-site from a smartphone and overlay them in AR.

Q: Is AR adoption progressing in the construction industry? A: Yes. With initiatives like the Ministry of Land, Infrastructure, Transport and Tourism’s “i-Construction” and the spread of BIM/CIM, the use of AR and 3D data on site has been rapidly expanding. Not only large general contractors but also small and medium-sized projects are increasing examples of tablet-based drawing sharing and AR construction checks. With more digitally native engineers and labor shortages as a backdrop, AR is beginning to contribute to site improvement as an easy-to-use tool for anyone.

Q: Can I rely solely on AR for position checks and omit conventional surveying? A: AR is an auxiliary tool. We recommend combining it with conventional surveying instruments for final inspections and critical reference setups. However, AR is very effective for interim checks and minor alignments during construction. Routinely use AR to monitor deviations between design models and actual construction, and perform traditional surveys at key stages to balance efficiency and quality while preventing mistakes.

Q: How much cost and effort are required to introduce AR on site? A: The barrier to AR adoption is not as high as you might think. You can use existing smartphones or tablets, and many AR apps are low-cost or free. Even when adding high-precision positioning, compact GNSS antennas (such as LRTK) are more affordable than total stations and other surveying equipment, and no special license is required. Some effort is needed up front to digitize design data into 3D and upload it, but once workflows are established, on-site operations are simple. Considering the labor and rework risks of conventional surveying, AR adoption can be well worth the investment. You can also introduce AR gradually—start with small projects or specific processes and expand as the site becomes accustomed. As industry-wide digitization of drawings progresses, AR’s benefits will increase, so we recommend incorporating AR into your site where feasible.