Top 3 Causes of AR Misalignment! How to Prevent Errors on Site

Table of Contents

• Cause 1: Initial position offset due to device positioning errors

• Cause 2: Inconsistency from visual alignment at a single viewpoint

• Cause 3: Model drifting caused by insufficient AR tracking accuracy

• How to prevent errors on site

• Simple surveying with LRTK

• Summary

• FAQ

In recent years, the use of AR (augmented reality) technology has advanced at construction and civil engineering sites. By overlaying design drawings and 3D models onto the real-world view through a smartphone or tablet camera, AR provides a groundbreaking method for sharing the completed image and preventing construction mistakes. Also, improvements in smartphone sensors and the emergence of LiDAR-equipped models have greatly enhanced AR stability and expressive power. From site supervisors to craftsmen and owners, everyone can intuitively grasp and share “what will be where and how” by viewing the same AR imagery, preventing rework caused by misunderstandings. However, a frequent problem when using AR on site is “AR misalignment.” Virtual models that are displayed may not match the real position, appearing offset by tens of centimeters (tens of in) to several meters (several ft). Large AR display misalignments can lead to risks such as inability to construct according to design or causing misunderstandings on site. AR displays that do not match reality can instead confuse the site. For that reason, managing AR accuracy is extremely important.

So why do these position offsets occur? This article explains the top three main causes of AR misalignment and how to prevent those offsets on site.

Cause 1: Initial position offset due to device positioning errors

When AR is launched on site, the displayed model or drawing can appear to float several meters away from the actual position. This is often due to insufficient positioning accuracy of the device (smartphone or tablet). The GPS of a typical consumer smartphone can have errors of several meters, so if an AR app places a model based on that position information, the model will inevitably be offset from the actual location. Especially when displaying AR for the first time in a wide outdoor area, this positioning error can cause the entire model to be shifted laterally or to appear to float above the ground. In addition, elevation (vertical) errors can be large—around 10 m (32.8 ft)—so a model intended to be placed on the ground may be displayed suspended in the air. In high-rise urban areas or mountainous regions where GPS signals are easily blocked, positioning errors greater than usual can occur, making the initial position alignment error even larger.

Furthermore, mismatches between the coordinate settings in the design data and the local survey coordinate system can also cause large position offsets. For example, if the drawing data is drawn in a proprietary local coordinate system or the reference point settings differ, the model placed in AR will not match the site position. Because origins or reference axes that should be aligned are not the same, the entire model becomes offset. In this way, insufficient device positioning accuracy combined with mismatched coordinate systems can cause meter-scale errors of several meters (several ft) at the initial stage of AR display.

Cause 2: Inconsistency from visual alignment at a single viewpoint

When overlaying a model onto the site in AR, sometimes alignment is done by eye at that location. However, if alignment is performed based only on a single viewpoint, inconsistencies can arise when viewed from other angles. You may have experienced that a drawing and reality seem to align perfectly from one point, but when you move to another location the model appears offset from buildings or terrain. This occurs because calibration was only performed from one viewpoint, preventing precise alignment of position and orientation. Visual alignment by eye is inevitably subject to human optical illusions and perspective effects, making perfect positioning difficult. Even if something looks correct from one place, if the model is not placed at the correct height or depth, the misalignment becomes apparent as soon as the viewpoint changes.

Inadequate number of points used for on-site reference alignment can also cause inconsistency. If the entire model is not placed with correct position, orientation, and dimensions, aligning only part of it will leave other parts offset. For example, even if you align the front corner of a building model to one point on site, if the model is slightly rotated, the opposite edge at a distance will be misaligned with the real site. Additionally, if the north direction in the design data differs from the site bearing or if unit system differences distort the model scale, then a temporary visual alignment will still result in offsets elsewhere. Thus, adjusting visually without using multiple viewpoints or reference points on site will reveal position and orientation inconsistencies later. In practice, one may judge alignment is correct from a certain direction and proceed with construction, only to discover foundation position errors from another angle later, causing rework.

Cause 3: Model drifting caused by insufficient AR tracking accuracy

There are cases where an AR model that initially overlapped correctly gradually drifts away from reality as the user walks around. The model position slowly drifting during AR display is due to the limits of the device’s AR tracking accuracy. Smartphone AR functions track the device’s movement using camera images and internal sensors (gyroscope and accelerometer), but this is relative position tracking. Small positioning errors that occur with movement accumulate, and over time or with distance traveled, the virtual object’s position can gradually become inaccurate. Generally, AR apps initialize the virtual space based on the device position obtained from GPS at startup, but after that they estimate the device position only from camera image feature points and IMU (inertial measurement unit) sensor information. Because absolute position is not being corrected in real time, small offsets can accumulate as you walk over a wide area. For example, a virtual marker that initially overlapped a stake may, after walking about 10 m (32.8 ft) and viewing from another position, appear to float a few centimeters (a few in) above the ground.

Insufficient anchor (reference point) setup can also cause model drifting. Typical smartphone AR has a function to fix a virtual model’s position based on specific markers or environmental feature points. However, if the chosen anchor is lost from the camera’s view or is in an area lacking distinct features, tracking becomes unstable and the model moves. AR easily loses position on featureless plain walls or wide open ground, causing the model to slide when you move slightly. Thus, the limits of single-device tracking accuracy and unstable anchors can cause AR display alignment to degrade while moving.

How to prevent errors on site

Based on the main causes of AR misalignment, here are measures and techniques to minimize errors on actual sites. By following the points below, you can improve AR display accuracy and prevent misalignment between the model and reality.

• High-precision positioning: Do not rely solely on the smartphone’s built-in GPS; where possible, use equipment that can provide centimeter-level positioning. For example, by connecting a small RTK-GNSS receiver to a smartphone, you can obtain high-precision current position within a few centimeters. Increasing absolute position accuracy allows the initial model placement to be performed with almost no offset, greatly reducing the risk of large position errors.

• Check and correct drawing coordinates: Confirm the coordinate system of the design drawings or model data in advance and check for discrepancies with the site coordinate system. If the drawing does not have absolute coordinates (latitude/longitude or plane rectangular coordinates), measure several known points on site (boundary stakes, building corners, etc.) and input those coordinates into the app to align the model. Verifying and calibrating with multiple reference points unifies the entire model to the correct position and orientation. If coordinate transformation is needed in advance, calculate the origin difference and bearing offset and adjust the data before going to the site if possible.

• Verify position from multiple viewpoints: After placing a model in AR, be sure to step back and change angles to check the model’s relationship with reality from various directions. Something that looks correct from one spot can reveal an offset from another angle. Checking that building outlines and equipment positions overlap the real objects from multiple viewpoints verifies that the overlay is accurate in practice, not just in appearance.

• Make effective use of anchors and reference points: Actively use anchor-fixation features in AR apps. For example, if you can place a marker on the ground and fix the model to it, ensure the marker is firmly installed (if using image markers like QR codes, affixing them at the reference locations on the drawing in advance is effective). When using surrounding buildings or terrain features as anchors, choose locations with distinct patterns or shapes to stabilize tracking. If necessary, place onsite targets such as printed markers or conspicuous tape as reference points. Systems that manage anchors with absolute coordinates make the model less likely to drift even when moving over a wide area.

• Calibrate device sensors: Properly calibrate the smartphone or tablet sensors to maintain accuracy. Before starting AR, adjust the electronic compass by moving the device in a figure-eight pattern and stimulate environmental recognition by moving the device up, down, left, and right after launch. If the device has LiDAR, scanning the surroundings first to capture ground height and obstacle positions helps prevent height-direction offsets of the model. When sensors are correctly calibrated, AR display stability improves.

• Consider environmental conditions: The site environment affects AR accuracy. When using GPS, position in a location with a clear view of the sky and avoid canyons between high-rise buildings or dense tree cover. Strong direct sunlight or backlighting makes the phone screen hard to see and degrades camera recognition, so secure shade or use auxiliary lighting when necessary. In rainy weather pay attention to waterproofing and reduced screen operability. Also, near heavy machinery that generates strong magnetic fields or vibrations—such as large cranes or generators—the phone’s electronic compass and sensors can be disturbed, causing position errors. Avoid such sources of interference when possible and watch for sensor anomalies. For long-duration work, stabilize the phone on a tripod and secure power with a mobile battery to keep equipment in good condition and prevent unexpected drift or interruptions.

• Recalibrate on site as needed: If you feel “it’s a little off” during work, stop and perform additional calibration rather than proceeding. Use app functions that allow measuring another known point to correct the model position during AR display. Even an already-displayed model can often be corrected by specifying two or more points again on site. Although it may seem time-consuming, correcting early is safer and more efficient than continuing with a misaligned model and risking rework.

Implementing these measures will greatly reduce AR display misalignment on site and enable a more reliable augmented reality experience.

Simple surveying with LRTK

As a solution to dramatically improve AR position accuracy, there is high-precision positioning using LRTK. LRTK is a small RTK-GNSS receiver that attaches to a smartphone and is very lightweight at about 125 g. Using this device you can receive correction information in addition to satellite positioning signals, reducing traditional GPS errors of several meters down to within a few centimeters. For example, LRTK can determine current position with horizontal ±1–2 cm (±0.4–0.8 in) and vertical ±2–3 cm (±0.8–1.2 in) accuracy, which is orders of magnitude more precise than conventional GPS. It requires no specialized surveying knowledge or large-scale equipment, and one person can easily achieve centimeter-level positioning (half-inch accuracy) on site.

By using LRTK on site, you can compare the high-precision coordinates obtained with the design data and the actual site, minimizing AR model placement errors to the limit. For example, if you scan a reference point with LRTK and import that coordinate directly into the AR app, the model will appear in the correct location almost instantly without tedious manual alignment. Because LRTK continuously provides cm level accuracy (half-inch accuracy) position to the smartphone even while moving, models are less likely to float or shift as users walk around. AR displays that once commonly had tens of centimeters (tens of in) of error can be improved to construction-usable precision with LRTK.

Furthermore, LRTK also functions as a simple surveying tool. You can measure ground feature points on site and update the AR display immediately based on the results with a single button. This lets you perform on-site surveying and AR-based as-built confirmation simultaneously, shortening work time and improving information sharing within the team. No special qualifications or long pre-work preparations are required, so the simple configuration of smartphone + LRTK allows you to perform surveying, AR projection, and verification in an integrated workflow. As a tool to promote DX (digital transformation) at the site, LRTK is a powerful ally.

Summary

AR-based site visualization has the potential to revolutionize traditional surveying and inspection tasks, significantly improving construction accuracy and efficiency. However, AR cannot deliver these benefits if the display is misaligned. By following the causes and countermeasures introduced in this article, performing correct position alignment procedures, and incorporating high-precision positioning equipment as appropriate, you can achieve “AR that does not misalign.” When centimeter-level overlay becomes possible, AR becomes a reliable tool for various site tasks such as confirming stake positions, locating underground utilities, and sharing completed images in advance. As digital construction becomes increasingly important, use accurately managed AR technology to drive productivity improvements and quality assurance. Consider adopting high-precision AR technology on your sites to take a step forward in construction DX. With further advances in positioning technology and wider adoption of high-speed communications (5G), AR accuracy and stability are expected to improve even more. As a site technician, actively use these new tools to realize smart construction.

FAQ

• Q: What equipment is required for AR overlay? A: Basically, an AR-capable smartphone or tablet and a compatible AR app are sufficient to display AR on site. To improve accuracy, it is recommended to use a small RTK-GNSS receiver such as LRTK in combination. Additionally, an external battery for long use and a tripod to secure the phone when needed will help stabilize the work.

• Q: What should I do if the drawing data does not include survey coordinates? A: Measure several known points on site and use those coordinate values to correct the drawing data. Many AR apps let you assign coordinates obtained on site to corresponding points on the drawing to move and rotate the entire model. In other words, measure building corners or stake positions on site and tell the app which points on the drawing they correspond to so that you can display AR correctly even for drawings without coordinates. If you can assign known point coordinates to the drawing data beforehand in CAD software, on-site adjustments will be smoother.

• Q: What should I do if the AR display is misaligned? A: First, check the device’s positioning status. Verify whether GPS or GNSS accuracy has degraded or whether the electronic compass is disturbed. Restarting the app or, if using LRTK, reinitializing positioning to apply the latest correction information can be effective. Then recalibrate by measuring multiple points on site. By measuring alternative reference points and fine-tuning the model position, you can resolve misalignment in most cases. If that does not improve the situation, reset the AR display and carefully perform position alignment from the beginning to restore correct display. The important thing is to calmly remeasure and realign rather than leaving the misalignment unattended.