How to Avoid Failures in Overlaying Drawings with AR (Procedure + Precautions): How to Improve Alignment Accuracy Using LRTK High-Precision Positioning

Table of Contents

• The significance of overlaying drawings with AR on site (purposes and benefits)

• General workflow for AR drawing overlay (3D models / plans / DXF, etc.)

• Specific steps to overlay drawings with AR on site

• Common failure examples and their causes

• Precautions for correct overlaying (positioning errors, viewpoint shifts, anchor settings, etc.)

• Benefits of alignment correction using LRTK high-precision positioning

• On-site use cases of drawing AR (pile position checks, sharing completion images, overlaying underground utilities, etc.)

• Case studies and effects of adopting drawing AR with LRTK

• FAQ

The significance of overlaying drawings with AR on site (purposes and benefits)

When working on a construction site based on drawings, construction errors and rework often occur due to misreading of design drawings or insufficient sharing of the intended image. For example, overlooking a slight positional discrepancy on a plan can cause the finished structure to be offset from the neighboring property boundary, or misinterpreting the indicated drainage slope can result in rainwater not flowing properly. These kinds of problems stem from the difficulty of grasping the finished image from two-dimensional drawings alone and a gap in communicating the designer’s intent to everyone on site.

AR (augmented reality) is attracting attention as a powerful means to bridge these gaps and improve construction quality. By overlaying design drawings or 3D models onto the real scene through a smartphone or tablet camera, you can intuitively confirm the finished form while on site. From site supervisors to craftsmen and owners, everyone can view the same imagery and share an understanding of “what will be where and how,” preventing troubles caused by misalignment in perception. The main benefits of overlaying drawings with AR on site are summarized below.

• Visualization of the finished image: You can experience the post-completion appearance—which is hard to grasp from plans and sections alone—realistically in the context of the actual scenery. Arrangements and heights of structures that are difficult to imagine from drawings can be confirmed at a glance, allowing accurate sharing of design intent.

• Prevention of construction errors: By overlaying the design model on the actual conditions in AR, discrepancies and interferences can be detected immediately during construction. For example, if you confirm formwork positions in AR before concrete pouring, any offset can be corrected before construction. Early detection and correction of errors can greatly reduce the risk of rework.

• Consensus building and improved customer satisfaction: Using AR to explain to owners and stakeholders allows sharing of the finished image that paper drawings fail to convey. It prevents misunderstandings like “this isn’t what I expected,” and enables concrete feedback at the proposal stage. Obtaining agreement while confirming the finished image beforehand can lead to higher satisfaction after handover.

• Efficiency of surveying and marking work: AR overlaying contributes to simplifying layout and marking work. Visualizing design reference lines and positions in AR and marking them on site enables anyone to accurately place pile positions that previously required experienced surveyors. This can shorten work time and reduce personnel burden.

General workflow for AR drawing overlay (3D models / plans / DXF, etc.)

To perform AR overlaying of drawings, you first need to prepare digital design data. This data can take various forms: three-dimensional model data (BIM/CIM models or 3D CAD data) or two-dimensional plan data (CAD drawings or images). If a 3D model is available, you can reproduce the shapes of columns, walls, and other three-dimensional structures in real space, making confirmation most intuitive. Even if only plans or CAD files (DXF, etc.) are available, you can lay the plan on the ground in AR or draw design lines as virtual glowing lines on the surface to achieve the necessary alignment. The key is to project the design information (points, lines, shapes) onto the site at the correct scale.

Next, you need to match the prepared design data with the actual site coordinates. Typical AR apps use several methods when placing virtual objects in real space. For example, you can place printed markers or QR codes at reference points on site and have the camera read them to align the model. Alternatively, users may manually move and rotate the virtual model in the AR app to match site feature points (corner positions or reference lines) by eye. It is important to unify the drawing’s coordinate system with the site’s coordinate system. If the design data already has absolute coordinates such as latitude/longitude or projected coordinates, the device’s position information can be used to automatically display the model at the correct location. If the drawing uses a site-specific local coordinate system, you can match it by measuring multiple known points on site and mapping them (for example, by indicating two or more corresponding points) to correct the model’s position and orientation in virtual space.

Once coordinate alignment is complete, the device’s screen will show an AR view combining the camera image and the design data. The user can then, through the screen, confirm that a virtual building or line exists at the designed location relative to where they stand. This workflow is basically the same for both 3D models and 2D drawings, and can be broken down into the steps: data preparation → coordinate alignment → AR display.

Specific steps to overlay drawings with AR on site

Now let’s look at a concrete on-site flow for displaying drawings in AR, step by step.

• Prepare the data: Load the preprepared design data (3D models or drawing files) into the AR app. It’s convenient to upload them in advance to a platform such as the LRTK cloud so they can be selected on site.

• Measure reference positions: To improve the accuracy of AR overlaying, first measure reference positions on site. Connect a high-precision GNSS receiver (RTK-capable) to your smartphone and acquire latitude, longitude, and height in centimeter units (cm (in)). Alternatively, align the device to known points on site (such as control marks or boundary markers) and enter those coordinates as references. This step minimizes offset between virtual space and real space.

• Start AR display: Start displaying the design data in the AR app on your smartphone or tablet. When you select the 3D model or drawing data you loaded earlier, the virtual objects will appear overlaid on the camera image. The model may initially appear somewhat offset from the actual position; you will adjust it in the next step.

• Adjust alignment: Check and adjust the virtual model’s position and orientation on the screen so that it precisely matches the actual site. For example, compare landmarks on the drawing—such as building corners or the road centerline—with the corresponding site points, and make fine adjustments if there is any offset. If high-precision positioning like LRTK is used, major adjustments are unnecessary, but verify alignment from multiple viewpoints. If the model appears buried in or floating above the terrain, perform vertical correction as well.

• Use and record: Once the drawing and reality are perfectly aligned, use the AR display to perform work. If marking is required, mark the ground following AR guides. For explanations to stakeholders, show the screen or take AR-overlaid photos and videos to share. Save the current AR display state and measurement data to the cloud as needed, which is useful for office records and reporting.

Common failure examples and their causes

Here are common failure scenarios when overlaying drawings with AR and their main causes.

• The AR drawing is displayed off by several meters: The model appears to float greatly away from the real position. The cause is likely low GPS accuracy on the device (positioning errors of several meters (several ft)), leading to initial alignment errors. Another cause is a mismatch between the design data coordinate system and the site coordinate system.

• Looks aligned but shifts when changing viewpoint: From one viewpoint the drawing seems to match reality, but moving reveals discrepancies. This is often caused by aligning by eye from a single viewpoint only, which does not achieve rigorous alignment. It occurs when there are insufficient real-world references and the AR model is not placed at the correct scale or angle.

• Model drifts gradually during AR session: The model was correct initially but drifts away from reality while walking around. This may be caused by insufficient AR tracking accuracy or unstable anchor (reference point) settings. Standard smartphone AR accumulates small errors with movement, causing the model to appear misaligned.

• Model orientation or scale is incorrect: A building model faces 90 degrees off or its size is too large or too small. The cause is a mismatch between the design data’s orientation/scale settings and the real site. For example, the north direction on the drawing might differ from true north on site, or unit differences may have distorted the scale.

Precautions for correct overlaying (positioning errors, viewpoint shifts, anchor settings, etc.)

To prevent the above failures and accurately overlay drawings, keep the following points in mind.

• Use high-precision positioning: Commercial smartphone GPS alone can have errors of around 5 m (around 16.4 ft), so use RTK-GNSS or other centimeter-class positioning devices when possible. Increasing the accuracy of absolute coordinates minimizes initial alignment offsets.

• Confirm the drawing coordinate system in advance: Understand which coordinate system the design drawing uses and convert it to the site survey coordinates if necessary. If local coordinates are used for each site, use calibration with known points or in-app coordinate registration features to ensure the drawing data is placed correctly.

• Check from multiple viewpoints: After placing the model, always move around and verify consistency from other angles even if it looks correct from one spot. If the virtual model and the real object are aligned in position and orientation from multiple directions, the overlay is reliable.

• Use anchors and reference points: Use anchor or “lock to position” features provided by the AR app when available. If you use ground markers, fix them securely so they do not move. If you use environmental feature points as anchors, choose areas with distinct features (such as patterned walls or terrain) so tracking is stable. Systems like LRTK that manage anchors by absolute coordinates prevent model drift even when moving over wide areas.

• Calibrate device sensors: Calibrating smartphone or tablet sensors is important. Move the device on first startup to help the AR kit recognize the environment, and calibrate the electronic compass to improve measurement accuracy. If the device has LiDAR, scanning the surroundings helps it recognize ground elevation and obstacles, preventing vertical mismatches.

Benefits of alignment correction using LRTK high-precision positioning

Even with the above precautions, standalone smartphone AR has unavoidable limits—one of them being positioning accuracy. Standard GPS has meter-level errors, so while coarse placement may be fine, it is insufficient for precise overlaying. Also, ARKit/ARCore and similar AR frameworks track device movement in relative coordinates, so accumulating errors while moving across a large site can cause an initially aligned model to gradually drift.

LRTK’s high-precision positioning (RTK-GNSS) addresses these issues. LRTK is a small positioning device attached to a smartphone that adds correction data to satellite positioning signals to compute current position with an error on the order of a few centimeters, offering a drastically higher level of accuracy. This allows AR apps to determine device position in global coordinates accurately, enabling absolute alignment of design data. Specific advantages include:

• Reduced initial alignment effort: With LRTK, coordinates match automatically, eliminating the need for tedious fine-tuning or marker placement. Just start the app and select the model, and the virtual model will appear almost instantly at the design location.

• Stable model positioning: LRTK provides continuous centimeter-level positioning while moving, so the model display is less prone to drift even when users walk around. The common AR issue of the model appearing to float when viewed from a distance is avoided, maintaining stable overlay over wide areas.

• Construction-grade accuracy: Conventional AR tolerated offsets on the order of tens of centimeters, but high-precision AR with LRTK can achieve accuracy usable for construction tasks like pile positioning and installation of structural elements. When AR display dimensions match drawing dimensions on site, virtual marking can be trusted for actual work.

• Vertical alignment: RTK-GNSS enables vertical positioning as well, allowing accurate alignment of height references. For example, depths of underground utilities or soil fill heights in earthworks can be accurately represented in AR.

By combining LRTK high-precision positioning with AR, drawing AR overlaying, which was previously challenging in terms of accuracy, becomes practical. On site, “AR that doesn’t drift” is highly valued, and layout tasks that used to rely on the intuition of veteran surveyors can now be performed accurately by anyone with a smartphone.

On-site use cases of drawing AR (pile position checks, sharing completion images, overlaying underground utilities, etc.)

Here are specific on-site scenarios where drawing AR is used.

• Checking pile positions: For placing foundation piles or structural element piles, AR provides a strong guide. Register pile center coordinates from the design in advance, and AR display on site will show virtual piles or markings on the ground. Following those marks, you can install piles in the design positions without measuring tapes or surveying equipment. Using LRTK’s coordinate guidance, the app can show prompts like “move X cm north,” guiding anyone to the precise location and enabling accurate layout without specialists.

• Sharing completion images: Prior to construction, AR helps owners and cross-disciplinary stakeholders understand the post-completion appearance. For example, displaying a 3D model of exterior landscape design or equipment on a vacant site lets customers imagine the final scene in context. On-site feedback like “lower the height a bit” can be exchanged immediately, enabling early consensus on the finished image. During construction, showing progress in AR can intuitively report that “work is proceeding as drawn,” building trust.

• Overlaying underground utilities: Visualizing buried pipes and cables in AR improves safety and efficiency of excavation. If you import utility drawings and survey data into LRTK, simply pointing the camera on site will show the pipes and cables that should lie beneath the ground. This reduces the risk of damaging existing infrastructure and helps workers intuitively know how deep to dig to find the utility. Excavation planning and inspections are smoother, and safety management benefits significantly.

Other applications include comparing the as-built condition with the design model on site for quality checks, and guiding heavy equipment operators with AR lines for high-elevation work. Drawing AR’s applications in construction are expanding across many tasks.

Case studies and effects of adopting drawing AR with LRTK

Sites that have used LRTK and AR report various benefits. A few case examples follow.

• Major reductions in work time and personnel: Mid-sized general contractor Company A introduced LRTK Phone and found that foundation layout work that previously required two people and half a day could be completed by one site staff in about one hour. The time-consuming process of measuring and marking from paper drawings disappeared, freeing personnel for other tasks.

• Zero rework on projects: Exterior works contractor Company B adopted AR to share the completed image with owners before construction. As a result, there were no specification changes or “this isn’t what I expected” disputes after starting work, and they have continued to complete jobs without rework. Owner trust increased and led to follow-on contracts.

• Safe, faster infrastructure work: A municipal road project trialed AR visualization of buried pipes using LRTK. Tasks that previously required cautious digging while referring to drawings were accelerated by accurately identifying pipe locations in AR, contributing to shortened schedules and enhanced safety. Anxiety about “not knowing until you dig” was reduced, improving workers’ peace of mind.

The combination of drawing AR and high-precision positioning dramatically improves on-site productivity and quality. Because it only requires a smartphone and a small device, adoption is rapidly increasing, making it a key technology supporting digital transformation in construction and civil engineering. Introducing simple surveying with LRTK on site can bring benefits not achievable by traditional methods.

FAQ

Q: What equipment and preparations are needed to perform AR overlaying on site? A: You need a smartphone or tablet and an AR app. Recent iPhones and iPads have AR functionality (ARKit) built in and can be used without additional devices, but to improve alignment accuracy it is recommended to use a high-precision GNSS receiver such as LRTK Phone. Also prepare the design data (3D models or drawing files) on the device or in the cloud in advance, and adjust coordinate systems as needed before starting.

Q: Can 2D drawing data be displayed in AR? Do I need 3D models? A: You can use 2D plan data in AR. Even without 3D models, you can project lines and shapes onto the ground or display markers and symbols at important points. For example, you can overlay DXF or image files on the AR background to check offsets from your current position. However, 3D models provide height information and allow interference checks, so prepare 3D data when possible.

Q: How accurate is the alignment of drawing AR? A: Standalone smartphones’ GPS and AR can produce offsets from several tens of centimeters to several meters (several ft), which may be acceptable for rough checks but is inadequate for precise marking. Using high-precision positioning like LRTK can reduce horizontal and vertical errors to within a few centimeters (within a few in), enabling AR overlays that essentially match the design drawings—construction-grade, centimeter-level accuracy (cm level accuracy (half-inch accuracy)).

Q: Is specialized knowledge or training required? Can site staff use it? A: No advanced CG software skills are needed; generally, anyone can use it by following the smartphone app instructions. LRTK systems are designed with UIs that allow even users with limited surveying experience to perform positioning and AR display via button operations. A short training session for site staff is usually sufficient to start using it in daily construction management.

Q: Do I need to set up markers or reference points in advance? A: With LRTK, special marker setup is generally unnecessary because GNSS makes the device itself the reference point and displays the model at the specified coordinates. However, indoors or in locations where GPS is unavailable, you will need to rely on ARKit’s plane detection or visual markers. Even then, using recognizable reference points (e.g., a corner of a wall or a pattern on the floor) improves placement accuracy. For wide outdoor sites, coordinate alignment using LRTK is the most efficient.