Introduction to AR Overlay of Drawings (Procedure + Precautions): Practical Steps to Minimize Pre-construction Checks with LRTK

What if you could point a smartphone at a site and have the design drawings appear overlaid on the real scene? You could greatly reduce the effort of comparing paper drawings while taking measurements or driving stakes to verify positions. The AR overlay of drawings projects design drawings or models into the real world through a camera so that pre-construction checks and as-built inspections can be done intuitively and quickly. Recently, DX (digital transformation) has been advancing in the construction and civil engineering industries, and this AR technology is attracting strong expectations for labor savings and improved accuracy on site. This article explains in detail the basics of AR overlay of drawings, its benefits, tips to realize high accuracy (using LRTK), practical procedures, precautions, comparisons with other methods, and examples of integration with point cloud data. Finally, as an easy-to-start solution for anyone, we introduce LRTK and propose key points for on-site adoption.

Table of Contents

• Basic concept and background of AR overlay of drawings

• Why AR overlay of drawings speeds up site checks

• Types of drawing data used and preparation methods (2D drawings / 3D models)

• Centimeter-level accuracy! The importance of high-precision alignment with LRTK (cm level accuracy (half-inch accuracy))

• Practical step-by-step guide to AR overlay of drawings using a smartphone

• On-site operational precautions (weather, visibility, satellite reception, etc.)

• Common failure cases and how to avoid them

• Comparison with other methods (paper drawings, marker-based AR, conventional surveying)

• Examples of AR integration with point cloud data and photogrammetry

• Recommendation for introducing simple surveying & drawing overlay using LRTK

• Frequently asked questions (FAQ)

Basic concept and background of AR overlay of drawings

AR overlay of drawings is a technology that overlays architectural and civil engineering design drawings (2D CAD drawings or 3D BIM models) onto the real construction site scene in real time. By compositing actual scenery and design data through a smartphone or tablet camera so that lines or models on the drawing appear as if drawn on site, it intuitively bridges the gap between the drawing and the field.

The attention to this technology stems from problems with conventional on-site verification work. Carrying paper drawings or PDFs and verifying positions or dimensions on site required advanced reading ability and imagination. Accurate alignment often required taking coordinates with surveying equipment or laying out marks on the ground, consuming time and manpower. Also, plans that looked fine on paper sometimes conflicted with surrounding structures or terrain when viewed on site. To discover and correct such discrepancies between drawings and the field early, AR overlay of drawings has begun to be introduced.

AR (Augmented Reality) itself was originally known in gaming and entertainment, but its use in construction has recently matured. Initiatives such as the Ministry of Land, Infrastructure, Transport and Tourism’s *i-Construction* and the spread of BIM/CIM have also encouraged attempts to utilize digital data on site. However, consumer smartphone GPS typically has errors of several meters (several ft), making it unsuitable for precise drawing overlay. This is where high-precision GNSS (RTK) positioning combined with smartphone AR comes in. With this, even without specialized equipment, you can determine your current position to within a few centimeters (a few in) and overlay drawing data onto the real world almost exactly.

Why AR overlay of drawings speeds up site checks

Why does AR overlay of drawings dramatically speed up pre-construction site checks? The main reason is that it allows you to intuitively compare design and actual conditions on the spot.

• Significant reduction of surveying and layout work: Traditionally, verifying drawing positions on site required setting out points with surveying instruments, staking out strings, or driving stakes. With AR overlay, design lines and models are displayed to scale on the smartphone screen, so those manual tasks can be omitted. For example, to confirm site boundaries or building placement, AR lets you grasp offsets at a glance without drawing temporary lines on the ground. As a result, you can greatly shorten the time spent on preparatory work and point verification.

• Immediate detection of discrepancies: Overlaying design data on the actual scene in AR makes positional or dimensional discrepancies instantly visible. In conventional methods, where manually measured values are later compared with the drawing, errors can take time to discover or may be overlooked. With AR you can detect differences at that moment, speeding up checks and reducing rework.

• Improved communication efficiency: Projecting drawings onto the site allows all stakeholders to share the same “completed image” and “design intent.” Instead of construction managers and workers huddling over paper to explain, viewing the AR overlay together enables immediate understanding and faster meetings and instructions. During client or designer site inspections, confirming with visuals rather than only verbal explanations usually leads to quicker agreement and faster decision-making.

In short, AR overlay of drawings “visualizes the drawing on site,” making verification work real-time and drastically cutting the time spent on surveying and reading drawings. This shortens pre-construction checks and as-built inspections, directly contributing to shorter schedules and improved quality.

Types of drawing data used and preparation methods (2D drawings / 3D models)

There are two main types of drawing data usable for AR overlay: 2D drawings and 3D models. Their preparation methods and use cases differ, so understand their characteristics.

• 2D drawing data: Refers to conventional 2D CAD drawings or paper drawings such as plans and longitudinal/cross sections. CAD data like DXF/DWG or scanned images/PDFs of paper drawings can be used. When displaying 2D drawings in AR, the drawing must generally have the correct scale and coordinate information set. For example, a plan created in CAD should be drawn to actual scale and placed in a coordinate system matching the survey coordinates. This allows the site coordinates and drawing coordinates to correspond and enables projection on the smartphone without manual adjustment. - If the drawing has no coordinates: Even for paper plans without survey coordinates, overlay is possible by performing on-site calibration in the AR app. For example, you can measure site points corresponding to feature points on the drawing (such as an intersection center or building corner) with smartphone RTK and then translate and rotate the drawing data to align to those points. Matching two or more points can also correct scale errors and attach a site coordinate system. Thus, even if the source drawing uses local coordinates or has no scale, you can enable AR overlay by acquiring and linking coordinates of feature points on site. - Use cases: 2D AR overlay is effective for checking site boundaries or design plans. For example, on a residential land development site you can display parcel lines in AR to confirm boundaries with neighboring plots, or overlay road alignment lines to visually check curves and widths. You can reproduce a state where design lines appear on the ground, making checks intuitive without driving stakes or string lines.

• 3D model data: Includes BIM models of buildings or infrastructure, 3D CAD data, and surface models of terrain. Formats such as IFC, LandXML, or various software 3D exports can be used. For 3D models, it is also important that they are created and positioned in the correct coordinate system. If a model is positioned relative to reference points during design, the full-scale model will be projected onto the site correctly in AR. If a model uses an arbitrary origin, preprocessing to translate and rotate the model into survey coordinates for AR is required. - Model preparation tips: Very detailed 3D models can slow mobile device rendering, so export only the necessary portions or simplify the model. Also decide where to set ground elevation 0 m (0 ft) as the known elevation reference. For example, align a building model’s GL (ground line) to the known elevation, or adjust a terrain model so its elevations match the site. Ensuring correct alignment in the vertical direction as well as horizontal prevents the model from appearing to float above or be buried in the ground. - Use cases: 3D model AR projection is powerful for “on-site completion preview” of unbuilt structures. For example, display a bridge or building BIM model at full scale on site to check interactions with surroundings, or render buried piping as translucent under the ground to warn during excavation. Visualizing unseen components (rebar, internal structures) in AR helps prevent construction mistakes and supports as-built inspections.

Summary of drawing data preparation: In any case, the key to success is to “prepare drawings and models consistent with the site’s survey coordinate system.” If possible, reflect public coordinates or reference point coordinates in the drawing/model at the design stage. If only existing materials are available, follow on-site calibration steps. Check drawing units, coordinate systems, and scale in advance, and simplify or hide unnecessary elements so the data is AR-display-friendly.

Centimeter-level accuracy! The importance of high-precision alignment with LRTK (cm level accuracy (half-inch accuracy))

To perform AR overlay at a practical level, device position measurement accuracy is critical. Consumer smartphone GPS has errors of several meters (several ft), which is inadequate for accurate overlay. The key is real-time kinematic (RTK) GNSS high-precision positioning and technology like LRTK that makes it easy to use RTK with a smartphone.

• Centimeter-class positioning with smartphone RTK: RTK-GNSS obtains high-precision positions by having a base station and a rover (the smartphone) observe multiple satellites simultaneously, and correcting the rover’s solution using error information computed at the base station. This can improve position accuracy to a few centimeters. Traditionally, survey-grade GNSS gear was required, but recently small high-performance GNSS antennas attachable to smartphones have appeared. LRTK is one such system: an RTK receiver integrated with a smartphone enables centimeter-level positioning without external equipment.

• Effects of centimeter-level accuracy: RTK can provide planar accuracy of around ±1–2 cm (±0.4–0.8 in) and vertical accuracy within a few centimeters. With that level of precision for your current position, the difference between design coordinates and measured site coordinates becomes negligible to the eye. When you project drawings in AR, design lines and existing structures or terrain will align almost perfectly, enabling practical, “non-sliding” AR for the field.

• No need for markers if high-precision: Many AR apps use markers (like QR codes) on the ground for alignment, but markers require installation and are only effective in a limited area. By combining RTK-based high-precision self-positioning with smartphone sensor calibration, absolute coordinate-based AR becomes possible, allowing models to be fixed at correct positions without placing markers on site. Users can walk around viewing from different angles and the model will remain stable without slipping or rotational drift—one of the main benefits of high-precision positioning.

Thus, centimeter-level positioning is indispensable for accurate AR overlay of drawings, and smartphone RTK solutions like LRTK meet this need. The importance of high-precision alignment becomes evident when you experience AR yourself: an AR shifted by meters is unusable, but within a few centimeters the AR is fit for on-site checks, making LRTK-enabled high-precision AR a key tool for site DX.

Practical step-by-step guide to AR overlay of drawings using a smartphone

Here is a step-by-step procedure to display drawing overlays in AR using a smartphone (+ high-precision GNSS device). This is a general flow; details may vary depending on the app and equipment used.

• Prepare required equipment and app: Attach a high-precision GNSS antenna (e.g., an LRTK terminal) to your smartphone and launch a compatible surveying & AR app. Import drawing data (2D or 3D) into the app in advance. The drawings should be prepared in the survey coordinate system as described above. Some apps sync project data via the cloud so you can call it up on site.

• Set up RTK positioning: On arrival, receive correction data and start RTK positioning. If deploying a base station, place it in an open area and set a known coordinate (or connect to a virtual reference station service online), then establish communication with the rover (smartphone). For network RTK, have the smartphone connected to mobile data and log into Ntrip, etc. Confirm the positioning status on the smartphone screen and ensure RTK is in a Fix solution to achieve centimeter accuracy. If the display shows “Float” or “DGPS,” accuracy is insufficient—improve signal conditions or reset settings until Fix is obtained.

• Alignment procedures: To overlay the loaded drawing or model onto the site, perform alignment operations as needed. If the drawing data already contains absolute coordinates, it should appear roughly in the correct place at this stage. For fine adjustments or for drawings without coordinates, use methods such as: - Align to known points: Move the smartphone to a site point corresponding to a point on the drawing (e.g., a reference point or structural corner) and link “this location = drawing point ○○.” This translates and rotates the drawing so it fits that point. - Correct with multiple points: If possible, match two or more points. One point corrects translation and rotation; a second point helps correct scale errors. This is effective for scanned paper drawings that may have scale distortions. - Check vertical alignment: For 3D models, align the model’s elevation reference (e.g., benchmark or existing structure elevation) to the site. Confirm that the model’s ground surface coincides with the site ground; if not, use the app’s Z-shift function to adjust.

• Switch to AR mode and start projection: Once ready, switch the smartphone or tablet to AR display mode. The camera image will be overlaid with the aligned drawing data. Design lines may appear on the ground or a full-scale model may appear in space. First, look around 360 degrees to confirm the projection is correctly positioned. Compare against nearby reference structures to check for misalignment.

• Walk the site and inspect: With the AR set up, walk around the site holding the smartphone to inspect each area. Verify that building corners are projected to the correct positions, road widths match existing conditions, and pipe routes avoid obstacles. Periodically confirm that GNSS maintains Fix status while you move. In areas where buildings or trees block the sky, accuracy may degrade—pause and carefully check for drift when entering such spots.

• Share findings and record: If you discover discrepancies between drawings and the field, you can mark them and discuss correction measures on the spot. Capture screenshots or record photos/videos of the AR view with the smartphone’s built-in functions for later sharing. These captures usually include position and timestamp metadata useful for reporting.

• Wrap-up: After finishing, close the app and pack up equipment. Power off GNSS units and remove any base stations. Upload screenshots and positioning logs to the cloud or store them in designated locations. Back at the office, summarize and share detected deviations so that they can be reflected in subsequent construction planning.

This is the general workflow. Although this is an easy surveying/AR setup anyone can use with a smartphone, novices may feel uncertain at first. Keep the precautions in the next section in mind and start with trial operations to gain familiarity. With experience, this becomes a powerful, ready-to-use tool for site verification.

On-site operational precautions (weather, visibility, satellite reception, etc.)

When using smartphone AR overlay outdoors, be aware of several points. Understand environmental conditions and device limitations to prevent issues.

• Ensure GNSS reception environment: RTK requires satellite signals to be received from above. Urban canyons surrounded by tall buildings, tunnels, or under dense tree canopy may prevent adequate satellite reception, degrading accuracy or causing loss of positioning. On site, position yourself where the sky is as open as possible and plan base station placement accordingly. For indoor or other GNSS-unavailable spaces, consider alternative methods such as aligning the model using known point coordinates.

• Maintain a Fix solution: Keeping a high-precision Fix RTK solution is vital. If the solution drops to Float, accuracy can degrade to tens of centimeters to 1 m (several in to 3.3 ft). Monitor RTK status on the app and avoid proceeding while Float persists. If Float continues, reset positioning or move to a more open area to reacquire Fix. If receiving corrections over the network, also check mobile communications quality.

• Calibrate device sensors: Smartphone sensors (gyroscope, accelerometer, magnetometer/compass, camera pose estimation) are essential for AR. If the compass is off, model orientation will be incorrect. Calibrate by moving the device in a figure-eight motion before use and occasionally reset gyro drift on a horizontal surface. Since sensor accuracy varies by device, verify orientation against multiple reference directions or align using the sun or known azimuths as needed.

• Weather and lighting: Smartphone screens are hard to see in bright sunlight. On sunny days, reflections and insufficient contrast can make AR overlays hard to discern. Increase screen brightness, use a simple sunshade, or position the screen in shadow to help visibility. Rain complicates handling and water on the lens reduces recognition accuracy; avoid use in severe weather and perform AR checks in stable conditions when possible.

• Battery and thermal management: Simultaneous GNSS positioning and AR display increase power consumption. Prepare mobile batteries for long operations. In cold weather battery performance drops, and in hot weather the device can experience thermal throttling or shutdown. Avoid leaving the device in direct sun for long periods; pause and cool the device when needed or use small fans to help heat dissipation.

• Data volume and rendering load: Large point clouds or highly detailed 3D models can cause slow rendering or app freezes. Pre-filter point clouds, simplify models, and limit the area to be displayed. Match data complexity to the smartphone’s capabilities to ensure smooth on-site use.

• Safety considerations: Don’t become so absorbed in AR that you neglect surroundings. Always watch your footing and the movement of heavy equipment or vehicles. Working in pairs—one operating the device and a second observing the surroundings—is safer. Avoid using AR at heights or on scaffolding; perform AR checks from the ground and then move only when safe.

Considering these points will reduce on-site troubles and support a stable AR overlay experience. Because this is new technology, inexperienced errors can occur—review typical failure cases in the next chapter to be prepared.

Common failure cases and how to avoid them

AR overlay of drawings is useful, but first-time operations often involve common mistakes. Below are typical field failure cases and countermeasures to avoid repeating them.

• Large offsets from incorrect coordinate systems: If drawing data or base station coordinates are set incorrectly, AR displays can be significantly shifted. For example, choosing the wrong zone in a plane rectangular coordinate system can create tens of meters of offset. Countermeasure: double-check coordinate systems and reference point info, and validate by overlaying the model on known site points before full deployment.

• Working with RTK in Float: Proceeding while accuracy is insufficient because of “it’s probably fine” is a common mistake. Float solutions can have errors of tens of centimeters to 1 m (several in to 3.3 ft) and may require rework. Always monitor RTK status and wait for Fix before proceeding.

• Incorrect device orientation: Compass errors or gyro drift can induce small angular offsets that become tens of centimeters at the far ends of long structures. Calibrate sensors before starting and verify alignment along straight reference structures. Use in-app “azimuth fine-tuning” if available.

• Overlooking vertical alignment: The model may be correctly positioned horizontally but appear floating or buried if the elevation reference is wrong. Forgetting to align the design GL to the site benchmark can cause tens of centimeters to several meters (several in to several ft) of vertical error. Confirm the model’s height reference and perform on-site Z-shift adjustments if needed, or at least know which vertical datum the model uses.

• Using the wrong data version: Displaying an old revision or a model from another project can cause confusion. Ensure the app contains the latest, correct data, and use clear file and project naming. When syncing via the cloud, watch for upload omissions.

• Model too complex and causing performance issues: Attempting to render overly detailed 3D models or massive point clouds can freeze the app or overheat the device. Test with lightweight data beforehand and understand device limits. Simplify models or split data into smaller areas as necessary.

• On-site human errors: Mistakes like selecting the wrong calibration point or confusing feature points are common when rushed. Before calibration, reconfirm reference points and employ verbal confirmation like pointing and calling “this is drawing point ○○.” Cross-check with multiple participants when possible.

• Neglecting safety checks: There are reports of near-misses where operators walked backward into ditches or failed to notice heavy machinery while watching the screen. To avoid this, hold a safety briefing covering AR-working areas and procedures, set exclusion zones, and consider assigning guides. Combining tech deployment with safety management is essential.

Many of these issues are preventable through thorough preparation and checks. Start with a small area, iterate with PDCA, and don’t hesitate to stop and verify if something seems off. Even with the latest tech, consistent verification is the foundation—so follow the rule: stop and verify if in doubt.

Comparison with other methods (paper drawings, marker-based AR, conventional surveying)

To clarify the strengths of AR overlay of drawings, compare it to conventional representative methods: paper drawings, marker-based AR, and traditional surveying.

• Paper-drawing field checks: This long-standing method is simple and accessible, but translating drawing positions into the real world requires surveying or staking. Paper drawings are easy to view without power, but mapping drawing information to the field relies on human spatial thinking. Even experienced personnel can misread drawings, and translating drawing data into on-site actions takes time. With AR overlay, drawing information is displayed directly on site, reducing cognitive load in spatial understanding. Complex structures that are hard to visualize on paper become immediately clear when overlaid on the scene. For efficiency and error reduction, AR has the advantage.

• Marker-based AR: Many AR apps place models relative to a physical marker or by recognizing planes. For instance, a printed marker sheet placed on the floor will anchor a model precisely relative to that marker. While accurate around the marker, it requires placing the marker correctly, making it unsuitable for large areas. Also, if the user moves away from the marker, tracking breaks. RTK-enabled AR removes the need for markers by anchoring models to absolute coordinates, enabling wide-area coverage and seamless site walkthroughs. Marker-based AR remains convenient indoors or for small objects, so choose accordingly: use RTK+AR for wide outdoor sites, image markers for small indoor targets.

• Conventional surveying and inspection: Traditional surveying teams using transits or total stations provide high reliability but require time and personnel. For example, measuring 50 points for an as-built inspection can take a full day including recording and plotting. AR overlay allows immediate, on-site identification of obvious deviations so corrections can be instructed the same day. While precise numeric verification with survey instruments remains necessary for final checks, AR can serve as a fast preliminary check to prevent rework. AR’s intuitive operation also allows supervisors and workers—not just survey specialists—to understand site conditions immediately.

Overall, AR overlay of drawings excels in “speed” and “intuitiveness,” complementing existing methods rather than fully replacing them. Final formal measurements and official inspection records may still rely on conventional survey methods, but AR streamlines preceding processes and updates site management.

Examples of AR integration with point cloud data and photogrammetry

Beyond design drawings, combining AR with on-site point cloud data and photogrammetry enhances functionality. Below are representative cases of AR×point cloud integration.

• As-built point cloud vs. design model difference checking: Increasingly, construction sites are scanned by 3D scanners or drone photogrammetry to obtain as-built point clouds. Overlaying these as-built point clouds with the design 3D model and creating a color-coded difference “heat map” is a common approach. Smartphone RTK like LRTK allows absolute coordinates to be embedded in the point cloud at capture time, eliminating the need for later coordinate alignment. Importing a heat map into the smartphone for AR display lets users visually identify large deviations on site. For example, areas where fill is higher than design can be shown in red—holding up the smartphone lets you immediately see where to correct, enabling rapid decision-making and shorter quality-control cycles.

• Visualizing buried utilities and photogrammetry: AR is effective for visualizing underground pipes and cables. Create a 3D model of buried utilities from design or past surveys and project it as a translucent overlay so crews avoid damaging them during excavation. After excavation, measure the exposed utilities with smartphone RTK, photograph them, and convert to point cloud data for future asset management. Photogrammetry can be performed with drones or by taking multiple images with a smartphone. Using LRTK’s high-precision coordinates gives accurate geolocation to the photogrammetric outputs, facilitating later checks and AR visualization even after backfilling.

• Progress monitoring and digital twin: Combining AR with point clouds is a step toward a digital twin. Regularly scanning the site and updating point cloud models, then overlaying them in AR, enables on-site, time-series progress checks. For example, if you update a point cloud weekly and compare it to the design in AR, stakeholders can discuss progress on site with the latest data. This real-time approach replaces previous workflows of collecting data and analyzing it off-site. Accumulating accurate 3D data paves the way for full digital twin capabilities, remote monitoring, and AI-driven automatic detection. AR acts as the interface connecting the real world and the digital representations.

In short, AR overlay is not just for design comparison—it becomes a tool to immediately leverage various digital on-site datasets. Integrating point clouds and photogrammetry increases actionable information and on-site accuracy, transforming AR into a data hub for the field rather than a mere gadget.

Recommendation for introducing simple surveying & drawing overlay using LRTK

The AR overlay and smartphone RTK surveying technologies discussed here are no longer exclusive to avant-garde sites. Equipment and services have become affordable, and an environment where any site can start quickly is emerging. A representative example is LRTK.

LRTK is a system composed of a very small RTK-GNSS receiver and a smartphone app that turns a single smartphone into a versatile surveying instrument. Without expensive dedicated gear, attaching an LRTK device to your smartphone enables centimeter-level positioning and supports point cloud capture and AR overlay of design data. Tasks that used to require a surveying team can now be handled by on-site technical staff, reducing outsourcing costs and scheduling delays.

When first introducing the system, you may be unsure about accuracy or practicality. We recommend starting with small-scale verification—try LRTK in a limited area, compare its measurements with conventional survey results, or run AR checks alongside traditional methods. Initial unfamiliarity is normal; evaluating results with stakeholders builds confidence. LRTK providers often offer support, and hands-on staff training accelerates adoption.

Sites that have implemented LRTK report benefits like “cutting surveying and drawing-check time by more than half,” “detecting problems missed on paper drawings,” and “sharing AR visuals with remote supervisors for quick instructions.” A small smartphone device can therefore materially boost site productivity. This approach aligns with national DX initiatives like the Ministry’s i-Construction, and such technology is likely to become an industry standard.

Start DX from familiar sites—LRTK makes it easy to bring centimeter-level surveying and AR overlay into daily operations. Experience the quick pre-construction checks, streamlined as-built inspections, and reduced human error. You’ll find that next-generation construction management becomes much more accessible.

Frequently asked questions (FAQ)

Q: *What equipment is required to perform AR overlay of drawings?* A: *Basically, a smartphone, a high-precision GNSS receiver (RTK-capable), and a compatible AR display app are required. A common example is an RTK antenna attachable to the smartphone with a dedicated app such as LRTK. The smartphone need not be the newest model, but it should support AR frameworks (ARKit or ARCore) and have reasonable performance. For long operations, carry a mobile battery for backup.*

Q: *Can anyone operate it with just a smartphone, or is specialized training required?* A: *Compared to traditional surveying gear, operation is more intuitive, but some training and practice are advisable. Learning app workflows, RTK basics, and precautions reduces confusion on site. The system is designed so non-survey specialists can use it—site managers and supervisors often master it after a few hours of guided practice. Start trials with experienced personnel and gradually expand usage.*

Q: *Do I need to set up a base station every time? Can it be used without internet?* A: *It depends on how you obtain RTK corrections. If public reference stations are nearby, you can use network RTK services (VRS, etc.) via mobile data without deploying your own base station, provided you have internet. In remote areas with unreliable connectivity, you can set up your own base station and transmit corrections wirelessly. In Japan, the quasi-zenith satellite system “Michibiki” offers the CLAS centimeter-class correction service, which can provide corrections without internet using compatible receivers. LRTK supports multiple correction methods to suit site conditions.*

Q: *What level of accuracy can be expected when overlaying drawings and reality? I’m worried about errors.* A: *Under good conditions you can expect planar errors of about 1–2 cm (0.4–0.8 in). Vertical errors are typically within a few centimeters, so visual misalignment is hardly noticeable in most cases. However, this requires that RTK maintains a Fix solution and device sensors are properly calibrated. In environments with poor satellite reception or with sensor heading errors, accuracy will drop. Therefore, always verify against known points or reference marks on site—this lets you assess and correct any small offsets in practice.*

Q: *Can AR overlay be used at night or in dark locations?* A: *Positioning itself works at night via GNSS, but AR relies on camera imagery, so poor lighting makes overlays hard to see. AR systems also use camera feature points to support pose estimation, which becomes difficult in the dark. Use portable lighting when working in low light, or devices with LiDAR (e.g., some iPad Pro models) which can handle darker environments better. For safety and reliability, daytime use is preferable; for night tasks rely more on pre-checked daytime AR planning or ensure adequate lighting.*

Q: *How about indoor use or locations where GPS cannot reach?* A: *Indoors or underground, RTK cannot provide absolute positions. One alternative is local coordinate AR using known points: place control points with coordinates determined by a total station and use them as anchors to manually set the AR coordinate system. There are also indoor positioning options using UWB or visual SLAM, but achieving centimeter-level accuracy indoors is still challenging. Where GNSS is unavailable, combine other positioning methods to extend AR utility.*

Q: *Is the introduction costly?* A: *Compared to full survey-grade GNSS sets or 3D scanners, a smartphone plus an RTK receiver is a relatively affordable option. Actual costs vary by device and service plans, but many times this setup costs only a fraction of a traditional survey GNSS set. Additionally, reduced outsourcing, shorter inspections, and fewer reworks contribute to cost recovery. Some LRTK services are offered by subscription, lowering initial costs for trial use. Start small, evaluate benefits, and expand gradually based on results.*