Centimeter-Level Positioning That Changes How 3D CAD Is Used On Site: The Power of LRTK

In recent years, the construction and civil engineering sectors have rapidly advanced the use of three-dimensional data such as 3D CAD and BIM/CIM. The detailed 3D models created for infrastructure designs like roads and bridges help with construction planning, consensus building, and sharing finished-image expectations. However, simply producing such digital design data is not enough to truly use it on the actual site. A technology that accurately links the data to real-world positions is indispensable. This article explains the importance of using 3D CAD data on civil engineering sites and what becomes possible with centimeter-level (half-inch-level) high-precision positioning. In particular, we will explore the power of the smartphone-linked positioning solution “LRTK” as an example.

The Importance of 3D CAD Use in Civil Engineering

In Japan’s construction industry, the use of 3D models in civil projects is being promoted as part of the “i-Construction” initiative to improve productivity and reduce labor. While 2D drawings used to be dominant, it is becoming common to create three-dimensional models (so-called 3D CAD data) from the design stage and leverage them for construction and maintenance management. Using 3D CAD makes it easier to understand complex terrain and structures three-dimensionally and helps stakeholders share a common image. Furthermore, consistent data utilization from design to construction can be expected to reduce human error and shorten schedules.

In civil engineering in particular, where work targets can span wide areas and terrain conditions change rapidly, being able to leverage 3D data on site can have a great impact. For example, using a 3D model from the design stage to run construction simulations allows you to pre-check heavy equipment travel paths and temporary structure placements, enhancing safety and efficiency. The communication benefits of sharing a finished-image with stakeholders to smooth consensus-building should not be overlooked. In short, 3D CAD data is not merely a set of design drawings but can become a powerful tool supporting on-site decision-making and operations.

Why Positioning Accuracy Holds the Key to On-Site Use

However, no matter how elaborate a 3D CAD model is, it is useless on site if its position alignment is off. If the location indicated by the model and the actual ground position differ by several meters, the data not only becomes unusable for construction but can cause confusion. In civil works, errors of a few centimeters can often determine quality, so it is no exaggeration to say that positioning accuracy decides whether the data can be used on site.

Consider the task of laying out a road centerline or the placement of structures on site. General positioning methods like GPS can have errors of several meters, so the position on the design model and the actual on-site position can be greatly misaligned. Under those circumstances, you cannot rely on the lines and points drawn in the 3D CAD to drive stakes. Ultimately, the conventional labor—surveyors using a total station to set up batter boards—will still be required. Similarly, when checking the as-built shape after construction, poor positioning accuracy prevents proper comparison with the design data, making accurate quality control difficult. To truly advance the on-site use of 3D CAD, positioning technologies that link digital data and real space with high accuracy are indispensable.

Basics and Necessity of Centimeter-Level Positioning (RTK-GNSS)

An essential positioning technology when discussing high-precision location information is the method known as RTK-GNSS. RTK (Real Time Kinematic) is a technique that corrects errors in satellite positioning (GNSS) in real time to achieve centimeter-level accuracy. Normally, standalone positioning like GPS produces errors of several meters due to atmospheric effects and satellite clock errors. With RTK, however, error factors are canceled out by using the difference between satellite signals received at a known base station (fixed station) and a rover (mobile station), yielding high-precision relative positions.

The reason centimeter-level positioning is necessary is that surveying and design values handled in civil engineering require extremely high accuracy. If a bridge pier position shifts by several tens of centimeters, it can have a serious structural impact, and even small deviations in a road’s longitudinal gradient can cause drainage or visibility problems. Traditionally, ensuring such accuracy required expensive, large surveying equipment (so-called Class-1 GNSS receivers or total stations). RTK-GNSS itself used to be perceived as a tool only specialist surveyors could handle, but recent technological advances and cost reductions are making it more accessible. In Japan, the infrastructure supporting satellite positioning has also progressed, lowering the barrier to using RTK-GNSS through national electronic reference point networks and commercial correction services. Positioning augmentation signals provided by the Quasi-Zenith Satellite System (QZSS, “Michibiki”) further support high-precision positioning, making the environment for such measurements increasingly approachable. In other words, centimeter-level positioning is no longer exclusive to special surveying teams; construction managers and on-site technicians can increasingly use it routinely.

How LRTK Achieves High-Precision Positioning (Smartphone Integration and Device Configuration)

One of the latest high-precision positioning solutions is “LRTK.” LRTK is a system that enables palm-sized centimeter-level positioning by combining a compact RTK-GNSS receiver with a smartphone app. By attaching a dedicated slim antenna receiver to a smartphone and connecting wirelessly, high-precision measurements that previously required stationary equipment can be realized easily. The receiver is designed to attach to a smartphone-specific case with one touch, and the device weight is light at about 100–150 g. Despite being compact enough to fit in a pocket, the acquired position coordinates include latitude, longitude, and height, and the accuracy rivals that of high-end stationary equipment.

The smartphone handles displaying positioning results and processing data in LRTK. Pressing the measurement button immediately records the current coordinate values on the phone along with date/time and notes. Positioning data can be converted and displayed in any coordinate system, such as Japan’s plane rectangular coordinates, and heights are automatically calculated up to geoid height. Recorded data is linked to cloud services, enabling one-touch sharing of field measurements with the office PC. In other words, precise coordinate data obtained on site can be instantly uploaded to the cloud and reviewed and used in the office without special software.

As for positioning accuracy, LRTK’s RTK method using signals from multiple satellites achieves horizontal accuracy of ±1–2 cm (±0.4–0.8 in) and vertical accuracy of about ±3 cm (±1.2 in). Even single short measurements often fall within the 1 cm range (0.4 in range), and averaging measurements can realize accuracy below 1 cm (below 0.4 in). Achieving precision comparable to expensive surveying equipment with an ordinary smartphone combined with a small device is a major appeal of LRTK. On site, the antenna receiver can be mounted on a pole (monopod), and height offsets can be corrected with a single button, enabling solo surveying workflows. Tasks that used to require two people can increasingly be completed by one technician with LRTK.

Furthermore, LRTK supports multi-GNSS (multiple satellite systems) and multi-frequency reception, which helps maintain high accuracy even in environments like mountainous or forested areas where conventional devices may experience unstable positioning. In practice, there have been reports where other manufacturers’ GPS units produced errors of 5 m (16.4 ft) or more in mountain sites, while LRTK achieved centimeter-order accuracy under the same conditions, demonstrating its high applicability on site.

Use Cases on Civil Engineering Sites (Design Line Verification, Temporary Structure Placement, As-Built Management, etc.)

Combining high-precision position information with 3D CAD data enables various applications on civil sites. Below are representative use cases.

• On-site verification of design lines: Design lines such as road centerlines or tunnel excavation lines can be accurately reproduced on site. With high-precision coordinates of reference points obtained by LRTK, walking along a route displayed on the smartphone lets you lay out the designed alignment on the ground. This allows you to check discrepancies between existing terrain and the design plan in advance and, if necessary, consider design changes or additional earthwork plans.

• Accurate placement of temporary structures: High-precision positioning is also useful for locating temporary fences, scaffolding, and temporary roads for construction. Even temporary elements that were traditionally positioned by measuring distances with a tape can be placed according to coordinates defined on the 3D design data, with LRTK confirming actual coordinates during installation. For example, when marking a foundation location for a temporary crane in advance, LRTK’s coordinate navigation can guide you to the designated point and enable marking within a few centimeters (a few inches), ensuring the temporary arrangement is correct immediately and preventing rework.

• As-built management and quality inspection: LRTK is powerful for measuring completed structures or developed land and comparing them to design data. With LRTK, you can quickly measure coordinates of key points and immediately grasp deviations from design values. For example, you can measure multiple points on the roadbed after grading to check whether heights and slopes match the design. Combining smartphone LiDAR functions makes it easy to capture 3D point clouds of as-built areas for whole-site checks. Because the acquired point clouds are georeferenced, you can bring them back to the office and overlay them with the design model for verification. These capabilities enable early detection of construction errors and more efficient proof of quality.

“One-Person Layout” Enabled by AR Display and Guidance of 3D CAD Data

High-precision positioning combined with mobile devices pairs extremely well with AR (augmented reality) technology. If you can view the site through a smartphone or tablet while overlaying the 3D CAD design model, you no longer need to refer to drawings and measure dimensions by hand. With systems like LRTK that know the user’s position to centimeter accuracy, the effort of aligning the 3D model on site is eliminated. The strength of AR display is that you can intuitively confirm whether the structure in the design data really fits in the intended location.

AR also enables a new working style of “one-person layout.” For example, stake-driving or marking that traditionally required a surveyor and an assistant can be done by a single technician with AR guidance. By following arrows or distance indicators shown on the smartphone screen to the target displayed, you can arrive at the specified coordinates. Alternatively, by displaying virtual stakes or component models in AR at the planned installation points and marking while viewing them, accurate layout can be completed on the spot. LRTK systems include a “coordinate navigation” function that sequentially guides points on site based on a preconfigured coordinate list in the cloud. Using this, tasks from finding boundary stakes to placing structures can be performed by one person without error. As labor shortages deepen, enabling one-person operations via AR plus high-precision GNSS will be a key to dramatically improving on-site productivity.

Effects on Design Verification, Construction Quality Improvement, and Management Efficiency

The integration of high-precision positioning and 3D data use is expected to bring the following impacts to civil construction sites.

• Improved accuracy of design verification: Discrepancies between design plans and on-site conditions can be accurately identified before construction begins. Projecting and verifying the 3D model on site makes it easier to judge whether construction can proceed as designed or whether design changes are necessary, greatly reducing the risk of rework or design errors discovered later.

• Improved construction quality: As-built shapes of structures can be strictly managed to prevent quality variability. Since it becomes easy to measure key positions and heights at any time and compare them to design values, construction errors can be minimized. Work that previously relied on the intuition of skilled craftsmen can be substantiated with data, leading to more uniform output and assurance of safety margins.

• Increased efficiency in construction management: Time and personnel required for surveying and inspection can be significantly reduced. If each worker carries a high-precision positioning tool, measurement and recording can be done whenever needed, and tasks that previously required outsourcing to specialist teams can proceed without wait times. Automatic cloud sharing of acquired data streamlines report creation and drawing revisions. On-site volume calculations using point cloud data can be performed instantly, enabling quick grasp of construction progress and responses. Additionally, reducing time spent entering hazardous areas for surveying or inspection yields secondary safety benefits. Overall, the fusion of digital and real-world data streamlines site management and enables high-level construction management even with limited personnel.

LRTK Implementation Example: How Simple Surveying and Model Guidance Change the Site

Finally, here is an example of the changes observed at a site that implemented LRTK. In a regional road improvement project, tasks that had previously required specialized surveying staff were handled directly by the site representative using an LRTK-equipped smartphone. Before construction, the current terrain was surveyed with LRTK and point cloud data were uploaded to the cloud, then overlapped with the 3D design model to pre-verify the construction plan. As a result, drainage planning defects that were not evident in the design drawings were identified and corrected before construction. During construction, the site representative used LRTK’s coordinate navigation to accurately mark installation positions for drainage structures and guardrails alone. Because the worker only needed to place stakes according to the AR model instructions on the smartphone screen, even less experienced personnel could position structures according to the drawings.

LRTK also proved powerful for as-built verification after concrete placement. The responsible person scanned the as-built area with LRTK mounted on a tablet, and compared the point cloud data with the design model. They confirmed on site that wall heights and tilts were within a few centimeters (a few inches) and immediately shared quality information with the client, facilitating smooth handover procedures. In this way, the introduction of LRTK’s simple surveying functions and 3D-model-based guidance is beginning to radically change site work. Data-driven construction reduces mistakes and improves work efficiency and quality, and it also has the potential to transform how field work itself is done. The fusion of high-precision positioning and 3D CAD is truly a pillar of DX (digital transformation) for future civil engineering sites.