Promoting Labor Reduction and DX on Site with Smartphone RTK and CAD Integration at Centimeter Accuracy

In the construction industry, CAD-based drawing and design have long been widely used, but there have been many challenges in linking those designs with field survey data. For example, conventional field surveying typically involved multiple people using total stations or GPS surveying instruments to measure key points, taking handwritten notes back to the office, and then creating CAD drawings—an analog workflow. This process required a lot of manpower and time, and because measurements were limited to specific points, it was often impossible to grasp the entire site accurately. Manual data transcription also introduced the risk of human error, leading to drawing mistakes and inconsistencies with the design. Furthermore, the aging of experienced survey technicians and a lack of successors are serious issues, and the very notion that “surveying is done by a team” is becoming increasingly unsustainable.

Against this backdrop, government-led *i-Construction* initiatives (a revolution in construction productivity through ICT technologies) and the application of work-style reform laws in 2024—known as the “2024 problem”—have made DX (digital transformation) urgent in the construction industry so that limited personnel can work efficiently. In particular, surveying and design—the starting point for on-site DX—are attracting major attention for new solutions. One such solution is the realization of “single-person surveying” through high-precision positioning using smartphone RTK and CAD integration. By linking smartphones with CAD, a new era is opening in which labor reduction and operational efficiency on site can be advanced at centimeter-level accuracy (half-inch accuracy).

The emergence of smartphone RTK and the benefits of centimeter-level positioning

RTK (real-time kinematic) is a technology that corrects error factors in satellite positioning such as GPS via communications to achieve real-time centimeter-level positioning accuracy. Traditionally, expensive and bulky setups were required, including stationary high-end GNSS receivers, base station sets, and radios, but recent miniaturization and cost reductions have led to the development of ultra-compact RTK receivers that can be attached to smartphones. This reduces the position error of smartphone-built-in GPS—which was typically around 5–10 m (16.4–32.8 ft)—to several centimeters, enabling accurate coordinates to be obtained on the spot. For example, if you attach a pocket-sized RTK receiver to your device, you can achieve immediate high-precision positioning with lightweight equipment that can be handled with one hand, including antenna and battery. There is no need to carry special tripods or long poles, and you can move nimbly even in confined or sloping areas, reducing the burden for elderly veterans or those with less strength.

A major advantage of smartphone RTK is not only the improved accuracy of location information. Intuitive smartphone apps allow anyone without specialized knowledge to complete positioning and data storage with the push of a button. Simply placing the device at a measurement point and pressing the app’s “measure” button will record latitude/longitude and elevation in real time, and measurement time, point names, and accuracy status (such as FIX) are automatically attached. The app can also automatically convert to Japan’s plane rectangular coordinate system and perform geoid height conversions, so users do not need to worry about complex calculations or coordinate transformations. This ease of handling high-precision positioning is the innovation of smartphone RTK, greatly lowering the barriers to field surveying.

Because positioning can be obtained at centimeter accuracy, height measurements and precise layout of design lines can also be carried out with just a smartphone. Height determination and layout work on the order of a few centimeters—tasks that were difficult with conventional smartphone GPS—are now possible with RTK. These technological advances offer a convenient alternative to traditional total stations on construction sites where surveying accuracy is required. Moreover, coordinates obtained with smartphone RTK can be aligned directly with the coordinate systems used in CAD and BIM, so data collected on site can be immediately reflected in CAD drawings and 3D models—another major benefit.

Concrete workflow from point-cloud surveying to AR visualization, CAD drawing, and BIM/CIM integration

By leveraging smartphone RTK, the workflow for acquiring and using detailed 3D site data is dramatically simplified. Here we look at the specific flow from point-cloud surveying to AR visualization, CAD drawing, and BIM/CIM integration.

• Digitalizing the site through high-precision point-cloud scanning By combining a smartphone’s LiDAR sensor or high-resolution camera with RTK positioning, the entire site can be captured as point-cloud data. Countless measurement points are recorded as 3D point clouds with global coordinates, enabling the immediate construction of a digital twin that includes terrain and structures down to the millimeter level. Scenes that used to rely on experience and only measured a few dozen points can now yield data on the scale of millions of points in a short time, enabling a comprehensive and detailed understanding of site conditions without omissions.

• On-site visualization of design information using AR Using the high-precision coordinates obtained, a smartphone’s AR (augmented reality) functions can project electronic drawings or 3D model design lines onto the actual site. Because RTK eliminates alignment errors, planned lines and structural models from the drawing can appear on site at their true positions. This makes it easy to check for clashes between the design and site terrain before construction, or to visually confirm pile-driving locations on the spot—enabling real-time reconciliation between design and site. Complex layout tasks can be accurately performed by a single person by following AR displays, helping to prevent construction mistakes.

• Converting point-cloud data into CAD drawings Point clouds and survey coordinate data collected on site can be shared immediately to office PCs via the cloud and directly utilized for CAD drawing. For example, cross-sections or plan views can be extracted from point clouds as base drawings for CAD, or measurement coordinates can be imported directly into electronic field tablets or design CAD for drafting. There is no need to recreate drawings from handwritten notes; the initial survey data can be used directly for design and construction drawings, eliminating duplicate data entry and transcription errors. Designers can instantly revise drawings or perform quantity calculations based on the latest survey information from the field, enabling faster feedback for design changes.

• Seamless integration into BIM/CIM High-precision data obtained with smartphone RTK is also valuable on 3D model-based platforms such as BIM/CIM. Importing point clouds and survey coordinates into BIM/CIM software makes it easy to simulate construction steps and perform 3D verification of as-built conditions. Overlaying design models with current point clouds enables intuitive visualization—using color-coding—of excesses and deficiencies in filling or excavation, making it immediately clear where rework is needed and helping to prevent backtracking. At project completion, before-and-after point cloud comparisons can be used to automatically generate as-built documents for electronic delivery. The linkage of smartphone RTK and CAD thus facilitates the preparation of digital deliverables compatible with the Ministry of Land, Infrastructure, Transport and Tourism’s BIM/CIM principle application. *（※As of fiscal 2023, BIM/CIM application began in principle for public works）*

Labor reduction and real-time utilization realized by single-person surveying and cloud sharing

The most direct effects of smartphone RTK × CAD use are reduced personnel for surveying and real-time data utilization. Surveys that once required two or more people—a person operating the instrument and another holding a prism or stake—can be completed by a single person with smartphone RTK. With a handheld smartphone surveying setup, you simply touch the point and record it, eliminating the need for another person to hold a target. This can reduce a survey that previously required two people half a day to a single person finishing within a few hours—an enormous reduction in labor. Not only are fewer people needed, but time spent on setup and cleanup is also shortened, dramatically reducing total work time.

Immediate cloud sharing from the smartphone app further contributes to labor reduction and efficiency. Measured point information and point clouds are uploaded to the cloud on the spot, allowing office staff to check site conditions in real time. For example, if the on-site person performs a solo survey and instantly sends the data, designers or supervisors in the office can view the latest measurements on their PCs and provide appropriate instructions. This enables a kind of remote presence—“remote site verification”—allowing decisions to be made without work being stalled while waiting for supervisor approval. The ability to measure immediately when needed and share results with everyone removes the waste of “work being suspended while waiting for a surveying team to be arranged.”

Personnel freed up by labor savings can be reassigned to other important tasks, improving overall productivity. On sites lacking experienced staff, young employees or non-survey personnel can perform data collection with smartphone RTK while veterans focus on key checks—an optimal division of roles. Constantly sharing the latest data via the cloud lowers the barriers between site and office, providing a foundation for the whole team to advance projects more efficiently.

Concrete examples of on-site DX accelerated by smartphone RTK × CAD

Centimeter-accuracy surveying with smartphone RTK and CAD linkage is creating many use cases that concretely drive on-site DX. Below are representative examples.

Faster design revisions through instant reflection of survey data in drawings

Previously there was a time lag from when points were measured on site to when they were reflected in drawings, delaying design changes and construction reviews. By instantly reflecting high-precision data obtained with smartphone RTK into CAD drawings via the cloud, site-originated feedback can be used in design in real time. For example, measured ground elevations or the actual positions of structures discovered during excavation can be added to drawings immediately and used as decision material for design changes within the same day. This significantly speeds up the design-construction PDCA cycle, enabling early correction of rework and design errors.

Advanced and efficient as-built management

Smartphone RTK × CAD is also powerful for managing as-built conditions during construction and at completion. Where previously selected finish dimensions were measured and checked, smartphone RTK and point-cloud technology allow you to measure entire construction objects in 3D to verify as-built status. Overlaying point clouds with design data makes it possible to intuitively identify excesses and shortages in embankment or excavation and to visualize finish deviations, ensuring no out-of-spec areas are overlooked. Quality control personnel can share these data on the cloud and immediately instruct corrective actions if issues are found. This minimizes rework and touch-ups, achieving both quality assurance and schedule shortening.

On-the-spot design verification and appearance checks

Combining smartphone RTK and AR allows design verification (validation of design content) to be conducted efficiently on site. For structures before completion, you can overlay the design model on the smartphone screen to check on the spot whether construction is proceeding according to design. For example, you can check whether the positions of rebar or bolts match the drawings by viewing them in AR. Compared with eyeballing drawings by hand, digital-to-digital verification is more precise and prevents overlooked checks. Projected 3D models can also be used to verify interactions with the surrounding environment or visibility. These uses enable faithful realization of design intent and early detection of changes.

Smooth response to construction inspections and electronic delivery

Digital data obtained with smartphone RTK is also effective for client inspections and interim inspections after construction. High-precision as-built data and current point clouds are stored electronically, allowing you to present objective evidence during inspections. For example, reporting discrepancies between as-built dimensions and design values enables inspectors to verify numbers easily, making explanations smoother. Electronic submission of deliverables is increasingly common, and point clouds or photos obtained with smartphone RTK (such as 360-degree images with geotags) can be submitted via cloud shared links. This allows you to present convincing digital deliverables that are difficult to achieve with paper drawings or photo books, enabling confident inspection responses. In cases where remote presence is accepted, you may even share cloud-based 3D data with inspectors and explain findings without being physically present—realizing remote inspection attendance. Overall, inspection processes become more efficient, smoothing the path to handover.

Implementation effects: cost benefits, improved safety, and ease of operation

Adopting smartphone RTK surveying and CAD integration brings many benefits in terms of cost-effectiveness, safety, and ease of training and operation.

• Improved cost performance: Smartphone RTK requires a lower initial investment compared to dedicated surveying equipment, and directly reduces outsourcing and personnel costs for surveying. If work that used to require two people can be done by one, labor costs are saved, and shortened surveying durations reduce costs such as heavy equipment standby fees and site management expenses. Real-time data sharing also helps reduce design mistakes and construction rework, which is another significant cost saver. Because precise surveying can be done in a short time, tasks that were previously outsourced to specialist firms can increasingly be brought in-house. Overall, the cost-effectiveness of introducing smartphone RTK is extremely high.

• Improved safety: Lightweight, compact smartphone surveying equipment enhances the safety of surveying tasks. There are fewer instances of transporting heavy equipment long distances or adopting dangerous postures at height to take measurements, so reduced workload leads to lower accident risk. Being able to measure in confined spaces alone also allows non-contact data acquisition in hazardous areas previously inaccessible to personnel. For example, displacement measurements on steep slopes or dimension checks in deep excavations can be performed by LiDAR scanning from a safe distance. Additionally, the simplicity of smartphone surveying enables more frequent measurements, allowing early detection of deviations or anomalies during construction. This helps prevent serious defects or disasters and raises overall site safety management standards.

• Ease of use for everyone: Surveying systems that run on smartphone apps are characterized by being easy to learn intuitively from juniors to veterans. Because measurements can be performed by following on-screen prompts and pressing buttons, new employees can be site-ready after a short training session. Unlike traditional surveying instruments, complex setup and specialized knowledge are unnecessary, encouraging non-survey staff to try measuring themselves. As a result, site supervisors and foremen can perform surveys and confirm conditions on the spot, which also aids skill transfer: even those with limited experience can achieve veteran-level results using digital tools, raising the organization’s overall technical level. Because the platform is a smartphone, functional expansion is easy, enabling multifunctional use such as point-cloud scanning, photo documentation, and AR surveying. The availability of measurement by anyone when needed dramatically improves information sharing and decision-making speed on site.

Conclusion: Accelerate on-site DX by adopting smartphone surveying

Using high-precision smartphone RTK and CAD integration can streamline every process on construction sites—from surveying to design, construction, and inspection—making it possible to achieve both labor reduction and improved quality. It is truly the case that “on-site DX starts with surveying,” and this digital technology is a trump card for a productivity revolution. The smartphone-attached RTK solution *LRTK*, which has emerged in this context, is attracting attention as a groundbreaking initiative that turns each worker’s smartphone into a versatile surveying instrument. Sites that have implemented LRTK report more than 30% reduction in surveying work time from the first week, along with optimized personnel allocation and quality improvements through instant measurement. Developed by a startup, LRTK is an ultra-compact receiver about 13 mm (0.51 in) thick and weighing about 125 g, which attaches to devices like iPhones and achieves centimeter-level positioning on its own. It includes a dedicated app and cloud service, and acquired data are immediately plotted and shared on maps. It supports network RTK that receives correction information from nationwide reference station networks over the internet, and in areas without communications infrastructure it is reinforced by CLAS signals from quasi-zenith satellites, enabling stable positioning even in underserviced locations.

Above all, LRTK is designed so that anyone can easily perform single-person surveying, and some sites even report that new employees learned to operate it like a game. From checking positioning status to saving data and sending it to the cloud, everything is completed with a single tap—paper field notebooks are unnecessary. The obtained point clouds and coordinate data can be directly imported into BIM/CIM and various CAD software, enabling on-the-spot comparison with design models and creation of as-built drawings. By effectively leveraging such solutions, high-precision surveying and immediate data sharing can dramatically transform on-site operations. In the context of MLIT-promoted i-Construction and construction DX, smartphone RTK-driven labor savings and sophistication are being adopted across regions, including by local governments.

Even starting with small sites or trial introductions, there is great value in experiencing the effects of smartphone surveying. On-site DX begins with the surveying under your feet. By proactively adopting the latest technologies and establishing a new site style where “each person is a surveyor” without clinging to past conventions, future construction sites will evolve to be smarter and more sustainable. Please consider introducing smartphone RTK solutions at this opportunity to accelerate on-site DX at centimeter accuracy. Smartphone surveying using LRTK should bring solid innovation to your sites as well.