3D CAD活用の新常識：スマホ測量LRTKで実現する現場DX

In the construction industry, designing with 3D CAD is becoming commonplace, but there are many voices saying that those data are not being fully utilized on-site. A gap still exists between 3D models and construction sites, and discrepancies between design drawings and the field have caused rework and inefficiencies. Emerging as a key to solving these issues and realizing true digital transformation on site (site DX) in recent years is smartphone surveying (LRTK). By combining smartphones with high-precision positioning technology, this approach makes it easy for anyone to digitize site conditions into 3D data and enables linkage with design data and immediate sharing. This article looks back at the traditional problem of the divide between 3D CAD and the field, explains the new workflows and bidirectional uses with 3D CAD data that smartphone surveying (LRTK) brings, explores the role smartphone RTK surveying plays amid trends like BIM/CIM and ICT construction, and finally introduces LRTK as a simple surveying solution that supports site DX.

3D CADと現場の断絶 – 従来の課題

Even when detailed design models are created with advanced 3D CAD software, the information has long been pointed out as not being fully utilized on site. Traditionally, construction sites often proceed based on paper drawings or 2D materials, causing the valuable 3D data to remain in the office. As a result, misalignments in understanding arise between design and site, and there are frequent cases where the as-built result differs slightly from the drawings.

This “divide between 3D CAD and the field” caused several problems. For example, structures that fit perfectly in the design model may not align in position or elevation in reality due to surveying accuracy errors on site or lack of terrain information, requiring adjustments after construction. Conventionally, surveyors would measure key points on-site after construction, compare them with the drawings, and only then confirm discrepancies. However, because design data and site information were not linked in real time, detection of small inconsistencies was delayed and sometimes caused rework.

Moreover, poor information sharing between the site and the office (design staff) was a major issue. Survey data and progress information generated daily on-site did not immediately reach designers; workers had to record data on paper or bring it back on USB drives to upload to office PCs, creating extra work. This time lag meant construction could continue without the latest site conditions being reflected in the model, putting stakeholders’ decisions and responses at a disadvantage. Compatibility issues when importing point cloud data or terrain models obtained by surveying into design software, and the complexity of data conversion between specialized software, also hindered on-site utilization. These factors combined led to a situation in which the site could not fully reap the benefits of the 3D CAD data that had been created.

スマホ測量（LRTK）が変える作業フロー

In recent years, smartphone surveying has emerged as a technology that significantly changes this situation. Smartphone surveying refers to a method that combines a smartphone with a high-precision GNSS receiver (RTK method) and, as needed, integrates the phone’s built-in LiDAR sensor or camera to easily perform surveying and 3D measurement on-site. LRTK is a representative example: a small RTK-GNSS receiver is attached to a smartphone to enable centimeter-level accuracy (half-inch accuracy) positioning while allowing 3D scanning and AR display. Tasks that previously required expensive dedicated equipment and skilled surveying techniques can increasingly be performed by anyone using a smartphone combined with LRTK.

The main innovations brought by smartphone surveying (LRTK) are as follows:

• 点群データの手軽な取得: Using the latest smartphones (for example, models equipped with LiDAR), you can scan terrain and structures while walking the site and obtain large collections of points (point cloud data). High-density 3D measurement that previously required terrestrial laser scanners or drone photogrammetry can now be achieved with just a smartphone. Processing the obtained point clouds yields detailed 3D models of the site, which can be used for as-built verification against design data or for recording construction progress.

• センチメートル級の高精度測位: With RTK-GNSS technology, even smartphones can obtain highly accurate position coordinates with errors reduced to a few centimeters (a few inches). Simply attaching a dedicated small receiver to a smartphone dramatically improves the errors that were several meters (several ft) with conventional GPS, enabling measurements directly tied to survey control points and design coordinate systems. This makes it possible to record latitude, longitude, and elevation of points at the push of a button or to perform precise stakeout in a plane rectangular coordinate system.

• 現況の即時把握と共有: A major advantage of smartphone surveying is the ability to confirm and share data obtained on-site immediately. Point cloud data and measured coordinates can be uploaded to the cloud directly from the smartphone, allowing designers and clients in the office to share information in real time. For example, if you scan the site right after a day’s work and share the as-built data in the cloud, office staff can check that 3D data the same day to perform quality checks or approve as-built conditions. Previously, it could take several days to process survey data and prepare reports after returning to the office, but smartphone surveying enables sharing the site’s “now” the same day, drastically speeding up decision-making.

• ARによる直感的な現場可視化: Point clouds obtained by smartphone surveying or pre-prepared 3D design models can be displayed as AR (augmented reality) on a smartphone or tablet. Thanks to high-precision positioning from RTK, digital models can be precisely overlaid onto the real world. For example, point cloud models can visualize the locations of underground pipes to guide excavation, or a planned building model can be overlaid on the actual landscape to share the expected finished appearance with the client. Conventional simple AR functions often suffered from positional drift, but RTK-based accuracy reinforcement prevents model displacement even with extended AR use. AR allows design intent to be communicated intuitively on-site, helping prevent construction errors and facilitating stakeholder consensus.

Furthermore, the Ministry of Land, Infrastructure, Transport and Tourism revised the as-built management guidelines in 2022 to explicitly mention mobile-device-based 3D measurement methods, and smartphone + RTK simple 3D surveying is increasingly recognized as a valid public method. Demonstration experiments confirmed that the error between point clouds obtained with smartphone LiDAR and verification points measured with a total station was about 1-2 cm (about 0.4-0.8 in), sufficiently meeting the conventional quality standard (within ±5 cm (±2.0 in)).

As described above, smartphone surveying dramatically streamlines the site surveying and measurement workflow. Tasks that previously required several people and a full day can, in some cases, be completed by a single person in tens of minutes. The simplicity of being able to complete measurements just by walking the site with a device also reduces the need to enter hazardous areas and lowers worker burden, delivering safety and labor-saving benefits. The environment in which anyone can perform high-precision site measurement routinely is taking shape, marking a major step forward in site DX.

3D CADデータとの親和性と双方向活用

As smartphone surveying becomes widespread, the linkage between data obtained on-site and 3D CAD data from the design stage will become dramatically smoother. This is especially because the absolute coordinates provided by RTK—such as those in global geodetic systems or public coordinate systems—allow on-site point clouds and measured coordinates to be unified with the design model’s coordinate system. Previously, point clouds obtained by laser scanners required post-hoc assignment of reference point coordinates for alignment, but smartphone + RTK can produce georeferenced 3D data at the time of acquisition. With such a data foundation in place, information can be used bidirectionally between design and construction.

• 設計データを現場で活用: Digital 3D design models can be directly used in field operations. If a design model is loaded into a smartphone app and displayed in AR, the finished shape—difficult to grasp from drawings alone—can be shared on-site, enabling all members of the construction team to work with a common understanding. Based on coordinates in the model, key stakeouts (marking pile-driving positions or guiding heavy equipment operation) can also be performed. In other words, rather than translating design data onto paper, referencing and using it digitally on-site makes it easier to accurately reflect design intent in the field.

• 現場データを設計にフィードバック: Point clouds and measured coordinates of as-built conditions obtained by smartphone surveying can be fed back to designers and construction managers immediately. Shared via the cloud, the latest site 3D data can be overlaid with office CAD models for rapid verification of construction progress and quality. Small deviations or issues discovered during construction can be identified early, allowing immediate model revisions or issuance of additional instructions if necessary. After completion, the high-precision as-built data can be used to create delivered 3D deliverables (As-built models) or be used as digital twins for maintenance management.

By adopting smartphone surveying, the cycle of design → construction → verification becomes seamlessly connected through data. Information that tended to flow one-way—from design to construction—transforms into a bidirectional digital flow from the field, keeping design models and on-site reality synchronized. This contributes to ensuring design quality, improving and advancing construction efficiency, and accelerating the PDCA cycle targeted by BIM/CIM.

BIM/CIM活用やICT施工におけるスマホRTK測量の位置付け

Smartphone RTK surveying (the use of smartphones + RTK technology) is beginning to occupy an important position within the accelerating trends of BIM/CIM utilization and ICT construction. BIM/CIM is an approach that uses 3D models to centrally manage information across construction projects, and the Ministry of Land, Infrastructure, Transport and Tourism is promoting its application to centrally managed projects, driving digitalization across the industry. To support these initiatives at the field level, it is essential to “bridge the gap between surveying and design models” and “connect the site and the office in real time.” Smartphone RTK surveying is a field-side solution to precisely these challenges.

Traditionally, ICT construction sites have focused on drone-based 3D surveying and machine-guided equipment. In addition to these, easy-to-use smartphone surveying is expected to be a tool that further advances site DX. For example, in places where drones cannot fly—such as indoors or mountainous areas—or for fine as-built checks that heavy equipment cannot handle, smartphone + RTK allows people to walk the site and collect data directly. It is suitable for small projects and daily progress management, and the agility of being able to “measure right when needed” without arranging large-scale equipment is a major advantage.

The reduced cost and simplification of smartphone surveying devices have also made it realistic to equip the site with “one device per person.” If site supervisors and foremen each carry an LRTK-equipped smartphone and can quickly perform surveying, measurement, and recording at any time, delays due to waiting for surveying can be eliminated. Because anyone on site—not just a specialized surveying team—can obtain survey data, parallel processing of tasks and rapid verification become possible, improving overall productivity. In addition, software that automatically handles complex calculations and coordinate corrections makes the tools easy to use even for less experienced staff, serving as a measure against the aging of skilled workers and labor shortages. Smartphone RTK surveying will increasingly establish itself as the next-generation standard supporting BIM/CIM and ICT construction.

現場DXを支援するスマホ測量ソリューション：LRTK

Finally, as one solution that makes it easier to introduce such smartphone surveying technology on-site, we introduce LRTK. LRTK is a pocket-sized device that transforms a smartphone into a surveying instrument with centimeter-level precision (half-inch accuracy). A dedicated ultra-compact RTK-GNSS receiver is attached to the smartphone with a single touch, and just by launching the app, high-precision positioning starts immediately. Then, by moving to the points you want to measure and following on-screen instructions, a single device can perform position measurement, point cloud scanning, photography, and AR display. Measurement data are saved to the cloud in real time, allowing data confirmation and sharing on-site without bringing data back to the office.

As an all-in-one surveying tool, LRTK is easy to deploy on-site. The device itself weighs only a few hundred grams and has a built-in battery, so it can be carried all day and used whenever needed. It is also much more affordable than traditional surveying equipment, making it a familiar tool that field practitioners can carry as their own. Actual sites where LRTK has been issued one-per-person and each worker performs measurements as needed are already appearing, proving that an environment where you can “measure when you want” directly links to productivity improvements.

A high-precision, easy-to-use smartphone surveying device like LRTK is a powerful partner for promoting site DX. By linking digital models created in 3D CAD with real-world construction sites in real time and removing the barriers between design and construction, its effects are substantial. The use of such digital technologies will dramatically improve site productivity and safety. If smartphone surveying technologies like this become established as the new normal for 3D CAD utilization, a future will come in which anyone can freely handle digital data while carrying out construction. As the first step toward site DX, why not consider introducing smartphone surveying LRTK?