Reducing Labor and Improving Efficiency in As-Built Management with cm-level accuracy (half-inch accuracy) Smartphone RTK and CAD Utilization

Challenges of Traditional As-Built Management and Drawing Creation

In civil engineering, as-built management is an important process that verifies and records whether the shapes and dimensions of completed structures and development sites match the design drawings. Proper as-built management ensures quality and smooth acceptance and handover to the client. However, traditional as-built management and surveying drawing creation have many challenges in terms of accuracy, time, and manpower. Representative examples are as follows.

• Heavy manpower and time burden: To measure as-built conditions in detail and produce drawings, multiple people, including skilled surveyors, were required to operate specialized equipment (levels, total stations, etc.). When measuring multiple locations across a large site, surveying and drawing creation could easily take a full day or more. Securing personnel and time was always a burden on the site.

• Limits to accuracy and missed details: Traditional methods could at best measure specified points one by one, making it difficult to capture the overall shape of a structure or ground. For example, cross-sectional surveys might only take points at intervals of several meters (several ft), risking the omission of undulations or gradient changes between points. Because confirmations could only be done at points, small discrepancies between paper drawings and the actual site might go unnoticed, creating the risk of being caught off-guard during later inspections with remarks like “this differs from the design.”

• Difficulty measuring hazardous locations: On steep slopes, under bridges, or inside narrow tunnels, performing as-built measurements with conventional methods can be unsafe or impractical. Attempting in-person measurements may require high-altitude work or traffic controls, posing risks to workers. As a result, hazardous areas were often left unmeasured, creating concerns for quality control.

• Inefficient manual recording and drawing work: Field measurements were recorded in handwritten field books or memos and later entered into spreadsheets or CAD software to create drawings. Height calculations and comparisons with design values were done manually, taking time and being prone to errors. Final documentation and reporting to clients were often paper-based, preventing real-time information sharing and causing rework.

As described above, the major challenge in as-built management has been how to achieve high accuracy with minimal personnel while reducing labor. Recently, initiatives like the Ministry of Land, Infrastructure, Transport and Tourism’s i-Construction are promoting 3D as-built management and the use of BIM/CIM, but handling high-accuracy 3D data with traditional methods is difficult. A new approach gaining attention is to leverage ICT to utilize point cloud data.

How RTK-GNSS Smartphone Surveying Works and Benefits of cm-level Accuracy (half-inch accuracy)

A promising new method to solve these problems is RTK-GNSS surveying with smartphones. RTK-GNSS, or real-time kinematic positioning, is a technique that dramatically improves positioning accuracy by correcting satellite positioning (GPS/GNSS) errors in real time using correction information from a ground reference station. In Japan, centimeter-class positioning augmentation services such as the Quasi-Zenith Satellite System’s CLAS are available, and using equipment that supports these services can achieve positioning accuracy within a few centimeters (within a few in). For example, while conventional smartphone GPS could be off by several meters (several ft) horizontally, using RTK can reduce horizontal error to about 2-3 cm (0.8-1.2 in) and vertical error to a few cm (a few in).

Recently, RTK positioning has become easy to use on smartphones. Previously, expensive GNSS receivers and base stations were required, but now compact RTK-capable GNSS receivers that attach to smartphones and dedicated apps can turn an everyday smartphone into a high-precision surveying device. The smartphone receives reference station data and satellite augmentation signals via the internet and instantly corrects measurements, so position errors that used to be several meters (several ft) are reduced to a few centimeters (a few in). This enables field technicians to perform centimeter-level measurements with ease.

The advantages of smartphone RTK surveying go beyond accuracy. There is no need to set up specialized surveying equipment; with just an antenna and a smartphone, one person can start surveying immediately. Measurement operations are simplified—pressing a button in the app can automatically record the current location—so results are stable regardless of the operator’s skill. The obtained position coordinates can be directly tied to a unified coordinate system such as Japan’s plane rectangular coordinate system, making it easy to compare measured points with design or CAD coordinates. Eliminating the coordinate transformations and calculations that were previously necessary is a major benefit. Furthermore, by using the smartphone’s camera or LiDAR sensor (laser scanner) to capture surrounding 3D data as point clouds and combining them with high-precision coordinates provided by RTK, advanced data utilization as described below becomes possible.

Immediate Drawing Generation from Point Clouds via CAD Integration

Because data acquired with smartphone RTK is digital and high-precision, it is revolutionary that drawings can be generated immediately without manual entry or drafting. With dedicated apps or integrated software, point cloud data collected in the field can be visualized on site and cross-sections or plan views can be automatically generated as needed. For example, many elevation points collected at a location can be used to draw cross-sections in real time, or the as-built profile can be checked on the smartphone screen immediately after measurement. Being able to verify measurement results on-site allows additional measurements to be taken immediately if omissions are discovered, preventing later rework.

Collected data can be shared instantly with the office PC via the cloud, allowing in-office designers and managers to review measurement results in real time. The receiving side can perform detailed drawing edits and analysis based on the point cloud and can automatically create verification drawings and reporting materials comparing them with the design as needed. Because surveying through drawing creation is seamlessly connected, time savings are significant and the lag between field and office is eliminated. Tasks that used to take a full day, such as creating as-built drawings, can now be completed on the same day as measurement.

Additionally, functions that extract necessary lines and surfaces from point cloud data and export them in CAD-friendly formats (e.g., DXF or LandXML) are available. This allows field-acquired data to be output directly as CAD drawings and incorporated into construction deliverables. Not only does this eliminate transcription errors and omissions, but it also reduces repetitive drawing work, significantly improving the efficiency of as-built management drawing creation.

Examples of Point Cloud Data Utilization: As-Built Heatmaps, BIM/CIM Integration, AR Visualization

High-precision point cloud data obtained with RTK-capable smartphones can be used in many ways beyond drawing creation. Representative use cases are introduced below.

• Quality checks using as-built heatmaps: By overlaying as-built point cloud data obtained after construction with the design model (3D design data or reference surfaces), a heatmap that color-codes the deviation of each point from the design can be generated. Areas with large positive deviations are shown in warm colors (reds), and areas with large negative deviations in cool colors (blues), visualizing errors by color. Variations in construction accuracy that might be overlooked in planar drawings or numerical lists can be grasped at a glance. For example, overfilled spots in embankments or uncut areas in excavation are emphasized in warm colors, making it intuitive to identify points that need immediate correction on site. Heatmaps are useful for on-site immediate inspections using tablets; colored 3D information can be checked without comparing drawings, making it easier even for less experienced technicians to understand. Uploading point cloud heatmaps to the cloud also enables remote inspections where office staff can check site as-built conditions over the internet.

• Data alignment with BIM/CIM models: Point cloud data integrates well with 3D design data such as BIM/CIM and contributes to advanced as-built management. BIM (Building Information Modeling) and CIM (Construction Information Modeling) are 3D design models used in architecture and civil engineering; overlaying as-built point clouds onto these models allows three-dimensional comparison and verification of design versus construction results. If acquired point clouds are unified in the same coordinate system as the BIM/CIM model, it is intuitive to see which parts deviate from design values. Besides quality checks during construction, as-built point clouds can be stored as digital records (a digital twin) after completion and used for monitoring long-term changes or planning future renovations. Point cloud data is not merely a pass/fail record but a valuable 3D asset useful throughout the lifecycle.

• Quantity calculation by point cloud analysis: Because point cloud data includes position coordinates for each point, it can be used for geometric calculations such as distance, area, and volume. For example, comparing pre- and post-construction ground point clouds allows accurate calculation of earthwork volumes, aiding not only as-built management but also schedule and progress management. Time-series differences in point clouds can also be used to monitor structural deformation or settlement.

• As-built visualization and guidance via AR: Using AR (augmented reality) on smartphones or tablets, design data or heatmap results can be overlaid on the real site view. For example, designers’ models can be displayed transparently over completed structures through a tablet screen, or heatmaps can be projected onto the ground to check finishing accuracy by color. This enables intuitive identification of discrepancies between design and actual conditions on site and helps locate corrective points immediately. Positioning tasks that were traditionally done with drawings and offset markings can be guided efficiently by AR displays indicating the “desired position.” AR, which superimposes the real world with digital information, is also a useful communication tool on site and makes explanations to clients and information sharing among stakeholders much easier.

Labor and Personnel Reduction and DX Benefits Brought by Smartphone Surveying

As described above, high-precision surveying using smartphones and data integration dramatically increases the efficiency of as-built management. Finally, the main effects on the field are organized from the perspectives of labor reduction, personnel reduction, and DX (digital transformation).

• Labor reduction: The total time from surveying to drawing creation and reporting is greatly shortened. Because field-collected data can be used directly, manual calculations and hand-drafting are reduced. For example, as-built measurement and drawing creation that used to take half a day or more can, in some cases, be completed in tens of minutes with smartphone surveying. The desk work burden on site supervisors is also reduced, allowing them to focus more on core construction management tasks.

• Personnel reduction: Since surveying can be completed with a single smartphone, one person can perform as-built measurements. The need for auxiliary workers or specialized survey staff can be greatly reduced, making it easier to cope with labor shortages on site. Because apps automatically handle surveying calculations and drawing generation, a certain level of accuracy can be ensured even without highly experienced personnel. Reducing task dependence on individuals and enabling anyone to perform stable-quality as-built management is beneficial for human resource development and workstyle reform.

• DX benefits: Data collected with smartphones can be instantly stored and shared in the cloud, digitally linking the field and office. New workflows for construction management that are not bound by location become possible, such as remote checks and approvals of as-built data and electronic acceptance approvals. Dependence on paper drawings and documents is reduced, helping prevent human error and speeding up information sharing. This aligns with the Ministry of Land, Infrastructure, Transport and Tourism’s push for i-Construction and ICT in construction, and further advances on-site DX.

Moreover, smartphone surveying reduces the risk of measurement omissions and re-surveying. By acquiring detailed point cloud data on the first pass, situations like “we forgot to measure that part” are less likely. If a deficiency is found, one person can quickly go back to the site to perform additional measurements, minimizing impacts on the schedule.

Introducing Smartphone RTK Surveying and CAD Utilization with LRTK

While the labor- and efficiency-saving potential of smartphone RTK and CAD integration is attractive, some may be concerned about whether they can implement it in-house. One solution to consider is LRTK, which enables easy high-precision surveying by combining a smartphone with a compact GNSS receiver. LRTK is a cutting-edge system for performing RTK positioning using smartphones and has proven compatibility with the Ministry of Land, Infrastructure, Transport and Tourism’s i-Construction initiatives. Specifically, an ultra-compact RTK-GNSS device is attached to an iPhone or Android device and a dedicated app receives correction information such as from the Quasi-Zenith Satellite System, enabling smartphone-based positioning with cm-level accuracy (half-inch accuracy). Using the smartphone’s built-in LiDAR or camera to perform 3D scans in that state allows anyone to easily acquire high-precision point cloud data.

By utilizing LRTK, the previously introduced combination of cm-level accuracy (half-inch accuracy) smartphone surveying and CAD data integration can be put into practice immediately on site. Because only a pocket-sized device and a smartphone are required, the initial implementation barrier is low (no large capital investment or specialized personnel required), and adoption by local governments and construction sites is increasing. There are also reports of use in disaster recovery sites and municipal public works. Features such as instant cloud sharing of survey results and one-touch heatmap analysis, along with intuitive operation that anyone on site can use, make it possible to incorporate these capabilities into in-house construction management without relying on specialized contractors. Take this opportunity to introduce smartphone surveying + CAD utilization using LRTK and experience the DX benefits in your as-built management.