Conventional Surveying VS Smartphone RTK! A Thorough Comparison of Efficiency in As-built Management

In site construction management, confirming that completed structures are built according to design—as-built management—is an indispensable and important process. Traditionally, experienced surveyors have measured as-built conditions using total stations (TS), tape measures, staffs, levels, and other tools, creating vast amounts of records. However, in recent years, a new technology combining smartphones and RTK-GNSS, " smartphone RTK surveying " , has emerged and is bringing about a dramatic change in the way as-built management is performed. This article thoroughly compares conventional surveying methods and smartphone RTK (LRTK), explaining the differences in efficiency, accuracy, and cost. Aimed at site managers, construction management engineers, municipal procurement officers, and ICT promotion staff, it details the advantages and disadvantages of the old and new methods and the potential that smartphone RTK can offer.

What is construction completion management? Its purpose and importance

"As-built control" is a construction management process that verifies and records whether the structures and terrain completed by the construction work have the shape and dimensions specified in the design. It is also an important task to demonstrate with measurement data that the actual finish falls within the allowable ranges of the specification standards (as-built control standards) set by the client (owner). Simply put, the purpose of as-built control is to inspect " whether the work was carried out according to the design drawings " and, if problems are found, correct them to ensure quality.

Especially in civil engineering and other public works, the results of as-built management become prerequisites for inspection approval and handover, so it is particularly emphasized among construction management. Also, in projects with long construction periods, parts that will be hidden after completion (such as buried items or the interior of structures) may no longer be visually verifiable later, so it is necessary to take measurements and photographic records at each stage during construction and to store them appropriately. For example, points such as whether the rebar before being covered with concrete matches the drawings, or whether the depth and slope of buried pipes before backfilling comply with the specifications, must be recorded before they are later covered. Through such continuous measurement and recording, it is ensured that the final as-built condition throughout the entire project falls within the allowable range of the design standards—this is the role of as-built management. It can be said to be an indispensable process for ensuring quality and fulfilling accountability to the client.

Conventional Methods of As-Built Management and Their Limitations

For many years, measurement for as-built quality control has been carried out mainly by direct measurement and photographic records. Using tools such as tape measures, staffs (leveling rods), and spirit levels / levels, heights, widths, and thicknesses at key points of the construction site are measured manually one by one. For example, in road construction, the thickness, width, and elevation of the roadbed and pavement are picked up and measured at several dozen locations after completion to check whether they fall within the standard values specified in the design documents (allowable tolerances). The typical process was to organize the measurement results into drawings and tables and create and submit as-built control drawings/tables and photo books.

However, several major challenges and limitations have been pointed out with this kind of manual, labor-intensive as-built management.

• Labor- and time-intensive: Measuring dimensions on site typically requires teams of two or more workers, and if there are many measurement points, surveying can take many hours. Even when using precision instruments such as total stations, setup and observations are time-consuming, and operation requires specialized skills. On busy sites, securing the personnel and time to carry out these measurements was a major burden for site supervisors and construction management engineers.

• Risk of insufficient coverage and overlooked issues: With manual measurements, there is a limit to the number of points that can be physically measured, making it difficult to check every part of the construction. Even if measurements at representative points are within standards, slight unevenness (surface irregularities) or dimensional errors between those points may go undetected. In practice, there have been cases where it was only during inspection that it became clear “part of it differs from the drawings,” resulting in urgent rework. The larger the structure, the greater the limitations of manual measurement, and the more likely variations in the as-built condition and minute deviations are to be missed.

• Possibility of human error: Measurement tasks and record-keeping are inherently subject to human mistakes. Due to being busy, omissions in records can occur; for example, if you forget to take photos before backfilling buried items, you may be unable to prove that the work was carried out after completion, which at worst could develop into a dispute. Numerical transcription errors when copying up handwritten notes can also happen. In this way, conventional methods—"the measurable range is limited to points" and "human errors can occur"—were not only a cause of quality risks and rework but also a major source of stress for on-site personnel.

Because of the issues described above, on-site practitioners have long been seeking a new method that can perform as-built management more efficiently and reliably.

A New Era in Construction Management: The Emerence of As-Built Management Using Smartphone RTK

In recent years, the wave of DX (digital transformation) has reached the construction industry as well, and the digitization and streamlining of construction management tasks have become major themes. The Ministry of Land, Infrastructure, Transport and Tourism has also been promoting innovation in construction using ICT (information and communication technology) under an initiative called *i-Construction*. As part of this, the introduction of three-dimensional measurement technologies into as-built management is progressing, such as photogrammetry using drone aerial photographs and non-contact measurement with terrestrial 3D laser scanners. For example, point cloud data obtained by laser scanners contain information about the entire space made up of countless measurement points, making them effective for quickly capturing the as-built conditions of large areas as a whole. The use of these 3D technologies is becoming the "new normal" in as-built management.

On the other hand, high-performance surveying instruments and laser scanners are very expensive and require specialized knowledge to operate, so they have posed high barriers for small- to medium-sized sites. A new approach that has attracted attention is combining smartphones and RTK-GNSS. By fusing the smartphone’s built-in cameras and sensors (recent iPhones include LiDAR scanners) with high-precision positioning technology using real-time kinematic (RTK), smartphone surveying that allows a single person to perform centimeter-level (cm level accuracy, half-inch accuracy) surveying and as-built measurement without special skills is becoming a reality. This is expected to greatly streamline as-built management, which has relied on expensive equipment and skilled personnel, and to improve productivity.

One representative solution is LRTK, developed by the startup Reflexia. LRTK is a pocket-sized, ultra-compact RTK-GNSS receiver designed to be attached to an iPhone or similar device; by connecting to a smartphone via Bluetooth, it enables high-precision positioning without cumbersome cables. It weighs about 165 g, is slim at just over 1 cm (0.4 in) thick, and its built-in battery allows several hours of continuous use. By simply attaching this small device to your smartphone, your everyday smartphone is transformed into a surveying instrument with centimeter-level accuracy (cm level accuracy (half-inch accuracy)).

A dedicated app that leverages LRTK also comes all-in-one with a wide range of functions needed for as-built management. In addition to single-point coordinate measurement, smartphone LiDAR-captured point cloud data measurement, area and volume calculations for as-built verification, layout (positioning) assistance that displays drawing coordinates on site, and even comparison with design data and simulations using AR (augmented reality) display, a variety of tools can be used within a single app. Positioning data, point clouds, and photos acquired on site are synced to the cloud in real time, and a system is in place that allows the office or remote locations to check the situation and share data. In other words, with one smartphone + LRTK, you can handle all surveying and as-built management tasks that previously required separate equipment and manual work.

These smartphone RTK-based as-built management methods are beginning to be positioned as formal measurement and recording methods that conform to the Ministry of Land, Infrastructure, Transport and Tourism's As-built Management Guidelines (Standards for As-built Management). In fact, point-cloud scanning using LRTK has been confirmed to meet the accuracy criteria of the latest as-built management guidelines (for example, the approximately ±5 cm (±2.0 in) accuracy required for as-built measurements of earthworks and slopes), making application to as-built management for public works possible. When combined with control points and reference marks as needed and the measurement results are corrected in absolute coordinates, as-built records with accuracy comparable to conventional TS surveying can be achieved. In terms of reliability for new technologies, methods that comply with official standards can also be adopted by clients with confidence.

Main features of Smartphone RTK (LRTK)

The main features provided by the smartphone RTK solution (LRTK) are summarized as follows:

• High-precision RTK positioning: Multi-GNSS-compatible RTK-GNSS enables real-time centimeter-level positioning (half-inch-level positioning) on a smartphone. Each acquired point is assigned latitude, longitude, and height in the World Geodetic System, allowing coordinates to be recorded with accuracy comparable to conventional surveying instruments.

• 3D point cloud scanning: Using smartphone‑embedded LiDAR sensors and cameras, you can rapidly scan the surfaces of structures and terrain to acquire high-density 3D point cloud data. Because the point clouds fused with LRTK’s RTK positioning information include absolute coordinates, the as-built condition of the scanned area can be preserved as a digital record of the entire space. A single person can measure large areas in a short time, capturing details comprehensively that conventional methods could not fully measure.

• As-built verification with AR: This function overlays design drawings and BIM/CIM 3D models on a smartphone and combines them with the actual site conditions using AR (augmented reality). This enables you to compare the design data for the finished form with the actual work in progress and visually confirm any discrepancies on the spot. For example, in slope construction you can display the designed slope gradient model in AR and add and shape the on-site soil until it matches the model. By using AR for as-built management, construction can proceed while checking in real time on site whether the work conforms to the design.

• Form and Report Output: This feature automatically generates and outputs the prescribed as-built management charts and reports from the measured as-built data. It greatly streamlines the preparation of documents for submission to the ordering party by extracting arbitrary cross-sections from point cloud data to compare with design cross-sections and by compiling the differences between measured values and design values into tables. Tasks that were previously done manually in Excel or CAD software—such as creating charts and tables—can be completed with the push of a button using smartphone RTK, reducing the burden on field technicians and helping to prevent errors.

• Cloud sharing and data utilization: With LRTK, survey point coordinates, point clouds, and photo data can be uploaded to the cloud from the field in real time, allowing the entire team to share the latest data over the Internet. In the cloud viewer, you can overlay 2D drawings and 3D models and perform analyses such as measuring distances, areas, and volumes. This enables seamless exchange of information between the field and the office, so all stakeholders can discuss and make decisions while viewing the same data. The data are stored securely and become easy to search and reuse in the future, so they also help with asset management (asset management) after construction completion.

Comprehensive Comparison: Conventional Surveying vs Smartphone RTK — Evaluation Across 10 Criteria

Now, let's compare conventional surveying methods and smartphone RTK from various perspectives. To make the differences in efficiency and accuracy clear, we will evaluate the following 10 items.

• Accuracy: Traditional surveying with TS and levels can achieve millimeter-level precision, but it requires linking survey points and is time-consuming. On the other hand, smartphone RTK, using RTK-GNSS, can achieve approximately ±1-3 cm (±0.4-1.2 in) accuracy on its own. Its horizontal accuracy rivals that of TS, and its vertical accuracy is sufficient to meet construction as-built management standards. By measuring a wide area as a point cloud, slight shifts between points can be detected, so it excels at combining necessary and sufficient accuracy and coverage.

• Working time: Measuring many points with a tape measure or total station required time for positioning, reading, and recording at each survey point. With smartphone RTK, you can simply walk the site and scan to acquire tens of thousands of data points in a matter of minutes. For example, a pavement thickness measurement that used to take half a day can be completed in about 10 minutes with a smartphone RTK, so you can dramatically reduce measurement work time. This, in turn, leads to overall efficiency improvements in construction management and shorter project schedules.

• Required personnel: Traditionally, operating surveying instruments and maintaining staff required at least two people, and in some cases teams of three or more. Smartphone RTK surveying can basically be completed by a single person. Because you can take measurements simply by walking while holding a smartphone in one hand, there is no need to allocate other workers. Even in situations where the site must be run with a small number of people, as-built management can be carried out without issues.

• Training costs: Handling precision surveying equipment requires specialized knowledge and experience, and training skilled personnel takes time and money. Smartphone RTK can be operated intuitively via a smartphone app, and the barrier to proficiency is low. By following the app’s guidance, non-surveying specialists can acquire the necessary data, and with short-term training anyone can learn to use it. This creates flexibility that allows everyone on site to take on measurement duties even amid labor shortages.

• Initial cost: Conventional TS and GNSS surveying instruments are expensive equipment that cost several million yen or more per unit, and when you factor in software and maintenance costs they required a large investment. With smartphone RTK, you only need to equip your handheld smartphone with a compact receiver costing several hundred thousand yen and an app service. Subscription-based usage plans are also available, so you can reduce initial expenses. Because the price point allows provisioning one device per person, it becomes easier to set up an environment where devices are ready to use whenever needed.

• Data organization: In manual surveying, it was necessary to perform hand calculations and enter data into Excel to produce charts and diagrams. With smartphone RTK, data are acquired digitally from the start and organized in the cloud. Because measurement results are automatically saved, linked with photos, and compared with design data in real time, cumbersome data organization and input errors are greatly reduced. The creation of as-built drawings is also automated, so you will no longer be burdened with preparing paperwork on site.

• Report handling: The as-built management documents to be submitted to the client (as-built management charts, photo books, etc.) have predetermined formats, and were traditionally compiled manually to match those formats. With smartphone RTK, you can automatically generate documents in the prescribed format from measurement data, shortening the time required to prepare submission documents. It is also easy to extract necessary cross-sectional drawings and height distributions from point cloud data and include them directly in reports. Because electronic delivery can also be handled smoothly, explanations and submissions to the client become more efficient.

• Safety: There have traditionally been situations that involved risk, such as measurements at height and surveying on roadways. With non-contact measurements using smartphone RTK, you can obtain data remotely without entering hazardous areas. It also contributes to ensuring worker safety because there is no need to have personnel enter areas where heavy machinery is operating. Also, because surveying can be completed in a short time, the risks of accidents and heatstroke from prolonged heavy labor can be reduced. If the positions of buried objects are visualized using AR functionality, it can also help prevent accidental damage during excavation.

• Maintenance and management: Surveying instruments require regular calibration and maintenance, and when they fail, manufacturer repairs can be costly and time-consuming. With smartphone RTK, the device itself has a simple structure, and functionality can be improved through software updates. Another advantage is that performance can be enhanced simply by swapping in a newer smartphone model when necessary. Also, because as-built data is accumulated digitally, it can be used directly for post-completion infrastructure maintenance and management (inspection and future renovation planning). This offers high long-term value by making the reuse of data, which was difficult with paper drawings or photo logs, easy.

• Client relations: With conservative clients, concerns about new technologies sometimes lead them to request implementation using traditional methods. However, ICT-based construction is now being promoted by both the public and private sectors, including the Ministry of Land, Infrastructure, Transport and Tourism, and as-built management using smartphone RTK is increasingly being recognized as a formal measurement method. In fact, if as-built data are submitted as point clouds or 3D data, clients can understand the quality in detail and feel reassured. Cloud sharing enables real-time information sharing with clients and allows them to check the as-built condition from the construction phase. In this way, digitizing communication with clients increases transparency and helps build trust.

From the above comparison, it is clear that as-built management using smartphone RTK offers greater efficiency and convenience than conventional methods in many respects. However, depending on site conditions (such as GNSS signal reception), there may be situations where conventional equipment is used complementarily, so a realistic approach is to transition by combining them appropriately where needed.

Benefits of Smartphone RTK: From the Perspective of Each Stakeholder

The introduction of as-built management using smartphone RTK brings significant benefits and effects to each stakeholder, from construction sites to clients.

• For site representatives and construction management engineers: The burden of surveying and record-keeping is reduced, enabling high-precision as-built management with fewer personnel and in less time. Being freed from cumbersome form creation allows more time to be devoted to process management and quality improvement. In addition, adopting digital measurement contributes to promoting on-site DX and realizes a smart way of working that appeals to young engineers.

• For municipal officials and procuring authorities: Because the results of as-built management can be obtained as detailed 3D data, it becomes easier to objectively verify quality during inspections. Having data-based evidence increases the procuring authority's confidence and smooths handover procedures. In the future, that data can also be used for maintenance management (infrastructure asset management), helping reduce lifecycle costs and enabling planned maintenance. In addition, ICT utilization aligns with national policy and may be regarded as an advanced example.

• For those in charge of ICT promotion: It provides a concrete means to achieve the goal of introducing smart technologies on-site. Smartphone RTK is a relatively inexpensive and immediately effective DX tool, and it should be easy to demonstrate results as a champion for promoting digitalization within the company. Because it can show quantitative effects such as improved safety and increased efficiency, it can also serve as persuasive material for management and other departments. Furthermore, information sharing via the cloud promotes collaboration both inside and outside the company, contributing to increased productivity across the company and strengthened competitiveness.

Conclusion: Easy As-Built Management Starting with Smartphone RTK

We have compared conventional surveying and as-built management using smartphone RTK—how did you find it? Smartphone RTK, which achieves both on-site labor savings and quality assurance, will become a powerful tool in construction management going forward. In particular, with the advent of portable smartphone RTK devices like LRTK, "simple surveying that one person can perform anytime, anywhere" has become a reality.

For those still accustomed to conventional methods, it may be met with skepticism at first. However, once you actually experience as-built management using smartphone RTK, you will be surprised by its efficiency and reliability. By combining the intuition and experience of seasoned professionals with the latest technology, you can build a more robust quality control system than ever before. Even on sites facing labor shortages, this approach—which enables high-precision surveying and record-keeping to be carried out swiftly—will bring significant benefits to all stakeholders.

Finally, if you feel your company's construction management has challenges, why not try introducing simplified surveying with smartphone RTK? By leveraging LRTK, cumbersome as-built management can be transformed into something surprisingly smart. Now is the time to make the latest technology your ally and take a step forward in on-site DX. We hope that the new era of efficient as-built management brought by smartphone RTK will bring significant transformation to your site.