Make as-built control simple and reliable with LRTK! Strengthen quality control for civil engineering site managers

In the work of civil engineering site managers, quality control (one of the key management items alongside safety, schedule, and cost), and in particular as-built control, is an indispensable and important task. You must confirm that the structures completed on site have the dimensions and shapes specified in the design drawings and meet the prescribed as-built control standards. To do this, meticulous surveying and comparison of measured values with design values are required, but conventional methods take a great deal of time and effort and carry the risk of human error.

For example, the method of measuring one by one with tools such as tape measures and levels and checking a few cross-sections or points on the drawings may not capture the entirety of wide areas or complex terrain. With only a limited number of survey points, the conditions “between points” are not visible, and unexpected bumps or out-of-spec sections may be overlooked. Manual recording and calculation mistakes, and variability between measurers (low reproducibility) are also issues. Even if you thought you had checked thoroughly before an inspection, you may have experienced being told about issues during an as-built inspection and hurriedly performing additional measurements or rework...

To solve these problems and strengthen the quality control performed by civil engineering site managers, digital technologies such as point cloud data and AR (augmented reality) have attracted attention in recent years. With the Ministry of Land, Infrastructure, Transport and Tourism promoting *i-Construction*, 3D surveying and ICT construction are becoming more widespread. In fact, the ministry is promoting as-built control using three-dimensional data in fields such as ICT earthworks, and situations requiring a shift from traditional methods have been increasing. Using point clouds and AR makes it possible to visualize as-built conditions and dramatically improve accuracy, speed, and reproducibility. Moreover, by leveraging data, document preparation and inspection responses can also be made more efficient.

This article explains, for active civil engineering site managers, the benefits and concrete effects of using point cloud data and AR technology for as-built control. We will cover the differences from conventional methods, improvements in accuracy and work efficiency, and labor-saving for inspection preparation through data utilization, and look at how on-site quality control will change. At the end of the article, using the new simple surveying tool for smartphones LRTK as an example, we introduce an easy way to start DX for as-built control.

Visualize as-built conditions with point cloud data

Point cloud data are three-dimensional data that record the surface of an object as a collection of countless points. They can be easily acquired by laser scanners, drone photogrammetry, and more recently LiDAR scanners built into smartphones and tablets, enabling detailed surveying of terrain and structures with millions of points. Each point contains spatial coordinates (X, Y, Z) and color information, and by viewing the collection of points you can digitally reproduce the three-dimensional shape of the site.

If you use this 3D point cloud for as-built control, you can visualize the post-construction shape without omission. Since a large number of survey points can be captured at once even on wide sites, details that were easily overlooked with conventional methods can be covered. In other words, “missed points” are almost eliminated and the need for additional surveying is reduced. For example, slopes that were conventionally surveyed by taking sections at 50 m (164.0 ft) intervals can be recorded entirely with point cloud measurement, allowing accurate understanding of undulations in the intermediate portions as well. You will no longer worry later, “I forgot to measure that spot’s elevation.” From a single point cloud dataset, it is also easy to re-measure dimensions or cross-sectional shapes of any desired location afterward.

Furthermore, point cloud data have strong visual communication power as a 3D model. When displayed three-dimensionally on a monitor, subtle undulations and gradient differences that are hard to notice in photos or 2D drawings become immediately apparent. In this way, using point clouds lets you digitize the as-built state as it is, enabling everyone to share the same image of the site.

Intuitive on-site checks with AR technology

AR (augmented reality) technology is also a strong ally for as-built control. AR overlays digital information onto real-world imagery viewed through a smartphone or tablet screen. By using this, you can confirm design data overlaid on the actual construction situation while on site.

For example, by displaying the 3D design model in AR and overlaying it transparently on the real structure or terrain, you can intuitively grasp where the as-built deviates. Because you can immediately see which parts are constructed according to the design and which are not, it becomes easy to identify areas that need rework and to issue instructions for additional work. Tasks that used to involve holding drawings and measuring with a tape can be visually confirmed on the screen with AR, allowing subtle judgments that relied on intuition or experience to be made based on data.

A more advanced use case is comparing current point cloud data with the design surface to generate a heat map showing excesses and deficiencies and projecting it onto the ground with AR. If you color-code information such as where to excavate by how many cm (how many in), or how many cubic meters of fill are lacking compared to the design, instructions to field workers and explanations during as-built inspections will become extremely easy to understand. AR visualization can streamline on-site verification work and has the potential to shift site management from an artisan-like approach based on the experience of the construction manager to highly reproducible management backed by data. This enables less-experienced staff to perform high-quality as-built checks and reduces reliance on the instincts of veteran staff.

Dramatic improvements in accuracy, speed, and reproducibility

Introducing the latest point cloud surveying and AR technologies dramatically improves the accuracy, speed, and reproducibility of as-built control. The main points are summarized below.

• Improved accuracy: Point cloud data provide extremely dense and highly accurate measurement results. They can record object shapes down to the millimeter level, and when combined with RTK-GNSS positioning, absolute coordinate accuracy can also be ensured. Because details that were difficult to capture manually can be accurately recorded, it becomes possible to correctly grasp as-built dimensions and shapes and minimize deviations from design values in construction management. Moreover, once acquired, point cloud data become a digital asset that records locations of buried objects and details of structures, which is useful for future maintenance and verification. When you want to know “what was this like before?”, the data make it immediately clear.

• Increased speed: Leveraging 3D laser scanning or photogrammetry allows surveying that previously took several people half a day to be completed in a short time. For example, in a case that trialed simple point cloud measurement with a tablet, on-site as-built measurement was completed in just 30 minutes, drastically shortening work time. Because wide areas can be captured at once, rework due to forgotten measurements is also reduced, leading to overall shortening of construction periods and improved efficiency. Even on sites with labor shortages, a small team can quickly perform quality checks.

• Improved reproducibility: Digital data–based measurement reduces variability between people. The same standard point cloud data are obtained regardless of who performs the measurement, and multiple personnel measuring dimensions from the same acquired data will obtain consistent results. Judgments that used to rely on a veteran’s “sense” can now be quantitatively supported by point clouds and AR, increasing the reliability of inspection results. Human errors such as misreading handwritten numbers in a field notebook are reduced, enabling as-built control with high reproducibility where the same results are obtained no matter who performs the work.

• Improved safety: Point cloud measurement, drone, and photogrammetry can be performed contactlessly, allowing safe data acquisition even in hazardous areas where people cannot enter. Surveying of high places or unstable slopes can be done without personnel approaching them when using point clouds. As a result, the risk of accidents during surveying is reduced, contributing to site safety.

In practice, sites that have introduced ICT-based as-built control report dramatic improvements in productivity and efficiency of quality checks. For example, in one road construction site a trial of simple 3D scanning with a tablet completed as-built surveying that previously took three people more than half a day in about 30 minutes by one person, drastically reducing work time compared to before. In another case, prior to an as-built inspection the point cloud data were shared in the cloud with the client, and on the day of the inspection the contractor displayed the measured 3D model on a tablet while explaining, which made the confirmation process smooth and led to significant time savings. In this way, the effects of introducing digital technology in the field are steadily appearing, and conventional wisdom in construction management is being positively updated. Going forward, these technologies will become indispensable for labor-saving and sophistication of construction sites.

Streamlining document preparation and as-built inspection responses

Using point cloud data and AR significantly streamlines document preparation and responses to as-built inspections.

First, the creation of various documents and drawings related to as-built control is simplified. Previously, you probably spent a lot of time on desk work after surveying—cleaning up numbers noted in field notebooks or creating cross-section drawings in CAD software. But with digitally acquired point cloud data you can immediately extract required dimensions in software. For example, by setting an arbitrary cross-section line you can instantly draw and quantify that cross-section, and you can calculate fill and excavation quantities with a single click. For photo management, high-accuracy photos that automatically record shooting position and orientation can be stored in the cloud, and report PDFs in prescribed formats can be generated with one button. Tools with such automatic report-generation functions drastically reduce post-survey clerical work, enabling site managers to spend more time on substantive quality analysis and construction planning.

As-built inspections and external reporting will also become smoother. By using point cloud data, you can present persuasive evidence to inspectors and clients. If you display a 3D point cloud model on a tablet at an on-site inspection and show “it has been constructed according to the design cross-sections,” it becomes easier to obtain immediate pass/fail judgments. If the client has already reviewed shared cloud data in advance, the day-of inspection may only require formal confirmation in some cases. Even if defects are pointed out, the locations requiring re-measurement are identifiable on the point cloud, allowing rapid countermeasures. For projects that require data delivery, creating three-dimensional deliverables for electronic submission from the start reduces post-processing work. In fact, there is a growing trend for central and local government–commissioned projects to require electronic delivery of three-dimensional as-built data (such as LandXML) for as-built control, and point cloud surveying makes it easy to meet such requirements. Overall, digital as-built control reduces the burden of “preparation” for inspections and helps build a system where you can confidently face inspection days.

Achieve simple, reliable as-built control with LRTK

Even if you want to implement digital as-built control, you may hesitate thinking, “Doesn’t this require expensive 3D scanners and specialized knowledge?” However, in recent years easy-to-use solutions that anyone can handle have appeared. A prime example is the simple smartphone surveying tool LRTK.

LRTK is a product composed of a compact high-precision GNSS receiver (RTK-GNSS) attached to an iPhone or iPad, a dedicated app, and cloud services. It is attractive because there is no need to procure expensive dedicated equipment, allowing comparatively low-cost introduction. By simply walking around the site with the LRTK device mounted on your smartphone, you can record the surrounding terrain and structures as point cloud data with absolute coordinates. The operation is simple and requires no special training. In fact, it has been demonstrated that even large slopes can be scanned in about 1 minute, and beginners can easily handle it with one hand.

Acquired point cloud data are instantly uploaded to the cloud, where you can measure distances, areas, and volumes in a browser and perform error checks by comparing with design data. Measurements and output of deliverables compliant with the Ministry of Land, Infrastructure, Transport and Tourism’s as-built control guidelines are possible, and can be used directly for official as-built documents. For example, comparing the current point cloud with the design surface automatically creates an as-built heat map (a color-coded map of deviations from the design), showing required earthwork quantities and areas that need rework at a glance. Generated 3D point clouds and reports can be shared with stakeholders via the cloud, allowing seamless digital workflows from internal checks to reporting to the client.

LRTK also integrates AR functionality. Because high-precision positioning is possible, absolute-coordinate 3D models acquired and registered design drawings can be projected on site without misalignment. There is no worry that the model will drift as you walk around, making it powerful for sharing completion images between contractors and clients and for checking as-built conditions during construction. It also offers features that automatically attach positioning information to photos and coordinate-guidance navigation that leads you to stake-out positions, providing an all-in-one support tool for various aspects of construction management. LRTK has already begun to be introduced in municipal infrastructure projects and disaster recovery sites, and its convenience and reliability are attracting attention.

By using LRTK in this way, you can immediately put into practice the point cloud and AR as-built control methods introduced above on site without special equipment or advanced skills. By leveraging cutting-edge technology, you can significantly strengthen your quality control duties as a civil engineering site manager. Digital, accurate, and easy-to-understand as-built control will enable you to approach inspections and document preparation with confidence. The wave of on-site DX is already within your reach. Try these smartphone surveying tools and take the first step toward simple, reliable as-built control. The use of the latest technologies will be the key to elevating quality control to the next level. Realize dramatic improvements in quality and productivity with digital power and further enhance on-site capabilities by making digital technologies your ally. Do not fall behind the digitalization trend; actively utilizing these technologies will be crucial for future construction management. The future of the field has already begun.