Photogrammetry Makes As-Built Management Easy! Instantly Share Centimeter-Level Accuracy Data with Smartphone GNSS (cm level accuracy (half-inch accuracy))

In construction and civil engineering sites, confirming that completed structures have been built according to design—known as as-built management—is indispensable. One technology drawing attention recently for streamlining this process is photogrammetry. By generating 3D point cloud data from numerous photos taken with drones or smartphone cameras, photogrammetry can record the shapes and dimensions of constructed elements in detail, and is spreading as an alternative to traditional manual measurement. This article explains high-accuracy photogrammetry using smartphone GNSS and introduces the LRTK device, which enables centimeter-level positioning (cm level accuracy (half-inch accuracy)). Combined with point cloud scanning, AR (augmented reality), and cloud sharing, photogrammetry can greatly simplify as-built management—let’s explore the benefits.

What is photogrammetry? A new standard for as-built management

Photogrammetry is a method that generates 3D survey data from multiple photos of a site using specialized software. By overlapping many photos taken from different camera positions and angles, the object’s shape is reconstructed and output as a point cloud (a collection of numerous measured points). This makes it possible to measure dimensions of structures and terrain, and to detect deviations by comparing with design drawings. While traditional as-built management relied on manually measuring representative points, photogrammetry allows wide areas to be measured densely in a short time, preventing oversights while keeping detailed records—one of its major advantages.

With policy support such as the Ministry of Land, Infrastructure, Transport and Tourism’s *i-Construction*, ICT-based as-built management using photogrammetry and point cloud measurement is becoming an industry standard. For example, aerial photogrammetry with drones and ground scanning using LiDAR scanners built into iPhones and iPads are enabling high-precision, non-contact measurement of areas previously out of reach. Digitally recording the entire construction situation with photogrammetry not only streamlines the creation of as-built drawings and quality checks at inspection time, but also provides data for future maintenance and earthwork volume calculations (embankment/ excavation volume computation). Introducing photogrammetry into as-built management is attracting attention as a digitalization solution that achieves both quality assurance and efficiency.

Challenges of traditional as-built management

To better appreciate the advantages of photogrammetry, let’s summarize the issues of conventional as-built management methods. Previously, direct measurement and photographic records were central: tape measures, staffs, and levels were used to manually measure heights, thicknesses, and widths at each location, and these were compared to design specifications. For example, in road works, multiple measurements of roadbed and pavement thickness, width, and elevation were taken after completion to check whether they fell within allowable tolerances. Such methods have posed the following problems:

• Labor- and time-intensive: On-site measurements require multiple personnel and long hours; the clerical work to compile results into tables adds to the technical staff’s burden. It was necessary to arrange skilled surveyors, and with personnel shortages it was not easy to proceed efficiently within the construction schedule.

• Limited measurement points and uncertain accuracy: The number of points that can be measured manually is limited, making it difficult to comprehensively grasp the as-built condition. Measuring only a few points risks missing slight deviations from the design, which can lead to last-minute corrections if discrepancies are pointed out during inspections. Larger structures especially expose the limits of manual measurement, making it easy to overlook variations in as-built conditions or subtle surface irregularities.

• Human errors such as missing records: Busy sites can suffer from forgotten photos or recording mistakes. In particular, buried pipes and other elements that will be covered can become impossible to prove if photographic records are not taken before backfilling. Such human mistakes and omissions are weaknesses of conventional methods.

As described above, traditional as-built management is time-consuming and prone to oversights, so sites have strongly demanded more efficient and reliable methods. A key response has been DX of as-built management using digital technologies such as photogrammetry.

LRTK: Centimeter-level positioning anyone can do with smartphone GNSS (cm level accuracy (half-inch accuracy))

Photogrammetry and point cloud scanning are extremely useful, but traditionally they required expensive specialized equipment like 3D laser scanners and high-performance GNSS receivers, posing a barrier for small-to-medium sites. A recently notable solution combines smartphones with satellite positioning RTK technology. RTK (Real Time Kinematic) is a technique that corrects satellite positioning errors in real time; by attaching a compact RTK-capable GNSS receiver to a smartphone, anyone can easily perform centimeter-level positioning (cm level accuracy (half-inch accuracy)).

A representative device is LRTK, developed by Reflexia, a startup spun out of Tokyo Institute of Technology. LRTK is a pocket-sized RTK-GNSS receiver weighing approximately 125 g and about 13 mm (0.51 in) thick, which attaches magnetically to iPhones and iPads. Working with a dedicated smartphone app, it applies RTK corrections to provide real-time high-precision positioning anywhere, anytime. This small device can revolutionize surveying and as-built measurement tasks that previously relied entirely on experienced personnel.

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Main things you can do with LRTK: With just a smartphone + LRTK you can handle a wide range of on-site positioning and recording tasks. For example, by pointing your smartphone at an inspection point and tapping a button, you can instantly obtain and save the coordinates (latitude, longitude, elevation) of that location. You can perform point cloud scanning using the smartphone’s built-in camera or LiDAR to acquire 3D models of structures and terrain. Using AR features that overlay design drawings or reference point positions on the smartphone screen, tasks such as batter boards and staking out (positioning) can be performed accurately by a single person. The device also offers diverse functions in one unit, such as automatically tagging photos with positioning information for management.

Measured positioning data and point cloud models can be synchronized to the cloud on the spot, enabling immediate sharing of field measurements with office PCs or other stakeholders. For example, uploading to the cloud immediately after surveying allows remote offices to check as-built conditions in real time and promptly issue inspection responses or additional instructions. Because the device price is far more affordable than conventional surveying instruments and existing smartphones/tablets can be used, deployment at a rate of one device per person is progressing. Many construction management engineers and workers now carry LRTK, and the simplicity of turning a smartphone into a high-precision surveying tool is changing on-site norms.

How photogrammetry × LRTK improves efficiency and quality in as-built management

How exactly does deploying the smartphone GNSS device LRTK change as-built management on site? Here are the main effects of combining photogrammetry with LRTK.

• Dramatic reduction in work time: Surveying and as-built checks that formerly took half a day can be completed quickly, allowing immediate progression to the next process without wait times. Being able to measure and record quickly in-house without outsourcing leads directly to shorter schedules and increased productivity.

• Labor savings and response to staffing shortages: With a smartphone and LRTK a single person can complete surveying tasks, eliminating the need to assign multiple people. Even with a shortage of surveyors, on-site staff can efficiently carry out as-built management themselves.

• Prevention of oversights through high-density measurement: Point cloud data from photogrammetry enables area-wide measurement of the entire object, so small differences from design values or minor irregularities are not missed. Fully understanding the as-built condition leads to early detection and correction of quality defects.

• Improved safety: Dangerous slopes and high places can be measured non-contact from a safe distance. Reducing the need for awkward postures or climbing lowers the risk of worker falls.

• Real-time sharing and remote supervision: Measurement results can be shared instantly via the cloud, allowing remote monitoring of on-site as-built conditions and easy issuance of instructions or confirmations. This shortens lead times for as-built management and enables rapid reporting and inspection responses to clients.

• Low-cost introduction: LRTK itself is relatively inexpensive and leverages existing smartphones, reducing initial investment. Its cost performance makes it possible to start site digitalization without purchasing costly dedicated equipment.

Thus, the combination of photogrammetry and LRTK dramatically improves the efficiency and accuracy of as-built management. Large amounts of measured data are accumulated in the cloud, enabling later cross-section checks or automatic generation of as-built drawings, and driving transformation of business workflows. For promoting DX in construction management, photogrammetry plus smartphone GNSS is an extremely powerful tool.

Easy operation! Smartphone surveying anyone can start

Despite being advanced technology, LRTK is surprisingly easy to operate. Its intuitive smartphone app lets even those without surveying expertise quickly implement high-precision as-built management. The basic on-site surveying workflow is as follows.

• Attach the LRTK receiver to the smartphone – Use the dedicated case to mount the RTK-GNSS receiver (LRTK) to an iPhone or iPad. A magnetic attachment allows one-touch mounting.

• Launch the app and start positioning – Open the LRTK app and start positioning with a single button. Correction information (GNSS base station data and quasi-zenith satellite signals) is obtained automatically, and centimeter-level high-precision positioning (cm level accuracy (half-inch accuracy)) is computed in real time.

• Measure and record points – At the desired point, press the “position” button on the smartphone screen to record the latitude, longitude, and elevation. Date/time and point names are saved automatically, and photos can be taken with positioning tags embedded for management. If needed, the smartphone’s LiDAR can be used to scan the surroundings and convert them to point cloud data.

• Upload to the cloud immediately – When measurement is complete, recorded data can be uploaded to the cloud from the field with one tap. By accessing the dedicated web page from an office PC or tablet, shared positioning results and point cloud models can be reviewed immediately.

As shown above, there is no complicated setup or operation like with traditional surveying instruments—LRTK’s appeal is the ease of measuring whenever inspiration strikes. No paper logbooks or notes are needed; all acquired data are automatically organized and saved, preventing record omissions. Simply powering on and pointing the smartphone enables high-precision as-built measurement, reducing on-site staff workload while improving quality control accuracy.

The low barrier to initial adoption is another advantage. The dedicated app is provided free, and once you obtain the device you can start using it with your existing smartphone. It is designed to be usable without special training, making internal rollout easy and enabling local governments and small businesses to adopt it with confidence.

With national and local governments recommending full use of ICT construction and 3D data, photogrammetry + LRTK-based as-built management is poised to become the new standard. As a first step in site DX, adopting this smartphone GNSS solution lets anyone achieve effortless high-precision simple surveying. Why not introduce photogrammetry with LRTK at your site and begin efficient, reliable as-built management?