From Infrastructure Inspection to Disaster Survey: Photogrammetry Use Cases and Their Benefits

In recent years, photogrammetry has attracted attention in the fields of infrastructure maintenance and disaster prevention. Photogrammetry is a technique that generates 3D models of objects from multiple photographic images. For example, structures and terrain are photographed from various angles with drones or digital cameras, and specialized software analyzes those images to construct high-density point cloud data and detailed three-dimensional models. As a result, it becomes possible to digitize the shapes of bridges and buildings with millimeter-level precision (mm), bringing unprecedented efficiency and accuracy to infrastructure inspections and disaster surveys.

This article explains specific photogrammetry use cases and the benefits they provide for municipal infrastructure managers, disaster prevention personnel, construction engineers, and surveying companies. From infrastructure inspections to immediate post-disaster situational awareness and structural deterioration diagnosis, we will examine how 3D data generated from photographs can transform fieldwork and contribute to improved safety, work efficiency, and accuracy.

Use of Photogrammetry in Infrastructure Inspection

In infrastructure inspections of road bridges, tunnels, elevated facilities, and the like, inspectors traditionally had to climb to high places or go underneath bridges for close visual inspection. This required erecting scaffolding, using aerial work platforms, imposing traffic restrictions, and other large-scale efforts and costs, and it always involved safety risks for workers. Using photogrammetry can drastically change these inspection methods. By mounting a high-resolution camera on a drone (small unmanned aerial vehicle) and photographing bridges and roads from the air, detailed image data of the inspection targets can be obtained in a short time. When many captured images are analyzed with photogrammetry and converted into 3D models, a digital inspection model that includes hidden and high-elevation parts of the bridge can be produced.

The advantages of drone photogrammetry for infrastructure inspection are primarily safety and speed. Inspectors do not need to perform dangerous high-altitude work and can safely collect data from the ground. Also, the need to erect scaffolding or implement long-lasting lane closures is reduced, minimizing social impact. In actual cases using drones, the time required to inspect a single bridge has been reduced from more than 8 hours with conventional methods to about 2–3 hours. Some projects have achieved inspection time reductions of up to approximately 70% and corresponding cost reductions of 40–60%, which is a significant benefit for sites that must maintain many infrastructure assets with limited budgets and personnel.

Furthermore, 3D models created by photogrammetry excel as precise records. Inspectors can check deterioration areas on the model and take measurements. Whereas inspection results were traditionally recorded in reports with planar drawings and photos, 3D models allow a three-dimensional understanding of the entire structure so that other personnel can accurately share the situation later. Introducing photogrammetry into infrastructure inspections therefore delivers high effectiveness across efficiency, safety improvement, and data accumulation.

Use of Photogrammetry in Disaster Surveys

Photogrammetry is also a powerful tool for situational awareness and damage surveys immediately after large-scale natural disasters. At sites of earthquakes, landslides, floods, and other events, the damage area can be extensive and may include locations too dangerous for people to enter. In such cases, 3D mapping using drone aerial photography plus photogrammetry is effective.

For example, at a landslide site, a drone can photograph the entire affected area from above, and from that set of images a 3D terrain model and orthophotos (overhead maps) can be created. Because the extent of the slide, the volume of displaced material, and the condition of damaged structures can be visualized quickly, disaster response headquarters can obtain detailed damage distribution maps on the day the event occurs. This enables rapid situational awareness and appropriate initial response. Decisions about which roads are severed and which areas should receive priority for rescue and relief can be made faster than before.

Also, immediately after a disaster there are many places at risk of collapse or secondary hazards, and protecting the safety of survey personnel is a major challenge. Photogrammetry allows remote acquisition of information from dangerous areas where people cannot safely approach, enabling necessary data collection while ensuring worker safety. Small drones can fly over narrow spaces and rubble and record damage from angles that are difficult to achieve by human access. Such data are useful not only for immediate disaster response but also for later damage verification and recovery planning. By using photogrammetry to create a “digital record” of the site from the time of occurrence, the situation can be accurately reconstructed and analyzed even after time has passed.

Structural Deterioration Diagnosis and Maintenance

Photogrammetry is also effective for diagnosing deterioration of structures such as bridge piers, dams, tunnels, and buildings. Deterioration phenomena such as cracks, delamination, and rust have traditionally been inspected by close visual examination and measurements. However, by using high-resolution 3D models and orthophotos obtained through photogrammetry, deterioration on structural surfaces can be comprehensively captured in a planar manner.

For example, photographing and modeling a bridge’s concrete surfaces with photogrammetry allows all occurring cracks to be visually identified on the model. It is easy to mark deterioration locations on the 3D model and measure their precise coordinates or crack lengths. In practice, initiatives exist that use defect distribution maps generated from photogrammetry (drawings that show deterioration across the entire structure) to extract and report crack distributions. This makes it visually very easy to show which parts have what level of deterioration, increasing the persuasiveness of diagnosis results.

Such high-precision, easy-to-understand data greatly contribute to developing maintenance plans. If digital records obtained by photogrammetry are accumulated at each periodic inspection, it becomes possible to quantitatively compare whether deterioration has progressed over time. Structural health assessments, which previously tended to rely on experience, can shift to objective, data-driven decisions, enabling accurate determination of repair priorities and timing.

Rapid Situational Awareness and Decision Support

The rapid situational awareness provided by photogrammetry greatly increases the speed of decision-making in infrastructure management and disaster response. Traditionally, obtaining an on-site understanding required people to walk every corner of the site, collect notes and photos, and bring them back for analysis. That process could take time and risk delaying responses.

In contrast, 3D models and orthomaps generated by photogrammetry can reproduce the current state of a site on a desk. Personnel can change viewpoints freely on a PC in the office and perform necessary measurements and analyses immediately. Sharing data among stakeholders lets multiple departments and experts discuss while viewing the same site model, smoothing consensus building. This is powerful not only during disasters but also in routine tasks such as planning infrastructure repairs. For example, if stakeholders share a complete bridge model before major repairs, problems can be identified and countermeasures considered without attending on-site briefing sessions.

Thus, rapid situational awareness through photogrammetry improves both the speed and quality of decision-making. When decision-makers have accurate information quickly, planning and execution of countermeasures proceed without delay, ultimately contributing to residents’ safety and peace of mind.

Improved Safety of Work

One major effect of using photogrammetry is improved safety of fieldwork. Infrastructure inspections and disaster surveys often involve hazardous tasks. Bridge inspection at height carries fall risk, and surveying steep terrain carries the risk of slips. Using drones and photogrammetry to eliminate the need to enter such hard-to-access areas is a significant advantage.

For example, where personnel formerly descended to steep cliffs or disaster-affected terrain to perform measurements, replacing those tasks with drone aerial photography eliminates the need to enter hazardous locations. Likewise, inspections of bridge undersides that were performed using aerial work platforms or suspended inspection vehicles can be substituted with drones to reduce the number of times workers must go to heights. These changes not only reduce the risk of falls and related accidents but also lessen the mental burden associated with such work.

Moreover, remote measurement with photogrammetry shortens work time under harsh environmental conditions such as extreme heat or cold. Because on-site work is more efficient than traditional total station surveying, long hours of strenuous or repetitive work are reduced, helping prevent heatstroke or frostbite. The safety benefits therefore extend beyond direct accident prevention to worker health management and reducing labor burdens.

Improved Accuracy and Data Usability

Photogrammetry is not only safe and fast but also excels in the accuracy and usability of the data obtained. Point clouds and 3D models generated from photographs can represent details finely, depending on camera resolution and shooting conditions. It is possible to capture minute cracks in structures and slight irregularities of ground surfaces, allowing detection of abnormalities that might have been missed by visual inspection.

In terms of surveying accuracy, well-planned photogrammetry surveys can cover wide areas with errors within several centimeters to several tens of centimeters (several inches to several feet). Furthermore, by combining RTK-GNSS (Real-Time Kinematic positioning), it is easy to assign centimeter-level position coordinates to the captured photos and point clouds. This makes it possible to align photogrammetry-derived 3D data precisely with public coordinate systems and overlay them with maps and CAD drawings. In the infrastructure management field, the use of digital models such as BIM/CIM is advancing, and models obtained by photogrammetry are suitable for integration into such platforms.

Regarding data usability, a major strength of photogrammetry outputs is that they are fully digital. Distances, areas, and volumes can be measured freely on 3D models, and cross sections can be extracted at arbitrary locations for drawing. For example, accurate volumes of displaced material can be calculated from point cloud data of a collapsed slope to aid removal planning, or cross sections of bridge models can be drafted to examine reinforcement work—the range of applications is wide. In addition, data can be shared and stored in the cloud, facilitating remote information sharing and future reanalysis. Once acquired, a 3D model remains as a nearly permanent record as long as the site itself is not lost. This is useful for long-term infrastructure asset management and building disaster archives.

*(※BIM/CIM: Three-dimensional integrated modeling methods in architecture and civil engineering. BIM stands for Building Information Modeling and CIM stands for Construction Information Modeling.)*

Key Benefits Expected from Introducing Photogrammetry

We have reviewed the effectiveness of photogrammetry from various perspectives. Finally, here are the main benefits you can expect by introducing photogrammetry into the field.

• Streamlined inspections and surveys: Wide areas can be converted into 3D data in a short time, greatly reducing work time compared to manual methods. Multiple locations can be surveyed and inspected quickly even on limited schedules.

• Improved safety: Reducing the need to enter dangerous areas and replacing on-site work at heights or disaster sites with remote methods lowers the risk of accidents and health-related harms to workers.

• Precise data acquisition: The shape of objects can be digitally recorded with millimeter- to centimeter-level precision (mm to cm), making it easier to detect anomalies that were previously invisible. Photogrammetric point clouds also include color information, allowing intuitive understanding of deterioration and damage conditions.

• Cost reduction: Reducing scaffold construction, heavy equipment use, and personnel deployment leads to long-term reductions in maintenance and survey costs. Indirect cost savings can also be expected through reduced duplicate surveys and faster decision-making enabled by data sharing.

• Data accumulation and reuse: With digital 3D records accumulated over time, analyses of long-term changes and future planning become possible. Sharing data in the cloud enables real-time collaboration between field and office, improving the decision-making process.

Making Photogrammetry Accessible with LRTK Simple Surveying

While the effectiveness of photogrammetry is clear, some may feel it seems difficult to implement or that specialized equipment and knowledge are required. Indeed, conventional setups often required high-resolution cameras mounted on drones, high-performance PCs, and specialized software, which gave the impression of a high barrier to entry. Recently, however, solutions that make these advanced technologies easy to use have appeared. One such solution is the simple surveying system for smartphones called LRTK.

LRTK is a next-generation surveying tool consisting of a pocket-sized device attached to a smartphone and a dedicated app. By attaching an ultra-compact RTK-GNSS receiver to a smartphone, centimeter-class positioning that formerly required specialized equipment becomes accessible to anyone. A single smartphone becomes a high-precision surveying instrument, and functions such as coordinate measurement, photo capture, point cloud scanning, and AR-based position confirmation can be handled with intuitive operation.

For example, using LRTK makes it simple to obtain high-precision point cloud data on site. By following prompts in the dedicated app and walking slowly around structures or terrain while pointing the smartphone, photos are automatically taken and 3D model generation by photogrammetry is performed. The resulting point clouds and models are tagged with precise RTK position information, allowing immediate measurement of distances and areas on site and instant sharing with the office via the cloud. The system is designed so that personnel without specialized training can use it, and the concept of one smartphone per person makes it revolutionary for advancing digitalization of field sites.

LRTK also includes features useful for infrastructure management, such as a “positioned photo” function that automatically records coordinates and orientation with captured images, and AR functions that overlay design drawings onto the site. Its price is much more affordable than conventional surveying equipment, and using a dedicated cloud service allows real-time sharing of data between field and office. LRTK is a solution that makes photogrammetry and high-precision 3D surveying—previously considered high-barrier technologies—usable in everyday operations by anyone.

To maximize the benefits of photogrammetry for infrastructure inspection and disaster surveys, it is important first to adopt a system that acquires digital data at the site. Tools like LRTK make it easy to take that first step. Why not leverage the latest technology to dramatically improve efficiency and safety in infrastructure maintenance and disaster prevention work? Introducing photogrammetry and simple surveying is likely to be the key to transforming future infrastructure management.