Combining drones and photogrammetry to create 3D models in GNSS-deprived locations could be a game-changer for the inspection industry. For people responsible for conducting inspections in hazardous, confined, hard-to-reach locations such as smokestacks, sewers and nuclear facilities, sending in a drone to collect detailed data about the structure without endangering the inspector is an attractive option.
Unique Indoor Inspection Challenges
Critical assets must be inspected on a regular basis to ensure integrity of structures and support maintenance efforts. For indoor applications, access to confined spaces can be difficult and involve ropes, ladders, scaffolding, and small openings, not to mention airborne chemicals, radiation and other hazardous toxins. Environmental conditions often include dust, condensation, low or no light, and air turbulence, and the lack of GNSS signals adds another level of complexity.
Drones equipped with cameras and other sensors offer access to the inside of an asset without exposing a person to any of the dangerous conditions found in chimneys, boilers, tanks, tunnels, etc. In addition, drone inspections can be performed faster and at a lower cost as compared to manned entry, without extensive interruptions in operations. For example, inspecting a boiler at a power plant requires shutting down operations for several days while scaffolding is constructed inside the boiler, the inspection is completed, and the scaffolding is deconstructed. Not only is it risky for the inspector to be several hundred feet off the ground on a scaffolding, the plant owner loses revenue whenever power is not being generated. A drone inspection can be completed in a fraction of the time.
The co-founder of Swiss company Flyability, Dr. Adrien Briod, developed and patented novel approaches for the safe navigation of flying robots in cluttered environments while completing his doctorate at École Polytechnique Fédérale de Lausanne (EPFL). Dr. Briod’s interest in using robotic methods to enter hazardous and confined spaces increased after the Fukushima nuclear disaster in 2011. This led to the development of the Elios drone, equipped with a video camera, lights and a protective cage enclosing the entire unit. The collision-resistant system is designed specifically for indoor inspections.
Instead of utilizing LiDAR or SLAM technology to orient itself in a GNSS-deprived environment, the Elios relies on the operator, from outside the structure, to safely navigate while watching a live stream transmitted by the drone. After data are collected, photogrammetric software, such as Pix4D, creates a 3D model from the overlapping images and provides meaning and context. Operators are trained to plan their inspection and organize the data in a systematic manner, which enables the inspector to precisely locate a specified data point within the asset. Furthermore, the 3D models allow for advanced analytics of the data, such as performing measurements of defects or volumetry.
“Since the model itself is a patchwork of pictures extracted from a video, it is necessary to have one known distance within a model to scale the measurements,” explains Alexandre Meldem, vice president of sales, Flyability. “In a sewer, for example, the distance between the center of both manholes is known, which enables the inspector to accurately scale the 3D model and to draw accurate measurements from it.”
To protect life and property and avoid interruptions in service, critical infrastructure is subjected to rigorous inspections. Depending on the type of structure, there are governmental and industry organizations that set standards and recommend best practices for conducting periodic reviews. To perform as well as a person, the resolution of the data captured by the camera is comparable to what one would get with a human eye at “arm’s length” from the target. The Elios 2 collects images with a Ground Sampling Distance (GSD) down to 0.18 mm/px (0.007 in/px) at a 30 cm (11.8 in) distance.
In May 2019, the American Petroleum Institute (API) published a “Guide for Developing a UAS Program in the Oil and Natural Gas Industry.” With safety as its number one priority, the organization continues to study how drones can be integrated into very complex processes and how they might be used for inspections. The oil and gas industry is typically slow to adopt new technology until there is a clear demonstration of capabilities and proven results and testing is ongoing. It can take years to write new standards, but with increasing pressure to cut costs as oil prices fall, drones should be getting more attention.
The American Society of Mechanical Engineers (ASME) is also in the process of developing drone standards to serve as guidelines for its members. A Mobile Unmanned Systems Standards Commission was established in 2019 focused on developing safe and reliable applications for unmanned systems. The use of drones for inspecting and maintaining industrial facilities, power plants, pipelines, and other equipment has a great deal of potential to keep human inspectors out of harm’s way while cutting costs.
Collecting data in hard-to-reach locations without a person entering a dangerous environment is a major benefit of drone inspections. Post-processing creates photogrammetric 3D models for measuring and analysis, while the high-quality live stream allows an inspector to watch real time as the drone moves around the inside of a structure, as well as review the video later for a thorough visual inspection. The drone is capable of following straight lines, such as along a weld seam, and maintaining a stable distance from the camera to the object and between different objects within the asset. In addition to visual inspections, various types of sensors can be installed on a drone to collect data for other purposes, such as a thermal camera to detect heat. All these factors help make the drone inspection comparable, and in some ways superior, to a human inspection, without the added risk and potential health hazards.
“Elios 2 is first and foremost a tool for inspectors,” says Meldem. “We designed it to be easy and intuitive to operate. Our users range from inspectors flying for the first time to seasoned pilots who have been in aviation their entire lives.”
A version of this article was originally published in the June 2020 issue of POB.