Inspecting Damage at Deerhaven Power Plant
Altavian recently seized a rare opportunity to work with a local utilities provider, while conducting research and development at the same time. Gainesville Regional Utilities (GRU) contacted Altavian about having drones assess damage suffered at one of their power plants. GRU did not want to risk workers surveying a structural integrity issue on a pollution control structure. Altavian wanted to test a new quadcopter in development with an actual project out in the field.
“Drones could provide GRU a close-up, birds-eye view of the damaged area quickly and without putting human lives in harm’s way. As a result, GRU and OEM representatives could thoroughly assess the initial damage and begin to plan the next safest course of action.” – Daniel Grant of GRU.
The timing was urgent with the threat of Hurricane Matthew churning toward the Florida coast. This created two goals for the job: (1) Have drones assess damage at the plant and deliver the information to GRU so they could make the best decision regarding the structure and, (2) Test the quadcopter’s ability to generate a 3D point cloud model using oblique imagery. In short, it was an ideal chance to tie-in with local business while also continuing development on a new technology.
Description of Site
The power plant’s pollution control tower suffered structural damage and was displaying visible signs of leaning. The tower itself was surrounded in scaffolding and weather stripping for protection which complicated matters. So, GRU wanted to survey the structural integrity without jeopardizing the safety of any of their workers. This was a great project for drones to tackle as they are cheap, safe, and can be deployed quickly. For the quadcopter, this would be a difficult structure to model in 3D, yet a task it should theoretically be able to achieve. To assess performance, we needed to put the quadcopter into action to learn about its capabilities and short-comings.
Altavian sent two operators to the plant to meet with GRU’s representatives and fly the missions all in one day. With the hurricane approaching, GRU’s representatives wanted “to quickly assemble as many structurally related data points as possible. One of these points being the most efficient way to externally attach to and support the damaged section before further damage could be done.”
The operators inspected the site and the surrounding area to plot out the best approach for the flights. GRU needed data points from of all sides of the tower as well as top-down imaging to assess the roof of the structure. The idea was to have drones assess damage existing currently to find suitable locations for securing the structure. With the tower secured, repair and safety crews could operate with minimal danger.
Planning the Flights
Altavian’s operators determined that approximately three flights were needed for a complete image survey due to the numerous obstacles surrounding the tower. They divided the flights into three functions: two vertical imaging flights that concluded with half-arcs around the structure and a final arc at a higher altitude and distance for depth and perspective before flying directly over the structure. The ground control station (GCS) would be located near the structure for the first two vertical flights. However, for the flights making broader arcs, the operators moved the GCS farther away for launching and landing.
The flights themselves would be relatively short, if all went well, so the data could move into processing quickly. Finally, the operating team would take hand-held photographs from the ground in an arc pattern along the outside. GRU could then look at the information provided to make the best decisions based on the aerial assessments.
The first two vertical flights each began at opposite ends of the tower structure. The drone would begin at one of these points and climb straight up snapping pictures. Once at altitude, the drone would make a half-arc, to the center axis of the tower, taking photographs. The drone began just above ground level and rose to a maximum height of 85m. After the conclusion of the first two flights, the operators relocated the GCS for the third flight.
The third flight was an arc flown at a broader diameter around the out-facing portion of the tower. The idea was to get some perspective and depth for the 3D construction. After completing the arc, the drone flew directly over the top of the tower. This gave GRU a top-down look at the structure and was important for generating the point cloud.
All three flights took approximately 17 minutes, combined, capturing 218 photographs.
Finally, Altavian’s operators took photographs from ground level around the base of the tower using a hand-held camera and GPS unit. Data processers could then combine the pictures to form a 3D point cloud model. The idea is to assemble the point cloud by utilizing depth and perspective from imaging captured on the arcing flights combined with the nadir images from flying directly over the structure.
GRU was able to assess and make decisions about the structure from the data collected. According to Daniel Grant: “Initially, the drone images were used as a tool to study the state and extent of damage done; however, as more became known about the actual damage, these same drone images were used to safely plan routes for work crews and further manned investigations.”
In this situation, the drones assessed the damage by capturing images without putting anyone in harm’s way. Later, they found a second purpose for the images: plotting safe routes for workers.
For Altavian, it was possible, using the data collected, to build a 3D point cloud. We built the 3D point cloud by aligning images captured in the half-arc flights and the nadir shots from straight over ahead. Then we could use the ground shots as reference points to generate the point cloud.
In the end, the operation was a valuable venture for Altavian. The quadcopter performed the flights with no major issues causing delay or damage to the drone. Also, Altavian gathered research and development knowledge about the drone’s operation in the field. GRU was able to make better decisions after having the drones assess damage safely. Plus, they got the data in a timely fashion with Hurricane Matthew approaching the Florida coast. Since Altavian’s founding, we have been improving the quality of data generated by drones that consistently deliver.