City Walls Team Postpones Drone Use
“Let’s start by trying it at 1 meter,” Nick Sipes programmed the drone to fly a short distance in a sheltered cove. For each following test, he programmed the drone to rise an additional meter. By the time the drone reached a mere 4 meters, it was too unruly to manage – and the drone would need to fly at 7+ meters to capture footage of the wall from above. Collaborator and Ph.D. candidate Manuel Saba advised the team that the area is rarely this windy, so the team hoped their luck would change with the wind.
Team member Nick Sipes teaches collaborator and Ph.D. candidate Manuel Saba how to safely operate the drone.
Unfortunately, the wind speeds continued to exceed expectations, and additional test flights brought the drone down with little accuracy to its programmed location on the map. Before these tests, the team had suggested tying fishing line to the drone to prevent it from crashing into the ocean or the road. However, the tests revealed that the drone could not stay on course for any reliable period of time to capture the footage we needed. The team decided to leave the drone with Manuel and train him in its use; on a less windy week, he could have easy access to capture more footage. In the meantime, the team would need to find a new process.
City Walls Gets a Bigger Tool Belt
The team felt frustrated; we had to keep stopping to recharge the camera, and we wondered whether we had any way to complete the project well without the drone. But team member Caoimhe O’Sullivan Roche took charge of the refocusing the project in a major collaboration session with Manuel Saba. Caoimhe said, “There is something about being on-site that helps you figure it out.” Losing functionality of the drone, while discouraging, opened the door for the team to look at other possible methods. Caoimhe said,
“We have a drone but other options too; we are diversifying our tool belt as a surveying and modeling group. Different methods are best suited to meet a variety of tasks.”
Caoimhe and Manuel collaborate to redesign the project without the use of the drone.
So, what are the changes being made to the procedure? First, the team made the final call to take all footage by hand. The team will walk the length of the wall from six different angles to gain images of the wall from every perspective. Team members will mark out a consistent distance from the wall using tape measures, hold the cameras in their hands, and function as the drone themselves by walking its programmed track. The new method will be painstaking yet equivalent in quality.
Almost all shots could be taken from the ground, but how could the team add perspective shots from above? With the drone, the team could easily aim fly the the camera over the walls, but they would now need these shots while earth-bound. Professor Audrey Barnes proposed a simple yet innovative solution for shots that would be needed from a higher perspective: the team purchased “selfie sticks” and will hold cameras 15 feet in the air to record footage of the walls from an above-angle perspective. The team will also hold the selfie sticks over the edge of the top of the wall to capture another above-angle of footage.
Sarah Paynter, Manuel Saba, Caoimhe O’Sullivan Roche, and Dustin Hux walk the length of the Santo Domingo Bastion to determine how the team can best capture footage of the wall on foot.
Because this method would be more time consuming, the team decided to limit its scope to a smaller section of the wall; Manuel could expand the scope of his study indefinitely with the drone when weather conditions cooperated. The section we chose was the Santo Domingo Bastion, the oldest and most endangered section of the wall. We chose this section of the wall because it is particularly exposed to traffic and erosion from the sea. It is also an important location for tourists as the location of a popular plaza and the Café Del Mar, which sits on top of this thick section of the walls.
Dustin Hux and Kiva Gayle use a selfie stick to take above-angle shots of the wall.
Finally, the team discovered we could expedite our image-processing method. Originally, the images were taken as part of a video and sliced into thousands of still pictures. Next, the team edited each picture in Photoshop to contain only the wall itself. Only then would the team input the pictures into AgiSoft image stitching software to create a 3D model. The team originally edited the images in Photoshop because test models revealed accuracy problems where the area of interest melded into its background. However, because the wall had enough contrast from the sky, the team was able to forego editing thousands of images in Photoshop and plug them right into AgiSoft for processing into a 3D image. When the images are processed, the team can edit the final model to contain only the wall.
An Endangered Cultural Artifact
“When I spoke with Manuel, I could see how much he cares. It felt like what we’re doing really matters. I know Manuel really wants this, not just for his Ph.D., but because he wants to make this good.” -Caoimhe
The drone team talks with Manuel about his love for the city’s walls.
Walk along the walls of the Cartagena, and you will see through its archway windows many different sets of people sitting in them – a couple snoozing beneath an umbrella, children with their parents, and townspeople taking pictures. Late one evening, I sat with Caoimhe at the dining room table and reflected on the unique way the town interacts with this beautiful historical landmark. Caoimhe noted its uniqueness with a glint of inspiration in her eye: the town itself is incorporated into the walls. Rarely does a tourist town proclaim such authenticity, but here, the locals want to spend their days and hang out at the walls. “It’s so beautiful that people want to be here and not avoid the tourist places. It’s cool to see how much the city loves it,” Caoimhe said.
The walls of Cartagena are an important economic, cultural, and historical artifact, but they are in danger. Their location next to the road and the ocean places them at special risk as the sea level rises.
For a landmark that is so loved by its community, the City Walls team sees that Cartagena may not realize that the wall is in danger. As is the nature of environmental changes, the threat to the wall is incremental, and the threat may not yet be recognized by the public. But the waves from the sea are already crashing above the barrier alongside the road that lines the wall, and the sea level rises 10 cm every year – it is foreseeable that these walls could be washed away within our lifetime. The city must embrace the wall it loves to save it, and with Manuel’s research on the structural stability of these walls, this conservation may be possible.
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