Mapping The “Mighty A”
Thompson Engineering used drone surveying equipment to map the USS Alabama Memorial Park to provide an orthophoto of the site along with a digital twin of the Battleship to assist with future improvements.
It’s 680 feet long, 108 feet to beam at its widest point, and displaces 35,000 tons of water. It is the centerpiece of one its state’s most popular tourist attractions. And mapping it with reliable data points could take a team of engineer’s weeks.
Enter LiDAR and photogrammetry from Microdrones.
Christened in 1942, the USS Alabama first served in the Atlantic in World War II but earned its battle stars for an extensive series of operations in the South Pacific. Decommissioned in 1947, the Alabama was rescued from the scrapyard and has sat in permanent dock in Mobile Bay since 1967 in the USS Alabama Battleship Memorial Park. Park officials are dedicated to constant improvement of the park experience and also manage a high volume of visitor traffic, which recently called for the creation of a highly detailed and accurate digital twin to aid in preservation and maintenance efforts.
Thompson Engineering of Mobile provided the necessary surveying and mapping work – a daunting task using conventional methods.
Brad Busby, Survey Team Lead, Thompson Engineering
It would take us weeks, maybe even months, to capture the data on foot, but could be done with the Microdrones system in just a few days.
“It would take us weeks, maybe even months, to capture the data on foot,” said Brad Busby, Thompson’s Survey Team Lead.
But using drone LiDAR and photogrammetry technology to survey, map, and create the digital twin, that process, “could be done with the Microdrones system in just a few days.” And it isn’t just speed – the systems produces a data-rich point cloud that create a true digital twin.
Or, in the words of Ross Kenney, UAS Sales and Support Lead from Navigation Electronics, Inc. (NEI), a distributor of Microdrones integrated systems, “We’re going to be able to scan every nook and cranny of that ship.”
The First Step | LiDAR
The USS Alabama Memorial Park sees about 15 million visitors a year, and while most of them are focused on visiting the battleship, the park encompasses 155 acres in total. The ship itself presents numerous challenges for data collection – the sheer size of the entire facility adds another layer of complication.
Robert Chrismon, PLS, explained the two-layer approach Microdrones uses to produce digital twins.
“We’ve got two Microdrones systems on site, the mdLiDAR1000HR, and we also have the mdMapper1000DG. We’re hoping to come away with two great datasets, one with LiDAR, one with photogrammetry,” Chrismon said.
For this job, Kenney piloted the LiDAR drone, first examining the site to ensure that the drone operated above the height of the tallest obstruction on site – in this case that was the Alabama itself (also known as “The Mighty A”) at just under 60 meters. Using the flight editor, Kenney was able to modify and customize the drone’s flight path on-site using mdCockpit. This is a key aspect of the Microdrones experience – a fully integrated geospatial workflow that starts with accessible flight software, fully integrated systems, and processing software to transform raw data into high-quality survey-grade deliverables.
“Even while we’re out here on the job site, I can go and create new mission plans in a matter of seconds,” said Kenney. Creation of the flight plan of the park was as simple as Kenney creating a block flight path, then pulling out the edges of the path to set parameters to include the edges of the park’s fields and a pier in Mobile Bay.
The mdLiDAR1000HR is often used in land surveying similar to the USS Alabama Memorial Park project, as well as in construction, oil and gas applications, and mining. It has a 90 degree field of view for both scanned points and imagery, and repeatedly provides a precision of 1.6 cm (.052 ft) at 1-σ when flown at 40 m (130 ft) at a speed of 8 m/s (18 mph).
As for the actual scanning process? It took less than a day.
“The benefits to use LiDAR for a site this size obviously is the efficiency,” said Adam McCullough, Survey Team Lead for Thompson. “Not only the efficiency, but the quality of the data.”
Next Up | Photogrammetry
The second phase of data collection utilized the mdMapper1000DG. This is a photogrammetry drone, which can provide a detailed orthophoto of the entire park as well as provide a colorized point cloud with a tremendous amount of detail. Cody Floyd, a surveyor with Thompson who also happened to have been an intern at the park after college, served as pilot for the photogrammetry mission on day two.
The mdMapper1000DG flight took place at 100 meters altitude and demonstrated the ease of operation of the drone in the hands of a skilled pilot. In the flying portion, Floyd also used mdCockpit to directly control the flight. Flights are monitored in real-time with telemetry, such as speed, heading, and altitude available. A GNSS receiver aids in navigation during automated and manual flight, and the airframe uses a plus configuration for more efficient use. In addition, the brushless motors operate at a low, failsafe RPM with large props to limit downtime.
This ease of operation and distance from the subject being surveyed was also essential as the crew performed the work in the summer – high time for tourist traffic.
“On of the challenges for this particular project is that we’re in the middle of the summer – that’s the busy season for the park,” McCullough said. “We knew that this facility was going to have a lot of people in it. So, we have to plan our mission accordingly, to be safe and mindful of the tourists and not fly when they’re on the ship.”
Putting it All Together | Creating the Digital Twin
While flying the drones in the field is the most visually compelling part of mapping, the processing of data back in the office is where the power of the Microdrones system is in full effect. Jason Gibson, PLS for Thompson Engineering, did the initial work of merging the photogrammetric data into a high quality ortho photo of the entire park.
The Thompson team also were able to experience mdInfinity from Microdrones – software for photogrammetry and LiDAR processing. To use mdInfinity, pilots select payload and default settings for that system or apply it to help simplify data processing. Several processing modules fine tune data. Raw LiDAR data is processed through georeferencing, which benefits from precision enhancement that reduces noise levels, while simultaneously preserving irregular features and removing outliers. Further features are used to colorize LiDAR point clouds and generate orthomosaics.
The colorized point cloud for the Alabama was remarkable, even with a few “shadow” areas in the LiDAR data due to differences in materials on the ship. Buildings on site were also mapped in detail.
“We got a lot of great data across the battleship,” said Chrismon. “We definitely got a lot of great information for a topo. Point density is great. Coverage is great. So, these guys are definitely going to be able to use this for topo data, for sure, planimetric work as well. For example, we’ve got enough information on the sides of the buildings to be able to do location work or extraction from the point cloud because of the sheer amount of data.”
McCullough was impressed with the deliverables from the mdLiDAR1000HR.
“To me, the data speaks for itself,” said McCullough. “Just looking at the point cloud here, how dense, and still crisp around the buildings, even on the planes and cars in the parking lot. Once we extract our ground surface from this, the topographic survey we give the park itself, will meet their needs without a doubt. I think it worked out really well.”
If you're interested in learning more about using drone surveying equipment to create digital twins, talk with one of our sales representatives today, for more information.