Fortifying Fort Pike
In response to attacks on our nation's capital and New Orleans, President James Monroe ordered the placement of an extensive coastal defense system following the War of 1812. The seacoast fortifications protected ports along New Orleans and rivers such as the Mississippi. Six new masonry forts were built in coastal Louisiana at that time; Fort Pike was one. Completed in 1826, Fort Pike, which was named after General Zebulon Montgomery Pike, an explorer and soldier, was designed to withstand attack from land or sea. Along with its vital military purpose, the fort was also an impressive architectural structure. Featuring a unique casemate design including narrow exit tunnels, the pie-shaped facility overlooks the Rigolets, a narrow passage between Lake Ponchartrain and the Gulf of Mexico, and houses two pointed bastions (fortified areas) that face the land. The fort originally featured two protective moats around the main structure and a glacis (an embankment designed to expose attackers to defending gunfire) and a covered way between the moats.
The fort's extended functions were varied. It provided housing for many officers and troops along with their service buildings such as bakeries, and merchandise and clothing stores. It also functioned as a staging area for troops en route to Florida, and provided a holding site for prisoners and slaves being transported to Oklahoma in the 1830s. In the 1840s, Fort Pike was a stopover for soldiers bound for Texas and Mexico. The fort was renovated in the 1850s when its original one-story citadel, used as a barracks, received a second floor. In 1861, the Louisiana militia captured the fort; it changed hands from the Confederates to the Union forces, the latter of which used the fort as a training center for former slaves who were taught to use heavy artillery and later became part of the United States Colored Troops. The citadel experienced two fires-in 1862 when the Confederates torched it in retreat and again in 1887, which left the site standing as a mere shell.
After a long stint protecting our coast, Fort Pike was officially abandoned in 1890. In 1972, it was placed on the National Register of Historic Places. Today Fort Pike stands as a fascinating chapter in Louisiana's history and welcomes numerous tourists every year. Visitors stroll along the grounds of Fort Pike, taking in the authentic brick archways, enjoying picnics near the mess hall of the old soldiers and imagining the life of early war years. The fort's 3-foot-thick walls are deteriorating, however, and the site is in need of monitoring and restoration. Funding through Save America's Treasures, a federally funded, matching grant initiative dedicated to the preservation and celebration of America's priceless historic legacy, provided for these efforts, and work began at Fort Pike in late 2003. The project called for traditional surveying and modern laser scanning applications-and included a couple of innovative provisions not seen on most surveying sites.
Setting the Scanning Control"We were called on to identify the conditions of life-safety issues related to the fort. Fort Pike is a visitor's attraction and part of the Louisiana Department of Culture and Tourism, Office of the State Parks," says Michael Lengyel, architectural conservator for John Milner Associates (JMA), a professional consulting firm providing architectural, historic preservation and cultural resources services. "It's long been in a state of deterioration due to its location, its proximity to the water, and its construction and age. We were tasked with performing a direct survey of the site, identifying the structural issues, identifying the life-safety issues and determining a course of action to address any concerns that we identified."
"We're collecting this information to document its as-is condition today and use it subsequently in the future as the fort is being impacted by future construction of the Rigolet Bridge [about a quarter mile away]," Lengyel adds. The nearby civil works project includes removal of the existing bridge and construction of a new, expanded bridge. Pounding pilings for the bridge into the channel bed may cause low-level vibration that could have an effect on the stability of the fort's exterior walls. "We wanted to document how it [the fort] is today to identify the structural repairs necessary to stabilize the fort," Lengyel says.
JMA's monitoring efforts at Fort Pike began in November 2003. In January 2004, Lengyel called on a local surveyor to provide control of the site. "We contract surveying services as we need them," Lengyel says. "It's the most cost-effective way of getting an overall plan of the site and being able to establish bench marks onsite using traditional surveying techniques."
Larry Porterfield, owner of MJ DeField & Associates of Baton Rouge, La., established bench marks for the site, but had another reason for taking on the job. "I'm interested in preservation of historical places from a surveying standpoint," Porterfield says. "We [he and his crew members] went down and provided traditional survey work to assist in the scanning that he [Lengyel] lined up. We did conventional surveying to provide QC for the project."
Porterfield and his crew spent two days surveying points of the interior and exterior of the fort using two Topcon (Livermore, Calif.) 811 total stations and one Topcon 800. Data was collected on the historic archways, the tops of walls, all dimensions of the fort and any architectural features. Data files for almost 750 shots were provided to Lengyel.
"Larry had the ability to do the general work that we asked for in the time frame that we needed it done, which was very short," Lengyel says. But Porterfield offered more than just his surveying expertise: he supplied a key element for completing the project. "He owns special equipment that was essential to us being able to perform the laser scanning portion of the project," Lengyel says. "That was the swamp buggy."
A Unique Scanning VehiclePorterfield's swamp buggy was essential given the surroundings of the fort. "The area is a swampy, muddy mess," Porterfield says. "I cured my marsh buggy and set it up where they could mount the scanner on top. If they had set it [the scanner] on a bank, they'd be beyond the range of the scanner. They needed to be closer."
Porterfield's buggy is a motorized machine designed for marshy sites. He bought it from Coast Machinery (Baton Rouge) in 1993. "They do things that are beyond belief," he says. It is a welded aluminum machine with hydraulic drive that looks like a bulldozer. It floats and can't turn over, Porterfield says proudly. "It can go down an incline into water-almost a straight 4 ft drop, [and] up to 48 to 50 degrees. We've gotten into creek bottoms and areas where you literally can't climb out, but we can throw a cable up on the bank and tie off to a tree. It's got a hydraulic wench that can just suck you right on up. It'll carry about 1,500 lbs of payload."
"We look for easier ways to do things," Porterfield says. "One of the things we can do is take our GPS antenna and mount it on top of the rack on our marsh buggy. If it's on solid ground, it's like driving a bulldozer over briars and vegetation. Most survey companies spend days and days and days cutting and staking and lining, and we're just out there driving around." It's this service vehicle that has Porterfield's phone ringing often. "We've done everything from helping alligator hunters to finding eggs to surveying," he says. "It's pretty neat."
The buggy prevented problems from occurring on the Fort Pike project; any other setup for the laser scanner would have cost much more money and created a logistical nightmare. "Everybody knows that we wouldn't have been able to do it had we not had that swamp buggy," Lengyel says.
Scanning with StatureLengyel, Porterfield and Tom Satterley, vice president of North American Operations for laser scanner maker iQvolution of Richboro, Pa., set out on the mission to scan Fort Pike in February 2004. After adapting the scanner to the customized marsh buggy for the exterior shots, the team headed out shortly after midnight. The design of the iQvolution iQsun 880 scanner at that time required the team to scan in the night hours. Satterley says that the invisible red laser on the 10 mW scanner does not perform well in direct sunlight. Since the Fort Pike project, iQvolution has released a 22 mW scanner that withstands sunlight and also offers a model equipped with a Nikon camera to provide color overlays.
"We ended up doing our scanning after dusk and before dawn," Lengyel says. "There are advantages to that. We didn't have people walking around, which was a great advantage. We basically had the place to ourselves. But the biggest advantage was that it worked!"
In addition to sporting a swamp buggy on the moat for data capturing, other conditions called for further creative measures. "We had over 300 feet of extension cords and we dropped them from the fort into the moat," Satterley says. "The biggest obstacle there, though, was Mother Nature. It got cold and it got windy. We started at 12 noon [shooting the interior] and finished at quarter to four in the morning."
Scanners can normally scan much more than what's needed for a project, an advantage to many projects. More sky and a varied degree of data from a sphere around the scanner provide great amounts of data. However, Lengyel learned that the scans weren't providing him with what he needed. "What we needed was scanning data of the ground," Lengyel says. "We found that even though the scanner was capable of scanning the ground, the scanner was too close to the ground so the data was skewed and distorted. We were going to have to come back to re-scan the ground plane and elevate the scanner in the air."
They found a way to meet this requirement using a scaffolding platform elevated about 15 feet in the air. "We were [then] able to get very satisfactory scans of the ground," Lengyel says.
Developing Dense DataJMA is no stranger to laser scanning technology. The multi-disciplined company has "a reasonable track record" with scanning, according to Lengyel. JMA has a growing list of projects utilizing scanning technology. Included are the Bah Relief of the Lincoln Memorial and the plaster ceilings in Fredericksburg's Kenmore mansion. JMA has utilized several scanners on the market, each selected for a specific purpose. "We have found that no one laser brand or model or type can do it all," Lengyel says. "[We] take a broad approach. By essentially using all the tools in the kit, we're able to use this technology more fully."
In the Fort Pike case, iQvolution's iQsun 880 fared well, according to Lengyel. "In a certain range, it was very good. At night it excelled," Lengyel notes. "It didn't require being so fixed in a certain position that any movement at all caused it to not function. In short, it was hardy. We were doing scans every 15 minutes, in the dark on uneven terrain, sitting the scanner 15 feet up in the air on a baker's scaffold, on the back of a swamp buggy in the middle of the water with an extension cord running out 150 feet hooked up to a generator." Withstanding those conditions, the iQvolution scanner gets high marks.
"As we analyzed the data we collected, we learned even more about its strengths and weaknesses in terms of the data that it produces. It was a very good learning experience all around," Lengyel adds.
"When it came time to register all of the scans together and make a coherent model, we realized that the best way to do it, even with modern software [was to marry the] benchmarked points established using traditional surveying techniques and the scanning from those locations"¦ to generate a more accurate model. It was fortunate we had that survey to work from because we were able to go back and use it to enhance our results," Lengyel explains.
How was that data? "The iQvolution data is very dense," Lengyel says. "We liked how fast [the scanner] was. It produced more data than can be interpreted. When it came to merging the data scans into a cohesive package, we really had to limit the amount of information we would use."
Satterley was equally impressed with the iQsun's results. "It performed better than I thought [it would]," he says. "There was a bridge about a quarter mile to a half-mile away and one of my scans picked up the bridge. My scanner is only supposed to go up to 76 meters."
Using InnovMetric's (Sainte-Foy, Quebec, Canada) Polyworks software, Lengyel handed off the data clouds for registration. "It [Polyworks] has the amazing ability to bring things together in a coherent manner using very few points," Lengyel says.
With a total of 97 scans compiled from measurements collected at 120,000 points per second at an accuracy level of Â±3 mm, Lengyel was equipped with the information he needed to further Fort Pike's restoration efforts.