by Martha McDonald
Building documentation has always been a time-consuming, labor-intensive job. For historic restoration projects, however, it’s the backbone of the job, guiding conservators, architects and other building professionals through a myriad of problems and solutions. Now newer digital techniques such as photogrammetry and hybrid drawings are providing not only a faster way to document a building but also more comprehensive information.
“While traditional photography and hand-drawn measured drawings remain essential tools, photogrammetry is simply faster than conventional hand measuring and more accurate than counting construction units and ‘guess-timating’ dimensions,” says Peter Aaslestad, a pioneer in the field and head of the building documentation department at Frazier Associates in Staunton, VA. “Photogrammetry is a tool that replaces labor-intensive and often error-ridden fieldwork. Conceptually, it’s akin to a virtual tape measure.”
“When photogrammetry-sourced CAD line drawings are combined with digital photography to create a hybrid drawing, they provide far more information than standard photographs,” Aaslestad explains. “Architectural photogrammetry is the science of making reliable decisions about a building’s size, shape and condition from photographs. Hybrid drawings present these findings through the integration of the two media associated with photogrammetry: digital photos and CAD files.”
Creating a hybrid drawing involves taking digital images and stretching or rectifying them to known three-dimensional points, and then incorporating them into drawings in a digital format. It combines the advantages of measured drawings with photography, providing both scale and context information. “When you look at a hybrid drawing you ask, ‘Is it a drawing that looks like a photograph or a photograph that behaves like a drawing?’” says Aaslestad.
His interest in building documentation started when Aaslestad was working in France after graduating from Virginia Tech Architecture School in 1989. He learned about photogrammetry and began using the technology in the U.S. in 1992, joining forces with Frazier Associates in 1996. “When I came back to the U.S., virtually no one here was using it for architecture,” he says.
His office is now kept busy documenting existing conditions on all types of buildings, including historic structures. Some of his recent projects include Church of the Advocate in Philadelphia, PA; Montpelier, James Madison’s home in Orange County, VA; the Renwick Smallpox Hospital ruins on Roosevelt Island, New York City; Thomas Jefferson’s Poplar Forest; George Washington’s estate at Mount Vernon; the United States Naval Academy as well as plenty of less illustrious sites scattered across the eastern seaboard.
At Church of the Advocate, the building team (the engineering firm of LZA Technology of New York City and Building Conservator William J. Stivale, also of New York) needed a set of accurate as-built drawings. Aaslestad went to Philadelphia, photographed the building using the specially calibrated equipment and then returned to the offices in Staunton to convert the information into a set of CAD files. The project took about a month, including two days at the site.
“The Church of the Advocate project was pretty straightforward use of the photogrammetry process, which capitalized on one of the technology’s strengths: providing measurements on a difficult-to-access building,” says Aaslestad. “It is an extremely complicated structure with many different surfaces. Trying to represent that with photographs alone would be confusing.”
“We have people on staff who do documentation,” says Derek Trelstad, senior project director, LZA Technologies, “but it’s incredibly labor intensive to do by hand and that’s a large, complicated building. Draftsmen do a decent job, but there is a limit, because they can only measure what they can reach. It doesn’t give us the same level of information as photogrammetry.”
“This documentation is generally less costly and more accurate than hand drawings,” says Stivale, who specializes in religious institutions. “This building is so tall and has so many inaccessible areas that it would be impossible to get into these spaces and measure them. It’s a large complicated structure, with many returns, various roof levels and several different types of spires. We needed elevations and plans so we could show the scope of the work. Once we got the drawings from Frazier, we could crawl around the building and mark up the condition. We are looking for patterns. If we find a situation in one type of spire, for example, we suspect that the others will need repair as well.”
He points out that this type of documentation is “fairly standard now, and is useful for a project of this scale. You get the information, the photos and the CAD drawings. It’s better documentation and easier to work with than hand drawings. What’s key,” Stivale adds, “is that this is a restoration project, not a new design. We are restoring what was there. Hand drawings are beautiful, but if you are doing restoration, the photography and CAD drafting are more valuable.”
Using the documentation supplied by Frazier, Stivale and LZA were able to determine that the Church of the Advocate needs about $2.5 million in masonry work and another $2.5 million in roofing repairs. The church is now studying the plans and organizing a budget.
Another complicated project that benefited from the use of photogrammetry involved Montpelier, James Madison’s historic home in Orange County, VA. Madison was nine years old when his family moved into the new eight-room brick house in 1760. Over the years, the house has gone through many changes. A four-room addition was added in 1797 when Madison returned from Philadelphia with his new bride, Dolley. A second front door was also added and for a while, the house was a duplex, shared with his parents.
In 1809, two wings were added on either side, the dividing wall in the middle was torn down, a central front door was added and the other doors were changed to windows. The house had 22 rooms when Madison finished remodeling. He died in 1836 and Dolley ran the plantation until it was sold in 1844. There were five owners during the next 57 years, including William duPont Sr. who purchased the house in 1901 and doubled its size in an ambitious building campaign. His daughter, Marion, inherited the estate in 1928 and added two horseracing tracks to the property. Numerous barns, homes and outbuildings were also added under the duPont ownership. When Marion duPont Scott died in 1983, she left the house, which bore very little resemblance to Madison’s home, to the National
Trust for Historic Preservation.
Montpelier was opened to the public in 1987 and in 2000 The Montpelier Foundation became the steward of the property. In the fall of 2001, the Foundation launched an initial investigation to determine the feasibility
of restoring Montpelier to what it was in Madison’s lifetime. The archi-
tectural investigation directed by Colonial Williamsburg’s Architectural
Research Department was made possible by a grant from the estate of philanthropist Paul Mellon.
This is when Aaslestad was called in to document the house. “As part of the team, we did measured drawings of the house using photogrammetry,” he says. “We created line drawings showing the existing conditions and then went into each Madison room and shot photos of the surfaces and assembled them into hybrid drawings.”
The scalable photographs were used as the framework for the information from the more than 350 probes, showing the many layers that occurred as the house changed from the 1860s to 2004. “Our survey helped keep all of that information in context,” says Aaslestad, “providing an over-arching context for the growing trove of information. When the house is restored, we’d like to go back in and add those layers as well.”
“We had nine months to do the initial research,” says Alfredo Maul, Associate Director of Architectural Research, The Montpelier Foundation. “There’s no way we could have done measured drawings in that time, so we decided to go with photogrammetry. It is cost effective and accurate, plus it could be done before we started our detective work throughout the house. Also, because it’s digital, it can be used in many other aspects of our research and methodology. For example, we can go to these photographs and drawings to locate the exact coordinates where paint samples were taken.”
Maul explains that more than 350 archaeological excavations were opened during the investigation, exposing layers of plaster, lath, framing and brick. “When you open an excavation, you are going from 2004 back to the 1760s and you find many different stages of building evolution along the way. Photogrammetry and hybrid drawings help record accurately some of this information,” Maul says. “A disadvantage of photogrammetry is that it’s not suitable for small places like closets. In those situations we used a combination of photogrammetry and traditional hand measuring techniques. Merging photogrammetry and the special contact of recording buildings by hand assures our team that information is well perceived and understood.”
The first phase of the investigation, the feasibility study, was conducted between October 2001 and August 2002. The second phase was completed spring 2004. It involved recording the post-Madison portions of the house, those sections that will be removed as Montpelier returns to its Madison-era condition. “Now we are working on the inside of the house,” says Maul, “getting the last crucial details to record the duPont additions in Madison spaces.” Research will continue through the restoration, which is expected to last four years and to cost approximately $30 million.
Hybrid drawings were also the solution for documenting the complex stonework at the Renwick Smallpox Hospital on Roosevelt Island in New York City. Designed by James Renwick, who also designed Saint Patrick’s Cathedral, it opened in 1856 to house and quarantine smallpox victims.
Abandoned in the 1950s, the building is now covered with ivy and dense growth. In fact, it has become known as “the Renwick Ruin.” The plan is to preserve what remains, keeping it as a romantic ruin, part of a restored garden and picnic area.
The New York City-based architectural firm of Page Cowley was brought in to direct the project. Aaslestad’s mission here was to document the ruins so they could be taken apart and reassembled in a different location. The ruinous state of the shell and unsafe interior conditions made it impossible to conduct other types of documentation.
“Photogrammetry is the first phase of any future preservation or adaptive reuse effort,” says Cowley. “It is a valuable tool in assisting to determine the appropriate methods for initial stabilization measures.”
“We took pictures from various vantage points, made measured drawings and then we took pieces of the photography and rectified them and pasted them into the drawings so it portrays all of the surfaces from different vantage points simultaneously,” says Aaslestad. “They needed a set of documents that would allow them to disassemble the building and catalog the pieces as they come apart, so they can put them back together.”
While photogrammetry is not the only building documentation system available, it is becoming more widely accepted as a valuable tool that takes both photography and measured drawings beyond their individual capabilities.
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Photogrammetry – The science of taking reliable measurements from photographs to create accurate measured drawings. It calculates three-dimensional measurements from photos and these can be turned into plan drawings, elevation drawings, profile drawings or reflected ceiling plans.
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Hybrid Drawing – An illustration which is the combination of a measured drawing and photographs stretched (rectified) to points in the drawing.
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Mosaic image – An image composed of different components. It can be created from multiple images taken from different vantage points or from several images taken from a single vantage point. If the mosaic image is rectified, it can then become a scalable photograph.
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Vector Drawings – Measured line drawings in digital format in which each individual entity represents the real world object on a one-to-one basis.
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Raster Images – A digital photograph or scanned image. Formats including TIF, JPG, BMP and GIF – these can be inserted to scale into an AutoCAD ™ file.
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