Rebuilding a Burned Farm From a Photograph: Computer Visualization at Antietam

The Battle of Antietam was the first Civil War battlefield photographed extensively soon after the fighting. Alexander Gardner, working for Mathew Brady, made over 95 photographs in September and October 1862, and leading newspaper artists, including Alfred Waud, Edwin Forbes and Frank Schell, also sketched the field. Antietam National Battlefield is also one of the best preserved mid-nineteenth-century rural landscapes in the Eastern Theatre, so National Park Service archeologists chose it as a place to test computer visualization for studying cultural landscapes.

The Mumma farm

During the battle the Confederates burned Samuel Mumma's farmhouse, springhouse and barn, to keep Union sharpshooters from using them. Alfred Waud sketched it on the spot.

Mumma farmstead burning, 1862. NPS

Two days after the battle Gardner photographed the ruins of the house and springhouse.

Alexander Gardner photograph, 1862. NPS

No picture of the house before the battle exists. The Park Service wanted to know how the ruins related to the layout of the rebuilt house, and how 1862 features such as trees related to the post-battle farm, and whether they could be located precisely enough for excavation.

Building the model

1. A joint National Park Service and URS Greiner field crew measured the foundations and the distances between the buildings and took over 100 photographs. The measurements went into AutoCAD to make a two-dimensional footprint.
2. The footprint and photos went into 3-D Builder, which built a three-dimensional wireframe model of the farmstead as it was in 1997.

Wireframe rendering of the Mumma farmstead. NPS

3. Gardner's 1862 photograph was scanned and given its own wireframe. Matching points shared by the 1862 and 1997 scenes, plus an estimated focal length, let the software calculate where Gardner's camera had stood.
4. In 3-D Studio Max, the 1862 photo became the background, the models were imported, and the virtual camera was placed at the calculated position, so the wireframes of the 1997 buildings could be aligned with the same parts in the 1862 photo.

In the field

With the camera position refined, the crew used 300-foot tape measures to triangulate from standing building corners and locate Gardner's 1862 position on the ground. There they set up a video camera linked to a laptop, and a URS Greiner animation specialist used Adobe Photoshop to align the 1997 video frame with Gardner's photograph for direct comparison.

Then the 1862 smokehouse and large tree were cut from Gardner's photo and placed into the 1997 video image, which fixed their locations relative to the structures that still stand. Archeologists can now find both with standard excavation techniques.

Sources

• National Park Service, Battlefield Images, Computer Visualization, and the Study of Cultural Landscapes, part of the series Archeology at Antietam: The Effect of Battle on an Agrarian Landscape; rewritten in hubnx's own words.