Structural engineering principles might offer insight into such archaeological questions about the reconstruction following the earthquake. Kirk Martini, an assistant professor of Architecture and Civil Engineering at Virginia and an IATH Fellow, has been applying terrestrial photogrammetry to create a 3-D model of the Macellum--a large market building on the Pompeii Forum.
Photogrammetry uses photographs to derive 3-D geometry, which can be modeled with methods such as the Virtual Reality Modeling Language (VRML). The 3-D models are generated by the EOS Systems Photomodeler program. The surface textures from the photographs are mapped onto the model so that it shows not only geometry, but also surface material and texture, effectively creating a 3-D photograph that can be viewed from any angle.
Martini and a multidisciplinary team of researchers and students at Virginia are currently creating a partial model of the Macellum using approximately 100 photographs: a challenge to the Photomodeler software that has led the team to develop a process called "stitching." Worthy Martin, professor of computer science, students Randy Hudson and Tony James, architecture student Rodrigo Abela, Martini, and IATH graphics specialist Chris Jessee are collaborating on the four-step process, which allows the modelers to create a large VRML model of the building by joining smaller models created with Photomodeler.
The motivation for this approach lies in the fact that photogrammetry is more effective when applied to a group of photographs that include many common points in a scene; the large building is broken into parts that can be covered by roughly six to 10 photographs, with some overlap common to the parts. The geometry of the parts can be calculated effectively, and then the parts can be stitched together at the overlaps.
The four steps of the stitching process are to identify corresponding regions of triangles between two models, calculate a transformation that roughly aligns one model with the other, calculate from that starting position a more refined transformation that minimizes the error in the alignment, and then merge the matched vertices to produce one complete model. In the future, Martini hopes to work closely with the NPACI Interactive Environments thrust area to expand these types of modeling activities.
The researchers can also enhance the models to recreate the building before the earthquake and use that data about prior form and seismic effect to extrapolate the effects of the earthquake on other structures. They can then compare the degree and chronology of reconstruction in private buildings to the reconstruction of the forum.
"Architects, archaeologists, and computer scientists build and analyze computer models of structures, and construct a chronology of events that matches the evidence in the masonry," Martini said. "The results drive urban historians' theories about the life of the civic center of Pompeii. Many disciplines contribute to the work of the project, and in the end we all benefit."--AF 