Flatland: A Tool for Transforming Historical Sites into Archival Drawings

Abstract

Detailed documentation of historical sites is important for archaeological discovery and cultural preservation. The traditional method of documentation is to hand sketch 2D drawings of the region. Laser range finders can be used to produce highly accurate geometric representations of the historical sites, and high resolution images provide vital detail. However, archaeologists are both used to and prefer a flat, two dimensional archival drawing of the region. Flatland provides the missing link for archaeologists between three dimensional representations and archival drawings. There are two critical pieces of Flatland texture mapping and geometric transformation. The texture map acquisition phase aligns the world geometry with the high resolution images. Many historical sites contain rocky, uneven terrain and structures that do not contain distinguishing features that would allow for automated methods of correspondence selection. Instead, manually selected correspondences between the point cloud and the high resolution image are used to compute the texture map. If the selected region is nonplanar, then a camera projection matrix is computed to determine the texture map for the point cloud. However, when the selected region is planar, the camera projection matrix can not be computed, and instead a homography is used to determine the texture map. The geometric transformation phase allows the archaeologists to essentially unfold both square and cylindrical surfaces to representations with a single dominant plane. A square room can be unfolded into four panels where geometric distance is preserved within each panel. An elliptical surface is unrolled about a flat rectangle with the height of the elliptical surface and the width equivalent to the circumference of the surface. The use of Flatland is demonstrated on scans from the Mesa Verde National Park.