3D Laser Scanning for Preservation and Structural Monitoring of Historic California Adobe Missions

At the University of San Francisco Architecture & Community Design Program, the Architectural Engineering curriculum utilizes a Leica ScanStation C10 3D Laser Scanner to document historic structures and monitor their structural behavior. Some of the oldest structures in the State of California are the historic adobe missions built by Native Americans and Spanish Catholic missionaries between 1769 and 1833. California is a region of very high seismic activity, and the adobe structures have withstood significant earthquakes and other erosive or destructive forces over their lifetime. However, they are sensitive structures in need of active preservation and very few original adobe buildings remain. Working together with local structural engineers who specialize in seismic restoration of historic adobe structures, USF students have conducted laser scanning at Mission Santa Cruz and Mission San Miguel Arcángel, creating extensive 3D point cloud records, and developing architectural drawings which establish the current state of these structures for the purposes of historic preservation and structural study. Because of the delicate and irregular nature of these structures, the 3D laser scanner is the most appropriate tool for detailed yet non-invasive documentation.

Completed in 1821, Mission San Miguel Arcángel suffered significant damage in the nearby 2003 San Simeon earthquake. The original adobe structure has undergone partial repairs such as banding at the top of the walls of the Sacristy. Using the 3D laser scanner, thorough scans are stitched together to create full interior and exterior 3D point cloud files, which are processed in Leica Cyclone and Autodesk Recap, and then imported into AutoCAD to create detailed line drawings of plans, elevations and sections of significant areas. Wall lean and other indicators of crack progress and deterioration are areas of special focus. With these records, a structural monitoring program has begun to document the condition of the buildings in wet seasons and dry seasons, and to determine the long-term effect of seismic restorations which have been implemented. This paper presents a detailed account of the process, pedagogical value and structural and architectural lessons learned over the course of the 3D scanning of these valuable heritage landmarks.