3D Modeling Aids San Juan Capistrano Restoration
The edifice, then crowned by a 125-foot (37-meter) bell tower, was once a great stone church built in nine years by the Juaneno Indians under the supervision of Spanish priest Junipero Serra. They worked without metals or modern tools, driving bullock-drawn carts to haul the volcanic tuff and sandstone from what is now Dana Point nine miles (14 kilometers) away.
Six years after the church was completed, a tremendous earthquake shook it to the ground. The giant bell tower came crashing down onto the dome's arches, causing them to collapse, killing about 50 Juanenos. The collapse left the remaining walls and the interior of the church exposed to wind, rain, and the ravages of time.
The Restoration Project
A 1991 conservation and restoration study documented the significant archeological value of the church's architecture and carvings as a vital historical source of the "materials, tools, construction, and level of skill in the period in which the church was built."
The Campaign to Preserve the Great Stone Church is a $7 million archeological effort that will literally preserve the ruin in time so that it will look as it did after the earthquake of 1812. The preservation campaign is carefully rooted in an extensive professional analysis and plan to preserve the church while retaining the fragile fabric of history.
The final phase of the restoration project is currently nearing completion. Its goals are to 1) consolidate the stone walls, 2) clear debris from tops of walls, 3) fill in fissures and crown and seal the wall tops, 4) stop further cracking by using steel pins to hold the walls together, and 5) restore the decorative stonework.
One of the most critical and time-consuming aspects of any restoration project is documenting the condition of the existing structure and planning its restoration and conservation. Normally, this is done by creating 2D CAD or paper drawings of the structure and performing the engineering calculations by hand.
There are several problems with this approach. It's difficult with conventional CAD tools to model the irregular shapes involved in an architectural ruin. And 2D drawings contain minimal information on the condition of the structure. This means that engineers are forced to go out to the field and make tedious hand measurements in order to determine what repairs are required.
The 3D Approach
Thirtieth Street Architects validated a much faster approach in the Mission San Juan Capistrano restoration project. The first step was selecting a 3D CAD program called VectorWorks from Nemetschek North America, Columbia, Maryland.
One reason for selecting this system is that it provides an easy-to-use freehand drafting tool that simplifies the definition of irregular shapes such as those often found in restoration projects. Also, the program provides a new approach to 3D modeling that makes it almost as easy as traditional 2D drawing.
VectorWorks provides a unique hybrid design environment that can automatically sweep or extrude 2D models into 3D. It reduces modeling time by creating many real-world 3D shapes as objects, such as columns and doors, that can be completed simply by typing in their dimensions. The program gives the user plenty of 3D tools including true Boolean operations.
Designers at Thirtieth Street found the software so easy to use that they decided at the beginning of the project to model the entire ruin in 3D. They easily created models of stone with regular shapes by using the object-based features of the software.
For example, to create a tapered column, designers simply had to pick a column icon and enter critical dimensions; the program instantly generated a 3D model of the object. Irregularities usually made it necessary to make minor changes and these could be accomplished simply by dragging and dropping node points of the object.
Similarly, many modeling tasks, which would probably have taken days with the conventional approach, were completed in less than half an hour. This same method was also used to create 3D models of other fairly regular shapes. For example, the sphere and rectangle objects in VectorWorks were combined to model the sacristy dome.
Saving Engineering Time
The ability to model the entire structure in 3D provided major time savings in the structural engineering phase. The designers accurately documented the shapes of each of the major stones used in the project. Once these 3D models were completed, engineers working on repairs could simply query the model to get the information they needed.
For example, engineers needed to know the weak points of the sacristy in order to design a support structure. Instead of going to the mission and taking measurements themselves, they were able to easily generate any needed cross-section in a minute or two.
The program could then automatically calculate the sectional area and volume of the object. The engineers didn't have to leave the CAD environment to design the perimeter tie rod structure used to support the dome. They simply designed it in another layer.
The intuitive layering system in the software proved invaluable throughout the entire project. Most of the documentation was created in four main layers.
The first layer shows the existing conditions of the structure. The second layer provides a detailed examination of specific problems such as cracks. The methods that have been engineered to repair the problems are superimposed on the third layer.
The fourth layer is being used to document the modifications that were actually made to the structure. This layer is important because it is often necessary to modify the plan in the field either because the conditions weren't totally understood or because they have changed.
VectorWorks makes it possible to move from one layer to another or to snap to a different layer with a single click of the mouse, eliminating the layering overhead imposed by some other systems.
A unique aspect of the documentation for this project was the superimposition of photographs of the actual ruins onto the 3D model. The dimensional accuracy of the model and the ability of the CAD software to easily import Photoshop files made this a relatively simple process.
When it was completed it gave an additional dimension to the drawing that greatly increased its utility by making it possible for people without a technical background to immediately grasp the condition of a particular area of the structure.
The resulting model looked almost like a photograph of the project yet was far more useful because it could be viewed from any angle and be used to produce accurate measurements of any dimension.
All in all, by reducing the amount of time required for documentation and planning, 3D modeling made it possible to maximize the amount of resources devoted to materials and labor. The use of 3D modeling also provided a superior level of detail, which meant better instructions for construction personnel, making their job go faster.
Thirtieth Street Architects, Inc. and the mission's architectural conservators won a state-wide award for the first phase of the conservation project using an earlier version of VectorWorks. The firm's principals believe that the phase-three documentation described here was several times better yet produced in about half the time.
John Loomis is a project architect and Elizabeth Sanchez a project manager with Thirtieth Street Architects, Inc., of Newport Beach, California.