by Jerry Laiserin, FAIA
Toward the end of the 19th century, amateur mathematician Edwin A. Abbott wrote a slim volume entitled Flatland: A Romance of Many Dimensions, which has since become a science-fiction classic. With wry humor, Abbott set forth the difficulties of comprehending any world containing a different number of dimensions from the observer's own. Thus, to the inhabitants of one-dimensional Line land, the comings and goings of two-dimensional Flatlanders appear as if by magic-leaping out of sight at one point along the linear world and abruptly reappearing at another, without seeming to traverse the intervening distance. Similarly, to Flatlanders the denizens of three-dimensional Spaceland seem to be alien creatures capable of hopping on and off the world plane at will.
As inhabitants of a world we experience primarily in three dimensions, we humans may be amused by the lesser-dimensioned orders of Abbot's fantasy. However, most of us remain puzzled by the prospect of four-dimensional worlds in which travelers can come and go wherever and whenever they please without seeming to traverse the intervening space or time. We see each other and the objects we create as three-dimensional snapshots fixed at specific moments in time. Yet four-dimensional beings, such as the fictional Trafalmadorians of Kurt Vonnegut's Slaughterhouse Five, would see us in the fullness of our lifespans-as glowing tubes extending through space and time (the fourth dimension) from birth to death.
Architects who work on historic buildings must learn to experience the built environment beyond the limitations of three-dimensional Spaceland and be come, in effect, the Trafalmadorians of de sign-describing and experiencing buildings in the fullness of their lifespans. Increasingly, these restoration architects (also called preservation architects or historic architects) turn to computer techniques to define and analyze different spatial manifestations of buildings over time.
Computer work on historic building projects typically follows a consistent sequence of data acquisition, historic analysis, and reconstruction visualization. Present working methods start with capturing information about an existing structure and integrating data from diverse sources that may represent different historical states of the building. Often this data is represented in 2D CAD drawings or 3D CAD models. But some architects have begun using this documentation as a kind of 4D CAD model, with the 2D or 3D views serving as an interface to "dial in" to specific historic moments in a building's history. Introducing new design interventions, such as new building services, can be accomplished by projecting forward in time to analyze phasing or staging of alterations. Finally, architects and computer scientists are jointly creating new techniques to help them visualize buildings, parts of buildings, or the condition of buildings that no longer exist (in time), yet do so in the context of their actual locations (in space).
|An exterior restoration of the 1890s Elk County Courthouse in Ridgeway, Pennsylvania, relied on a false-color image generated from Quantapoint laser-scanned data to distinguish major building components. (Image courtesy Quantapoint.)|
Architects communicate their 3D designs, whether generated by hand or computer, through highly stylized orthographic projections called elevations, sections, and plans. Combinations of these 2D views can be integrated into 3D models, but most such integration occurs only in the architect's mind or in the occasional scale model. Describing existing buildings without the use of computers entails a tedious and labor-intensive process of hand measuring building elements and drawing them to scale manually. CAD systems can be used to automate the drawing task, but they still leave the measuring to manual means and result in discontinuous 2D views. In circumstances where original construction drawings (or, for historic structures, measured drawings from the Historic American Buildings Survey-HABS) are available, the existing drawings can be scanned and vectorized (converted from scanned raster format to CAD vectors) or directly digitized (typically by laborious tracing). Yet even then, only 2D information is produced.
Recent developments in image processing allow for direct capture of 3D data from existing buildings. One such approach is photogrammetry, which derives measurements and 3D models from software that traces multiple overlapping photographs taken from different angles. This technique, exemplified by PhotoModeler Pro from Eos Systems (Vancouver, BC), is an economical way to produce accurate 3D data, but at a trade-off in speed. Another approach, laser scanning of 3D scenes and objects, is effectively instantaneous, extremely accurate, and detailed, generating point clouds of information as the laser device scans across and is reflected back from building elements within the laser's field of view. Post-processing software then rectifies and, if necessary, stitches together various point-cloud views to create a 3D data model that can be exported to 3D CAD software for further manipulation.
|This false-color image of the pre-Civil War Rebecca Place, an extended nursing care facility in Pittsburgh, reveals the different ages and materials for various parts of the structure in preparation for renovations. (Image courtesy Quantapoint.)|
Available laser-scanning systems include Mensi (Norcross, GA), Inovx (Irvine, CA), and Cyrax. The latter system, from Cyra Technologies (Oakland, CA) is commonly used to document complex process piping installations in petrochemical industries, but has been tested on historic renovation projects such as the recently completed seismic retrofit of San Francisco's City Hall. To scan 100-foot high by 40-foot wide sections of the two-layered dome structure and to post-process the data took about 2.5 hours. In contrast, even if direct physical measurements had been possible across all inaccessible parts of the domed rotunda, the resulting manual process would have entailed many days of staff time and significant cost.
An even faster laser-scanning technique has recently become available from Quantapoint (Pittsburgh, PA). The core technology is a laser scanner with a 360-degree horizontal field of vision and a 60-degree vertical aperture. Quantapoint's ability to scan an entire room or interior space from a single setup location greatly accelerates the scanning process. The hardware and software technologies are spin-offs from machine-vision experiments at the robotics labs of nearby Carnegie Mellon University, so they were designed for rapid image processing.
|Cyrax laser scans of San Francisco City Hall provided accurate measurements of the domed rotunda, which would have been difficult to measure by hand. (Images courtesy of Cyra Technologies)|
Although not yet rolled out to a nationwide market, Quantapoint's service has enjoyed early regional success in the northeastern US, an area particularly rich in historic structures. For example, the Boston-based architectural firm Goody Clancy & Associates commissioned Quantapoint to document significant exterior and interior elements of Trinity Church, the 1871 Boston icon designed by H.H. Richardson. Architectural work included reconstruction and repair of exterior masonry as well as designs for expanded community functions in previously unoccupied basement spaces.
When the Quantapoint data was converted into AutoCAD format, project architect Jane Carroon reportedly observed that her firm likely knew more about many details of Trinity through the Quantapoint-derived models than even Richardson himself knew at the time of the church's construction. In effect, the laser-scanned CAD data enabled the architects to "drill through time" to reveal original design elements obscured by decades of maintenance and repairs. Similar work is underway across Boston's Copley Square, where Boston's SBRA Architects, corporate descendants of Richardson's firm, retained Quantapoint to document McKim Meade and White's 1895 Boston Public Library.
|These images of the main entrance (directly above) and the Sargent Gallery (top) of the 1895 McKim Building of the Boston Public Library are not photographs, but Quantapoint Qviews that consist of laser-scanned data saved as JPG files. (Images courtesy SB|
This 4D CAD technique of drilling through time to uncover original elements concealed, altered, or removed over a building's lifespan can be applied to more recent structures as well. The 1930s-vintage Radio City Music Hall in New York City recently has undergone a major revitalization that included retrofitting modern environmental and theatrical systems as well as restoring what is widely acknowledged to be one of the greatest Art Deco or Moderne interiors ever created. This project, which was undertaken by Hardy Holzman Pfeiffer Associates (HHPA) of New York, was based on scanned and rasterized versions of the original architectural drawings, supplemented by period photographs. HHPA senior associate Stewart Jones, who has led similar projects at New York's New Victory and New Amsterdam theaters, observes that 4D CAD technology is particularly useful in several aspects of such jobs.
First is the ability to show the visual impact of proposed changes to landmarked spaces to appropriate public reviewing agencies. "If you put in enough data," says Jones, "you can show changes in seating, sightlines, finishes, and so on, which can result in a constructive dialog."
|Architects used color-coded drawings for restoration work at Cooper Union to convey different materials, conditions, and needed repairs to the contractor. (Image courtesy Pratt Bayard Dovell Architects.)|
Second is the computer's ability to simplify the restoration or reproduction of highly detailed elements. Working in AutoCAD, HHPA could more economically document complex elements, saving their design effort for higher quality restoration or reproduction of damaged or missing pieces.
Finally, because theater interiors often depend on the rich interplay of colors and patterns to create an impact, 4D CAD techniques often can be used in an almost forensic manner to reconstruct lost patterns. According to Jones, worn textile wall coverings at the rear of the Radio City auditorium had been patched and replaced over the years with repeating fragments of a larger pattern until the overall pattern was lost. Working in AutoCAD, HHPA assembled pattern fragments from the remaining cloth and combined them with historic photographs to extrapolate and reproduce the full original pattern.
Sometimes the historical evidence is fragmented and not easily accessible. For example, documentation techniques such as laser scanning and photogrammetry only work when there is a clear line of sight to the space or building to be documented. Occasionally, documentation must proceed when repair or restoration work already is underway, with construction scaffolding obscuring the view.
Such were the circumstances confronting Platt Bayard Dovell Architects (PBDA) of New York at the Foundation Building of the Cooper Union in New York's Greenwich Village. Partner Paul Bayard, who is the author of The Architecture of Additions and also the director of the Historic Preservation Program at the Columbia University School of Architecture, Planning, and Preservation, observes that the 1858 Cooper Union structure had been altered and expanded in several waves through the 1880s and again through the 1970s. PBDA's master plan of 1997 relied on HABS drawings from the 1970s, supplemented by field survey drawings the PBDA staff did by hand (facilitated by scaffolding that prevented use of photogrammetry or laser methods).
At the time, PBDA was using Arris CAD software, though the firm has since converted to AutoCAD. Arris supported intricate color-coding of elements on the drawings. For example, different colors represented various materials, such as brownstone, limestone, terra cotta, copper, and so forth, while different hatchings represented different types of repair or replacement work that was typically distinguished by the age or condition of the underlying material. According to PBDA senior associate Anne Holford-Smith, providing the contractor with color plots as construction documents enabled the firm to communicate the multi-dimensional layering of complex historic work within the limitations of 2D paper documents.
An architect's ability to document and analyze fragments of buildings, significantly altered buildings, or buildings that have been totally destroyed (whether by fiat, war, or natural disaster) is limited by the inability to visualize and experience such historic building models in their appropriate spatial context. Current technologies allow for computer model reconstructions, but do not easily support virtual reality or other simulated walkthroughs in which existing spaces are merged with models restored from other times.
This limitation may soon be eliminated as a result of work conducted jointly by researchers from Columbia University's Computer Science and Architecture departments. Led by computer science professor Steven Feiner, the project known as MARS (Mobile Augmented Reality System) combines a transparent head-mounted display, head-tracking gear, global positioning satellite (GPS) system, and wireless Internet data superposed on the user's view of his or her environment. Because the MARS system knows where the user is (via GPS) and where the user is looking (via head-tracking), it is able to stream wireless Internet data to the user's head-mounted display that is synchronized to and in registration with the user's view of the physical environment.
MARS applications include campus guides, with interactive paths and signage projected onto the user's view of the environment, so that real buildings are tagged with virtual directories of classroom locations and faculty offices. Such views need not be limited to the present condition of current buildings, but could extend to reveal earlier incarnations of current buildings-or even buildings that no longer exist-in their original locations. With such a system, loaded with sufficient computer-generated data, historic architects of the future will be able to view buildings, campuses, perhaps even entire cities and regions as four-dimensional streams of information, and analyze how their spatial configurations morph over time. Such architects truly will become the Trafalmadorians of design.
|Users of Mobile Augmented Reality Systems (right) can view images of long-vanished building on their former sites (above). (Images courtesy Columbia University.)|
Architect Jerry Laiserin, FAIA, provides strategic consulting services to architects and their technology providers. He can be reached at firstname.lastname@example.org