The Field

Point Cloud Surveys of Historic Landscapes

When the US Secretary of the Interior first introduced the Standards and Guidelines for Architectural and Engineering Documentation: HABS/HAER  in 1983, Ronald Reagan was in the White House and most of us did not yet know how to type—let alone know how to work on a PC.  This document was formulated in a pre-digital age and is, not-surprisingly, pre-digital in orientation; specifying such parameters for the documentation of historic structures as the use of black and white photography, the requisite submission of film negatives and consistency of hand-lettering.  Today, some of the specific requirements seem almost quaint: “Level I measured drawings will be lettered mechanically (i.e., Leroy or similar) or in a hand printed equivalent style.”  Incidentally, these standards served as a prototype for the Historic American Landscape Survey (HALS) when it was initiated in 2000.

In the decades since 1983, we have witnessed a revolution in Information Technology.  It has resulted in fundamental changes to the way that disciplines such as landscape architecture and history are practiced.  In the 1990s, Computer-Aided Design transformed the workflow of landscape architectural practice from design and documentation through construction.  A second wave of transformation has arrived with Building Information Management (BIM) / Site Information Management (SIM) applications and is beginning to transform the roles of designer and contractor in project delivery.  In the study of history today, the use of Geographic Information Systems (GIS) for research and analysis is not uncommon.  Other new technologies and software applications are now emerging with the potential to transform a wide array of disciplines from ecology to historic preservation.   What follows is a discussion of one of these tools in particular—the digital “Point Cloud Survey”—and a review of its use in the context of a preservation and adaptive reuse project in Saudi Arabia.

LOCATION

Atturaif was the site of the first Saudi capital in the 18^th century and on into the 19^th century.  Situated on a drainage-way (or wadi) and on important trade routes, it was a site of political, economic, and religious importance for many years.  After being sacked repeatedly by the Ottomans, its citadel was abandoned in the 19^th century, and the center of Saudi power moved elsewhere; eventually to be reestablished in nearby Riyadh in the 20^th century.  A small agricultural settlement persisted alongside the mud brick ruins of the original building complex.  In recent years, the site has received recognition as a UNESCO World Heritage Site, as the Saudi government has been investing in scholarship of the site and infrastructure for visitors and tourists.

As part of this investment, our firm, Ayers Saint Gross, was engaged as part of a multidisciplinary, international team to design and plan for an open air “Living Museum.”  Our work included the design of a new visitor center, a visitor arrival forecourt, a museum, the restoration of homes, a footbridge, and an elevated walkway through the ruins.   Since the design for these elements needed to preserve the integrity of the extant historic structures, the team needed more than a traditional topographic survey.  We needed an accurate three-dimensional digital survey to avoid conflicts between the proposed features and the existing irregular landscape of ruins. Field measuring was not a realistic option, and a conventional topographic survey would not have captured enough information.  Instead, a Point Cloud Survey was commissioned, providing the necessary level of detail and accuracy in a reasonable amount of time.

PROCESS

A Point Cloud Survey results in a data set that consists of a very large number of individual vertices, each with x, y, and z values.  The vertices can be combined into wireframe, triangle-mesh, or smooth surface models of great detail and complexity.  The data set is collected by a three-dimensional laser scanner.  At our Atturaif site, the 3D laser scan was ground-based.  Station points were established by physically tagging existing structures to provide 3D benchmarks. The scanning units were positioned at various points on the ground, where they span and laser-scanned the surrounding features, collecting a “point cloud” of individual vertices.  Worthy of note here are air-based versions of point- cloud surveying, which make use of a small remote-control helicopter drone with cameras.  The resulting surveys are not as accurate as ground-based methods, but may be suitable for larger sites or projects where cruder models are permitted.

A decade ago, such models would have been too large for a typical PC workstation to handle.  Today, it has become relatively easy to use such models because of the greater byte storage capacity and higher processing speeds of most workstations on the market.  The project is currently in construction, but at the time that we were developing the design (about 4 years ago) we were able to import the Point-Cloud generated model into SketchUp.  These surveys sometimes are delivered in a proprietary model format, but are usually readily converted or imported into more common programs such as AutoCad, SketchUp or Revit.  The incredibly detailed survey data of Atturaif was used in our design to determine profiles and elevations for proposed features and to work with the archeological features that will be showcased in the design.  When ground-proofing the model on site, we were amazed at the accuracy: You can see each stone in the digital model and sections can be cut anywhere in the site and are accurate to 1/8.”

While the potential of this technology seems to be limitless, there are physical constraints. Working in the desert, laser equipment shuts down at 122  F (50  C), so the survey crews therefore had to start at dawn and would work until it reached 122 , which was usually before noon.  These surveys are also not inexpensive, sometimes costing tens of thousands of dollars.  Nevertheless, they can help pay for themselves by reducing the cost of field verifications and the expense of construction delays resulting from inaccurate base information.

Other tools are being developed that will continue to revolutionize the way in which we collect information about the built environment.  As one example, AutoDesk has just released a new program called 123D Catch, which purportedly can create a 3-dimensional digital model from a series of photographs of an object from different vantage points.  Although our preliminary experiments with this application have yielded mixed results, we fully anticipate that such tools will become valuable resources for gathering data about and documenting historic landscapes.

EVALUATION

An obvious question is: Where does all of this leave the older standards for documenting historic structures and landscapes?  In a day when a historic landscape can be cloud-surveyed and documented as a 3D digital model with an accuracy of plus or minus 1/8”, are such archives still relevant?  We would argue that, while there is certainly a need for modernization—which may involve broadening the media for documentation—the HABS/ HAER /HALS programs still retain their value because of their commitment to 4 critical performance standards, which are spelled out in the introduction to the standards:

1. Documentation shall adequately explicate and illustrate what is significant or valuable about the historic building, site, structure, or object being documented.
2. Documentation shall be prepared accurately from reliable sources with limitations clearly stated to permit independent verifications of the information.
3. Documentation shall be prepared on materials that are readily reproducible, durable, and in standards sizes.
4. Documentation shall be clearly and concisely produced.

Yes, point cloud surveying is capable of gathering an almost infinite amount of information and detail, but without interpretation, the significance and value of what is being modeled can be lost.  And, how well will digital models transmit from one generation to the next?  From one year to the next?  Software is constantly changing, and all it takes is a new and better file format/software to render obsolete and inaccessible an earlier-generation of a digital model.  So before we push for new media for HALS documentation and abandon the old, we must be careful to develop a tested strategy for ensuring the “durability” and accessibility of our archives to future generations.

In the case of Atturaif, the digital models were used not only by the designers—traditional 2D survey drawings were one type of output—but by archeologists studying and documenting the site, by the contractors constructing the buildings, by filmmakers, and by exhibition contractors who use the models for animations and virtual recreations of the site.  One of the basic outputs of the point cloud is the 2D drawing, which can be archived as survey documentation, but the collateral materials can be used for years in various ways for education and scholarship.  The digital models have been archived with the ‘reader’ software, which will enable future users of the models to navigate and use them.

In the midst of most revolutions, there is usually little time for critical reflection.  As we assimilate new technologies into our practice of landscape architecture or historic preservation, it is important that we also pause to reflect on the benefits and costs of technological change.  We need to ask and discuss important questions, such as: how are the new technologies transforming practice—positively and negatively—and how they can be steered to the best advantage?  Also, what best practices and performance standards from the past are still applicable?

SELECTED LINKS AND SOURCES:

Birnbaum, Charles A. “Protecting Cultural Landscapes: Planning, Treatment and Management of Historic Landscapes,” Preservations Briefs (36).  Washington, DC: US Department of the Interior National Park Service Cultural Resources, 1994.

Lavoie, Catherine and Dana Lockett.  “Producing HABS/HAER/HALS Measured Drawings from Laser Scans: the Pros and Cons of Using Laser Scanning for Heritage Documentation.” Washington, DC: US Department of the Interior National Park Service Cultural Resources, 2011.

Lockett, Dana, Paul Davidson. “Documentation to the Secretary of the Interior’s Standards: Assessing the Value of Laser Scan Data.” Unpublished Abstract.  Research presented at NCPTT, 2012.

“Secretary of the Interior’s Standards and Guidelines for Architectural and Engineering Documentation: HABS/HAER Standards.” Originally published in the Federal Register (September 29, 1983). Washington, DC: US Department of the Interior National Park Service Cultural Resources, 1990.

by Jonathan Ceci, ASLA, and Dan Henderer

Jonathan Ceci is the director of the landscape architecture studio at Ayers Saint Gross and 2013 chair of ASLA’s Historic Preservation PPN. His practice is focused on campus planning and site design for colleges, universities and cultural institutions in both historic and contemporary settings.  Among his recent projects are the Atturaif Gateway and a new trails network through cultural and natural landscapes on the site of an ante-bellum plantation in South Carolina, which today serves as the College of Charleston’s environmental studies campus.  He is an avid heirloom vegetable gardener and has a flock of egg-laying Plymouth Rock chickens at his home in northern Maryland.

Dan Henderer is a Senior Associate at Ayers Saint Gross.  Since 2011, he has been based in Riyadh, Saudi Arabia overseeing construction of the projects mentioned in this article.  His professional focus has been on cultural projects.  He has contributed as a designer and project manager on the Visitor Reception Center, Atturaif Gateway, Addiriyah Museum, Atturaif Footbridge and Site Multimedia projects.