Integrating 3D Surface and Sub-surface Data for Heritage Preservation and Planning

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Digital 3D data capture technology, such as laser scanning, airborne LiDAR and ground penetrating radar–GPR, are on the verge of revolutionizing the investigation and preservation of our cultural heritage worldwide. We think it is essential that here in North America leading academic programs, preservation organizations, commercial developers and agencies including the National Park Service take the opportunity to explore and embrace preservation technology that is responsive, accurate, and cost effective.

The value of 3D imaging archaeological properties through laser scanning is beginning to be recognized by the Historic American Buildings Survey (HABS), Historic American Engineering Record (HAER), and Historic American Landscapes Survey (HALS). Airborne LiDAR surveys are revealing ancient, but subtle land forms in dense tropical jungles in Central America that are revolutionizing this profession. Geophysical surveys of archaeological sites and landscapes are increasing across the United States.

We believe there is a significant opportunity and utility to combining subsurface geophysical data with above ground terrestrial scanned data that is not being addressed. This article will briefly present our case for pursuing this approach.

Over the past five years technological advancements are enabling the rapid collection of multiple spatial data sets over large geographic areas. As a result, the measurement data collected can be both large in scale and dense leading sometimes to complicated data integration and analysis. This can be a challenge for the end user who needs specific information such as guidance for the placement of a trench, or on a smaller scale, a position to cut through a floor or wall surface. While the ever developing technologies for data capture continue to increase survey speed and data density, we need to engage these techniques for more than just the novelty of `Big Data’ but to better understand the , archaeological significance of that data. (Gaffney & Gaffney, 2011)

In 2011 the National Center for Preservation Technology Training sponsored Archaeological Survey Technologies, Data Integration, and Applications Workshop and Seminar (ASTDA) where we began to explore the integration of above and below ground imaging technologies and methods. This workshop was the first to address the application of these combined methods for the management of historic properties, especially those threatened by erosion, development, and other destructive processes. While this research focuses on archaeological problem solving, the methods for data capture, integration, and analysis are directly transferable to more mainstream utility, infrastructure, and Built Environment applications.

Hosted at the Longfellow House– Washington’s Headquarters National Historic Site in Cambridge, Massachusetts (Figure 1), the workshop introduced methods for non-invasive data acquisition, such as ground penetrating radar [GPR], electrical resistivity, magnetometry, conductivity, magnetic susceptibility, and 3D laser scanning (Figure 2). Preliminary data fusion integrated modeled subsurface features, exiting site structures, and the related landscape in a single spatial environment.

Equally important, the workshop focused on how to effectively engage the results of these methods in the investigation, planning, and preservation of archaeological properties. The ASTDA Seminar included participants from groups associated with historic properties: managers, developers, and public outreach groups. The half day seminar presented the benefits of using this type of integrated data environment for site management and provided information on how to successfully integrate this type of approach into their existing work flow.

GIS (Geographic Information System) was used to combine and interpret spatial data that included historic, modern, and archaeological maps, utilities, aerial photos, and geophysical survey results (Figure 3). While 3D laser scanning demonstrated different mapping contexts (interior and exterior of standing structures and the context of the structure in its surrounding landscape, Figure 4) the resulting point clouds are not easily incorporated into the spatial environment of a GIS.

Currently there is not a simple, affordable, off the shelf process (or software) to convert, integrate, and analyze these different types of above and below ground spatial data into a single geo-spatial environment. Preliminary integration and visualization was performed in Pointools (Figure 5). While the images appear impressive, the fundamental spatial components of these data remain inaccessible. Continuing research is exploring different software approaches that will support the combination of these data types into a single environment that will enable both visual and quantitative analysis of the results.

This research is also investigating data types from the Built Environment including 3D laser scans, CAD utility plans, and GPR survey (in concrete slab and exterior environment utility mapping). Specific goals for this aspect of the research focus on developing a workflow guideline for data capture, conversion, and integration into a single geo-spatial environment. In addition to the development of a workflow guideline, information on how to effectively design a request for proposal (RFP) document for contracting elements of site survey from various subcontractors will be provided. Thus, from the beginning this will enable the establishment of an accurate site spatial control framework (x, y, z) and present suggested data sampling rates and methods toward ease of data capture and integration to the conversion, integration, and analysis workflow.

With the increasing adoption of integrated project delivery (IPD) the potential and benefits of early capture, modeling, and integration of above ground structure and sub-surface elements can begin to be realized. Utilization of terrestrial laser scanning as a basis for existing conditions modeling and mechanical, engineering, and plumbing (MEP) verification has expanded rapidly over the past four years driven, in part, by the growth of building information modeling (BIM)based developments. The application of GPR, and multiple geophysical survey techniques, as fundamental tools in the investigation of concrete structure and subsurface utility detection has grown in parallel while remaining largely separate workflows. The potential expanded upon initially in the heritage framework can be dynamically applied to the commercial development sectors by allowing for a spatially accurate blending of the building/site interface.

Trade integration through the medium of BIM seeks to minimize risk and maximize virtual design/build benefits born out of accurate existing conditions modeling and new build planning. Subsurface information can be integrated alongside above ground datasets in 3D. This can be achieved by the manipulation of geophysical volume data, particularly GPR, and delivered in point cloud form in a manner similar to laser scanning data. It can also be taken further by modeling geophysical anomalies as solid surfaces (with reasonably applied levels of certainty dependent on the particular technique). These can then be integrated within packages similar to Autodesk Navisworks to be analyzed in terms of potential clash or interference tolerances.

Key to this effort is the underpinning of the combined techniques and subsequent modeling by solid survey control, established coordinate system and vertical datum. Horizontal control is relatively easily coordinated by specific survey control points; targets from laser scanning, grid points or profile locations from geophysical surveys, or by GPS integrated systems. The vertical positioning of above ground 3D datasets in relation to a specific Z datum can be readily established. The relative Z subsurface depth of geophysical survey results depends upon accurate depth calibration (for GPR) and specification of local or global coordinate systems being utilized for the survey. In terms of the transition of building/site interface, the ability to position the models and data derived from these multiple sources should not be seen as a challenge, but more as an element of early site spatial coordination. Final data deliverables seek to integrate with BIM-related products in a readily documented path.

We seek to bring together the survey methods and final deliverables discussed above with currently available off the shelf software packages. The greater challenge may come in rethinking the timing, and scale of the survey and modeling effort when considering a more `traditional’ commercial development cycle. With a greater understanding of the benefits, cost saving, and risk management in this approach to accessing the full potential of our data, its place should be earlier in the planning and implementation stage of a project thus maximizing the value of the combined data and its application to effective project development and site management.

Gaffney, V. and C. Gaffney, 2011. Through an Imperfect Filter: geophysical techniques and the management of archaeological heritage. EAC occasional paper No. 5. 117-129.

Meg Watters is an Adjunct Post-Doctoral Research Associate, Anthropology, University of Massachusetts Amherst, and specializes in 3D visualization of remotely sensed and excavated data for a new perspective on non-invasive modeling and analysis of archaeological sites.

Stephen Wilkes, Director of 3D Services for Feldman Land Surveyors, Inc., has been working in laser scanning and surveying for the built environment for more than 10 years. This has also included integration and 3D visualization of GPS, GIS, terrestrial laser scanning, airborne LiDAR, and metrological surface scanning datasets.

A 3.378Mb PDF of this article as it appeared in the magazine complete with images is available by clicking HERE