This poster was presented at the 3D Digital Documentation Summit held July 10-12, 2012 at the Presidio, San Fransisco, CA.
Mind the Gap: the Need to Supplement Laser Scan Data in HABS Documentation Projects
The HABS poster will discuss the use of laser scanning in relation to the documentation of historic buildings. When HABS uses laser scanning in its projects, it is in conjunction with more traditional methods of collecting data. We use the ScanStation 2 frequently in our field work, and our familiarity with the machine and its strengths and limitations as a piece of long-range surveying equipment allows us to quickly assess whether a hand-measurement of some kind is preferable to laser scanning. This is generally for one or more of the following reasons: because traditional techniques produce a higher quality and clarity of information, because they allow the data to be collected more quickly and efficiently, because the resulting data requires less processing or manipulation in the office, or because of issues of limited access.
For example, scanning often presents difficulties in determining the profiles of molding and door and window jambs due to poor edge definition. The use of a molding comb [fig. 1, fig. 2] is a fast and inexpensive way of capturing this information, while giving the user the opportunity to interpret the original condition of the detail through layers of paint. Digital photography is often used in areas of sculptural relief, where a laser scanner may fail to provide a high enough resolution to ascertain minute changes in elevation [fig. 3, fig. 4]. The result is highly legible and easy to decipher in CAD. Laser scanning building interiors divided into many rooms is at this time still impractical and time consuming; measuring rooms by hand remains the most efficient way to gather the needed dimensions. Some spaces are too confined to position or operate the laser scanner from; in these instances, there is little choice but to document these areas by hand.
High definition laser scanning has proven useful, and the technology is now an important tool in HABS’ toolbox. It is not yet, however, the only tool. It remains critical to have skilled individuals on the ground that can make decisions regarding the optimal methods for recording a given structure efficiently, accurately, and intelligently–decisions that have a calculable impact on the strength of the interpretive documentation that results.
Daniel De Sousa and Jason McNatt are both HABS Architects with the Historic American Building Survey of the National Park Service.