1999 Conditions Assessment Survey of the Exterior Marble:
~~ Laser Scanning

		This illustration is a copy of the unedited laser scan "point cloud" file imported into AutoCAD 14®. Additional manipulation to this base file can be done in the Cyra CGP software and in AutoCAD®.

During the course of the fieldwork a demonstration of a laser scanning process for recording existing structures was conducted by Cyra Technologies at the Second Bank of the United States. This process utilizes a Class 2 laser to record variations in the surface topography of a building at a predetermined level of detail (highest level of precision currently is plus or minus 2mm). The scanned points are then imaged as "point clouds" in the Cyra CGP software where they can be enhanced and exported into a CAD or modeling program for further rendering.

The purpose of the demonstration was to see if laser scanning could record the areas of the surface in 3-D where there was dimensional loss of stone, and to determine to what degree these conditions would be visible and measurable in the final rendering. Since the laser only perceives the variations in surface topography, conditions that do not create loss (mild accretions on the surface, staining, patches, etc.) would not be accounted for in the scanned information. However, despite these limitations, if successful, the laser scanning process could provide a means for accurately creating datum points to measure surface loss in selected areas.

The results of the survey at the Second Bank were excellent with regards to the level of detail in the changes of the surface that the laser was able to record. Areas of dimensional loss, contour scaling and spalling were very apparent in the graphic files produced from the scans. There were, however, "holes" in scanned areas depending on the complexity of the forms being scanned. The angle and distance from the subject can be adjusted to try and encompass as many visible surfaces as possible from a given perspective. But, in order to catch the sides, top, or bottom of a surface in addition to the face, multiple scans must be taken and then stitched together to form a completed 3-D model of all the surfaces which can then be viewed from different angles within the software program.

The savings in time and the amount of detail collected during the scanning process were successfully demonstrated at the Second Bank. However, using the software to create the type of digital information necessary to formulate architectural drawings, details, or models was not easily implemented into the digitizing process. The learning curve, and the number of steps or levels through which the data must be processed or manipulated before it is useable, could turn out to offset any savings in time that were gained by improving the recording in the field. (It should be noted, that this first attempt at using the laser scanning system during the survey of the north and west facades of the Second Bank did not provide enough background time to prepare to use the software and to integrate into, or alter the existing documentation process).