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Vertical aerial photograph stereoscopic pairs are the principal resource for making topographic maps and terrain profiles. Based on the same principle, close-up stereophotographs were taken of a strongly weathered surface of Georgia marble. Profiles were drawn of the now roughened surface, and the surface reduction was measured against inclusions of unweathered hornblende. Overlapping close-up photographs were taken at a 1:1 size ratio with a Canon macrolens on a nonautomatic Canon AT camera mounted on a sturdy Velbon-Mini tripod. With the optical axis perpendicular to the stone surface, light was provided by both a ringflash mounted in front of the lens and reflected natural light. An ultrafine-grained black and white film (Kodak Technical Pan, TP 2415) was used, printed onto 12.7 by 17.8-cm (5 by 7-in.) contrast paper for a 5:1 enlargement of the original surface.
A simple Abrams Heightfinder was attached to a small folding pocket stereoviewer with about two- to three-power magnification lenses. The accuracy of the optical height measurements was about ±0.1 mm, based on comparison with measurements employing a needle-point depth micrometer.
The method described here is applied to the comparison of uncleaned with cleaned stone surfaces in terms of both surface shape and surface reduction.
masonry, masonry cleaning, stone surface macrostereogrammetry
Professor, University of Notre Dame, Notre Dame, IN