Structural Deflection Measurement with a Range Camera

Abstract

Range cameras offer great potential for the measurement of structural deformations because of their ability to directly measure video sequences of three-dimensional coordinates of entire surfaces, their compactness, and their relatively low cost compared with other active imaging technologies such as terrestrial laser scanners. Identified limitations of range cameras for high-precision metrology applications such as deformation measurement include the high (centimeter level) noise level and scene-dependent errors. This paper proposes models and methodologies to overcome these limitations and reports on the use of a SwissRanger SR4000 range camera for the measurement of deflections in concrete beams subjected to flexural load-testing. Results from three separate tests show that submillimeter precision and accuracy—assessed by comparison with estimates derived from terrestrial laser scanner data—can be achieved. The high-accuracy range camera results were realized by eliminating the systematic, scene-dependent bias of internal scattering through measurement differencing and by reducing the influence of random errors with temporal and spatial filtering strategies. Additional experiments to validate some of the fundamental modeling assumptions and to explain the possible causes of residual, submillimeter biases in the deflection estimates are also reported.