Structured light surface measurement techniques

Abstract

This chapter describes some of the techniques used to measure the three-dimensional surface shape of objects in biomechanics. Structured light methods rely on knowing the details of the pattern of illumination, rather than correlating multiple views. Hologrammetry is one such method, covered in Chapter 4, but this chapter is confined to non-coherent illumination. The pattern of light falling on a scene tells us something about its three dimensional nature. Artists indicate the three-dimensional nature of their subjects by shades and highlights. Shades and highlights are a product of the position of the source of light, the viewer’s position relative to the position of the subject and the angle of the surface. But only occasionally do artists realize that the apparent shape of a shadow is altered by the shape of a three-dimensional surface. If you know the shape of a pattern of illumination, or shadow, its shape on an object tells you something about the shape of that object. For example, as the straight-line shadow of a horizontal glazing bar falls on the back of a hanging curtain, we see a convoluted pattern which corresponds to the folds of the curtain and the height of the sun. This is the phenomenon exploited by structured light techniques for surface shape measurement.