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Application and Optimisation of the Spatial Phase Shifting ...

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6.7 Extensions <strong>of</strong> SPS by temporal unwrapping 173<br />

Fig. 6.32: Overall displacement after heating <strong>and</strong> cooling. Residual tilts are visible in <strong>the</strong> sawtooth image (left);<br />

rigid-body displacements are revealed in <strong>the</strong> "temperature" height map (right). Arrows mark locations <strong>of</strong><br />

possible misinterpretations <strong>of</strong> <strong>the</strong> sawtooth image.<br />

On <strong>the</strong> o<strong>the</strong>r h<strong>and</strong>, <strong>the</strong> sum <strong>of</strong> <strong>the</strong> sawtooth images lacks important information. At <strong>the</strong> black arrow, a<br />

substantial piston-type displacement is not discernible from <strong>the</strong> sawtooth image, while at <strong>the</strong> white arrow,<br />

<strong>the</strong> nearly matching fringe positions almost conceal <strong>the</strong> step <strong>of</strong> 0.3 µm (1 fringe) that has actually<br />

remained. On <strong>the</strong> contrary, <strong>the</strong> results based on <strong>the</strong> height maps from <strong>the</strong> temporally unwrapped data are<br />

unambiguous. They need no interpretation <strong>and</strong> thus allow an easier assessment <strong>of</strong> object changes.

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