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Phase-measuring deflectometry (PMD) is an established measurement method for determining the topography of specular free-form surfaces. However, since each camera pixel only contains information about the location of the observed screen point, but not about the incident ray direction, the surface slope cannot be determined unambiguously without prior knowledge of the height. In order to overcome this difficulty (known as the ”height problem” of PMD), several cameras with overlapping fields of view are often used. This, however, requires a very large screen and additional installation space in order to ensure sufficiently diverse viewing directions within the overlap region. Other solutions, such as multiple measurements with shifted screen positions or the use of additional measuring equipment to determine the object position, also have considerable drawbacks due to the longer measurement time and the greater calibration effort. A new method is presented which avoids these disadvantages.
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