Table 1 Comparison of three categories of PMD
From: A brief review of the technological advancements of phase measuring deflectometry
| Â | Â | Advantage | Disadvantage |
|---|---|---|---|
Single screen and sensor based PMD | PMD based on paraxial approximation | simple set up | can only measure objects with small size |
PMD based on flat reference | simple set up | can only measure near-plane surfaces | |
PMD based on an estimated shape and positon of SUT | simple set up, can measure objects with high curvature change | difficult to accurately estimate rough position of SUT | |
Multi-screen based PMD | PMD based on screen movement DPMD | do not need to estimate position of SUT can obtain absolute depth information | large system size, time-consuming due to screen movement cannot obtain gradient information |
Multi-sensor based PMD | Stereo deflectometry | can achieve both relative depth and absolute depth information | time-consuming due to search process applied |