In measuring a transmission matrix (TM) of a scattering medium, the normal way requires projecting a large number of patterns, resulting in significant measurement time. Here, we propose to do imaging through scattering media using a path-planning-based downsampling TM. The proposed method is verified by measuring TMs for imaging through scattering media when Walsh, Cake-cutting, and Russian doll Hadamard transforms (HTs) are adopted. Based on the spectral characteristics of different HTs of natural images, corresponding sampling paths are artificially planned, which guarantees the method to preferentially measure components in TM in relation to the more important spectra. This means that our method can reduce the number of patterns during measurement, thus improving the imaging speed while only sacrificing a little imaging quality. Experimental results demonstrate the effectiveness of the proposed method.
A calibration method for cantilever length of non-orthogonal cantilever coordinate measuring machine(CCMM) based on the double reversal method is proposed in this paper, aiming at the calibration problems of CCMM. The cantilever length calibration restricted by virtual axis is realized by the symmetrical rotation of the cantilever of the CCMM. By the symmetrical rotation of the probe head, the other parameters of the CCMM in the calibration process can be eliminated, and then the influence of the other mechanism errors on cantilever length calibration can be negligible, and the calibration accuracy of cantilever length is then improved a lot. Experiments show that the method discussed is easy to operate. The precision and effectiveness of the proposed method is verified by actual measurement experiment and practice, such as measuring standard gauges within its measurement range.
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