Metrological analysis of the three-dimensional reconstruction based on close-range photogrammetry and the fusion of long-wave infrared and visible-light images

This work proposes evaluating statistically the metrological performance of three-dimensional reconstructions built with fused long-wavelength infrared (LWIR) and visible-light (VL) images. The image fusion procedure was essentially based on two-dimensional wavelet transform and two pixel-level fusion rules: the maximum intensity level, presented in a previous work of the authors, and a new fusion rule, which replaces the VL information with the LWIR information in the region of the measured object on the images. The reconstructions of a translucent cube were performed with a point triangulation-based procedure and its dimension measurements were employed as evaluation criteria. The results show that the fused images have more contrast but also more artifacts. The fusion procedures generated denser reconstructions with at least 34.83% more points. Considering the metrological result, reconstructions with only visible-light images resulted in maximal 89.31% less measurement bias but at least 47.25% more uncertainty than the fusion ones. The new fusion rule provided the best results, with more points in the dense cloud and lower uncertainty. The work is important to provide a metrologically viable alternative for three-dimensional reconstruction of objects in situations of low contrast or poor texture information in the visible spectrum, and in which no target can be applied to the inspected part.