Watershed segmentation of topographical features on freeform surfaces and its application to additively manufactured surfaces
Shan Lou, Luca Pagani, Wenhan Zeng, Xiangqian Jiang, Paul J. Scott
Abstract
With the advancement of modern enabling technologies, surfaces of high value-added products are changing from traditional simple geometries to complex geometries that feature freeform shapes. The analysis of topographical features on freeform surfaces is challenging because surface shapes are no longer planar and measurement data often require surface description in the form of triangular meshes. An approach is proposed to extend the watershed segmentation from planar surfaces to freeform surfaces. Surface topography is first extracted from measured surfaces (mesh surfaces) using proper mathematical operations, e.g. fitting and filtration. The watershed segmentation based on Maxwell's theory is extended to 3D triangular meshes and applied to the extracted surface topography defined as a scalar function associated with the vertices of the mesh surface. Critical surface points such as peaks, pits and saddles are identified to construct a Pfaltz graph. Ridge lines and course lines are then traced starting from saddles and following the steepest uphill and downhill paths to peaks and pits, respectively. Wolf pruning of the change tree is employed to merge over-segmented regions. The extended watershed segmentation method is applied to segment surface topography of the additively processed scaffold and lattice surfaces.