Multi-scale Vortex Extraction of Ocean Flow

A simple and intuitionistic method of vortices extraction is put forward in this paper. It includes two parts work: the vortex core detection and the vortex hull extraction. The former is based on Sperner’s Lemma to label the velocity vector direction of triangle vertices and identifies the fully-labeling triangle cells that are most likely to contain critical points. Combining with triangle subdivision scheme and recording the number and the position of the intersection of a surround streamline with the four axes under the coordinate system originated from the examined vortex core to determine the existence of the swirling flow pattern of vortices. Thus from visual and logical perspective, the actual vortex core regions are verified and the specific swirling range of vortex can be obtained by recording the outmost ring of the intersection points on the swirling streamlines surrounding the examined core. This approach can not only suppress false positives but also make the vortex extraction process easily and efficiently. Furthermore, an interactive vortex-scale factor is used for selective extracting and visualizing the vortex in ocean flow. This method is very flexible for user to perform multi-scale vortex feature analysis. The visualization results of the real ocean investigation data can prove the effectiveness of our method by comparing our results to the method of Jiang’s. In addition, it also shows the potential of the interactive visual analysis by the abstraction properties of feature extraction process in physical oceanography and in engineering practice.