Fig. 1. Clustering based analysis detects symmetry at different scales in a 3D cryo-electron microscopy image of AMP-activated kinase (EMDB-1897). (left) The three-fold rotational symmetry is apparent from the volume rendering. (center) Contours are represented as points in a high-dimensional shape descriptor space (illustrated in 2D). Symmetric contours form a cluster in the descriptor space and can be easily identified. Three such clusters are shown in gold, blue, and pink. (right) Three symmetric regions of different sizes, highlighted in gold, blue, and pink, detected by the method.Abstract-The complexity in visualizing volumetric data often limits the scope of direct exploration of scalar fields. Isocontour extraction is a popular method for exploring scalar fields because of its simplicity in presenting features in the data. In this paper, we present a novel representation of contours with the aim of studying the similarity relationship between the contours. The representation maps contours to points in a high-dimensional transformation-invariant descriptor space. We leverage the power of this representation to design a clustering based algorithm for detecting symmetric regions in a scalar field. Symmetry detection is a challenging problem because it demands both segmentation of the data and identification of transformation invariant segments. While the former task can be addressed using topological analysis of scalar fields, the latter requires geometry based solutions. Our approach combines the two by utilizing the contour tree for segmenting the data and the descriptor space for determining transformation invariance. We discuss two applications, query driven exploration and asymmetry visualization, that demonstrate the effectiveness of the approach.