Discrete scalar field topology provides tools to extract the topology of a scalar field without derivation, interpolation, or integration. It allows purely combinatorial and thus consistent computations, whereas numerical schemes based on root finding and gradient curve integration are impaired by the noise of the underlying function. Combining discrete topology with persistence-based simplification enables a number of applications. We present two recently developed, novel applications:
Extraction of Salient Edges on Triangular Meshes:
Salient edges are perceptually prominent features of a surface. Most previous extraction schemes utilize the notion of ridges and valleys for their detection, thereby requiring curvature derivatives which are rather sensitive to noise. We introduce a novel method for salient edge extraction which does not depend on curvature derivatives. It is based on a topological analysis of the principal curvatures and salient edges of the surface are identified as parts of separatrices of the topological skeleton. Previous topological approaches obtain results including non-salient edges due to inherent properties of the underlying algorithms. We extend the profound theory by introducing the novel concept of separatrix persistence, which is a smooth measure along a separatrix and allows to keep its most salient parts only. We compare our results with other methods for salient edge extraction.
Topology-based Smoothing of 2D Scalar Fields with C1-Continuity:
Data sets coming from simulations or sampling of real-world phenomena often contain noise that hinders their processing and analysis. Automatic filtering and denoising can be challenging: when the nature of the noise is unknown, it is difficult to distinguish between noise and actual data features; in addition, the filtering process itself may introduce "artificial" features into the data set that were not originally present. In this paper, we propose a smoothing method for 2D scalar fields that gives the user explicit control over the data features. We define features as critical points of the given scalar function, and the topological structure they induce (i.e., the Morse-Smale complex). Feature significance is rated according to topological persistence. Our method allows filtering out spurious features that arise due to noise by means of topological simplification, providing the user with a simple interface that defines the significance threshold, coupled with immediate visual feedback of the remaining data features. In contrast to previous work, our smoothing method guarantees a C1-continuous output scalar field with the exact specified features and topological structures.
Applications of Discrete Scalar Field Topology: Salient Edges on Meshes and Smoothing of Scalar Fields
Dr. Tino Weinkauf, Courant Institute of Mathematical Sciences (New York University)
May, 14th 2010, 13:00ct, G29-R335