Load-Balancing for Parallel Delaunay Triangulations

Computing the Delaunay triangulation (DT) of a given point set in $\mathbb{R}^D$ is one of the fundamental operations in computational geometry. Recently, Funke and Sanders (2017) presented a divide-and-conquer DT algorithm that merges two partial triangulations by re-triangulating a small subset of their vertices - the border vertices - and combining the three triangulations efficiently via parallel hash table lookups. The input point division should therefore yield roughly equal-sized partitions for good load-balancing and also result in a small number of border vertices for fast merging. In this paper, we present a novel divide-step based on partitioning the triangulation of a small sample of the input points. In experiments on synthetic and real-world data sets, we achieve nearly perfectly balanced partitions and small border triangulations. This almost cuts running time in half compared to non-data-sensitive division schemes on inputs exhibiting an exploitable underlying structure.Comment: Short version submitted to EuroPar 201

Joint segmentation of color and depth data based on splitting and merging driven by surface fitting

This paper proposes a segmentation scheme based on the joint usage of color and depth data together with a 3D surface estimation scheme. Firstly a set of multi-dimensional vectors is built from color, geometry and surface orientation information. Normalized cuts spectral clustering is then applied in order to recursively segment the scene in two parts thus obtaining an over-segmentation. This procedure is followed by a recursive merging stage where close segments belonging to the same object are joined together. At each step of both procedures a NURBS model is fitted on the computed segments and the accuracy of the fitting is used as a measure of the plausibility that a segment represents a single surface or object. By comparing the accuracy to the one at the previous step, it is possible to determine if each splitting or merging operation leads to a better scene representation and consequently whether to perform it or not. Experimental results show how the proposed method provides an accurate and reliable segmentation

Hierarchical Salient Object Detection for Assisted Grasping

Visual scene decomposition into semantic entities is one of the major challenges when creating a reliable object grasping system. Recently, we introduced a bottom-up hierarchical clustering approach which is able to segment objects and parts in a scene. In this paper, we introduce a transform from such a segmentation into a corresponding, hierarchical saliency function. In comprehensive experiments we demonstrate its ability to detect salient objects in a scene. Furthermore, this hierarchical saliency defines a most salient corresponding region (scale) for every point in an image. Based on this, an easy-to-use pick and place manipulation system was developed and tested exemplarily.Comment: Accepted for ICRA 201

Numerical Structure Analysis of Regular Hydrogen-Oxygen Detonations

Large-scale numerical simulations have been carried out to analyze the internal wave structure of a regular oscillating low-pressure H2 : O2 : Ar-Chapman-Jouguet detonation in two and three space-dimensions. The chemical reaction is modeled with a non-equilibrium mechanism that consists of 34 elementary reactions and uses nine thermally perfect gaseous species. A high local resolution is achieved dynamically at run-time by employing a block-oriented adaptive finite volume method that has been parallelized efficiently for massively parallel machines. Based on a highly resolved two-dimensional simulation we analyze the temporal development of the ow field around a triple point during a detonation cell in great detail. In particular, the influence of the reinitiation phase at the beginning of a detonation cell is discussed. Further on, a successful simulation of the cellular structure in three space-dimensions for the same configuration is presented. The calculation reproduces the experimentally observed three-dimensional mode of propagation called "rectangular-mode-in-phase" with zero phase shift between the transverse waves in both space-directions perpendicular to the detonation front and shows the same oscillation period as the two-dimensional case