Fast Normal Approximation of Point Clouds in Screen Space

Displaying large point clouds of mainly planar point distributions yet comes with large restrictions regarding the surface normal and surface reconstruction. Point data needs to be clustered or traversed to extract a local neighborhood which is necessary to retrieve surface information. We propose using the rendering pipeline to circumvent a pre-computation of the neighborhood in world space to perform a fast approximation of the surface in screen space. We present and compare three different methods for surface reconstruction within a post-process. These methods range from simple approximations to the definition of a tensor surface. All these methods are designed to run at interactive frame-rates. We also present a correction method to increase reconstruction quality, while preserving interactive frame-rates. Our results indicate, that the on-the-fly computation of surface normals is not a limiting factor on modern GPUs. As the surface information is generated during the post-process, only the target display size is the limiting factor. The performance is independent of the point cloud’s size

Das Potential der Full-Waveform-Prozessierung topo-bathymetrischer LiDARDaten

Aufsatz veröffentlicht in: "Wasserbau-Symposium 2021: Wasserbau in Zeiten von Energiewende, Gewässerschutz und Klimawandel, Zurich, Switzerland, September 15-17, 2021, Band 2" veröffentlicht unter: https://doi.org/10.3929/ethz-b-00049975

The 3D Grazing Collision of Two Black Holes

We present results for two colliding black holes (BHs), with angular momentum, spin, and unequal mass. For the first time gravitational waveforms are computed for a grazing collision from a full 3D numerical evolution. The collision can be followed through the merger to form a single BH, and through part of the ringdown period of the final BH. The apparent horizon is tracked and studied, and physical parameters, such as the mass of the final BH, are computed. The total energy radiated in gravitational waves is shown to be consistent with the total mass of the spacetime and the final BH mass. The implication of these simulations for gravitational wave astronomy is discussed.Comment: 4 pages, 7 figures, revte

Reconstructing power cables from LIDAR data using eigenvector streamlines of the point distribution tensor field

Starting from the computation of a covariance matrix of neighborhoods in a point cloud, streamlines are utilized to reconstruct lines of linearly distributed points following the major Eigenvector of the matrix. This technique is similar to fiber tracking in diffusion tensor imaging (DTI), but in contrast is done mesh-free. Different weighting functions for the computation of the matrix and for the interpolation of the vector in the point cloud have been implemented and compared on artificial test cases. A dataset stemming from light detect and ranging (LIDAR) surveying served as a testbed for parameter studies where, finally, a power cable was reconstructed

Reconstructing Power Cables From LIDAR Data Using Eigenvector Streamlines of the Point Distribution Tensor Field

Starting from the computation of a covariance matrix of neighborhoods in a point cloud, streamlines are utilized to reconstruct lines of linearly distributed points following the major Eigenvector of the matrix. This technique is similar to fiber tracking in diffusion tensor imaging (DTI), but in contrast is done mesh-free. Different weighting functions for the computation of the matrix and for the interpolation of the vector in the point cloud have been implemented and compared on artificial test cases. A dataset stemming from light detect and ranging (LIDAR) surveying served as a testbed for parameter studies where, finally, a power cable was reconstructed

Fiberbundle-Based Visualization of a Stirred-Tank Flow

We describe a novel approach to treat data from a complex numerical simulation in a unified environment using a generic data model for scientific visualization. The model is constructed out of building blocks in a hierarchical scheme of seven levels, out of which only three are exposed to the end-user. This generic scheme allows for a wide variety of input formats, and results in powerful capabilities to connect data. We review the theory of this data model, implementation aspects in our visualization environment, and its application to computational fluid dynamic simulation of flow in an impeller-stirred tank. The computational data are given as a velocity vector field and a scalar pressure field on a mesh consisting of 2088 blocks in curvilinear coordinates