2,581 research outputs found
As-Built 3D Heritage City Modelling to Support Numerical Structural Analysis: Application to the Assessment of an Archaeological Remain
Terrestrial laser scanning is a widely used technology to digitise archaeological, architectural
and cultural heritage. This allows for modelling the assets’ real condition in comparison with
traditional data acquisition methods. This paper, based on the case study of the basilica in the Baelo
Claudia archaeological ensemble (Tarifa, Spain), justifies the need of accurate heritage modelling
against excessively simplified approaches in order to support structural safety analysis. To do this,
after validating the 3Dmeshing process frompoint cloud data, the semi-automatic digital reconstitution
of the basilica columns is performed. Next, a geometric analysis is conducted to calculate the structural
alterations of the columns. In order to determine the structural performance, focusing both on the
accuracy and suitability of the geometric models, static and modal analyses are carried out by means of
the finite element method (FEM) on three different models for the most unfavourable column in terms
of structural damage: (1) as-built (2) simplified and (3) ideal model without deformations. Finally,
the outcomes show that the as-built modelling enhances the conservation status analysis of the 3D
heritage city (in terms of realistic compliance factor values), although further automation still needs to
be implemented in the modelling process
Interactive inspection of complex multi-object industrial assemblies
The final publication is available at Springer via http://dx.doi.org/10.1016/j.cad.2016.06.005The use of virtual prototypes and digital models containing thousands of individual objects is commonplace in complex industrial applications like the cooperative design of huge ships. Designers are interested in selecting and editing specific sets of objects during the interactive inspection sessions. This is however not supported by standard visualization systems for huge models. In this paper we discuss in detail the concept of rendering front in multiresolution trees, their properties and the algorithms that construct the hierarchy and efficiently render it, applied to very complex CAD models, so that the model structure and the identities of objects are preserved. We also propose an algorithm for the interactive inspection of huge models which uses a rendering budget and supports selection of individual objects and sets of objects, displacement of the selected objects and real-time collision detection during these displacements. Our solution–based on the analysis of several existing view-dependent visualization schemes–uses a Hybrid Multiresolution Tree that mixes layers of exact geometry, simplified models and impostors, together with a time-critical, view-dependent algorithm and a Constrained Front. The algorithm has been successfully tested in real industrial environments; the models involved are presented and discussed in the paper.Peer ReviewedPostprint (author's final draft
The Phase Diagram of Fluid Random Surfaces with Extrinsic Curvature
We present the results of a large-scale simulation of a Dynamically
Triangulated Random Surface with extrinsic curvature embedded in
three-dimensional flat space. We measure a variety of local observables and use
a finite size scaling analysis to characterize as much as possible the regime
of crossover from crumpled to smooth surfaces.Comment: 29 pages. There are also 19 figures available from the authors but
not included here - sorr
ColDICE: a parallel Vlasov-Poisson solver using moving adaptive simplicial tessellation
Resolving numerically Vlasov-Poisson equations for initially cold systems can
be reduced to following the evolution of a three-dimensional sheet evolving in
six-dimensional phase-space. We describe a public parallel numerical algorithm
consisting in representing the phase-space sheet with a conforming,
self-adaptive simplicial tessellation of which the vertices follow the
Lagrangian equations of motion. The algorithm is implemented both in six- and
four-dimensional phase-space. Refinement of the tessellation mesh is performed
using the bisection method and a local representation of the phase-space sheet
at second order relying on additional tracers created when needed at runtime.
In order to preserve in the best way the Hamiltonian nature of the system,
refinement is anisotropic and constrained by measurements of local Poincar\'e
invariants. Resolution of Poisson equation is performed using the fast Fourier
method on a regular rectangular grid, similarly to particle in cells codes. To
compute the density projected onto this grid, the intersection of the
tessellation and the grid is calculated using the method of Franklin and
Kankanhalli (1993) generalised to linear order. As preliminary tests of the
code, we study in four dimensional phase-space the evolution of an initially
small patch in a chaotic potential and the cosmological collapse of a
fluctuation composed of two sinusoidal waves. We also perform a "warm" dark
matter simulation in six-dimensional phase-space that we use to check the
parallel scaling of the code.Comment: Code and illustration movies available at:
http://www.vlasix.org/index.php?n=Main.ColDICE - Article submitted to Journal
of Computational Physic
Path tracing using lower level of detail for secondary rays
Path tracing is a computationally expensive method of three dimensional rendering that aims to accurately simulate the propagation of light. A large amount of time is typically spent calculating intersections between rays and the scene, which is composed of triangular meshes stored in some form of bounding volume. This time can be reduced by lowering the overall number of triangles in the scene. Path tracing works by casting rays from the camera into the scene, reflecting until they hit a light source. Secondary rays, or rays which occur after the first intersection, usually contribute less to the overall image, yet require much more time to calculate than primary rays. This thesis found that significant performance gains can be made by using lower level of detail (LOD) triangular meshes for secondary rays. While the lower LOD models are less accurate, they still provide a good approximation of the mesh for secondary rays. Scenes with 1.4 million faces could be rendered up to 10% faster using a 1/32 ratio level of detail for secondary rays. A study with 14 subjects who ranked images based on image quality showed they were unable to differentiate between low LOD and full LOD images
3D Mesh Simplification. A survey of algorithms and CAD model simplification tests
Simplification of highly detailed CAD models is an important step when CAD
models are visualized or by other means utilized in augmented reality applications.
Without simplification, CAD models may cause severe processing and storage is-
sues especially in mobile devices. In addition, simplified models may have other
advantages like better visual clarity or improved reliability when used for visual pose
tracking. The geometry of CAD models is invariably presented in form of a 3D
mesh. In this paper, we survey mesh simplification algorithms in general and focus
especially to algorithms that can be used to simplify CAD models. We test some
commonly known algorithms with real world CAD data and characterize some new
CAD related simplification algorithms that have not been surveyed in previous mesh
simplification reviews.Siirretty Doriast
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