2,696 research outputs found
Multi-scale data storage schemes for spatial information systems
This thesis documents a research project that has led to the design and prototype
implementation of several data storage schemes suited to the efficient multi-scale
representation of integrated spatial data. Spatial information systems will benefit from
having data models which allow for data to be viewed and analysed at various levels
of detail, while the integration of data from different sources will lead to a more
accurate representation of reality.
The work has addressed two specific problems. The first concerns the design of an
integrated multi-scale data model suited for use within Geographical Information
Systems. This has led to the development of two data models, each of which allow for
the integration of terrain data and topographic data at multiple levels of detail. The
models are based on a combination of adapted versions of three previous data
structures, namely, the constrained Delaunay pyramid, the line generalisation tree and
the fixed grid.
The second specific problem addressed in this thesis has been the development of an
integrated multi-scale 3-D geological data model, for use within a Geoscientific
Information System. This has resulted in a data storage scheme which enables the
integration of terrain data, geological outcrop data and borehole data at various levels
of detail.
The thesis also presents details of prototype database implementations of each of the
new data storage schemes. These implementations have served to demonstrate the
feasibility and benefits of an integrated multi-scale approach.
The research has also brought to light some areas that will need further research before
fully functional systems are produced. The final chapter contains, in addition to
conclusions made as a result of the research to date, a summary of some of these areas
that require future work
Using polyhedral models to automatically sketch idealized geometry for structural analysis
Simplification of polyhedral models, which may incorporate large numbers of faces and nodes, is often required to reduce their amount of data, to allow their efficient manipulation, and to speed up computation. Such a simplification process must be adapted to the use of the resulting polyhedral model. Several applications require simplified shapes which have the same topology as the original model (e.g. reverse engineering, medical applications, etc.). Nevertheless, in the fields of structural analysis and computer visualization, for example, several adaptations and idealizations of the initial geometry are often necessary. To this end, within this paper a new approach is proposed to simplify an initial manifold or non-manifold polyhedral model with respect to bounded errors specified by the user, or set up, for example, from a preliminary F.E. analysis. The topological changes which may occur during a simplification because of the bounded error (or tolerance) values specified are performed using specific curvature and topological criteria and operators. Moreover, topological changes, whether or not they kept the manifold of the object, are managed simultaneously with the geometric operations of the simplification process
Fast Simulation of Skin Sliding
Skin sliding is the phenomenon of the skin moving over underlying layers of fat, muscle and bone. Due to the complex interconnections between these separate layers and their differing elasticity properties, it is difficult to model and expensive to compute. We present a novel method to simulate this phenomenon at real--time by remeshing the surface based on a parameter space resampling. In order to evaluate the surface parametrization, we borrow a technique from structural engineering known as the force density method which solves for an energy minimizing form with a sparse linear system. Our method creates a realistic approximation of skin sliding in real--time, reducing texture distortions in the region of the deformation. In addition it is flexible, simple to use, and can be incorporated into any animation pipeline
Coarse-grained Multiresolution Structures for Mobile Exploration of Gigantic Surface Models
We discuss our experience in creating scalable systems for distributing
and rendering gigantic 3D surfaces on web environments and
common handheld devices. Our methods are based on compressed
streamable coarse-grained multiresolution structures. By combining
CPU and GPU compression technology with our multiresolution
data representation, we are able to incrementally transfer, locally
store and render with unprecedented performance extremely
detailed 3D mesh models on WebGL-enabled browsers, as well as
on hardware-constrained mobile devices
Shape optimisation with multiresolution subdivision surfaces and immersed finite elements
We develop a new optimisation technique that combines multiresolution
subdivision surfaces for boundary description with immersed finite elements for
the discretisation of the primal and adjoint problems of optimisation. Similar
to wavelets multiresolution surfaces represent the domain boundary using a
coarse control mesh and a sequence of detail vectors. Based on the
multiresolution decomposition efficient and fast algorithms are available for
reconstructing control meshes of varying fineness. During shape optimisation
the vertex coordinates of control meshes are updated using the computed shape
gradient information. By virtue of the multiresolution editing semantics,
updating the coarse control mesh vertex coordinates leads to large-scale
geometry changes and, conversely, updating the fine control mesh coordinates
leads to small-scale geometry changes. In our computations we start by
optimising the coarsest control mesh and refine it each time the cost function
reaches a minimum. This approach effectively prevents the appearance of
non-physical boundary geometry oscillations and control mesh pathologies, like
inverted elements. Independent of the fineness of the control mesh used for
optimisation, on the immersed finite element grid the domain boundary is always
represented with a relatively fine control mesh of fixed resolution. With the
immersed finite element method there is no need to maintain an analysis
suitable domain mesh. In some of the presented two- and three-dimensional
elasticity examples the topology derivative is used for creating new holes
inside the domain.The partial support of the EPSRC through grant # EP/G008531/1 and EC through Marie Curie Actions (IAPP) program CASOPT project are gratefully acknowledged.This is the final version of the article. It was first available from Elsevier via http://dx.doi.org/10.1016/j.cma.2015.11.01
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