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Interactive tensor field design and visualization on surfaces
Designing tensor fields in the plane and on surfaces
is a necessary task in many graphics applications, such as
painterly rendering, pen-and-ink sketch of smooth surfaces, and
anisotropic remeshing. In this paper, we present an interactive
design system that allows a user to create a wide variety of
surface tensor fields with control over the number and location
of degenerate points. Our system combines basis tensor fields
to make an initial tensor field that satisfies a set of user specifications.
However, such a field often contains unwanted
degenerate points that cannot always be eliminated due to
topological constraints of the underlying surface. To reduce the
artifacts caused by these degenerate points, our system allows the
user to move a degenerate point or to cancel a pair of degenerate
points that have opposite tensor indices.
We observe that a tensor field can be locally converted into
a vector field such that there is a one-to-one correspondence
between the set of degenerate points in the tensor field and the
set of singularities in the vector field. This conversion allows
us to effectively perform degenerate point pair cancellation
and movement by using similar operations for vector fields. In
addition, we adapt the image-based flow visualization technique
to tensor fields, therefore allowing interactive display of tensor
fields on surfaces.
We demonstrate the capabilities of our tensor field design
system with painterly rendering, pen-and-ink sketch of surfaces,
and anisotropic remeshing.Keywords: Tensor field design and visualization, nonphotorealistic rendering, tensor field topology, remeshin
Fast, Scalable, and Interactive Software for Landau-de Gennes Numerical Modeling of Nematic Topological Defects
Numerical modeling of nematic liquid crystals using the tensorial Landau-de
Gennes (LdG) theory provides detailed insights into the structure and
energetics of the enormous variety of possible topological defect
configurations that may arise when the liquid crystal is in contact with
colloidal inclusions or structured boundaries. However, these methods can be
computationally expensive, making it challenging to predict (meta)stable
configurations involving several colloidal particles, and they are often
restricted to system sizes well below the experimental scale. Here we present
an open-source software package that exploits the embarrassingly parallel
structure of the lattice discretization of the LdG approach. Our
implementation, combining CUDA/C++ and OpenMPI, allows users to accelerate
simulations using both CPU and GPU resources in either single- or multiple-core
configurations. We make use of an efficient minimization algorithm, the Fast
Inertial Relaxation Engine (FIRE) method, that is well-suited to large-scale
parallelization, requiring little additional memory or computational cost while
offering performance competitive with other commonly used methods. In
multi-core operation we are able to scale simulations up to supra-micron length
scales of experimental relevance, and in single-core operation the simulation
package includes a user-friendly GUI environment for rapid prototyping of
interfacial features and the multifarious defect states they can promote. To
demonstrate this software package, we examine in detail the competition between
curvilinear disclinations and point-like hedgehog defects as size scale,
material properties, and geometric features are varied. We also study the
effects of an interface patterned with an array of topological point-defects.Comment: 16 pages, 6 figures, 1 youtube link. The full catastroph
Approximation of tensor fields on surfaces of arbitrary topology based on local Monge parametrizations
We introduce a new method, the Local Monge Parametrizations (LMP) method, to
approximate tensor fields on general surfaces given by a collection of local
parametrizations, e.g.~as in finite element or NURBS surface representations.
Our goal is to use this method to solve numerically tensor-valued partial
differential equations (PDE) on surfaces. Previous methods use scalar
potentials to numerically describe vector fields on surfaces, at the expense of
requiring higher-order derivatives of the approximated fields and limited to
simply connected surfaces, or represent tangential tensor fields as tensor
fields in 3D subjected to constraints, thus increasing the essential number of
degrees of freedom. In contrast, the LMP method uses an optimal number of
degrees of freedom to represent a tensor, is general with regards to the
topology of the surface, and does not increase the order of the PDEs governing
the tensor fields. The main idea is to construct maps between the element
parametrizations and a local Monge parametrization around each node. We test
the LMP method by approximating in a least-squares sense different vector and
tensor fields on simply connected and genus-1 surfaces. Furthermore, we apply
the LMP method to two physical models on surfaces, involving a tension-driven
flow (vector-valued PDE) and nematic ordering (tensor-valued PDE). The LMP
method thus solves the long-standing problem of the interpolation of tensors on
general surfaces with an optimal number of degrees of freedom.Comment: 16 pages, 6 figure
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