80 research outputs found
Placental Flattening via Volumetric Parameterization
We present a volumetric mesh-based algorithm for flattening the placenta to a
canonical template to enable effective visualization of local anatomy and
function. Monitoring placental function in vivo promises to support pregnancy
assessment and to improve care outcomes. We aim to alleviate visualization and
interpretation challenges presented by the shape of the placenta when it is
attached to the curved uterine wall. To do so, we flatten the volumetric mesh
that captures placental shape to resemble the well-studied ex vivo shape. We
formulate our method as a map from the in vivo shape to a flattened template
that minimizes the symmetric Dirichlet energy to control distortion throughout
the volume. Local injectivity is enforced via constrained line search during
gradient descent. We evaluate the proposed method on 28 placenta shapes
extracted from MRI images in a clinical study of placental function. We achieve
sub-voxel accuracy in mapping the boundary of the placenta to the template
while successfully controlling distortion throughout the volume. We illustrate
how the resulting mapping of the placenta enhances visualization of placental
anatomy and function. Our code is freely available at
https://github.com/mabulnaga/placenta-flattening .Comment: MICCAI 201
Shape manipulation using physically based wire deformations
This paper develops an efficient, physically based shape manipulation technique. It defines a 3D model with profile curves, and uses spine curves generated from the profile curves to control the motion and global shape of 3D models. Profile and spine curves are changed into profile and spine wires by specifying proper material and geometric properties together with external forces. The underlying physics is introduced to deform profile and spine wires through the closed form solution to ordinary differential equations for axial and bending deformations. With the proposed approach, global shape changes are achieved through manipulating spine wires, and local surface details are created by deforming profile wires. A number of examples are presented to demonstrate the applications of our proposed approach in shape manipulation
Practical Distance Functions for Path-Planning in Planar Domains
Path planning is an important problem in robotics. One way to plan a path
between two points within a (not necessarily simply-connected) planar
domain , is to define a non-negative distance function on
such that following the (descending) gradient of this
distance function traces such a path. This presents two equally important
challenges: A mathematical challenge -- to define such that has a
single minimum for any fixed (and this is when ), since a local
minimum is in effect a "dead end", A computational challenge -- to define
such that it may be computed efficiently. In this paper, given a description of
, we show how to assign coordinates to each point of and
define a family of distance functions between points using these coordinates,
such that both the mathematical and the computational challenges are met. This
is done using the concepts of \emph{harmonic measure} and
\emph{-divergences}.
In practice, path planning is done on a discrete network defined on a finite
set of \emph{sites} sampled from , so any method that works well on the
continuous domain must be adapted so that it still works well on the discrete
domain. Given a set of sites sampled from , we show how to define a
network connecting these sites such that a \emph{greedy routing} algorithm
(which is the discrete equivalent of continuous gradient descent) based on the
distance function mentioned above is guaranteed to generate a path in the
network between any two such sites. In many cases, this network is close to a
(desirable) planar graph, especially if the set of sites is dense
Animating ultra-complex voxel scenes through shell deformation
version draft du mémoireInternational audienceVoxel representations have many advantages, such as ordered traversal during rendering and trivial very decent LOD through MIPmap. Special effect companies such Digital Domain or Rhythm&Hues now ex- tensively use voxels engines, for semi-transparent objects such as clouds, avalanches, tornado or explosions, but also for complex solid objects. Several gaming companies are also looking into voxel engines to deal with ever more complex scenes but the main problem when dealing with voxel representations is the amount of data that has to be manipulated. This amount usually prevents animating in real time. To solve these is- sues, ARTIS team developed the Gigavoxels framework: a very powerful voxel engine based on GPU ray-casting, with advanced memory man- agement, so that very complex scenes can be rendered in real-time. The purpose of the TER was to develop a solution for animating voxel objects in real-time, implement it and eventually integrate it to the Gigavoxels framework
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