453 research outputs found
Compression for Smooth Shape Analysis
Most 3D shape analysis methods use triangular meshes to discretize both the
shape and functions on it as piecewise linear functions. With this
representation, shape analysis requires fine meshes to represent smooth shapes
and geometric operators like normals, curvatures, or Laplace-Beltrami
eigenfunctions at large computational and memory costs.
We avoid this bottleneck with a compression technique that represents a
smooth shape as subdivision surfaces and exploits the subdivision scheme to
parametrize smooth functions on that shape with a few control parameters. This
compression does not affect the accuracy of the Laplace-Beltrami operator and
its eigenfunctions and allow us to compute shape descriptors and shape
matchings at an accuracy comparable to triangular meshes but a fraction of the
computational cost.
Our framework can also compress surfaces represented by point clouds to do
shape analysis of 3D scanning data
How smooth are particle trajectories in a CDM Universe?
It is shown here that in a flat, cold dark matter (CDM) dominated Universe
with positive cosmological constant (), modelled in terms of a
Newtonian and collisionless fluid, particle trajectories are analytical in time
(representable by a convergent Taylor series) until at least a finite time
after decoupling. The time variable used for this statement is the cosmic scale
factor, i.e., the "-time", and not the cosmic time. For this, a
Lagrangian-coordinates formulation of the Euler-Poisson equations is employed,
originally used by Cauchy for 3-D incompressible flow. Temporal analyticity for
CDM is found to be a consequence of novel explicit all-order recursion
relations for the -time Taylor coefficients of the Lagrangian displacement
field, from which we derive the convergence of the -time Taylor series. A
lower bound for the -time where analyticity is guaranteed and shell-crossing
is ruled out is obtained, whose value depends only on and on the
initial spatial smoothness of the density field. The largest time interval is
achieved when vanishes, i.e., for an Einstein-de Sitter universe.
Analyticity holds also if, instead of the -time, one uses the linear
structure growth -time, but no simple recursion relations are then obtained.
The analyticity result also holds when a curvature term is included in the
Friedmann equation for the background, but inclusion of a radiation term
arising from the primordial era spoils analyticity.Comment: 16 pages, 4 figures, published in MNRAS, this paper introduces a
convergent formulation of Lagrangian perturbation theory for LCD
Mesh-based 3D Textured Urban Mapping
In the era of autonomous driving, urban mapping represents a core step to let
vehicles interact with the urban context. Successful mapping algorithms have
been proposed in the last decade building the map leveraging on data from a
single sensor. The focus of the system presented in this paper is twofold: the
joint estimation of a 3D map from lidar data and images, based on a 3D mesh,
and its texturing. Indeed, even if most surveying vehicles for mapping are
endowed by cameras and lidar, existing mapping algorithms usually rely on
either images or lidar data; moreover both image-based and lidar-based systems
often represent the map as a point cloud, while a continuous textured mesh
representation would be useful for visualization and navigation purposes. In
the proposed framework, we join the accuracy of the 3D lidar data, and the
dense information and appearance carried by the images, in estimating a
visibility consistent map upon the lidar measurements, and refining it
photometrically through the acquired images. We evaluate the proposed framework
against the KITTI dataset and we show the performance improvement with respect
to two state of the art urban mapping algorithms, and two widely used surface
reconstruction algorithms in Computer Graphics.Comment: accepted at iros 201
3D Object Reconstruction from Hand-Object Interactions
Recent advances have enabled 3d object reconstruction approaches using a
single off-the-shelf RGB-D camera. Although these approaches are successful for
a wide range of object classes, they rely on stable and distinctive geometric
or texture features. Many objects like mechanical parts, toys, household or
decorative articles, however, are textureless and characterized by minimalistic
shapes that are simple and symmetric. Existing in-hand scanning systems and 3d
reconstruction techniques fail for such symmetric objects in the absence of
highly distinctive features. In this work, we show that extracting 3d hand
motion for in-hand scanning effectively facilitates the reconstruction of even
featureless and highly symmetric objects and we present an approach that fuses
the rich additional information of hands into a 3d reconstruction pipeline,
significantly contributing to the state-of-the-art of in-hand scanning.Comment: International Conference on Computer Vision (ICCV) 2015,
http://files.is.tue.mpg.de/dtzionas/In-Hand-Scannin
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