1,558 research outputs found
SurfelMeshing: Online Surfel-Based Mesh Reconstruction
We address the problem of mesh reconstruction from live RGB-D video, assuming
a calibrated camera and poses provided externally (e.g., by a SLAM system). In
contrast to most existing approaches, we do not fuse depth measurements in a
volume but in a dense surfel cloud. We asynchronously (re)triangulate the
smoothed surfels to reconstruct a surface mesh. This novel approach enables to
maintain a dense surface representation of the scene during SLAM which can
quickly adapt to loop closures. This is possible by deforming the surfel cloud
and asynchronously remeshing the surface where necessary. The surfel-based
representation also naturally supports strongly varying scan resolution. In
particular, it reconstructs colors at the input camera's resolution. Moreover,
in contrast to many volumetric approaches, ours can reconstruct thin objects
since objects do not need to enclose a volume. We demonstrate our approach in a
number of experiments, showing that it produces reconstructions that are
competitive with the state-of-the-art, and we discuss its advantages and
limitations. The algorithm (excluding loop closure functionality) is available
as open source at https://github.com/puzzlepaint/surfelmeshing .Comment: Version accepted to IEEE Transactions on Pattern Analysis and Machine
Intelligenc
Obtaining Potential Field Solution with Spherical Harmonics and Finite Differences
Potential magnetic field solutions can be obtained based on the synoptic
magnetograms of the Sun. Traditionally, a spherical harmonics decomposition of
the magnetogram is used to construct the current and divergence free magnetic
field solution. This method works reasonably well when the order of spherical
harmonics is limited to be small relative to the resolution of the magnetogram,
although some artifacts, such as ringing, can arise around sharp features. When
the number of spherical harmonics is increased, however, using the raw
magnetogram data given on a grid that is uniform in the sine of the latitude
coordinate can result in inaccurate and unreliable results, especially in the
polar regions close to the Sun.
We discuss here two approaches that can mitigate or completely avoid these
problems: i) Remeshing the magnetogram onto a grid with uniform resolution in
latitude, and limiting the highest order of the spherical harmonics to the
anti-alias limit; ii) Using an iterative finite difference algorithm to solve
for the potential field. The naive and the improved numerical solutions are
compared for actual magnetograms, and the differences are found to be rather
dramatic.
We made our new Finite Difference Iterative Potential-field Solver (FDIPS) a
publically available code, so that other researchers can also use it as an
alternative to the spherical harmonics approach.Comment: This paper describes the publicly available Finite Difference
Iterative Potential field Solver (FDIPS). The code can be obtained from
http://csem.engin.umich.edu/FDIP
Discrete curvature approximations and segmentation of polyhedral surfaces
The segmentation of digitized data to divide a free form surface into patches is one of the key steps required to perform a reverse engineering process of an object. To this end, discrete curvature approximations are introduced as the basis of a segmentation process that lead to a decomposition of digitized data into areas that will help the construction of parametric surface patches. The approach proposed relies on the use of a polyhedral representation of the object built from the digitized data input. Then, it is shown how noise reduction, edge swapping techniques and adapted remeshing schemes can participate to different preparation phases to provide a geometry that highlights useful characteristics for the segmentation process. The segmentation process is performed with various approximations of discrete curvatures evaluated on the polyhedron produced during the preparation phases. The segmentation process proposed involves two phases: the identification of characteristic polygonal lines and the identification of polyhedral areas useful for a patch construction process. Discrete curvature criteria are adapted to each phase and the concept of invariant evaluation of curvatures is introduced to generate criteria that are constant over equivalent meshes. A description of the segmentation procedure is provided together with examples of results for free form object surfaces
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