1,686 research outputs found
Understanding the Limitations of CNN-based Absolute Camera Pose Regression
Visual localization is the task of accurate camera pose estimation in a known
scene. It is a key problem in computer vision and robotics, with applications
including self-driving cars, Structure-from-Motion, SLAM, and Mixed Reality.
Traditionally, the localization problem has been tackled using 3D geometry.
Recently, end-to-end approaches based on convolutional neural networks have
become popular. These methods learn to directly regress the camera pose from an
input image. However, they do not achieve the same level of pose accuracy as 3D
structure-based methods. To understand this behavior, we develop a theoretical
model for camera pose regression. We use our model to predict failure cases for
pose regression techniques and verify our predictions through experiments. We
furthermore use our model to show that pose regression is more closely related
to pose approximation via image retrieval than to accurate pose estimation via
3D structure. A key result is that current approaches do not consistently
outperform a handcrafted image retrieval baseline. This clearly shows that
additional research is needed before pose regression algorithms are ready to
compete with structure-based methods.Comment: Initial version of a paper accepted to CVPR 201
Emergent states in heavy electron materials
We obtain the conditions necessary for the emergence of various low
temperature ordered states (local moment antiferromagnetism, unconventional
superconductivity, quantum criticality, and Landau Fermi liquid behavior) in
Kondo lattice materials by extending the two-fluid phenomenological theory of
heavy electron behavior to incorporate the concept of hybridization
effectiveness. We use this expanded framework to present a new phase digram and
consistent physical explanation and quantitative description of measured
emergent behaviors such as the pressure variation of the onset of local moment
antiferromagnetic ordering at T_N, the magnitude of the ordered moment, the
growth of superconductivity within that ordered state, the location of a
quantum critical point, and of a delocalization line in the
pressure/temperature phase diagram at which local moments have disappeared and
the heavy electron Fermi surface has grown to its maximum size. We apply our
model to CeRhIn_5 and a number of other heavy electron materials and find good
agreement with experiment.Comment: 20 pages, 8 figures, 1 tabl
Canonical and gravitational stress-energy tensors
It is dealt with the question, under which circumstances the canonical
Noether stress-energy tensor is equivalent to the gravitational (Hilbert)
tensor for general matter fields under the influence of gravity. In the
framework of general relativity, the full equivalence is established for matter
fields that do not couple to the metric derivatives. Spinor fields are included
into our analysis by reformulating general relativity in terms of tetrad
fields, and the case of Poincare gauge theory, with an additional, independent
Lorentz connection, is also investigated. Special attention is given to the
flat limit, focusing on the expressions for the matter field energy
(Hamiltonian). The Dirac-Maxwell system is investigated in detail, with special
care given to the separation of free (kinetic) and interaction (or potential)
energy. Moreover, the stress-energy tensor of the gravitational field itself is
briefly discussed.Comment: final version, to appear in Int. J. Mod. Phys.
Virtual Delamination Testing through Non-Linear Multi-Scale Computational Methods: Some Recent Progress
This paper deals with the parallel simulation of delamination problems at the
meso-scale by means of multi-scale methods, the aim being the Virtual
Delamination Testing of Composite parts. In the non-linear context, Domain
Decomposition Methods are mainly used as a solver for the tangent problem to be
solved at each iteration of a Newton-Raphson algorithm. In case of strongly
nonlinear and heterogeneous problems, this procedure may lead to severe
difficulties. The paper focuses on methods to circumvent these problems, which
can now be expressed using a relatively general framework, even though the
different ingredients of the strategy have emerged separately. We rely here on
the micro-macro framework proposed in (Ladev\`eze, Loiseau, and Dureisseix,
2001). The method proposed in this paper introduces three additional features:
(i) the adaptation of the macro-basis to situations where classical
homogenization does not provide a good preconditioner, (ii) the use of
non-linear relocalization to decrease the number of global problems to be
solved in the case of unevenly distributed non-linearities, (iii) the
adaptation of the approximation of the local Schur complement which governs the
convergence of the proposed iterative technique. Computations of delamination
and delamination-buckling interaction with contact on potentially large
delaminated areas are used to illustrate those aspects
Benchmarking Particle Filter Algorithms for Efficient Velodyne-Based Vehicle Localization
Keeping a vehicle well-localized within a prebuilt-map is at the core of any autonomous vehicle navigation system. In this work, we show that both standard SIR sampling and rejection-based optimal sampling are suitable for efficient (10 to 20 ms) real-time pose tracking without feature detection that is using raw point clouds from a 3D LiDAR. Motivated by the large amount of information captured by these sensors, we perform a systematic statistical analysis of how many points are actually required to reach an optimal ratio between efficiency and positioning accuracy. Furthermore, initialization from adverse conditions, e.g., poor GPS signal in urban canyons, we also identify the optimal particle filter settings required to ensure convergence. Our findings include that a decimation factor between 100 and 200 on incoming point clouds provides a large savings in computational cost with a negligible loss in localization accuracy for a VLP-16 scanner. Furthermore, an initial density of ∼2 particles/m 2 is required to achieve 100% convergence success for large-scale (∼100,000 m 2 ), outdoor global localization without any additional hint from GPS or magnetic field sensors. All implementations have been released as open-source software
Generally covariant quantization and the Dirac field
Canonical Hamiltonian field theory in curved spacetime is formulated in a
manifestly covariant way. Second quantization is achieved invoking a
correspondence principle between the Poisson bracket of classical fields and
the commutator of the corresponding quantum operators. The Dirac theory is
investigated and it is shown that, in contrast to the case of bosonic fields,
in curved spacetime, the field momentum does not coincide with the generators
of spacetime translations. The reason is traced back to the presence of second
class constraints occurring in Dirac theory. Further, it is shown that the
modification of the Dirac Lagrangian by a surface term leads to a momentum
transfer between the Dirac field and the gravitational background field,
resulting in a theory that is free of constraints, but not manifestly
hermitian.Comment: final version, to appear in Annals Phy
- …