6,873 research outputs found
Robust visual odometry using uncertainty models
In dense, urban environments, GPS by itself cannot be relied on to provide accurate positioning information. Signal reception issues (e.g. occlusion, multi-path effects) often prevent the GPS receiver from getting a positional lock, causing holes in the absolute positioning data. In order to keep assisting the driver, other sensors are required to track the vehicle motion during these periods of GPS disturbance. In this paper, we propose a novel method to use a single on-board consumer-grade camera to estimate the relative vehicle motion. The method is based on the tracking of ground plane features, taking into account the uncertainty on their backprojection as well as the uncertainty on the vehicle motion. A Hough-like parameter space vote is employed to extract motion parameters from the uncertainty models. The method is easy to calibrate and designed to be robust to outliers and bad feature quality. Preliminary testing shows good accuracy and reliability, with a positional estimate within 2 metres for a 400 metre elapsed distance. The effects of inaccurate calibration are examined using artificial datasets, suggesting a self-calibrating system may be possible in future work
Why Do Granular Materials Stiffen with Shear Rate? : Test of Novel Stress-Based Statistics
Peer reviewedPublisher PD
Support Vector Machine classification of strong gravitational lenses
The imminent advent of very large-scale optical sky surveys, such as Euclid
and LSST, makes it important to find efficient ways of discovering rare objects
such as strong gravitational lens systems, where a background object is
multiply gravitationally imaged by a foreground mass. As well as finding the
lens systems, it is important to reject false positives due to intrinsic
structure in galaxies, and much work is in progress with machine learning
algorithms such as neural networks in order to achieve both these aims. We
present and discuss a Support Vector Machine (SVM) algorithm which makes use of
a Gabor filterbank in order to provide learning criteria for separation of
lenses and non-lenses, and demonstrate using blind challenges that under
certain circumstances it is a particularly efficient algorithm for rejecting
false positives. We compare the SVM engine with a large-scale human examination
of 100000 simulated lenses in a challenge dataset, and also apply the SVM
method to survey images from the Kilo-Degree Survey.Comment: Accepted by MNRA
Deep space network support of the manned space flight network for Apollo, volume 2 Technical memorandum, 1969 - 1970
Deep Space Network support activities for Apollo 9 through 13 flights and associated equipmen
Transients in sheared granular matter
As dense granular materials are sheared, a shear band and an anisotropic
force network form. The approach to steady state behavior depends on the
history of the packing and the existing force and contact network. We present
experiments on shearing of dense granular matter in a 2D Couette geometry in
which we probe the history and evolution of shear bands by measuring particle
trajectories and stresses during transients. We find that when shearing is
stopped and restarted in the same direction, steady state behavior is
immediately reached, in agreement with the typical assumption that the system
is quasistatic. Although some relaxation of the force network is observed when
shearing is stopped, quasistatic behavior is maintained because the contact
network remains essentially unchanged. When the direction of shear is reversed,
a transient occurs in which stresses initially decrease, changes in the force
network reach further into the bulk, and particles far from the wheel become
more mobile. This occurs because the force network is fragile to changes
transverse to the force network established under previous shear; particles
must rearrange before becoming jammed again, thereby providing resistance to
shear in the reversed direction. The strong force network is reestablished
after displacing the shearing surface , where is the mean grain
diameter. Steady state velocity profiles are reached after a shear of . Particles immediately outside of the shear band move on average less than
1 diameter before becoming jammed again. We also examine particle rotation
during this transient and find that mean particle spin decreases during the
transient, which is related to the fact that grains are not interlocked as
strongly.Comment: 7 pages, 11 figures, accepted to Eur. Phys. J. E, revised version
based on referee suggestion
Autocalibration with the Minimum Number of Cameras with Known Pixel Shape
In 3D reconstruction, the recovery of the calibration parameters of the
cameras is paramount since it provides metric information about the observed
scene, e.g., measures of angles and ratios of distances. Autocalibration
enables the estimation of the camera parameters without using a calibration
device, but by enforcing simple constraints on the camera parameters. In the
absence of information about the internal camera parameters such as the focal
length and the principal point, the knowledge of the camera pixel shape is
usually the only available constraint. Given a projective reconstruction of a
rigid scene, we address the problem of the autocalibration of a minimal set of
cameras with known pixel shape and otherwise arbitrarily varying intrinsic and
extrinsic parameters. We propose an algorithm that only requires 5 cameras (the
theoretical minimum), thus halving the number of cameras required by previous
algorithms based on the same constraint. To this purpose, we introduce as our
basic geometric tool the six-line conic variety (SLCV), consisting in the set
of planes intersecting six given lines of 3D space in points of a conic. We
show that the set of solutions of the Euclidean upgrading problem for three
cameras with known pixel shape can be parameterized in a computationally
efficient way. This parameterization is then used to solve autocalibration from
five or more cameras, reducing the three-dimensional search space to a
two-dimensional one. We provide experiments with real images showing the good
performance of the technique.Comment: 19 pages, 14 figures, 7 tables, J. Math. Imaging Vi
Self-Calibration of Cameras with Euclidean Image Plane in Case of Two Views and Known Relative Rotation Angle
The internal calibration of a pinhole camera is given by five parameters that
are combined into an upper-triangular calibration matrix. If the
skew parameter is zero and the aspect ratio is equal to one, then the camera is
said to have Euclidean image plane. In this paper, we propose a non-iterative
self-calibration algorithm for a camera with Euclidean image plane in case the
remaining three internal parameters --- the focal length and the principal
point coordinates --- are fixed but unknown. The algorithm requires a set of point correspondences in two views and also the measured relative
rotation angle between the views. We show that the problem generically has six
solutions (including complex ones).
The algorithm has been implemented and tested both on synthetic data and on
publicly available real dataset. The experiments demonstrate that the method is
correct, numerically stable and robust.Comment: 13 pages, 7 eps-figure
Electricity Reform and Retail Pricing in Texas
Electricity market reforms have pursued two main goals, both aimed at increasing economic efficiency. The first is to make prices more reflective of costs so that consumers can make more efficient decisions about where and when to consume electricity. The second goal is to ensure that suppliers minimize the costs of supply. How successful has electricity market reform in Texas been with regard to achieving these goals? We focus on one aspect of this overall set of desired outcomes, namely whether movements in retail prices reflect wholesale market prices and whether reform has delivered cost reductions in the delivery of energy services by retailers. We find clear evidence that retail prices in competitive market areas better reflect wholesale prices and have moved favorably for consumers relative to wholesale prices. The same is not necessarily true for consumers in non-competitive market areas. This suggests that competitive retail markets have delivered cost reductions consistent with electricity service providers reducing their marginal costs. The effort that Texas undertook over a decade ago to introduce competition into the retail electricity supply thus appears to be yielding the benefits to consumers that were intended in competitive areas. Consumers in less competitive areas do not appear to have benefited as much
Exploring the use of strategic frameworks in dental practice
This paper explores the use of strategic frameworks in NHS and private dental practice. It reviews the policy context of dentistry and suggests the challenges in this context will require dental practices to prioritise understanding and engagement with a strategic approach. A strategic approach will be required in order to enhance and improve performance. Two specific strategic frameworks will be explored in terms of their relevance to NHS and private dental practic
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