7,459 research outputs found
Efficient generic calibration method for general cameras with single centre of projection
Generic camera calibration is a non-parametric calibration technique that is applicable to any type of vision sensor. However, the standard generic calibration method was developed with the goal of generality and it is therefore sub-optimal for the common case of cameras with a single centre of projection (e.g. pinhole, fisheye, hyperboloidal catadioptric). This paper proposes novel improvements to the standard generic calibration method for central cameras that reduce its complexity, and improve its accuracy and robustness. Improvements are achieved by taking advantage of the geometric constraints resulting from a single centre of projection. Input data for the algorithm is acquired using active grids, the performance of which is characterised. A new linear estimation stage to the generic algorithm is proposed incorporating classical pinhole calibration techniques, and it is shown to be significantly more accurate than the linear estimation stage of the standard method. A linear method for pose estimation is also proposed and evaluated against the existing polynomial method. Distortion correction and motion reconstruction experiments are conducted with real data for a hyperboloidal catadioptric sensor for both the standard and proposed methods. Results show the accuracy and robustness of the proposed method to be superior to those of the standard method
Towards dynamic camera calibration for constrained flexible mirror imaging
Flexible mirror imaging systems consisting of a perspective
camera viewing a scene reflected in a flexible mirror can provide direct control over image field-of-view and resolution. However, calibration of such systems is difficult due to the vast range of possible mirror shapes
and the flexible nature of the system. This paper proposes the fundamentals of a dynamic calibration approach for flexible mirror imaging systems by examining the constrained case of single dimensional flexing.
The calibration process consists of an initial primary calibration stage followed by in-service dynamic calibration. Dynamic calibration uses a
linear approximation to initialise a non-linear minimisation step, the result of which is the estimate of the mirror surface shape. The method is
easier to implement than existing calibration methods for flexible mirror imagers, requiring only two images of a calibration grid for each dynamic
calibration update. Experimental results with both simulated and real data are presented that demonstrate the capabilities of the proposed approach
Monopole decay in the external electric field
The possibility of the magnetic monopole decay in the constant electric field
is investigated and the exponential factor in the probability is obtained.
Corrections due to Coulomb interaction are calculated. The relation between
masses of particles for the process to exist is obtained.Comment: 13 pages, 8 figure
Quantum Group Covariance and the Braided Structure of Deformed Oscillators
The connection between braided Hopf algebra structure and the quantum group
covariance of deformed oscillators is constructed explicitly. In this context
we provide deformations of the Hopf algebra of functions on SU(1,1). Quantum
subgroups and their representations are also discussed.Comment: 12 pages, to be published in JM
Finite difference methods for singularly perturbed problems on non-rectangular domains
Singularly perturbed problems arise in many branches of science and are characterised mathematically by the presence of a small parameter m u ltip ly in g one or more of the highest derivatives in a differential equation. This thesis concerns singularly perturbed problems posed on non-rectangular domains. The methodology used is to perform a co-ordinate transformation to pose the problem on a rectangular domain and to then study the transformed problem.
We first consider a class of parabolic problems. We classify the problems in the transformed problem class according to the nature and location of the layers present in th e ir solution. This classification then enables us to design numerical methods specific to each class of problems. Known theoretical results are stated for the convergence of some of the methods. We then examine in detail one particular method. Under certain assumptions it is shown that the numerical solutions generated by the method converge uniformly with respect to the singularly perturb ed parameter. Detailed numerical results are then presented which verify the theoretical results.
The next class of problems considered is a class of elliptic problems. In this case the transformed differential equation contains a new term and the situation is thus more complex. For this reason we consider only the case when regular layers are present. An appropriate numerical method is constructed and under various assumptions it is proved th a t the numerical solutions converge uniformly, in the perturbed case, i.e., when the singularly perturbed parameter is small. This is the central result of the thesis. Extensive numerical computations are presented which verify the theoretical result
Braided Oscillators
The braided Hopf algebra structure of the generalized oscillator is
investigated. Using the solutions two types of braided Fibonacci oscillators
are introduced. This leads to two types of braided Biedenharn-Macfarlane
oscillators.Comment: 12 pages, latex, some references added, published versio
Simplified Vacuum Energy Expressions for Radial Backgrounds and Domain Walls
We extend our previous results of simplified expressions for functional
determinants for radial Schr\"odinger operators to the computation of vacuum
energy, or mass corrections, for static but spatially radial backgrounds, and
for domain wall configurations. Our method is based on the zeta function
approach to the Gel'fand-Yaglom theorem, suitably extended to higher
dimensional systems on separable manifolds. We find new expressions that are
easy to implement numerically, for both zero and nonzero temperature.Comment: 30 page
Symmetry Breaking in the Schr\"odinger Representation for Chern-Simons Theories
This paper discusses the phenomenon of spontaneous symmetry breaking in the
Schr\"odinger representation formulation of quantum field theory. The analysis
is presented for three-dimensional space-time abelian gauge theories with
either Maxwell, Maxwell-Chern-Simons, or pure Chern-Simons terms as the gauge
field contribution to the action, each of which leads to a different form of
mass generation for the gauge fields.Comment: 16pp, LaTeX , UCONN-94-
The Complexity of Repairing, Adjusting, and Aggregating of Extensions in Abstract Argumentation
We study the computational complexity of problems that arise in abstract
argumentation in the context of dynamic argumentation, minimal change, and
aggregation. In particular, we consider the following problems where always an
argumentation framework F and a small positive integer k are given.
- The Repair problem asks whether a given set of arguments can be modified
into an extension by at most k elementary changes (i.e., the extension is of
distance k from the given set).
- The Adjust problem asks whether a given extension can be modified by at
most k elementary changes into an extension that contains a specified argument.
- The Center problem asks whether, given two extensions of distance k,
whether there is a "center" extension that is a distance at most (k-1) from
both given extensions.
We study these problems in the framework of parameterized complexity, and
take the distance k as the parameter. Our results covers several different
semantics, including admissible, complete, preferred, semi-stable and stable
semantics
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