22,440 research outputs found
Visualizing curved spacetime
I present a way to visualize the concept of curved spacetime. The result is a
curved surface with local coordinate systems (Minkowski Systems) living on it,
giving the local directions of space and time. Relative to these systems,
special relativity holds. The method can be used to visualize gravitational
time dilation, the horizon of black holes, and cosmological models. The idea
underlying the illustrations is first to specify a field of timelike
four-velocities. Then, at every point, one performs a coordinate transformation
to a local Minkowski system comoving with the given four-velocity. In the local
system, the sign of the spatial part of the metric is flipped to create a new
metric of Euclidean signature. The new positive definite metric, called the
absolute metric, can be covariantly related to the original Lorentzian metric.
For the special case of a 2-dimensional original metric, the absolute metric
may be embedded in 3-dimensional Euclidean space as a curved surface.Comment: 15 pages, 20 figure
Reflectance Hashing for Material Recognition
We introduce a novel method for using reflectance to identify materials.
Reflectance offers a unique signature of the material but is challenging to
measure and use for recognizing materials due to its high-dimensionality. In
this work, one-shot reflectance is captured using a unique optical camera
measuring {\it reflectance disks} where the pixel coordinates correspond to
surface viewing angles. The reflectance has class-specific stucture and angular
gradients computed in this reflectance space reveal the material class.
These reflectance disks encode discriminative information for efficient and
accurate material recognition. We introduce a framework called reflectance
hashing that models the reflectance disks with dictionary learning and binary
hashing. We demonstrate the effectiveness of reflectance hashing for material
recognition with a number of real-world materials
Embedding nonrelativistic physics inside a gravitational wave
Gravitational waves with parallel rays are known to have remarkable
properties: Their orbit space of null rays possesses the structure of a
non-relativistic spacetime of codimension-one. Their geodesics are in
one-to-one correspondence with dynamical trajectories of a non-relativistic
system. Similarly, the null dimensional reduction of Klein-Gordon's equation on
this class of gravitational waves leads to a Schroedinger equation on curved
space. These properties are generalized to the class of gravitational waves
with a null Killing vector field, of which we propose a new geometric
definition, as conformally equivalent to the previous class and such that the
Killing vector field is preserved. This definition is instrumental for
performing this generalization, as well as various applications. In particular,
results on geodesic completeness are extended in a similar way. Moreover, the
classification of the subclass with constant scalar invariants is investigated.Comment: 56 pages, 9 figures, v3:Minor correction
A Visualization Tool Used to Develop New Photon Mapping Techniques
We present a visualisation tool aimed specifically at the development and optimisation of photon map denoising methods. Our tool allows the rapid testing of hypotheses and algorithms through the use of parallel coordinates, domain-specific scripting, color mapping and point plots. Interaction is carried out by brushing, adjusting parameters and focus-plus-context, and yields interactive visual feedback and debugging information. We demonstrate the use of the tool to explore high-dimensional photon map data, facilitating the discovery of novel parameter spaces which can be used to dissociate complex caustic illumination. We then show how these new parameterisations may be used to improve upon pre-existing noise removal methods in the context of the photon relaxation framework
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