14,760 research outputs found
An Overview of Rendering from Volume Data --- including Surface and Volume Rendering
Volume rendering is a title often ambiguously used in science. One meaning often quoted is: `to render any three volume dimensional data set'; however, within this categorisation `surface rendering'' is contained. Surface rendering is a technique for visualising a geometric representation of a surface from a three dimensional volume data set. A more correct definition of Volume Rendering would only incorporate the direct visualisation of volumes, without the use of intermediate surface geometry representations. Hence we state: `Volume Rendering is the Direct Visualisation of any three dimensional Volume data set; without the use of an intermediate geometric representation for isosurfaces'; `Surface Rendering is the Visualisation of a surface, from a geometric approximation of an isosurface, within a Volume data set'; where an isosurface is a surface formed from a cross connection of data points, within a volume, of equal value or density. This paper is an overview of both Surface Rendering and Volume Rendering techniques. Surface Rendering mainly consists of contouring lines over data points and triangulations between contours. Volume rendering methods consist of ray casting techniques that allow the ray to be cast from the viewing plane into the object and the transparency, opacity and colour calculated for each cell; the rays are often cast until an opaque object is `hit' or the ray exits the volume
Understanding micro-image configurations in quasar microlensing
The micro-arcsecond scale structure of the seemingly point-like images in
lensed quasars, though unobservable, is nevertheless much studied
theoretically, because it affects the observable (or macro) brightness, and
through that provides clues to substructure in both source and lens. A curious
feature is that, while an observable macro-image is made up of a very large
number of micro-images, the macro flux is dominated by a few micro-images.
Micro minima play a key role, and the well-known broad distribution of macro
magnification can be decomposed into narrower distributions with 0,1,2,3,...
micro minima. This paper shows how the dominant micro-images exist alongside
the others, using the ideas of Fermat's principle and arrival-time surfaces,
alongside simulations.Comment: Accepted for publication in MNRA
Narrow Atomic Features from Rapidly Spinning Neutron Stars
Neutron stars spinning at moderate rates (~300-600Hz) become oblate in shape
and acquire a nonzero quadrupole moment. In this paper, we calculate profiles
of atomic features from such neutron stars using a ray-tracing algorithm in the
Hartle-Thorne approximation. We show that line profiles acquire cores that are
much narrower than the widths expected from pure Doppler effects for a large
range of observer inclinations. As a result, the effects of both the oblateness
and the quadrupole moments of neutron stars need to be taken into account when
aiming to measure neutron star radii from rotationally broadened lines.
Moreover, the presence of these narrow cores substantially increases the
likelihood of detecting atomic lines from rapidly spinning neutron stars.Comment: 7 pages, 8 figures, accepted to Ap
A bright radio HH object with large proper motions in the massive star-forming region W75N
We analyze radio continuum and line observations from the archives of the
Very Large Array, as well as X-ray observations from the \emph{Chandra} archive
of the region of massive star formation W75N. Five radio continuum sources are
detected: VLA 1, VLA 2, VLA 3, Bc, and VLA 4. VLA 3 appears to be a radio jet;
we detect J=1-0, v=0 SiO emission towards it, probably tracing the inner parts
of a molecular outflow. The radio continuum source Bc, previously believed to
be tracing an independent star, is found to exhibit important changes in total
flux density, morphology, and position. These results suggest that source Bc is
actually a radio Herbig-Haro object, one of the brightest known, powered by the
VLA~3 jet source. VLA 4 is a new radio continuum component, located a few
arcsec to the south of the group of previously known radio sources. Strong and
broad (1,1) and (2,2) ammonia emission is detected from the region containing
the radio sources VLA~1, VLA~2, and VLA~3. Finally, the 2-10 keV emission seen
in the \emph{Chandra}/ACIS image shows two regions that could be the
termination shocks of the outflows from the multiple sources observed in W75N.Comment: 26 pages, 7 figure
Power Deposition on Tokamak Plasma-Facing Components
The SMARDDA software library is used to model plasma interaction with complex
engineered surfaces. A simple flux-tube model of power deposition necessitates
the following of magnetic fieldlines until they meet geometry taken from a CAD
(Computer Aided Design) database. Application is made to 1) models of ITER
tokamak limiter geometry and 2) MASTU tokamak divertor designs, illustrating
the accuracy and effectiveness of SMARDDA, even in the presence of significant
nonaxisymmetric ripple field. SMARDDA's ability to exchange data with CAD
databases and its speed of execution also give it the potential for use
directly in the design of tokamak plasma facing components.Comment: 13 pages, 20 figure
Sketching-out virtual humans: A smart interface for human modelling and animation
In this paper, we present a fast and intuitive interface for sketching out
3D virtual humans and animation. The user draws stick figure key frames first and
chooses one for âfleshing-outâ with freehand body contours. The system
automatically constructs a plausible 3D skin surface from the rendered figure, and
maps it onto the posed stick figures to produce the 3D character animation. A
âcreative model-based methodâ is developed, which performs a human perception
process to generate 3D human bodies of various body sizes, shapes and fat
distributions. In this approach, an anatomical 3D generic model has been created with
three distinct layers: skeleton, fat tissue, and skin. It can be transformed sequentially
through rigid morphing, fatness morphing, and surface fitting to match the original
2D sketch. An auto-beautification function is also offered to regularise the 3D
asymmetrical bodies from usersâ imperfect figure sketches. Our current system
delivers character animation in various forms, including articulated figure animation,
3D mesh model animation, 2D contour figure animation, and even 2D NPR animation
with personalised drawing styles. The system has been formally tested by various
users on Tablet PC. After minimal training, even a beginner can create vivid virtual
humans and animate them within minutes
Generating Surface Geometry in Higher Dimensions using Local Cell Tilers
In two dimensions contour elements surround two dimensional objects, in three dimensions surfaces surround three dimensional objects and in four dimensions hypersurfaces surround hyperobjects. These surfaces can be represented by a collection of connected simplices, hence, continuous n dimensional surfaces can be represented by a lattice of connected n-1 dimensional simplices. The lattice of connected simplices can be calculated over a set of adjacent n-dimensional cubes, via for example the Marching Cubes Algorithm. These algorithms are often named local cell tilers. We propose that the local-cell tiling method can be usefully-applied to four dimensions and potentially to N-dimensions. We present an algorithm for the generation of major cases (cases that are topologically invariant under standard geometrical transformations) and introduce the notion of a sub-case which simplifies their representations. Each sub-case can be easily subdivided into simplices for rendering and we describe a backtracking tetrahedronization algorithm for the four dimensional case. An implementation for surfaces from the fourth dimension is presented and we describe and discuss ambiguities inherent within this and related algorithms
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