32,956 research outputs found
BSP-fields: An Exact Representation of Polygonal Objects by Differentiable Scalar Fields Based on Binary Space Partitioning
The problem considered in this work is to find a dimension independent algorithm for the generation of signed scalar fields exactly representing polygonal objects and satisfying the following requirements: the defining real function takes zero value exactly at the polygonal object boundary; no extra zero-value isosurfaces should be generated; C1 continuity of the function in the entire domain. The proposed algorithms are based on the binary space partitioning (BSP) of the object by the planes passing through the polygonal faces and are independent of the object genus, the number of disjoint components, and holes in the initial polygonal mesh. Several extensions to the basic algorithm are proposed to satisfy the selected optimization criteria. The generated BSP-fields allow for applying techniques of the function-based modeling to already existing legacy objects from CAD and computer animation areas, which is illustrated by several examples
Acceleration of methods for multidimensional polarized radiative transfer and their application
Multidimensional radiative transfer is an essential ingredient of modern approach
to modeling of astrophysical objects. Realistic modeling calls for the assumption
of non-local thermodynamic equilibrium (NLTE), which, in turn requires
self-consistent solution of coupled equations of radiative transfer statistical equilibrium.
This approach allows us to compute emergent spectrum from a given model of
the object, which is, in principle, a necessary step in interpretation of observational
results. Thanks to the high-resolution and high signal to noise observations, it is
often possible to measure not only intensity of the light but also its state of polarization.
For interpretation of such observations it is necessary to solve radiative
transfer problem for polarized radiation.
This thesis deals with non-LTE transfer of (generally polarized) radiation in twodimensional
media. Thesis can be divided in two parts. In the first part, we present
a numerical method for the formal solution of the radiative transfer equation in 2D
Cartesian coordinate system. This method allows us to explicitly account for the
contribution of non-local source functions to the local specific intensity, and, hence,
to the local scattering integral. The knowledge of these contributions is necessary
for an iterative solution of coupled equations of radiative transfer and statistical
equilibrium. Based on this formal solution we introduce two novel schemes for
multidimensional NLTE radiative transfer which have so far been used only in 1D
geometry: symmetric Gauss-Seidel iteration and “Sweep-by-sweep” implicit lambda
iteration, latter one being based on “Forth-and-back” implicit lambda iteration.
Both methods utilize implicit use of the local source function and the source function
corrections each sweep of the computational grid (four times per iteration).
“Sweep-by-sweep” implicit lambda iteration also uses the idea of iteration factors
and achieves acceleration of about factor of seven with respect to the referent ..
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