Recent Advances in VisIt: AMR Streamlines and Query-Driven Visualization Page: 4 of 6
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4 Weber et al.
Figure 2. Streamlines extracted from an AMR vortex core merger simula-
tion. When one does not explicitly check whether one enters a refined level,
the simulation effectively considers only the root level, leading to a significant
loss in streamline accuracy.
Two extreme parallelization strategies are possible. The first method dis-
tributes streamlines to processors. Each streamline remains on the same pro-
cessor, which load data blocks dynamically as a streamline enters them. This
strategy avoids communication and keeps a balanced work load among proces-
sors (each processor gets assigned roughly the same number of streamlines).
However, in most cases it leads to significant data duplication.
The second method distributes data blocks evenly among processors. Each
processors "owns" those streamlines that are currently located in one of its data
blocks. This strategy avoids data duplication. However, streamlines need to be
communicated from processor to processor as they enter and leave data blocks
stored on different processors. Furthermore, this strategy may lead to severe
load imbalance if streamlines are distributed unevenly among the data blocks
belonging to each processor. VisIt 1.12 implements a third method, which is
enabled by default, that uses heuristics to transition its behavior between both
methods and attempts minimize data duplication while maintaining an even load
balance among processors. In Pugmire et al. (2009) we performed an extensive
analysis on the trade offs between the various schemes. In many cases, it is safe
to use VisIt's new defaults. However, for a more in-depth understanding, we
refer the reader to that paper.
2.3. AMR-aware Streamline Calculation
Another improvement to VisIt's streamline calculation lies in proper handling
of AMR hierarchies. This work is in a research prototype stage, and we plan
to make this functionality available in a later VisIt release. VisIt's current
streamline implementation continues streamlines as they transition from one
block to another and can trace a streamline through an AMR data set, see
Fig. 2 (left). However, this implementation does not detect when a streamline
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Weber, Gunther; Ahern, Sean; Bethel, Wes; Borovikov, Sergey; Childs, Hank; Deines, Eduard et al. Recent Advances in VisIt: AMR Streamlines and Query-Driven Visualization, article, November 12, 2009; Berkeley, California. (digital.library.unt.edu/ark:/67531/metadc1013741/m1/4/: accessed October 23, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.