Master's Thesis - Studierstube Augmented Reality Project - Graz ...

6.3 Results
6.3 Results
To complete this chapter some images resulting from the so far described algorithms
and datasets can be presented in this section. The following figures show several more
or less simple flow structures since more complex ones would not be feasible for these
static images due to missing interactivity. Referring to that, it can be underlined
that the more complexity a velocity field contains the more important interactivity
gets, even if it is only the ability to rotate, pan and zoom the scene. Due to these
inconveniences not always the same but the most instructive perspective was chosen
for similar datasets. The diagrams 6.8 to 6.9 in section 6.4 subsequently compares the
main techniques due to their performance in frames per seconds on the two reference
systems which were presented in section 6.1.
• Cash-Flow and glyph-based visualizations are shown in figure 6.2.
• Different applications for particles are shown in figure 6.3.
• Stream lines and path lines are shown in figure 6.4.
• Different types of cutting planes are shown in figure 6.5.
• Stream tubes are shown in figure 6.6.
• Examples for a combination of visualizations are shown in figure 6.7.
6.4 Scalability
Diagram 6.8 to 6.9 show that a glyph renderer is faster when less glyphs are rendered. In
this case we varied the render positions between rendering every fifth velocity value to
rendering every 20 th position. Since this algorithms is mainly performed on the CPU
and every frame all positions are passed to the graphics cards, a frame rate higher
than 60 could not be expected and also a not so high difference between the reference
systems.
The performance of GPU based visualizations highly depends on the amount of
rendered elements and therefore on the used buffer sizes. The buffer size n × m determinates
in the case of a particle based visualization the number of possible rendered
particles by n∗m and in the case of lines n determinates the number of lines and m the
supporting-point count of each line. We tested quadratic buffer sizes from 256 to 1024
pixels in each direction. Rectangular buffer textures are possible as well, but perform
with the same results as quadratic ones until one size exceeds the next possible power
of 2 (for example 256, 512, 1024,...). Consequently, a quadratic buffer size leads to
an optimal result. Since all buffer positions are definitely processed each render pass,
techniques for an early line termination, for example when the line moves out of the
velocity field, would not increase the performance.
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