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

5.3 Visualization nodes and subgraphs
Figure 5.13: The development of stream tubes based on a pre-calculated line texture
with stream- or path line supporting points. A vertex shader places the pre-defined
vertices of a quad strip relative to available supporting points and defines an arbitrary
color and a normal vector perpendicular to the viewing direction. With the interpolated
color and normal vector values a fragment shader can perform a Phong based even
realistic illumination.
1024 and the frame rate was evaluated with one certain artificial flow dataset.
Some modifications of this algorithm would lead to stream ribbons (see section 2.1.1.2
and figure 2.14(a) in chapter 2). In this case the vertex displacement relative to the
line may not occur perpendicular to the viewing direction but dependent on the surrounding
field’s rotor. A vertex’ normal vector perpendicular to the ribbon itself would
complete this modification.
5.3.3.6 Cutting-Plane Techniques
A simple but effective technique to represent parts of the field is the insertion of different
kinds of planes in a volumetric velocity field. This plane can consist of many vertices
organized in a triangulated mesh quad (mesh-plane) or of a simple quad bordered by
four vertices (quad-plane). Both techniques can be used with different benefits.
An obvious parameter to map onto this plane would be the color coded magnitude of
the velocity value in perpendicular direction to the plane. The sampling of the volume
with mesh vertices would provide the advantage of an additional linear interpolation
within the plane if, for example, the complete linear interpolation of the velocity 3D
texture is not possible due to performance reasons and a nearest neighbor interpolation
is used for 3D textures instead. In this case the sampling of the volume is made with
a vertex shader directly with the vertices’ coordinates and the interpolation with the
built-in varying gl_Color. In the quad-plane based approach the sampling can be
done by mapping the processed texture coordinates between the four vertices into the
velocity volume texture.
The result will be in both cases the same at a first sight. The differences are given if
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