Visual Exploration of Simulated and Measured Blood Flow - Scientific Visualization: Uncertainty, Multifield, Biomedical, and Scalable Visualization - page 301

Fig. 25.9 GPU-generated long pathlines, statically seeded in the heart chambers to capture aorta
and pulmonary arteries. a shaded imposter tuboids. The left-hand side shows a larger versions
of the pathlines, respectively without and with halos and contours. b pathsurfaces presented as
tube-shaped surfaces. The latter may be nested, approximately capturing the wave-front profile. A
stripe pattern is employed to convey rotation [ 47 ] © IEEE. Reprinted, with permission, from IEEE
transactions on visualization and computer graphics 17(12)
Integral curves are often rendered as illuminated lines or shaded tuboids. Percep-
tion of the spatial relations between pathlines is improved by means of halos [ 9 ].
VanPeltetal.[ 47 ] additionally applied contours in order to enhance the structure
of the pathlines (see Fig. 25.9 a). Two types of seeding strategies are also proposed
by Van Pelt et al. [ 46 ]. On the one hand, lines may be seeded statically from a fixed
position in space and time. On the other hand, integration curves may be seeded
dynamically, tracing the lines from a fixed spatial location, and varying seed time
with the current time frame of the cardiac cycle. Dynamically seeded pathlines con-
sist of comparatively short traces. Although the covered temporal range is relatively
narrow, the pathlines are more reliable, and provide an approximative depiction of
the pulse-wave in the cardiovascular system. The drawback is that it does not provide
enough information on a large scale; it only provides sufficient local information.
Integral surfaces are a generalization of integral lines. Integral surfaces are formed
by a continuum of integral curves. The surfaces enable surface shading techniques
which improve the perception of 3D structures. Integral surfaces are initialized by a
seeding curve which defines the topological connection between the integral curves.
Depending on the integral curve used there exist: streamsurfaces, pathsurfaces and
streaksurface. Integral surfaces have been recently studied for blood flow [ 20 , 47 ].
The seeding curve used for initialization is crucial for the correct interpretation
of the integral surface. Krishnan et al. [ 20 ] define the seeding curve as the boundary
of segmented regions based on flow maps. Van Pelt et al. [ 47 ] presented cross-
shaped and tube-shaped patterns of the integral surfaces (see Fig. 25.9 b). Integral
surfaces allow shading and texturing. For example, for tube-shaped surfaces stripes
texturing emphasizes the rotational motion around the centerline. The color may
convey various derived measures of the blood flow. In the user evaluation of Van
Pelt et al. [ 47 ], the integral surfaces were considered valuable to explore the local
rotational aspects of the flow.