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

2.1 Technical Visualization
Figure 2.9: Perspectively arranged rays sampled through a volumetric dataset and
evaluated by a transfer function are commonly known as Ray casting. Several smart
sampling techniques and ray termination assumptions have to be made to guarantee
interactive handling abilities. The ray-casted image of the heart is taken from
[Kerwin2007]; a related illustration can be found in [Engel2006].
images in the style of X-Ray angiography images can be denoted here referring to
[Heidrich1995]. This function simply projects the value with the highest intensity value
found on the given ray. Actually this algorithm is commonly used with angiography
methods since for these applications the vessels and the contained blood will produce
the highest signal. Projecting this maximum intensities will result in a almost clear
sight on the arteries or veins, depending on the time between the injection and the
scan. Additionally a two pass rendering was presented by [Hauser2001] which makes
it possible to combine a MIP with another volume rendering transfer function to show
additional interesting features. Nevertheless, figure 2.10 taken from [ClincalMRI2006]
points out, that the pure MIP rendering method can proof its value only with an either
interactive or permanent rotation of the volume.
The remaining direct volume rendering approaches were not described in this section
due to the following reasons:
• 2D texture slicing, even performed with graphics hardware implementations as
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