Direct vs Indirect Methods
← Principle of Volume Visualization | ● | Iso Surfaces →
Direct vs. Indirect Volume Visualization Methods:
Direct Method: Direct Volume Rendering is the reversal of the scanning process: It used the stack of images to produces a virtual X-Ray image for a particular point of view.
Indirect Method: An iso surface is the set of points ot the data set that have the same iso value. The point set forms a closed surface, which can be extracted and represented by a triangle mesh. This procedure is called iso surface extraction.
DVR absorption rendering (left), isosurface extraction by Marching Cubes Algorithm (right):
vs. 
Comparison Demo:
We install the VVV (Versatile Volume Viewer) and use the QtV3 app to reproduce the above renderings!
Advantages and Disadvantages:
Advantages of DVR:
- Interactive display of the entire data set.
Disadvantage of DVR:
- Requires hi-end graphics hardware.
Advantages of iso surfaces:
- Occlusion of hidden surfaces.
- Triangle mesh can be shaded.
Disadvantages of iso surfaces:
- Not the entire data visible, only parts with a respective iso value.
- Mesh extraction is not interactive.