MedicalVisualization
Contour Tracing
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Main disadvantage of iso surface extraction: For each iso value all tetrahedra need to be visited, although the iso surface does only intersect a small fraction of those. Visiting all cells does not allow interactive change of the iso value.
Based on the assumption that iso surfaces are continuous (water-tight) the contour tracing method accelerates the standard iso surface extraction, by only touching those cell that are actually cut by the iso surface:
Find a cell which intersects the iso surface
- Extract the surface element
- Examine the neighbour cells
- Since the iso surface is closed (C1-continuous), at least one adjacent cell needs to be cut by the iso surface, also.
- If an adjacent cell is cut, repeat the procedure unless the cell has already been visited.
Further acceleration of the intersection test by MIN/MAX-Test:
- Octrees [Wilhelms ‘92]
- Interval-trees [Cignoni ‘97]