TAn v.2, a Volume Visualization System

TAn v.2  is our new multiresolution visualization system for Volume Data based on tetrahedra tessellation.

The Tetrahedra Analyser (TAn) system supports multiresolution management and visualization of volumetric dataset adopting a representation based on tetrahedral decomposition.

TAn provides tools to:

• load and process a multiresolution representation based on simplicial cells;
• manage multiresolution interactively, by supporting multiple methods to extract uniform or variable LOD from the multiresolution data representation;
• define transfer functions interactively [ TF: data_range --> RGBAlpha ];
• visualize data, supporting multiple rendering approaches:
  1. isosurface fitting;
  2. direct volume rendering (DVR) via a splatting approach;
  3. hybrid (isosurf + DVR) rendering.

Images of the TAn v.2 systems are in a dedicated page.

TAn manages multiresolution via a new representation scheme which stores all of the intermediate steps of a simplification process. The simplification of a tetrahedra mesh is operated only once, as a preprocessing phase, by using our tetrahedra mesh simplifier based on edge collapse.
In particular, the system supports the following LOD selection strategies:

• Uniform LOD: the resolution of the current mesh used in rendering is uniform over the domain based on an approximation
  error threshold specified by the user.
• Variable LOD based on spatial location in the domain: the user specifies both an error threshold and a focus volume, e.g., an axis-aligned box. The focus volume is used as a sort of 3D magnifying glass in order to explore a dataset by increasing resolution only locally. The current mesh satisfies the error threshold specified by the user just inside the focus volume, while outside it is coarser.
• Variable LOD based on field value: the current mesh satisfies the error threshold specified by the user just in proximity of the isosurface values currently selected, while the resolution of the mesh in areas that do not contain such values is coarser. The quality of the resulting isosurfaces is the same we would obtain at uniform resolution, but the size of the current mesh is smaller.
• Variable LOD based on the Transfer Function: in DVR mode we can make resolution depend on the current Transfer Function (TF). We take into account the alpha component of the TF: cells that give a negligible contribution (alpha nearly 0) can be represented using a coarser resolution.

The new TAn v.2 system has been implemented in the Windos NT environment and runs on standard PCs. 

Papers

(Under revision)

Images