File:
Loading data sets and .iv scene files

Viewing:
Visualization options
- for fast iso-surface rendering a second texture is created in which the material gradients are stored

Editors:
The material editor and the volume editor
- in the material editor for each color channel a colored curve shows the selected transfer function.
- choose between Luminance/Alpha or RGBA internal format
- click the appropriate button to edit the color in the render area
- the threshold min slider in the volume editor selects the active iso-value
- in the volume editor the button use alpha blending on slices allows for 3D texture based direct and iso-surface rendering
- the volume resolution slider allows selecting the number of slices for direct rendering of Cartesian and tetrahedral grids

VolTools:
Choosing the appropriate blending function and the internal texture representation

Clipping:
Slecting pre-defined clipping geometries or user-defined shapes and up to five clipping planes. To edit or move a clipping object hide the bounding box (VolTools) and pick the clipping geometry.

File formats:

Two different input file formats can by understood by IVoR. Files of either of both types can be specified as command line argument or they can be loaded via the Edit sub-menu.

*.dat configuration files
*.iv Inventor files

Example *.dat file:
Options:
ObjectFileName: fileName
Resolution: 64 64 64
SliceThickness: 1.0 1.0 1.0
Format: FLOAT UCHAR/USHORT
ObjectModel: CINDEX EMISSIONABSORPTION / RGBA
ObjectType: TEXTURE_VOLUME TETRAHEDRAL_VOLUME

For Cartesian volume data which should be rendered via 3D textures the ObjectType has to be TEXTURE_VOLUME. The raw volume data is stored in fileName as a stream of X*Y*Z voxels of the specified format. Only the resolution in z does not have to be a power of two. For example, a data sets of 64*64*39 voxels is internally extended to 64*64*64 voxels.

In CINDEX model all voxels are interpreted as one-component scalar values which are mapped via a color table into Lumi/Alpha or RGBA color values.

In EMISSIONABSORPTION model all voxels are interpreted as two-component scalar values. The emission value is specified first, followed by the absorption value.

In RGBA model all voxels are interpreted as four-component RGBA values in this order. No color table manipulation is possible in this model.

For tetrahedral grids the ObjectType has to be TETRAHEDRAL_VOLUME. The grid structure and the per-vertex material values are stored in ascii format in fileName.

Example: 5 vertices/material values, 2 tetrahedra

5 2
v 1.0 1.0 1.0
v 1.0 0.0 0.0
v 0.0 1.0 1.0
v 0.0 0.0 0.0
v 1.0 1.0 0.5
to 1///1 2///2 3///3 4///4 /* first index maps into vertex list, second maps into material list
to 2///2 3///3 4///4 5///5
pc 0.0
pc 0.2
pc 0.4
pc 0.8
pc 1.0

All other entries in the *.dat file have no effect.

Example files:
texture.dat MRI.bin
tetra.dat Fe.ascii

Machine dependencies:

IVoR actually runs exclusively on high-end SGI graphics workstation . The available executable was compiled on IRIX 6.2 and should run on KONAL/RE/IMPACT architectures.

Executable: IVoR.gz licence expires after 30 days

Bugs and abnormal behavior:

When clipping geometries are used manipulators and bounding boxes might be rendered incorrectly with respect to z-buffering.
Where no stencil buffer or only a stencil buffer with less than 8 bits is available most of the visualization options won't work !!
Using clipping planes and clipping geometries during rendering of tetrahedral grids yields strange
results.
After loading a tetrahedral grid the framebuffer won't be updated correctly. Touch the scene once in order to get the result.
While direct rendering of tetrahedral grids is active intermediate results are drawn into the front buffer.
Don't select Auto Update in the color editor for tetrahedral grids. Change the transfer function and press update.
Ask SGI for faster stencil buffer operations and pixel textures

Don't expect a perfectly running program !!!
But test it and let us know about the results.

Coming soon:

Volume shading with 3D textures
Shadow effects for iso-surface rendering
A real parser for tetrahedral grid data

Contact:

wester@vismail.informatik.uni-stuttgart.de
Ove.Sommer@informatik.uni-stuttgart.de