COVISE VOLRE (Volume Rendering):

The volume rendering module of COVISE allows the direct visualization of three dimensional scalar fields both on the desktop and in virtual environments (see Fig. 1).

The standard visualization algorithms for volumetric scalar data in COVISE are cutting planes and iso-surfaces. Both visualize a subset of the dataset: cutting planes display a spatial subset, and iso-surfaces display a subset in the data value domain. The idea of direct volume rendering is to visualize the whole dataset. Transfer functions, which can be set by the user, assign color and opacity to the data values, so that features defined by a subset of the data value range can be pulled out.

COVISE's direct volume rendering algorithms originate in research conducted at the High Performance Computing Center Stuttgart (HLRS), which had the goal of fast interactive volume visualization.


Features

The VOLRE module offers the following functionality in both the desktop renderer and COVER (unless otherwise noted):

• Interactive frame rates even in multi-screen virtual environments.
• Support for transient (time dependent) datasets.
• Interactive definition of transfer functions with a practical editor (COVER only).
• Concurrent display of volumetric and polygonal data representations.
• Adjustable trade-off between image quality and frame rate.
• Image refinement when idle (desktop renderer only).
• Reads a variety of volume file formats (XVF, RVF, AVF, TIFF3D, NRRD, VMR, VTC, raw data).
• Reads sequences of slice images and converts them to volume datasets (PPM, PGM, SGI RGB, DICOM).
• Writes volume data to a volume file or a sequence of slice images (XVF, RVF, NRRD, raw data, PPM, PGM).
• Transfer functions can be saved with volume files (COVER only).
• Support for color volume datasets, for instance photographic slice images (COVER only).

For optimum use of the functionality please note:

• Make sure your graphics hardware provides texturing acceleration.
• Scalar data on uniform grids can be processed directly. Other grid types have to be resampled.
• Any one time step of the dataset has to fit in texture memory.

Transfer Function Editor (see Fig. 2)

Transfer functions are required to pull out specific features of volume datasets. There is a color and an opacity transfer function. They can be edited from within a virtual environment, changes are reflected in the image instantaneously.


Additional Exploration Modes

The transfer function editor allows to define the visual appearance of volume data in the data value domain (see Fig. 3). Additionally, COVER offers a volume clipping plane to cut off a part of the dataset (see Fig. 4), and a detail probe mode, in which only a cubic subset of the volume is visible (see Fig.5). Both the clipping plane and the cubic region can be placed with the input device with real-time visual feedback.

Fig. 1 Demonstration in the Cave

Fig. 2 Transfer Function Editor

Fig. 3 lambda

Fig. 4 Clipping Plane

Fig. 5 Detail Probe Mode