Using Graphics Hardware for Multiple Datasets Visualization

Gaurav KhandujaDr. Bijaya B. Karki

Louisiana State University, Department of Computer Science

Baton Rouge, LA – 70803 USA

Multiple Datasets Visualization (MDV)

• Means more than one datasets are visualized simultaneously.

• Not possible to make an inference based on single dataset.

• Examples: Time-varying data, charge density data, medical data.

Figure: Visualization of electron density difference induced by the Mg (left), Si (centre) and O (right) vacancies in the 60-site MgSiO3 system.

Texture Based MDV

• Volume Rendering• Clipping • Isosurface Generation

Texture Based Volume Rendering

• 3D Scalar Data is loaded.

• Transfer Function• 3D Textures is

generated.• 3D Texture Slices are

view aligned.• Rendering with Alpha

Blending enabled.

0

1

1CUTR MAXR

MINR 2CUTR

Surface Based Clipping [Kha06]• Only the outermost

surface of the volume is mapped.

• Volume is represented as 12 triangles.

Figure: Planar (upper two) and box (bottom two) clipping.

Voxelized Clipping• We need an extra clipping

texture defining the clipping geometry.

• Each voxel of the volume texture is tested against the clipping texture and the opacity value is adjusted. [Wie03]

• Alpha test is performed on these textures the render the clipped volume texture.

(a)

(b)Figure 4: Voxelized clipping. (a) Spherical

Clipping Object. (b) Ellipsoidal Clipping Object

Isosurface• Each element in the

3D texture is assigned the scalar value

• (RMAX) > isoValue > (RMIN) is applied, to find the voxels containing the isosurface.

• Then alpha test is used

Figure: Isosurface Extraction of MgSiO3 showing Mg, Si and O vacancy from left to right with isovalue 0.021.

Result

Figure : Rendering time for various techniques without volume shading. The inset shows the first transition in the low N regime. (VR- Volume Rendering, SR – Surface Rendering, VC- Voxelized Clipping, IE- Isosurface Extraction)

Volume Shading• Volume Rendering

+ Lighting = Volume Shading

• Implemented a phong model for volume shading at GPU level.

• Normals are precomputed and are stored in another texture.

Figure: Rendering time for various techniques with shading.

Multi-Resolution• Change the Resolution depending upon number of datasets, or

rendering time, or any other user-defined criteria.

Figure: (a) Rendering time for various techniques without shading with DR. (b) Rendering time for various techniques with shading with DR.

(a) (b)

References• [Cab94] Cabral, B., Cam, N. and Foran, J. Accelerated volume rendering and

tomographic reconstruction using texture-mapping hardware. Proc. Symp. Volume Visualization. 91-98, 1994.

• [Kha06b] Khanduja, G. and Karki, B. B. A Systematic Approach to the Multiple Dataset Visualization of Scalar Volume Data. GRAPP, pp. 59-66, 2006.

• [Wei03] Weiskopf D., Engel, K., and Ertl, T. Interactive Clipping Techniques for Texture-Based Volume Visualization and Volume Shading. IEEE Transactions on Visualization and Computer Graphic, 9, 298-312, 2003.

• [Wes98] Westermann, R. and Ertl, T. Efficiently using graphics hardware in Volume Rendering Applications. SIGGRAPH Conf. Proc., pp. 169-179, 1998.

• [Wil94] Wilson, O., Van Gelder, A. and Wilhems, J. Direct volume rendering via 3d textures. Technical Report UCSC-CRL-94-19, Jack Baskin School of Eng., Univ of California at Santa Cruz., 1994.

Thank You

• For further information contact:• khanduja@bit.csc.lsu.edu• karki@csc.lsu.edu