2. Using Graphics Hardware for Multiple Datasets Visualization Gaurav Khanduja Dr. Bijaya B. Karki Louisiana State University, Department of Computer Science Baton Rouge, LA – 70803 USA

3. 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.

4. Figure: Visualization of electron density difference induced by the Mg (left), Si (centre) and O (right) vacancies in the 60-site MgSiO 3 system.

5. Texture Based MDV Volume Rendering Clipping Isosurface Generation

6. 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.

7. 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.

8. 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

9. Isosurface Each element in the 3D texture is assigned the scalar value (R MAX ) > isoValue > (R MIN ) is applied, to find the voxels containing the isosurface. Then alpha test is used Figure: Isosurface Extraction of MgSiO 3 showing Mg, Si and O vacancy from left to right with isovalue 0.021.

10. 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)

11. 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.

12. 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)

13. 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.

14. Thank You For further information contact: khanduja@bit.csc.lsu.edu karki@csc.lsu.edu