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Using Graphics Hardware for Multiple Datasets Visualization

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. Multiple Datasets Visualization (MDV). Means more than one datasets are visualized simultaneously.

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Using Graphics Hardware for Multiple Datasets Visualization

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  1. 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

  2. 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.

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

  4. Texture Based MDV • Volume Rendering • Clipping • Isosurface Generation

  5. 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.

  6. 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.

  7. 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

  8. 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.

  9. 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)

  10. 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.

  11. Multi-Resolution • Change the Resolution depending upon number of datasets, or rendering time, or any other user-defined criteria. (a) (b) Figure: (a) Rendering time for various techniques without shading with DR. (b) Rendering time for various techniques with shading with DR.

  12. 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.

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

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