using graphics hardware for multiple datasets visualization gaurav khanduja dr. bijaya b. karki...
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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
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