We provide a survey of the major results obtained within the CYBERSAR project in the area of massive data visualization. Despite the impressive improvements in graphics and computational hardware performance, interactive visualization of massive models still remains a challenging problem. To address this problem, we developed methods that exploit the programmability of latest generation graphics hardware, and combine coarse-grained multiresolution models, chunk-based data management with compression, incremental view-dependent level-of-detail selection, and visibility culling. The models that can be interactively rendered with our methods range from multi-gigabyte-sized datasets for general 3D meshes or scalar volumes, to terabyte-sized datasets in the restricted 2.5D case of digital terrain models. Such a performance enables novel ways of exploring massive datasets. In particular, we have demonstrated the capability of driving innovative light field displays able of giving multiple freely moving naked-eye viewers the illusion of seeing and manipulating massive 3D objects with continuous viewer-independent parallax.233-23

Agus, Marco

Bettio, Fabio

Marton, Fabio

Pintore, Giovanni

Zorcolo, Antonio

P-arch

FINAL WORKSHOP OF GRID PROJECTS, ”PON RICERCA 2000-2006, AVVISO 1575” 1Advances in massive modelvisualization in the CYBERSAR projectM. Agus1, F. Bettio1, F. Marton1, G. Pintore1, and A. Zorcolo11 CRS4, Pula, Italy, vic@crs4.itAbstract—We provide a survey of the majorresults obtained within the CYBERSAR projectin the area of massive data visualization. Despitethe impressive improvements in graphics andcomputational hardware performance, interactivevisualization of massive models still remains achallenging problem. To address this problem, wedeveloped methods that exploit the programma-bility of latest generation graphics hardware, andcombine coarse-grained multiresolution models,chunk-based data management with compression,incremental view-dependent level-of-detail selec-tion, and visibility culling. The models that canbe interactively rendered with our methods rangefrom multi-gigabyte-sized datasets for general3D meshes or scalar volumes, to terabyte-sizeddatasets in the restricted 2.5D case of digitalterrain models. Such a performance enables novelways of exploring massive datasets. In particular,we have demonstrated the capability of drivinginnovative light field displays able of giving mul-tiple freely moving naked-eye viewers the illusionof seeing and manipulating massive 3D objectswith continuous viewer-independent parallax.I. INTRODUCTIONOVER the last several decades, there havebeen significant advances in model acqui-sition, computer-aided design (CAD), and sim-ulation technologies. These technologies haveresulted in massive data sets of complex ge-ometric models. These data include complexCAD environments, natural landscape models,scanned urban data, and various scientific simu-lation data. These massive data typically requiregiga byte size and even tera byte size. Han-dling such massive models presents importantchallenges to software and system developers.This is particularly true for highly interactive3D applications, such as visual simulations andvirtual environments, with their inherent focuson interactive, low-latency, and real-time pro-cessing. In the last decade, the graphics commu-nity has witnessed tremendous improvements inthe performance and capabilities of computingand graphics hardware. Despite the continuedincrease in computing and graphics processingpower, it is clear to the graphics community thatone cannot just rely on hardware improvementto cope with arbitrarily large data sizes for theforeseeable future. This is not only because theincreased computing power also allows usersto produce more and more complex datasets,but also because memory bandwidth and dataaccess speed grow at significantly slower ratesthan processing power and become the majorbottlenecks when dealing with massive datasets.As a result, massive datasets cannot be inter-actively rendered by brute force methods. Thereal challenge is in designing rendering systemsthat capture as much of this performance growthas possible. When dealing with massive mod-els, achieving high performance requires meth-ods for carefully managing bandwidth require-ments, controlling working set size, and ensur-ing coherent access patterns. Furthermore, givencurrent multi-core CPUs and GPUs, solutionswhich can be formulated in a (data) parallelfashion will be able to continually take advan-tage of improved hardware performance. In thiscontribution, we provide a survey of the majorresults obtained within the project CYBERSARin this field of research. Specifically, we willfocus on the methods we developed to dealwith huge models. The techniques exploit theprogrammability of latest generation graphicshardware, and combine coarse-grained multires-AGUS et al.: MASSIVE MODEL VISUALIZATION IN THE CYBERSAR PROJECTolution models, chunk-based data managementwith compression, incremental view-dependentlevel-of-detail selection, and visibility culling.The models that can be interactively renderedwith our methods range from multi-gigabyte-sized datasets for general 3D meshes or scalarvolumes, to terabyte-sized datasets in the re-stricted 2.5D case of digital terrain models.Such a performance enables novel ways ofexploring massive datasets. The rest of the paperis organized as follows: section II describesour multi-resolution out-of-core techniques forrapid high-quality visualization of textured dig-ital terrain models and high resolution urbanenvironments, section III deals with processing,distribution, and rendering of massive dense3D meshes and huge complex 3D models, andsection IV describes our method for renderingmassive scalar volumes employing single passGPU raycasting. Finally, section V describesour techniques for harnessing the power ofnovel 3D displays able of giving multiple freelymoving naked-eye viewers the illusion of see-ing and manipulating massive 3D objects withcontinuous viewer-independent parallax.II. TERRAINS AND URBAN ENVIRONMENTSFig. 1. Terrain rendering: Interactive inspection ofcomplex terrain datasets.Real-time 3D exploration of remote digitalelevation models built from high resolution im-agery and elevation data has long been one ofthe most important components in a numberof practical applications, and extensive researchhas been carried out in terms of methods andtechniques for processing, distributing, and ren-dering very large datasets. The increased avail-ability of broadband networks and high per-formance graphics PCs has made this technol-ogy, once limited to professional applications,increasingly popular, as testified by the suc-cess of Internet geo-viewing tools like GoogleEarth, NASA WorldWind, and Microsoft Vir-tual Earth. The efficient implementation of suchtools requires a combination of technologies foradaptively rendering high quality terrain viewsat high frame rates and techniques for efficientlystreaming data from the systems serving theterrain database to a large number of renderingclients. In this field, we introduced the BDAMmethods [1], multi-resolution out-of-core tech-niques for rapid high-quality visualization oftextured digital terrain models and high reso-lution urban environments. The BDAM frame-work introduced one of the first methods forrapidly generating seamless variable resolutionsurfaces by assembling precomputed patches.In the context of the CYBERSAR project, weimproved the BDAM framework by introducinga compressed multiresolution representation anda client-server architecture for supporting inter-active high quality remote visualization of verylarge textured planar and spherical terrains[2].The approach incrementally updates a chun-ked level-of-detail BDAM hierarchy by usingprecomputed wavelet coefficient matrices [3]decoded from a compressed bitstream originat-ing from a thin server. The structure combinesthe aggressive compression rates of wavelet-based image representations with the ability toensure overall geometric continuity for variableresolution views of planar and spherical terrainswith no need for run-time stitching [4]. Theefficiency of the approach was demonstrated ona large scale interactive remote visualization ofglobal and local terrains on ADSL networks.A library implementing this approach [5] hasbeen incorporated into widely distributed geo-viewing systems [6], [7] (see figure 1). A sur-vey on semi-regular multiresolution models forinteractive terrain rendering has been also pre-sented [8], illustrating the principal techniquesbased on tiled blocks and nested regular grids,quadtrees and triangle bin-trees triangulations,as well as cluster based approaches.2FINAL WORKSHOP OF GRID PROJECTS, ”PON RICERCA 2000-2006, AVVISO 1575”Fig. 2. Massive models: Digital Michelangelo David 1mmRendering.III. MASSIVE MODELSMany important applications domains, in-cluding 3D scanning, computer aided design,and numerical simulation, require the interactiveinspection of huge geometric models. In thisfield, we considered methods for supportinginspection of surface models characterized bya high sample density, such as those gener-ated by laser scanning. We also focused onmethods able to support very large arbitrarysurface models with high topological genus,highly variable depth complexity, fine geometricdetail, ”Bad” tessellations. Our main contribu-tions are the introduction of Tetrapuzzles [9], acoarse grained multiresolution model based onhierarchical volumetric decomposition, that leadto the first GPU bound high quality techniquefor large scale meshes, and Far Voxels [10],an efficient approach for end-to-end out-of-core construction and interactive inspection thatmethod tightly integrates visibility culling andout-of-core data management with a level-of-detail framework. The efficiency and general-ity of the approaches have been estensivelydemonstrated with the interactive rendering ofextremely complex heterogeneous surface mod-els on current commodity graphics platforms.The methods have been employed on a numberof test cases, ranging from laser scans,includingall Digital Michelangelo models, to isosurfaces,to extremely large CAD models, including thefull Boeing 777 model (see figures 2 and 3).Fully interactive performance is obtained evenfor large windows on current single processorPCs.In the context of the CYBERSAR project, weintroduced a cluster parallel multiresolution ren-derer able to drive a lightfield display [11], [12].The method is a parallel spatial 3D display-aware version of the Adaptive TetraPuzzlestechnique. It dynamically adapts model resolu-tion by taking into account the particular spatialaccuracy characteristics of the display.Fig. 3. Massive models: Interactive inspection of complexdatasets.Between the most relevant results, surveysand contributions to specialized courses havebeen presented in the most important computergraphics conferences [13], [14], [15], [16], illus-trating the massive model rendering methods tothe graphics community.IV. MASSIVE SCALAR VOLUMESFig. 4. Massive scalar volumes rendering. Interactivevolume exploration of multi-giga voxels datasets on adesktop PC.3AGUS et al.: MASSIVE MODEL VISUALIZATION IN THE CYBERSAR PROJECTThe ability to interactively render rectilinearscalar volumes containing billions of sampleson desktop PCs is of primary importance for anumber of applications, which include medicalvisualization and numerical simulation resultsanalysis. In this field, in the context of the CY-BERSAR project, we introduced MOVR [17],an adaptive out-of-core technique for renderingmassive scalar datasets within a single-passGPU raycasting framework. The method ex-ploits an adaptive loader executing on the CPUfor updating a working set of bricks maintainedon GPU memory by asynchronously fetchingdata from an out-of-core volume octree repre-sentation. At each frame, a compact indexingstructure, which spatially organizes the currentworking set into an octree hierarchy, is encodedin a small texture. This data structure is thenexploited by an efficient raycasting algorithm,which computes the volume rendering integralby enumerating non-empty bricks in front-to-back order and adapting sampling density tobrick resolution. In order to further optimizememory and bandwidth efficiency, the methodalso exploits feedback from the renderer toavoid refinement and data loading of occludedzones. The resulting method is extensible, fullyadaptive, and able to interactively explore multi-giga-voxel datasets on a desktop PC (see fig-ure 4).V. INTERACTIVE VISUALIZATION ON NOVEL3D DISPLAYSFig. 5. Real-time interaction with the light field display.Real-time inspection of a large volumetric model containinga CT dataset of a biological specimen. Pictures are takenwith an hand-held camera at different viewing angles, inorder to highlight the horizontal parallax of the light fielddisplay.Multiscopic visualization is an emerging dis-play technology that aims to reproduce three di-mensional scenes by generating observer inde-pendent light fields. In the CYBERSAR project,Fig. 6. Massive model visualization on a 50Mpixelspatial 3D display. The display has a screen dimension of1.6x0.9 meters, and provides continuous horizontal parallax.Interactive rates in the manipulation of massive geometricmodels are guaranteed by a cluster-parallel spatial 3Ddisplay aware coarse grained multiresolution technique.we contributed to this field by developing meth-ods for driving displays of this type [11], [18].Specifically, we built a parallel multiresolu-tion rendering system [11] driving a spatial3D display able to give multiple viewers theillusion of seeing virtual models floating atfixed physical locations situated in a human–scale working volume (see figure 6). Eachviewer sees the scene from their point of viewand enjoys full, continuous, horizontal parallaxwithout specialized viewing devices. The effi-ciency of the approach is demonstrated by anapplication supporting interactive manipulationof massive colored highly tessellated modelson a large (1.6x0.9 meters) 50Mpixel displaythat allows for a room-size working space.We also developed a prototype medical datavisualization system exploiting a small scalelight field display and custom direct volumerendering techniques to enhance understandingof massive volumetric data, such as CT, MRI,and PET scans [18], [19], [20]. The systemcan be integrated with standard medical imagearchives and extends the capabilities of currentradiology workstations. The system allows mul-tiple untracked naked-eye users in a sufficientlylarge interaction area to coherently perceiverendered volumes as real objects, with stereoand motion parallax cues (see figure 5). In thisway, an effective collaborative analysis of volu-metric data can be achieved. Evaluation testsdemonstrated the usefulness of the generated4FINAL WORKSHOP OF GRID PROJECTS, ”PON RICERCA 2000-2006, AVVISO 1575”depth cues and the improved performance inunderstanding complex spatial structures withrespect to standard techniques.REFERENCES[1] P. Cignoni, F. Ganovelli, E. Gobbetti, F.Marton,F. Ponchio, and R. Scopigno, “BDAM: Batched dy-namic adaptive meshes for high performance terrainvisualization,” Computer Graphics Forum, vol. 22,no. 3, pp. 505–514, Sept. 2003.[2] F. Bettio, E. Gobbetti, F. Marton, and G. Pintore,“High-quality networked terrain rendering from com-pressed bitstreams,” in Proc. ACM Web3D Interna-tional Symposium, ACM Press. New York, NY, USA,April 2007, pp. 37–44.[3] E. Gobbetti, F. Marton, P. Cignoni, M. D. Benedetto,and F. Ganovelli, “C-BDAM – compressed batcheddynamic adaptive meshes for terrain rendering,” Com-puter Graphics Forum, vol. 25, no. 3, September 2006,proc. Eurographics 2006.[4] P. Cignoni, F. Ganovelli, E. Gobbetti, F. Marton,F. Ponchio, and R. Scopigno, “Planet-sized batcheddynamic adaptive meshes (P-BDAM),” in IEEE Visu-alization, 2003, pp. 147–154.[5] “Ratman,” Url: ratman.sourceforge.net, 2009.[6] “Sardegna3d,” Url: www.sardegna3d.it, 2007.[7] “Italia3d,” Url: www.italia3d.it, 2008.[8] R. Pajarola and E. Gobbetti, “Survey on semi-regularmultiresolution models for interactive terrain render-ing,” The Visual Computer, vol. 23, no. 8, pp. 583–605, 2007.[9] P. Cignoni, F. Ganovelli, E. Gobbetti, F. Marton,F. Ponchio, and R. Scopigno, “Adaptive tetrapuzzles:Efficient out-of-core construction and visualizationof gigantic multiresolution polygonal models,” ACMTrans. on Graphics (SIGGRAPH 2004), vol. 23, no. 3,pp. 796–803, 2004.[10] E. Gobbetti and F. Marton, “Far Voxels – a mul-tiresolution framework for interactive rendering ofhuge complex 3d models on commodity graphicsplatforms,” ACM Transactions on Graphics, vol. 24,no. 3, pp. 878–885, August 2005, proc. SIGGRAPH2005.[11] F. Bettio, E. Gobbetti, F. Marton, and G. Pintore,“Scalable rendering of massive triangle meshes onlight field displays,” Computers & Graphics, vol. 32,no. 1, pp. 55–64, February 2008.[12] ——, “Multiresolution visualization of massive mod-els on a large spatial 3d display,” in Proc. Euro-graphics Symposium on Parallel Graphics and Visu-alization, Eurographics Association. Aire-la-Ville,Switzerland, May 2007.[13] A. Dietrich, E. Gobbetti, and S.-E. Yoon, “Massive-model rendering techniques: A tutorial,” IEEE Com-puter Graphics and Applications, vol. 27, no. 6, pp.20–34, nov/dec 2007.[14] E. Gobbetti, D. Kasik, and S. eui Yoon, “Technicalstrategies for massive model visualization,” in Proc.ACM Solid and Physical Modeling Symposium, ACMPress. New York, NY, USA, 2008, pp. 405–415. [Online]. Available: http://www.crs4.it/vic/cgi-bin/bib-page.cgi?id=’Gobbetti:2008:TSM’[15] S. eui Yoon, A. Dietrich, E. Gobbetti, D. Manocha,F. Marton, M. Agus, R. Pajarola, and P. Slusallek,“Interactive massive model rendering,” SIGGRAPHAsia 2008 Course Notes, SIGGRAPH Asia 2008,Singapore, December 2008.[16] D. Kasik, A. Dietrich, E. Gobbetti, D. Manocha,F. Marton, P. Slusallek, A. Stephens, and S. euiYoon, “Massive model visualization techniques,” SIG-GRAPH 2008 Course Notes, SIGGRAPH 2008, SanDiego, August 2008.[17] E. Gobbetti, F. Marton, and J. Iglesias Guitia´n, “Asingle-pass GPU ray casting framework for interactiveout-of-core rendering of massive volumetric datasets,”The Visual Computer, vol. 24, no. 7-9, pp. 797–806,2008, proc. CGI 2008.[18] M. Agus, F. Bettio, A. Giachetti, E. Gobbetti, J. A. I.Guitia´n, F. Marton, J. Nilsson, and G. Pintore, “Aninteractive 3d medical visualization system based ona light field display,” The Visual Computer, vol. 25,2009, to appear.[19] M. Agus, A. Giachetti, E. Gobbetti, J. Iglesias Guitia´n,and F. Marton, “Towards advanced volumetric displayof the human musculoskeletal system,” in Eurograph-ics Italian Chapter Conference. Conference held inSalerno, Italy: Eurographics Association, June 2008.[20] M. Agus, E. Gobbetti, J. Iglesias Guitia´n, F. Marton,and G. Pintore, “Gpu accelerated direct volume ren-dering on an interactive light field display,” ComputerGraphics Forum, vol. 27, no. 3, pp. 231–240, 2008,proc. Eurographics 2008.5

Advances in massive model visualization in the CYBERSAR project

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Advances in massive model visualization in the CYBERSAR project

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