We present a system capable of handling several thousands of varied animated characters within a crowd. These characters are designed to have geometric, color animation and behaviour variety, nevertheless when a crowd becomes bigger, more memory is needed and is often difficult to achieve this objective. To solve this problem, we implemented two complementary data structures

Rudomín, Isaac

Toledo Díaz, Leonel Antonio

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Level of detail for complex urban scenes with varied animated crowds, using XML

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Level of Detail for Complex Urban Scenes with Varied Animated Crowds, using XML  Leonel Antonio Toledo Díaz​#1​, Isaac Rudomín​#1 # ​Barcelona Supercomputer Center, Barcelona,Spain. 1​leonel.toledo.diaz@​gmail.com, isaac.rudomin@bsc.com  Keywords​— ​Crowd Simulation, GPU, Level of Detail. EXTENDED ABSTRACT Crowd simulation has gained attention recently in the        movie and video game industry, still there are broader         applications in which crowd simulation is associated,       transportation and urbanism are some examples. Even tough hardware capabilities are surpassed constantly       by each new generation of hardware, the number of polygons,          memory and computational resources are not enough to        properly simulate dense crowds composed by millions of        characters. This cannot be achieved without the aid of         rendering techniques such as Level of Detail (LOD).        Interactive virtual crowds require high-performance     simulation, animation and rendering techniques to handle       numerous characters in real-time. These characters must be        believable in their actions and behaviors. Real-time crowd        simulation brings different challenges compared with systems       that involve a small number of interacting characters (i.e. most          contemporary computer games) and non-real-time (i.e. crowds       seen in movies or visualizations of crowd evacuations after         offline model computations). In comparison with single agent        simulations, the main conceptual difference is the need for         efficient variety management at every level, whether is        visualization, motion-control, animation or sound rendering      [1]. A. Hybrid Hierarchical LOD System for large crowds using configuration files We present a system capable of handling several thousands         of varied animated characters within a crowd. These        characters are designed to have geometric, color animation        and behaviour variety, nevertheless when a crowd becomes        bigger, more memory is needed and is often difficult to          achieve this objective [2]. To solve this problem, we         implemented two complementary data structures. The first       structure is a skeleton with associated octrees for each limb          that is used for applying, transferring animations and        generating variety for characters at any level of detail, as          shown in figure 1. The second structure is a scene tiling with            an associated quadtree that represents the environment. This        structure is used for rendering, LOD selection and for         combining characters in areas far away from the viewer to          further reduce resource consumption, allowing us to handle        dense crowds.   Figure 1: Creation of the skeleton and how LOD is built using our octree system. Each limb has an associated octree and data is stored inside the structure.   Extending this hybrid LOD method, and adapting it to use          instructions from newer versions of OpenGL, we are        implementing a complete authoring system based on XML        configuration files with which we can create virtual        environments that include buildings, trees, vehicles and       people. We can declare the size of the crowd and create           different groups, each of which will have different base         geometry, rules for variety, distribution and behavior, and can         be based on  data that the user can provide to the system.   B. Results Our LOD method outperforms traditional impostors and the        most common variations in terms of memory requirements        and/or computation. The work by Rudomin et al. [3] states          that 12 megabytes of memory are used for each impostor,          whereas the presented method only needs 75,532 kilobytes of         memory to simulate a crowd composed of 65,536 characters.         This is achieved because variety, animation and LOD are         computed directly on the GPU, making possible to generate         diverse crowds in real time. In comparison, traditional        impostors would need 12 * 65536 Megabytes of memory to          display the same crowd. Our representation needs less        memory or computation that any of the traditional impostor         methods (at run-time, since there is an initial cost of          4th BSC Severo Ochoa Doctoral Symposium60generating and filling hierarchical structures when loading the        scene). Figure 2 shows the achieved results using our method.     Figure 2: A crowd composed by 65,536 varied and animated characters.  The system is not limited to crowds composed only by          humans, it is possible for us to create urban environments and           incorporate props into the simulation. Figure 3 shows an         example of a simulation created using this method.    Figure 3: A scene created with the system presented in this paper. It is possible to combine different kinds of geometry to create complex urban environments C. Conclusion and Future Enhancement Some of the main challenges faced in this work are to           remove the least perceptible details for the simulation to         preserve the global vision aspects without compromising       visual quality and meanwhile, significantly improve      computation times. This work is mainly focused on discrete         level of detail, but some variations are interesting to study as           well, for example adaptive LOD which gives more importance         to certain areas of the geometry or the environment, enhancing          visual quality without compromising the quality. Nevertheless       LOD applications are broader than geometry simplification, in        fact it is possible to make simulations more complex by          implementing LOD variations that consider behavior,      animation and collision avoidance just to mention a few.   References  [1] Thalmann D.: Crowd Simulation. John Wiley      Sons,Inc.,2007.URL: http://dx.doi.org/10.1002/9780470050118.ecse676​,  doi:10.1002/9780470050118.ecse676. [2] Toledo L., De Gyves O., Rudomin I.: Hierarchical level         of detail for varied animated crowds. The Visual        Computer 30, 6-8 (2014), 949{961. URL:      http://dx.doi.org/10.1007/s00371-014-0975-9, doi:10.1007/s00371-014-0975-9. [3] RM06] Rudomin I., Millan E.: A comparison between        impostors and pointbased models for interactive rendering       of animated crowds.  Author biography   Leonel Toledo ​received his Ph.D from      Instituto Tecnológico de Estudios    Superiores de Monterrey Campus    Estado de México in 2014, where he       was a full-time professor from 2012 to       2014. He was an assistant professor and       researcher and has devoted most of his       research work to crowd simulation and visualization       optimization. He has worked at the Barcelona       Supercomputing Center using general purpose graphics      processors for high performance graphics. His thesis work was         in Level of detail used to create varied animated crowds.          Currently he is a researcher at Barcelona Supercomputer        Center.    Isaac Rudomin is a senior researcher at the        Barcelona Supercomputer Center, which he     joined in 2012. His focus is on crowd        rendering and simulation including    generating, simulating, animating, and    rendering large and varied crowds using      GPUs in consumer-level machines and in      HPC heterogeneous clusters with GPUs.     Previously, Isaac was on the faculty at       Tecnologico de Monterrey Campus Estado de Mexico (from        1990 to 2012). He finished his Ph.D. at the University of           Pennsylvania under Norman Badler on the topic of cloth         modeling. 4th BSC Severo Ochoa Doctoral Symposium61

Level of detail for complex urban scenes with varied animated crowds, using XML

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