REAL-TIME SIMULATORS DEVELOPMENTS: CURRENT AND NEW TRENDS Rafael J. Martínez Durá Instituto de Robótica, Universidad de Valencia C/ Catedrático José Beltrán, 2 46980, Paterna, SPAIN [email protected] ABSTRACT the simulated environment is smaller than the time that This article briefly describes some technologies applied is being simulated. As a consequence, every simulation to current real-time simulation training systems. It model, or the image rendering phases, should not be as focuses on nowadays and future trends both in hardware complex as desired, having to assume some kind of and software architectures. The most important open simplifications (reduce the integration step, simplify the source and commercially available physics engines are dynamical model, reduce the number of polygons in the briefly described along with some scene graph scene, use levels of detail in the objects, etc.). management libraries. Additionally, cluster-based Training by means of simulation has several simulator issues are also discussed, including the main advantages against the use of the real machine, although problems that arise from using distributed GPU in any case the simulator can substitute the real one, due programming. An analysis of current state of the art mainly to the fact that the simulator will always regarding web browser-based simulators is also done. simplify the working environment. The main Finally new trends and cutting-edge research that is characteristics that make the simulators an done in the real-time simulation field are discussed. indispensable element in the training process are: Keywords: real-time simulation, browser-based • Risk avoidance simulation, GPU clusters, shaders • Training costs savings • Ability to reproduce extreme situations 1. INTRODUCTION • Ability to train with faulty machinery Simulation issues always deal with a set of techniques • Objective evaluation of user skills that allow reproducing the behaviour of both physical processes, such nuclear reactions, store stocks When designing a training simulator, special care fluctuations or vehicles, and human behaviours, such as must be taken with the details of the simulated evacuation systems or collaborative works. Nowadays, environment in order to keep it close to reality, since due mainly to the availability of high performance this will greatly influence in the decrease of the time computer systems, it is possible to simulate in real time involved in the training process. The term presence the behaviour of devices, machinery, vehicles, control (Sheridan 1992 and Slater, Khanna, Mortensen and Insu rooms, allowing the user to be trained to obtain the Yu 2009) refers to the user impression of “being there”, necessary skills to handle the real system with high in the virtual world that the computer simulates. In confidence. order to achieve a high presence, every user sense must A training simulator is built based upon a set of be stimulated as much as possible and also as real as functional blocks, being the most important the image possible. Therefore, when integrating a simulator, it is generation subsystem, the dynamical models that highly recommended to use immersive visualization compute the behaviour of the simulated objects, the technologies, moving platforms, real dimension cabins input/output subsystem that connect the user interfaces, and controllers, 3D sound surround systems and mainly the instructor subsystem, the user management graphical scenes and dynamical models highly accurate. subsystem and the evaluation subsystem. All of them Along this paper a review of the technology related are closely coupled, in a way that the actions over any with real-time training simulator design will be done. simulator controller are computed by the dynamical Section 2 deals with new trends in computers and I/O models and produce a reaction that is observed hardware that will be used in future simulators. immediately by the simulator operator, indicating some Following, in Section 3, the most important simulation kind of interactivity. engines are described and also the new trends that exist This capability presented in any real-time in multi GPU programming. Next section describes the simulator is achieved whenever the computation time state in the art in browser-based simulators and finally that the systems dedicates to calculate the evolution of Proceedings of the International Conference on Harbor, Maritime and Multimodal Logistics Modeling & Simulation, HMS 2009 ISBN 978-84-692-5416-5 1 some open problems and current research lines regarding simulation are explained. 2.1.2. Game Consoles based Systems Another important line to take into account is all the 2. HARDWARE ISSUES hardware related with video games. Video games are When building a simulator, it can be done using many similar to simulators in many aspects, so the computer hardware alternatives. The decision will depend on the architectures specially developed for them also have presence and accuracy that the simulator must provide. enough power to drive a simulator, but with very low Following, a description of the future trends in the costs. The only restriction is that video game consoles computational systems commonly used in the are thought to have just a single screen, so they are not implementation of training simulators is done. good for multi display systems, however clusters of them can be easily built in the way that traditionally has 2.1. Computer Architectures been done with the PC-based simulators. The most The computer used to execute a simulator always important game consoles that are currently available depends on the number of different views that the are: simulator employs. There are simulators that have one or two screens, like those used in crane simulators, three Sony PlayStation 3 (http://www.playstation.com): screens, used in vehicle simulators and even five in Its parallel Cell processor and the NVidia RSX general purpose simulators implemented with CAVES architecture (based on a GeForce 7800) provide high (C. Cruz-Neira, D. J. Sandin, T. A. DeFanti, R. V. performance to this videoconsole, allowing the Kenyon and J. C.Hart 1992). Every view has to be development of highly parallel applications. Although computed by a graphic card, so the simulator computer an official software development kit exists, it is also system at least must provide the capability to include all possible to install Linux Yellow Dog and other of them inside, and additionally, it must have enough distributions for the PS3. They include a set of performance to be able for rendering the images at high compilers and libraries for programming the Cell refresh rates. Processor. The main drawback they show is that their For these two main reasons, PC-based simulators kernels restrict the access both the GPU and some and virtual reality systems were traditionally built with peripherals, avoiding the development of high computer clusters, since a graphic card could be performance applications (See Barttlet 2007). plugged in every node and there are also several CPUs that allow the implementation of parallel algorithms and Microsoft XBOX 360: It is based on a 3 core complex dynamical and visual models. In such systems, Xenon CPU with an ATI Xenos graphic card that designers had to cope with the problems derived from supports unified shaders. Microsoft has developed a free the synchronization of simulation data, scene graphs API (Application Program Interface) that allows the and user inputs. development of applications for this architecture. In Nowadays, the evolution of PCs performance and order to develop professional games a subscription to the ability to plug several graphic cards in the same the Xbox Registered Developer Program must be done computer, make clusters being superseded by low-cost (http://www.xbox.com/dev). single computers, avoiding the synchronization issues present in clusters. Computer architectures for real-time simulation are thus evolving in two main directions. On the one hand, 2.1.1. PC based configurations examples the use of Personal Supercomputers offers an alternative Following some advice is given for choosing the to clusters, reducing cost and system complexity. On hardware to build a simulator, based, as viewed before, the other hand, the use of clusters is also being reviewed in the number of views it has to provide. by the introduction of Video Game Consoles which When building a simple simulator, a single graphic provide a step ahead in parallelism and reduce costs. card with several heads can be used (the Matrox M9140 LP has four inside) for connecting several displays. If 2.2. Input Devices high quality images are needed, as motherboards with Professional simulators trend to use the same devices up to four PCI-e 16X slots are already available, it is employed in game simulators and other video game possible to have several graphic cards plugged in the applications. Main reasons are that its interfaces are same PC. They can be configured to act as a single card very well defined and supported by the operating with high resolution and antialiasing capabilities (SLI system and that these devices have very low costs. from NVidia and CrossFire from ATI) or in an One example is the WiiRemote. It is one of the independent way providing several outputs. Another most common computer input devices in the world. It similar solution is provided by NVidia. Its Quadro Plex also happens to be one of the most sophisticated. It Model II is capable of connecting eight displays (it uses contains a 1024x768 infrared camera with built-in four NVidia Quadro FX 4500 X2) and the NVIDIA hardware blob tracking of up to 4 points at 100Hz, a 3- Quadro Plex Model IV, is capable of connecting four axis accelerometer also operating at 100Hz and an synchronized displays (it uses two NVidia Quadro FX expansion port for even more capability. Its Bluetooth 5600 with GSync boards). interface allows connecting the device to any personal Proceedings of the International Conference on Harbor, Maritime and Multimodal Logistics Modeling & Simulation, HMS 2009 ISBN 978-84-692-5416-5 2 computer.