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high-performance computing


aquifers in Florida are within intrusion range – a mile or so – of salt water. Today’s standard open source tools for


visualisation include ParaView and VisIt, which are built on the Visualization ToolKit VTK, supported by Kitware. To visualise the water flow in the Florida aquifer, the team used a plug-in developed by TACC that allows VTK- based applications such as ParaView and VisIt to render with the OSPRay framework, which in turn was developed by Intel for building distributed applications which use ray tracing such as scientific visualisation tools. Te point is, Jeffers said, that he and his team


are building the underlying infrastructure to allow people to run the sorts of applications with which they are already very familiar. ‘We don’t


MOST VISUALISATION


TAKES ADVANTAGE OF THE GRAPHICS CAPABILITIES OF GPUS


want to change the use-model, but we do want to provide a new enabling technology underneath,’ he said. Tey can continue to use the same menu


systems, the same interface that they’re used to with ParaView, but down inside the soſtware they are moving to these tools that produce ray- traced images. Most visualisation at present takes advantage


of the graphics capabilities of GPUs, and of Nvidia products in particular (the initials do, aſter all, stand for Graphics Processing Unit). Teir highly parallel structure makes them


more effective than general-purpose CPUs for algorithms where processing of large blocks of data is done in parallel. On the soſtware side, most visualisation systems are built on OpenGL, which has been industry standard for more than two decades.


Rasterise or trace the rays? According to Nvidia’s Steve Parker, OpenGL has evolved over that time: ‘It’s grown up to be a very sophisticated graphics API, and Nvidia’s main business is OpenGL. Almost all applications are OpenGL – from Maya [Autodesk’s 3D animation soſtware] or CAD systems all the way to scientific visualisation. So if you’re building a display wall most of the time it will end up being a Quadro system because we’ve made sure that that product is capable of the best graphics. Tere’s also an increasing number of games that make use of OpenGL and our GeForce product line is also based on the same underlying technology. All of those things are built around rasterisation. We can rasterise about three billion triangles per second on benchmarks and for large data sets being able to process that quickly is key to the insight you can get out of it.’ For Jeffers, Intel’s line of development,


however, offers a further bonus, in that this line of development opens up ray tracing as an alternative to rasterisation and OpenGL. Ray tracing is, he believes, a method that will deliver that higher fidelity in scientific visualisation that he sees as one of the demands driving developments. As always, the very large data sets in the oil and gas industry loom large. According to Jeffers: ‘Tey are already doing ray tracing because of the improved fidelity


and understanding they can get. My team has developed pretty much the fastest ray tracing architecture and implementation. Certainly on CPUs, it’s the fastest.’ Te memory available to CPUs is typically


larger than that available to GPUs and so for small datasets (i.e. data that fits into GPU memory), rasterisation on a modern GPU will frequently outperform ray tracing on a CPU or GPU. However, for very large datasets, the performance of ray tracing becomes competitive and, according to Intel, CPUs can outperform GPUs on ray tracing. Nonetheless, Jeffers stressed that ‘We don’t


think the OpenGL rasterisation pipeline is going away. We’re complementing it for those cases where the ray tracing can add a capability. We’re building the tools underneath, to enable that across an HPC cluster and to tune the user’s problem to the scale of the cluster and the scale of the allocation the user has received.’ However, Steve Parker cited Nvidia’s


collaboration with John Stone at the University of Illinois Urbana Champaign on an open source ray tracing visualisation system called VMD. ‘It’s the main application for molecular dynamics visualisation. He adopted a library that Nvidia has called OptiX, which does GPU based ray- tracing. We’re working with him on the ability to remotely stream an OptiX application. So in this case, VMD ran on a workstation and would transmit data to an Nvidia Visual Computing Appliance (VCA) and, using the same underlying technology of video streaming and high-bandwidth low-latency data movement, it could interactively ray-trace those images.’ Te process was demonstrated at SC14, with the cluster in California and the application in New Orleans. Parker pointed out that he, then at the


University of Utah, and his group had won the best paper award at the Visualization 1998 conference for the first applications using ray tracing in scientific visualisation. He explained that applications such as VMD use ray tracing ‘because they can represent some shades, in this case molecules, with higher fidelity and sometimes higher performance.’ Nvidia has a bunch of ray-tracing products, he said, including Iray a physically correct, photo-realistic rendering solution. Historically, he went on, ray tracing has always


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been too slow to use interactively. ‘I don’t think the whole world is going to go for ray tracing but it will be an important use case because you can add shadows and this helps you understand complex shapes and occlusion. Tese kinds of things are easier to add with ray tracing, just a few lines of code.’ He believes it will come down to a trade-off between performance and ease of use.


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