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Transcript
From Simulation to Visualization: Astrophysics Goes Hollywood Frank Summers January 17, 2002 Simulation Visualization Done for research purposes Presentation to wide audience Simulations Attempts to replicate & explore aspects of nature on a computer Mathematical abstraction of a physical process (equations) Time sequence Example: Earth orbiting the Sun Sun Earth Sun Earth Sun Earth Sun Earth Star Planet Star Planet Object 2 Object 1 Simulation is just numbers … Position, velocity, and mass Object Position (AU) Velocity (km/s) Mass (g) Sun (0, 0, 0) (0, 0, 0) 2 x 1033 Earth (1, 0, 0) (0, 30, 0) 6 x 1027 … numbers changing over time Earth position changes Day X Y Z 1 1.0 0.0 0.0 2 0.9999 0.0172 0.0 3 0.9994 0.0344 0.0 … … … … 364 0.9994 -0.0344 0.0 365 0.9999 -0.0172 0.0 Simulation Details Initial Conditions position, velocity, density, temperature, etc. for all objects at starting time Equations gravity, hydrodynamics, radiation, magnetic fields, expansion of the universe Simulation Details Time Evolution Calculate forces, heating, other changes Update position, velocity, etc. with new values Repeat Data Output Write file of positions, velocities, etc Series of files covering simulation time Scientific Accuracy Simulations expensive, but necessary Artist’s conceptions difficult Well removed from normal experience Complex 3D behaviors Coupled feedback between physics Scientists can’t describe it sufficiently Scientific simulations physics equations programmed in 3D, complexity, and feedbacks included Visualization Turn those numbers into pictures Visualizations Data Transformation Representation Choreography Rendering Compositing Graphics vs Visualization Science Graphics Pictures, plots, charts Illustrations to scientific argument Requires background knowledge to interpret Representational Content more important than form Scientific Visualization Images and movies Tells its own story Must play off of audience’s knowledge More literal Visual message is the strongest Data Transformation Comprehend the dataset What quantities? What time period? What are the assumptions? Convert from research quantities to more generally meaningful quantities Representation How literal? How artistic? How best to promote message? How to be least misleading? Shading Geometry can get very complex ex., surface of an orange Shading solution - Use simple shapes ex., sphere Add complexity when drawing the surface Texture - color, pattern Bumps - small shape distortions Light – reflection, transparency Programmability = Flexibility Shading Example: 3 Balls Shading Example: Teapot Shading Stars Simple Geometry - Disks Disks w/ Star Shader Shading Stars Gaussian Exponential Stars by Magnitude Combination Calibration using local starfield Globular Star Cluster 47 Tucanae Globular Star Cluster Viz Data - N-body simulation, 6144 stars (Zwart) 3D position, absolute brightness, mass, & type color derived from mass, type, and spectra* Stars as point objects size depends on apparent brightness size calculated in pixels, not 3D space Star shader in renderman calculate app. brightness - each star, each frame combination of gaussian and exponential glows Calibrated by reproducing constellations Shading Gas Clouds Choreography Camera motion Invaluable for giving 3D feel Missing from most science animations XY Projection YZ Projection XY Projection YZ Projection Orion Nebula Rendering Lots of computer time Over 2 hours per frame for NASM 1500 frames – 125 CPU days Renderfarms Clusters of computers dedicated to rendering Renderfarm in 331B Gathered unused OPO machines Installed Red Hat Linux Connected to a switch and created an isolated private network of five machines Total out-of-pocket cost $80 Computer 1 Computer 2 Computer 3 Computer 4 Computer 5 Red Hat Linux 7.2 Red Hat Linux 7.2 Red Hat Linux 7.2 Red Hat Linux 7.2 Red Hat Linux 7.2 Dual P3 933 MHz Dual P3 800 MHz P2 400 MHz P2 400 MHz P3 850 MHz private network switch Visualization Wall Schematic Computing Cluster Node 1 Node 2 Node 3 Display Node 4 Node 5 Node 6 1 2 3 4 Node 8 5 9 13 6 10 14 7 11 15 8 12 16 Node 7 Master Computer Node 9 Node 10 Node 11 Node 12 Node 13 Node 14 Node 15 Node 16 Compositing Add multiple elements together Provide context Galaxy Collision Viz Data - N-body + Hydro simulation 262,144 particles (Mihos & Hernquist) young stars, old stars, gas, dark matter