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Interactive 3D Simulation and Visualization

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AbstractWe describe a multidisciplinary effort for creating interactive 3D graphicalmodules for visualizing optical phenomena. These modules are designed foruse in an upper-level undergraduate physics course. The modules are devel-oped in Open Inventor, which allows them to run under both Unix and Win-dows. The work is significant in that it applies contemporary interactive 3Dvisualization techniques to instructional courseware, which represents aconsiderable advance compared to the current state of the practice.1. IntroductionOptics developed as a scientific field primarily through the experi-ments of Isaac Newton (who considered light as particles) andChristiaan Huygens (who considered light as waves) in the late sev-enteenth century. The theoretical basis of classical optics was devel-oped in the nineteenth century by Thomas Young, AugustinFresnel, and James Clerk Maxwell. More recently, the invention ofthe laser has promoted research in optics since the 1960’s. Fiberoptics and quantum optics also drive optics research in the 1990’s.Improving understanding of optics is consequently a significanteducational goal.Each year at colleges and universities nationwide, some 10,000 stu-dents take a course on optics, typically through a department ofphysics. The method of instruction has changed very little in thepast 40 years, and many of the textbook illustrations have remainedessentially the same over this time. In particular, the illustrationsrely heavily on line drawings and 2D graphs. Certain key conceptsin the study of optics possess fundamentally 3D aspects, which aretypically demonstrated in a classroom laboratory. The lab equip-ment may include light sources, apertures, lenses, and polarizingfilters. The 2-dimensional diagrams in a textbook may illustrateinvisible but important features of light (such as the electric fieldvector at a given point as a function of time), whereas the laboratoryreveals 3-dimensional visible features of light (like focus and inter-ference that vary according to position).There are several existing computer-assisted instructional modulesdesigned to support the teaching of optics by visualizing opticalphenomena. These systems are primarily 2D and use line drawingssimilar to the ones found in traditional textbooks [JENKINS] [LIP-SON]. Some of these software systems are semi-interactive: a stu-dent types in different values for various parameters, and the systemrecalculates the display in response. Because these systems aredesigned for low-end personal computers without hardware accel-eration for 3D graphics, interactive 3D visualization has not yetbeen a significant design-objective for such instructional software.2. The Optics ProjectThe Optics Project serves to amplify lessons learned in class byproviding interactive demonstrations both inside and outside ofclass. This section gives an overview of the project and describesthe workings of four of the modules.Interactive 3D Simulation and Visualization of Optical PhenomenaDavid C. Banks* John T. Foley✝Kiril N. Vidimce* Ming-Hoe Kiu✝✝Jay Brown**NSF Engineering Research Center ✝Department of Physics and AstronomyMississippi State University✝✝Lattice Semiconductor Corporation2.1 Overview of TOPIn 1994, work first began on The Optics Project (TOP) at Missis-sippi State University. This multidisciplinary effort has involvedstudents and faculty from three Departments (Physics and Astron-omy, Computer Science, and Electrical and Computer Engineer-ing), constructing stand-alone modules to complement a standardundergraduate course in optics. The first software modules wereimplemented using OpenGL; OpenInventor has now become ourgraphics library of choice for developing new modules and updat-ing old ones.Each module is designed to be (1) interactive, (2) dynamic when-ever animation is appropriate, and (3) three-dimensional. We identi-fied eight fundamental topics that would lend themselves tointeractive 3D visualization. These are summarized below.1 Wave Simulation - Circular waves and linear (parallel wave-fronts) in a ripple tank.2 Reflection and Refraction - Vectorial treatment of monochro-matic plane waves incident upon a planar interface. Total inter-nal reflection, critical angle, Brewster’s angle.3 Geometrical Optics - Systems of thin lenses. Stops aperturesand pupils. Optical instruments.4 Polarization - Different kinds of polarization, action of polar-ization elements.OpenInventorOpen Inventor (OI) is an API developed by SGI in 1991.It is an object-oriented 3D graphics toolkit built on top ofOpenGL. OI provides an object abstraction of 3D geo-metric primitives and a directed acyclic graph (DAG)called scene graph. The scene graph serves as an objectdatabase. The objects stored in the database can be wiredtogether using connections to propagate changes of statefrom one object to another. OI has engines that providebehavior in the scene graph, like recalculating shape orcolor, by evaluating inputs from connections with otherobjects.Sensors generate interrupts based on changes in time,changes in another object or changes in the scene graph.OI is a powerful tool for building intuitive 3D interfacesby using its generic event model and its implementationof the Brown University 3D widgets [CONNER]. OI alsoprovides a self-contained file format that describes bothgeometry and behavior. OI is cross-platform compatible;it has been ported to other platforms including Windows,HP-UX, Solaris, AIX.5 Interference - Two slits, N slits, Michelson interferometer,and thin film interference.6 Fraunhofer Diffraction - Single slit, multiple slit, diffractiongrating, circular aperture, Rayleigh resolution criterion.7 Fresnel Diffraction - Single slit, transition to Fraunhofer, cir-cular aperture, double slit.8 Coherence - Temporal and spatial coherence.The modules allow a student to visualize effects that either (1) can-not easily be made visible or (2) cannot be controlled very well in aphysical laboratory experiment. As an example of an important butinvisible feature of optics, consider the dynamic evolution of theelectric field vector as it reflects off a surface or transmits through amedium. The vector can easily be made visible in a graphics systemby drawing an arrow. As an example of an important parameter tocontrol in a laboratory exercise, consider the effect of changing theangle of incidence of a beam of light on the reflected beam’s inten-sity. The student adjusts a mirror to the proper angle,


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