Modelling and Simulation

1. Modelling and Simulation Modeling Techniques

2. Modeling and simulation • Modeling and simulation (M&S) is getting information about how something will behave without actually testing it in real life. For instance, if we wanted to design a racecar, but weren't sure what type of spoiler would improve traction the most, we would be able to use a computer simulation of the car to estimate the effect of different spoiler shapes on the coefficient of friction in a turn. We're getting useful insights about different decisions we could make for the car without actually building the car.

3. WHAT IS MODELING? • Modeling is the process of producing a model; a model is a representation of the construction and working of some system of interest. A model is similar to but simpler than the system it represents. One purpose of a model is to enable the analyst to predict the effect of changes to the system. On the one hand, a model should be a close approximation to the real system and incorporate most of its salient features. On the other hand, it should not be so complex that it is impossible to understand and experiment with it. A good model is a judicious tradeoff between realism and simplicity. Simulation practitioners recommend increasing the complexity of a model iteratively. An important issue in modeling is model validity. Model validation techniques include simulating the model under known input conditions and comparing model output with system output.

4. WHAT IS SIMULATION? • A simulation of a system is the operation of a model of the system. The model can be reconfigured and experimented with; usually, this is impossible, too expensive or impractical to do in the system it represents. The operation of the model can be studied, and hence, properties concerning the behavior of the actual system or its subsystem can be inferred. In its broadest sense, simulation is a tool to evaluate the performance of a system, existing or proposed, under different configurations of interest and over long periods of real time.

5. WHAT IS SIMULATION? • Simulation is used before an existing system is altered or a new system built, to reduce the chances of failure to meet specifications, to eliminate unforeseen bottlenecks, to prevent under or over-utilization of resources, and to optimize system performance. For instance, simulation can be used to answer questions like: What is the best design for a new telecommunications network? What are the associated resource requirements? How will a telecommunication network perform when the traffic load increases by 50%? How will a new routing algorithm affect its performance? Which network protocol optimizes network performance? What will be the impact of a link failure?

6. Modeling Techniques • Box/Subdivision Modeling. • Edge/Contour Modeling. • NURBS/Spline Modeling. • Digital Sculpting. • Procedural Modeling. • Image Based Modeling. • 3D Scanning.

7. Modeling Techniques • Box/Subdivision Modeling • Box modeling is a polygonal modeling technique in which the artist starts with a geometric primitive (cube, sphere, cylinder, etc.) and then refines its shape until the desired appearance is achieved. • Box modelers often work in stages, starting with a low resolution mesh, refining the shape, and then sub-dividing the mesh to smooth out hard edges and add detail. The process of subdividing and refining is repeated until the mesh contains enough polygonal detail to properly convey the intended concept. • Box modeling is probably the most common form of polygonal modeling, and is often used in conjunction with edge modeling techniques (which we'll discuss in just a moment). We explore the box/edge modeling process in greater detail here. http://www.youtube.com/watch?v=c1pgqpBKBRg

8. Modeling Techniques • Edge/Contour Modeling • Edge modeling is another polygonal technique, though fundamentally different from its box modeling counterpart. In edge modeling, rather than starting with a primitive shape and refining, the model is essentially built piece by piece by placing loops of polygonal faces along prominent contours, and then filling any gaps between them. • This may sound needlessly complicated, but certain meshes are difficult to complete through box modeling alone, the human face being a good example. To properly model a face requires very strict management of edge flow and topology, and the precision afforded by contour modeling can be invaluable. Rather than trying shape a well-defined eye socket from a solid polygonal cube (which is confusing and counter-intuitive), it's much easier to build an outline of the eye and then model the rest from there. Once the major landmarks (eyes, lips, brow line, nose, jawline) are modeled, the rest tends to fall into place almost automatically. http://www.youtube.com/watch?v=gDT0Pz1UtWM&list=PLA9DA4AD0D650676F

9. Modeling Techniques • NURBS/Spline Modeling • Non-uniform rational basis spline (NURBS) is a modeling technique used most heavily for automotive and industrial modeling. In contrast to polygonal geometry, a NURBS mesh has no faces, edges, or vertices. Instead, NURBS models are comprised of smoothly interpreted surfaces, created by "lofting" a mesh between two or more Bezier curves (also known as splines). • NURBS curves are created with a tool that works very similarly to the pen tool in MS paint or Adobe Illustrator. The curve is drawn in 3D space, and edited by moving a series of handles called CVs (control vertices). To model a NURBS surface, the artist places curves along prominent contours, and the software automatically interpolates the space between. • Alternately, a NURBS surface can be created by revolving a profile curve around a central axis. This is a common (and very fast) modeling technique for objects that are radial in nature—wine glasses, vases, plates, etc. http://www.youtube.com/watch?v=GcdVRlSmQkA

10. Modeling Techniques • Digital Sculpting • The tech industry likes to talk about certain breakthroughs they've termed disruptive technologies. • Technological innovations that change the way we think about achieving a certain task. The automobile changed the way we get around. The internet changed the way we access information and communicate. Digital sculpting is a disruptive technology in the sense that it's helped free modelers from the painstaking constraints of topology and edge flow, and allows them to intuitively create 3D models in a fashion very similar to sculpting digital clay. • In digital sculpting, meshes are created organically, using a (Wacom) tablet device to mold and shape the model almost exactly like a sculptor would use rake brushes on a real chunk of clay. Digital sculpting has taken character and creature modeling to a new level, making the process faster, more efficient, and allowing artists to work with high-resolution meshes containing millions of polygons. Sculpted meshes are known for previously unthinkable levels of surface detail, and a natural (even spontaneous) aesthetic. http://www.youtube.com/watch?v=kj0ZYKhqrr0&list=PLP29SoS4b1ZUf0DEgC0wM8_Yd6VCEC8H5

11. Modeling Techniques • Procedural Modeling • The word procedural in computer graphics refers to anything generated algorithmically, rather than being created manually by the hand of an artist. In procedural modeling, scenes or objects are created based on user definable rules or parameters. • In the popular environment modeling packages Vue, Bryce, and Terragen, entire landscapes can be generated by setting and modifying environmental parameters like foliage density and elevation range, or by choosing from landscape presents like desert, alpine, coastal, etc. • Procedural modeling is often used for organic constructs like trees and foliage, where there is almost infinite variation and complexity that would be very time consuming (or impossible altogether) for an artist to capture by hand. The application SpeedTree uses a recursive/fractal based algorithm to generate unique trees and shrubbery that can be tweaked through editable settings for trunk height, branch density, angle, curl, and dozens if not hundreds of other options. CityEngine uses similar techniques to generate procedural cityscapes. http://www.youtube.com/watch?v=8zlKofCqWp8

12. Modeling Techniques • Image Based Modeling • Image based modeling is a process by which transformable 3D objects are algorithmically derived from a set of static two-dimensional images. Image based modeling is often used in situations where time or budgetary restrictions do not allow for a fully realized 3D asset to be created manually. • Perhaps the most famous example of image based modeling was on The Matrix, where the team had neither the time nor the resources to model complete 3D sets. They filmed action sequences with 360 degree camera arrays, and then used an interpretive algorithm to allow for “virtual” 3D camera movement through traditional real-world sets. http://www.youtube.com/watch?v=1hff6uUTMXQ

13. Modeling Techniques • 3D Scanning • 3D Scanning is a method of digitizing real world objects when an incredibly high level of photo-realism is required. A real world object (or even actor) is scanned, analyzed, and the raw data (typically an x,y,z point cloud) is used to generate an accurate polygonal or NURBS mesh. Scanning is often used when a digital representation of a real-world actor is required, as in The Curious Case of Benjamin Button where the lead character (Brad Pitt) aged in reverse throughout the film. • Before you go worrying about 3D scanners replacing traditional modelers, consider for a moment that the bulk of the objects modeled for the entertainment industry have no real-world equivalent. Until we start seeing space ships, aliens, and cartoon characters running around, it's safe to assume that the modeler's position in the CG industry is probably safe.