3D - The Basics


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3D - The Basics

  1. 1. 3D–The Basics
  2. 2. 3D–The BasicsUse of 3DDisplaying and Constructing 3D ModelsExamining 3D Software ToolsConstraints
  3. 3. Use of 3DIn general, there are fundamental differences between Movie and Game generated assets.A primary concern is polygon count and efficiency. Currently the only way to model in videogames is by using polygons, which can require a denser mesh to emulate smoother or morenatural looking models such as humans and animals. NURBS models can be created, butneed to be converted and optimized to polygons for use in the game. In pre-renderedmovies, any technique is allowed to create your models.Movie models can be generated up to millions of polygons using several differenttechniques at once. A model consisting of NURBS and polygons as well as subdivisionsurface models is normal and completely acceptable.Gaming models have to be more efficient in their use of modeled details to maintain amanageable data set to render. The reasoning here is that an efficient streamlinedenvironment composed of the lower poly assets will render more smoothly and give betterframe to frame renders during gameplay. What your gaming system is in essence, is arenderer that constantly has the task of rendering each frame of gameplay at 30 frames persecond. Some games hit the magic number of 60 frames a second. If this rate drops duringthe game the result is a poor experience and hampered gameplay. This applies to PC gamesas well, although they will typically have more processing power to run higher resolutionmodels.With constant innovations and improvement in next-gen consoles and technology,development of more advanced techniques and processes give us more detailed lookingmodels at a lower cost. One of these advances is the use of normal mapping. A normalmap acts like a bump map, in that is adds surface detail without adding polygons. Normalmaps go a step further because they actually replace the surface normal with new multi-channel data to represent an X, Y, Z coordinate system. What this means is that we cancreate a high resolution model of 2 or 3 million polygons and bake the high resolution detaildown to a normal map that retains the component space data of that high resolutionmodel. It is then a process to create a streamlined model that emulates the generalproportions of the high density model, but at a much more efficient poly count of 2500, forexample. Once the normal map data is applied to this low-res rendition of our high-resmonster, the model immediately looks more complex geometrically but at an affordablerendering cost. Movie productions also use Normal Mapping techniques, but the asset thatthey use the Normal Map on is typically a more detailed model than the one used in games.Another difference between movie and game modeling is the fact that not everything needsto be built for a movie or pre-rendered model. It is common practice for film to only buildthose elements in the scene that you can actually see on the screen. In a gameenvironment, it is necessary to make most things viewable from 360 degrees. Can youimagine walking around your favorite game level and not seeing the back side of 3D car youjust walked up to? Or not being able to see the back of the character you just spoke to? Itwouldn’t keep you immersed in the game very long. Well in a movie if the camera nevertravels to the rear of that set or never moves around the corner, it doesn’t need to be built.This is certainly true for aspects of the gaming world, like the far off detail of the mountains,or implied buildings that you as a player can’t actually get to in the game.
  4. 4. A common practice among the two disciplines is that of creating LOD models, or Level OfDetail models. In a game, when a character carrying a machine gun walks up to you fromthe far end of a long hallway, chances are it is not a consistent model the entire journey forthe character or gun. When it is far away, a lower resolution model, with lower resolutiontextures is used. The reasoning for this is that the details cannot be discerned at thatlength so there is no need to use CPU time to render those higher resolution elements. Asthe character approaches, there may be 2 or 3 changes that swap the model and texturesout with higher and higher resolution assets, until it has walked right up to you in camera. Ifdone properly, these “swap outs” go unnoticed for the most part.Movie modeling might use aspects of LOD’s too. There are close up models and modelsbuilt for distance shots too. The main difference for film models is that rarely do the variousLOD’s have to seamlessly blend. Much of this decision making process lies in the story oraction that needs to be conveyed for that shot. For the very next shot, it may require acompletely different set of assets and details that didn’t apply to the first shot. Typicallythere are three levels of modeling that occur for movie models: Block, Medium andDetailed. Each stage identifies and solves different problems for the production. At the block stage, the overall proportions are identified with a simple low detailmodel. This helps to define the silhouette of the model and have a low resolution assetuseful for animatics or test renders. Medium level models take the next step and begin byadding other details onto the Block model that help to define the finished look of themodel. Additions like antennae, guns, rear view mirrors or other details that are notdefining the general shape of the model qualify. This stage helps to identify moving partsand areas that may require special attention from a technical artist. Finally there is theDetailed model, which contains all of the detailed parts and pieces on a higher resolutionchassis.An example utilizing these ideas is a space-ship model that flies past the screen as it speedstowards its destination. Because we only see the one side of the ship, this is the only partthat needs to be built. This close fly by model needs to have a high amount of detail andgeometry to look convincing.There are no concerns for efficiently, really, in the movie created asset. As long as themodel can render, it is considered to be acceptable. For a pre-rendered sequence, rendertime can be extensive, but typically there are large render farms that can tackle the job.There is also the safety factor for these models that any render anomaly can be fixed inPost, where the game model must work all the time at every frame it is rendered in. Otherstipulations sometime burden the game model such as the fact that at times the game assetmust be “water tight”. What this means is that all of the vertices on the model need to bewelded or merged. Render times for real-time shadows and advanced lighting can becomplicated if a model is not sealed at the vertex level, and therefore they take longer tocompute.It is a common expression that there is a time and place for everything. Nothing could bemore true when discussing modeling for Movies or Games. There are certainly similaritiesbetween the two mediums and many different approaches to solve the task at hand. Asgame systems become more and more advanced, these two approaches may become moreand more alike. Perhaps one day there may be no distinction in the modeling processbetween the two.
  5. 5. This Article is about the company 3D Museum that describes how theyconstruct and represent a 3D model.Laser ScanningThe first step in building a three-dimensional (3D) model is to digitize theobject. A high-speed and high-accuracy laser scanner (Minolta Vivid 910) isbeing used, which not only samples the model with high precision, but alsoprovides rich color information. Due to its light weight, the 3D scanner cantravel with us to other collections. Data ProcessingThe raw 3D scan data need to be processed to produce a complete surfacemodel of the fossil. The crucial step is to accurately merge the individual scansinto a single mesh. Most of our processing is done in Raindrop GeomagicStudio, but Rapidform has also been used. PresentationFor research purposes, high resolution 3D data is being kept, but for dataexchange via the web they reduce the filesize – this guarantees fast andsmooth loading of the 3D objects.Rapidform offers a 3D compression and publishing tool using ICF (INUSCompression Format). The two other file formats we are providing, Wirefusion(WF) and 3D Compression (3DC), are based on VRML (Virtual Reality ModelingLanguage). 3DC files do not preserve the vertex colors of VRML files, leavingfossil images monotone.Sources: http://www.siggraph.org/publications/newsletter/volume-41-number-2/modeling-techniques-movies-vs-games,http://en.wikipedia.org/wiki/Video_game, http://www.guardian.co.uk/life-in-3d/gaming-and-3d-technology,http://www.cyberjam.com/3d_interactive_media.html,http://3dmuseum.org/?page_id=241
  6. 6. 3D Modelling TechniquesDrafting has come a long way from blueprints into the new world of 3D Modeling wherefiles can be updated almost instantly, and sent online through email. CAD designers cancreate computer files with CAD software which can be read by manufacturing machines toproduce products. The 3D CAD designer is the one who actually materializes the 3D model.CAD drafting services offer a wide array of services to the public also.With the new advancements in technology recently, almost every type of technical drawingis done with the use of computers. Blueprints are still used in the field, and for otherreasons, but all the drawings are done on a computer. In the past if an update needed to bemade to the blueprints the draftsmen would have to either erase, or start all over. With CADthough, the draftsmen will simply open the file, and make the necessary changes. Anothergreat feature is that the file can be saved to your computer, some type of external harddrive, or online. Just make sure its somewhere safe.The person behind the scenes of 3D modeling is the CAD designer. They use special CADsoftware to create the 3D models. Within the software the developers have incorporatedtools for creating lines, circles, arcs, and other 2D related objects. Also this software hascommands for sculpting, cutting, revolving, mirroring, and other 3D tools. Also the softwarehas the ability to render images with color, texture, lighting, and backgrounds. With all ofthis at the CAD designers disposal, anything imagined can be designed.Drafting encompasses many different practices and principles within it. There is mechanicaldrafting, architecture drafting, civil drafting, electrical drafting, structural drafting, draftingfor plumbing, 3D modeling, and drafting for just about anything you can imagine. CADsoftware has designed programs for each one of these fields and has made specialaccommodations for each. For example, within architectural programs there is a commandfor creating walls, doors, roofs, slabs, and other architectural features. This allows the CADdrafter to work much faster, and be more efficient within drawing.3D models have allowed the design process to be done more accurately and efficiently thanin the past. Drafting has had many changes over the years, and updates to CAD software aremade routinely. These new type of blueprint are much more flexible and allow for changesto be made at a moments notice. Once a design is complete it can go directly to themanufacture to be developed. CAD is used with everything from architecture to inventionsand is the main tool used in any type of technical drawing. This technology allows engineersto examine work before production, and has made life on the general public more safe.
  7. 7. Displaying and Constructing 3D ModelsModeling is the first part of the graphic pipeline. When we are modeling in 3Dwe are in Cartesian space. When we are modeling we use shapes; the mostbasic ones e.g. cone, cylinder, sphere, box.In 3D animation, a polygon is the exact same thing, only these polygons areconnected to build your 3D model. Individual polygons are stitched togetheralong the sides or at the vertex points to create the full model. Think of it asputting together puzzle pieces to create a whole, except that rather thanseeing a printed image on the pieces, youre instead forming a whole otherthree-dimensional shape whose boundaries and volume are defined by smallertwo-dimensional shapes. Polygons are the wrapper on the chocolate Easterbunny; the candy coating on your M&Ms.More polygons in a model can mean more detail and smoother renders, but itcan also mean longer render times and more problems caused by overlappinglines and vertices.Application Programming Interface(API):Application Programming Interface (API) is a set of functions and rules that acomputer use to communicate with each other to do certain jobs, just like howa player communicates to a game by pressing a certain button to do certainaction. (application programming interface, eg Direct3D, OpenGL; graphicspipeline, egmodelling, lighting, viewing, projection, clipping, scan conversion,texturing and shading,display; rendering techniques (radiosity, ray tracing);rendering engines; distributed rendering techniques;lighting; textures; fogging;shadowing; vertex and pixel shaders; level of detail.)
  8. 8. ConstraintsThe 3 main constraints that are used in 3D modeling are:  Polygon count  File size  Rendering Time.Polygon count is easy to understand, this is important as the processor has to calculate theposition of each and every vertex of each and every polygon used to make up that model, somore polygons means more processor power is needed, which in turn means that there’sless processor power for everything else needed to make the game run smoothly. Thismakes the frame rate in game drop dramatically and a ‘lag’ experience for the player andcan be avoided simply by reducing the polygon count of less important models or removingpolygons that just are not needed.File size is less of a constraint but in the past it was a big problem, where 128MB was themaximum size of a cartridge. Whereas today a shot 4 hour game can exceed 4GB, to makesure many hours of gaming was achieved came down to reducing the file size by taking outthings that weren’t necessary or cut down on models which became hard when trying tomake the game look as good as it could be.Rendering time I would say is the second most important constraint, game need to be ableto render objects and textures easily and quickly to get a seamless experience, the longer ittake to render an object it would lower the frame rate of the game and also you willrandomly encounter, for example a wall of a building, which you thought was an entrance,appearing right before your eyes when trying to walk past it, it becomes very unrealistic anddampening down the entire experience. To reduce render times, game developers make itwhere only close objects will render and only far away object would render when you comeinto a certain distance from them, this also works the other way round, when you get acertain distance away from an object, it will stop being rendered, this saves processorpower and prevents the game from having a low frame rate.
  9. 9. Rendering:Rendering is a way to display 3d objects, lighting and textures together, tocreate an image or animation from the data sent by the 3D modeling program.There are 4 types of renders: Rasterize Raycasting Raytracing RadiosityRasterize:Rasterize is majorly used on real time applications such as games. It is done similarly to whatmost technologies in digital graphics of any sort uses to display a render, instead ofrendering the whole scene pixel by pixel, it renders the geometries that you see on screenand it will change accordingly. A good example of rasterizing would be Oblivion as you travelacross the land of Tam riel.Rasterization is performed by a raster image processor (RIP),which turns text and images into the matrix of pixels (bitmap) that will be displayed onscreen or printed on the page. Various conversions may take place. For example, themathematical coordinates of vector and outline fonts as well as vector drawings must beconverted into bitmaps. Existing bitmaps may have to be scaled into different-sizedbitmaps.Unless output is printed on a vector graphics plotter, which literally draws theillustration with pens, all text and graphics must be rasterized into a bitmap for display orprinting.
  10. 10. Raycasting:Raycasting is similar to Raytracing since they both share similar algorithms. The only thingthat distinguishes the two is that Raycasting is a faster version of Raytracing and that itcannot render secondary rays, where asRaytracing can.Ray Casting is the graphic techniqueof using 2D data to display what would look like a 3D environment. This technique has beenused in games such as Wolfenstein 3D, and even more advanced in the Doom series. Raysare drawn from the point the player would be in to the environment to the front. Wherevereach ray hits, that distance is recorded into the appropriate column of pixels. When all ofthe pixels are allotted, the screen will appear to look 3D.Raytracing:Ray tracing is a technique that renders out an image by casting out rays onto the scene andas the rays cast upon the geometry, the colour value of that pixel is calculated. It canproduce high degree of visual realism, but it will cost time to render the scene. It is capableof simulating different variety of visual effects such as reflection (an example would a glass),scattering (where the light rays hits the geometry and it bounces back and scatters) andrefraction (refraction is used on water or air and it will change depending on the change ofdirection).Example of using raytracing:
  11. 11. Radiocity:Radiosity is a technical term in which it is uses two types of lights, an incidentlight (in which the light source hits onto the subject) and a reflective light(where the light reflects off from the subject’s surface). This is used especiallyon interior design.Example of using Radiosity:and a video example http://www.youtube.com/watch?v=NO3uvnbwCKMVertex Lighting:Vertex Lighting (also known as Gouraud shading) is a method that is used todisplay and simulate differing effects of light across the surface of a 3d object.This is done by calculating the vertices around the subject as well as where thelight source is projecting at, the more amount of vertex there is, the better thespecualar lighting, the lower the amount of vertices there is, the less qualityyou will have from a high poly specular lighting.Distributed renderingDistributed rendering (also known as DR) is a technique in which lots ofcomputers are rendering the same scene and that it helps reduce therendering time that it originally has.Vray on 3ds Max is capable of doing thisprocess. The process is done by using TCI/ IP protocols and when you’re usingVray, there are two things you need to know, there is a Render Clients andRender Servers.
  12. 12. Sources:http://animation.about.com/od/glossaryofterms/g/What-Is-A-3d-Polygon.htmhttp://www.fastgraph.com/help/3D_clipping.htmlhttp://en.wikipedia.org/wiki/Projective_geometryhttp://www.google.co.uk/search?hl=en&q=what+is+clipping+3d%3F&metahttp://www.spot3d.com/vray/help/150SP1/distributed_rendering.htmhttp://en.wikipedia.org/wiki/3D_computer_graphicshttp://en.wikipedia.org/wiki/3D_modelhttp://www.best3dsolution.com/services/3d-rendering/http://www.blender.org/http://www.pcmag.com/encyclopedia_term/0,1237,t=rasterize&i=50198,00.asphttp://www.giantbomb.com/ray-casting/92-1517/