THREE-DIMENSIONAL THREE-DIMENSIONAL OBJECT REPRESENTATION REPRESENTATIONS:S:-
Graphics is a field of many different kind of objects display on the screen e.g.;-trees, flowers, clouds, rocks etc. In 2-D object representations we can’t access the proper proper view of an object, its only give the front view of the object.so to make the object clear there is a 3-D object representation creating a proper view of any natural scene i.e .Externally and Internally.Now to desi design gn an obje object ct in 3-D 3-D form form we have have to cate catego goris rised ed the the obje object ct into into some some mode modell representation:•
Polygon and quadric surfaces=Euclidean objects
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Spline surfaces and construction technique=aircraft wings with curved surfaces
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Fractle construction and particle system=accurate natural objects
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Physically based modelling method=non-rigid behaviour of an object
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Octree encoding=internal features of object like CT images
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Visualization technique=3-D discrete data sets to obtain visual representation of the data
Represent scheme for solid objects are:1. Boun Bounda dary ry repres represen enta tati tion on:-t :-tel ells ls abou aboutt 3-D 3-D set set of surfa surface ces, s, sepa separa rate te the the obje object ct interior from the environment. 2. Space-partitioning representation:-tells about interior properties, partitioning the spatial region.
Example:-oc-tree representation.
In 3D com comput puter er gra graphi phics cs,, 3D mode modeli ling ng is the the proc proces esss of deve develo lopi ping ng a
mathematical
representation of any three-dimensional surface surface of object either inanimate inanimate or living living
via
specialized specia lized softwa software re.. The product is called a 3D model. It can be displayed as a twodimensional image through a process called 3D rendering or used in a computer computer simulation simulation of physical phenomena. The model can also be physically created using 3D Printing devices. Mode Models ls may may be creat created ed auto automa matic ticall ally y or manu manuall ally. y. The The manu manual al mode modeli ling ng proc proces esss of preparing geometric data for 3D computer graphics is similar to plastic to plastic arts such as sculpting sculpting..
3-D Models
3D models represent a 3D object using a collection of points in 3D space, connected by various geometric entities such as triangles, lines, curved surfaces, etc. Being a collection of data data poin points ts,, 3D mode models ls can can be crea create ted d by hand hand,, algorithmically algorithmically procedural procedural mode modeling ling, or scanned or scanned.. 3D mode models ls are wide widely ly used used anyw anywhe here re in 3D graph graphics ics.. Actual Actually, ly, their use predates predates the widespread use of 3D graphics on personal computers. computers. Many computer games used prerendered images of 3D models as sprites before computers could render them in real-time. Today, 3D models are used in a wide variety of fields. The medical industry uses detailed models of organs. The movie industry uses them as characters and objects for animated and real-life motio motion n pictu pictures res.. The video game indu industry stry uses them as assets for comp for computer uter and video vid eo gam games es.. The The scie scienc ncee sect sector or uses uses them them as high highly ly deta detail iled ed mode models ls of chem chemic ical al compounds compounds.. The architecture architecture industry uses them to demonstrate demonstrate proposed buildings buildings and landscapes through Software Architectural Models. Models. The engineering community uses them as designs of new devices, vehicles and structures as well as a host of other uses. In recent decades the earth science community has started to construct 3D geological models as a standard practice.
3-D Representation Almost all 3D models can be divided into two categories.
Solid - These models define the volume of the object they represent like a rock. These
are more realistic, but more difficult to build. Solid models are mostly used for non visual simulations such as medical and engineering simulations, for CAD and specialized visual applications such as ray tracing and constructive solid geometry
Shell/boun Shell/boundary dary - these models models represent represent the surface, e.g. the boundary boundary of the object,
not its volume like an infinitesimally thin eggshell. These are easier to work with than solid models. Almost all visual models used in games and film are shell models. Because Because the appearance of an object depends depends largely on the exterior of the object, boundary object, boundary representations are common common in compu computer ter graph graphics ics.. Two dimens dimension ional al surfaces are a good analogy for the objects used in graphics, though quite often these objects are non- manifold manifold.. Sinc Sincee surf surface acess are not not finit finite, e, a disc discret retee digi digita tall appr approx oxim imat atio ion n is requi require red: d: polygonal polygonal meshes and and to a less esser extent subd subdivisi ivision on surfa surfaces ces are by far the most common
representation, although point-based although point-based representations have been gaining some popularity in recent years. Level sets are a useful representation for deforming surfaces which undergo many topological changes such as fluids fluids.. The process of transforming representations of objects, such as the middle point coordinate of a sphere and a point on its circumference into into a poly polygo gon n repres represen enta tati tion on of a sphe sphere re,, is called tessellation tessellation.. This step is used in polygon-based rendering, where objects are broken down down from from abst abstrac ractt repres represen enta tatio tions ns prim primit itiv ives es such such as sphe spheres res,, cones etc etc., to socalled meshes, which are nets of interconnected triangles. Meshes of triangles instead of e.g. squares are are popul opular ar as they they have ave pro proven ven to be eas easy to rend render er using ing scan-line rendering.. Polygon representations are not used in all rendering techniques, and in these cases rendering the tessellation step is not included in the transition from abstract representation to rendered -scene.
3-D Modeling processes There are five popular ways to represent a model:
Polygonal Polyg onal model modeling ing - Points Points in 3D space, space, called called vertices, vertices, are connec connected ted by line line
segments to form a polygonal mesh. Used, for example, by Blender. The vast majority of 3D models today are built as textured polygonal models, because they are flexible and because computers can render them so quickly. However, polygons are planar and can only approximate curved surfaces using many polygons.
NURBS mode modeli ling ng - NURB NURBS S Surfa Surfaces ces are defin defined ed by spli spline ne curv curves es,, whic which h are are
influe influence nced d by weight weighted ed contro controll points points.. The curve curve follow followss but does does not necess necessari arily ly interpolate the points. Increasing the weight for a point will pull the curve closer to that point. NURBS are truly smooth surfaces, not approximations using small flat surfaces, and and so are are part partic icul ular arly ly suit suitab able le for for orga organi nicc mode modeli ling ng.. Maya Maya,, Rh Rhin ino o 3d and solid Thinking are the most well-known commercial software that uses NURBS natively.
Splines & Patches modeling - Like NURBS, Splines and Patches depend on curved
lines to define the visible surface. Patches fall somewhere between NURBS and polygons in terms of flexibility and ease of use.
Primitives modeling - This procedure takes geometric primitives like balls, cylinders,
cones or cubes as building blocks for more complex models. Benefits are quick and easy construction and that the forms are mathematically defined and thus absolutely precise, also the definition language can be much simpler. Primitives modeling is well suited for
technical applications and less for organic shapes. Some 3D software can directly render from primitives like POV-Ray POV-Ray,, others use primitives only for modeling and convert them to meshes for further operations and rendering.
Sculpt modeling - Still fairly new method of modeling 3D sculpting has become very
popular in the few short years it has been around. There are 2 types of this currently, Displacement which is the most widely used among applications at this moment, and volumetric. Displacement uses a dense model often generated by Subdivision surfaces of a polygon control mesh and stores new locations for the vertex positions through use of a 32bit image map that stores the adjusted locations. Volumetric which is based loosely on Voxels has similar similar capabi capabilit lities ies as displa displacem cement ent but does does not suffer suffer from from polygo polygon n stretching when there are not enough polygons in a region to achieve a deformation. Both of thes thesee meth method odss allo allow w for for very very artis artisti ticc expl explor orat atio ion n as the the mode modell will will have have a new new topology created over it once the models form and possibly details have been sculpted. The new mesh will usually have the original high resolution mesh information transferred into displacement data or normal map data if for a game engine. The modeling stage consists of shaping individual objects that are later used in the scene. There are a number of modeling techniques, including:
constructive solid geometry
implicit surfaces
subdivision surfaces
Modeling can be performed by means of a dedicated program , or an application component or some scene description language . In some cases, there is no strict distinction between these phases; in such cases modeling is just part of the scene creation process . Complex materials such as blowing sand, clouds, and liquid sprays are modeled with particle systems,, and are a mass of 3D coordinates which have either points, systems points, polygons polygons,,texture splats, splats, or sprites or sprites assign to them. 3D Representations provide the foundations for
Computer Graphics, Computer-Aided Geometric Design, Visualization, Robotics •
They They are are lan langu guag ages es for for des descr crib ibin ing g geom geomet etry ry
Semantics Syntax
values data structures
operations algorithms
Set of 3D points mapping to pixels of depth image
TYPES OF SURFACES TO DISPLAY 3-D OBJECT:1.
Polygon Polygon surfaces:surfaces:-it
2.
curved line and surfaces:-It represent the surface from an
repres represent ent a polyh polyhedr edron on prec precise isely ly which defines the surface features o f the object. It consist of polygon tables, plane equation and polygon meshes.
inpu inputt set set of math mathem emat atic ical al func functi tion on in whic which h a set set of data data points are specified. Example:-quadrics Example:-quadrics and super-quadrics. super-quadrics.
3.
Quadric Quadric surfaces surfaces::-thes these e are are part partic icul ular arly ly sp sphe here res s and and ellipsoids that are common element of graphic scenes and they are available on the graphics packages as primitives to construct more complex objects.
It is mainly consist of sphere,ellipsoid, sphere,ellipsoid, torus.
4. SuperQ SuperQuad uadri rics: cs:-It -It is incor incorpor porati ation on ofaddi ofadditi tiona onall param paramete eters rs into into quad quadri ric c equa equati tion ons s to prov provid ide e incr increas ease e flex flexib ibil ilit ity y for for adjusting object shapes. No. Of additiona additionall parameter parameters=dime s=dimension nsion of the object It consist of superellipse superellipse and superellipsoid superellipsoid 5. Blobby Blobby objects: objects:-th -these ese objects objects can be defini defining ng as blobbi blobbines ness s and are simply refer as a blobby object because there shapes show a certain degree of fluidity.
3-D view of blobby objects
3D object representation using canonical views
partitioning the viewing hemisphere of 3D object in areas of similar views - aspect bubbles
comparison of tracking and matching techniques for bubbles generating (utilizing Gabor wavelets)
distribution of areas of view bubbles for TOM sequence for tracking and matching. Warmer colors encode larger areas of view bubbles.
BIBLIOGRAPHY www.answers.com www.ask.com www.w3schools.com www.workstuff.com
