Lec02 Modeling Concepts And Techniques PDF 2021/22

EIE 3101 Computer Animation Lec 02 Modeling Concepts and Modeling Techniques 1 Isaac Kerlow, The art of 3D computer animation and effects, 4th ed., Hoboken, N.J.: John Wiley & Sons, 2009. Chapter 3, 4 2021/22 sem 1 3 Content  Ch3 Modeling Concepts  Ch4 Modeling Techniques  Geometric Primitive...

EIE 3101 Computer Animation Lec 02 Modeling Concepts and Modeling Techniques 1 Isaac Kerlow, The art of 3D computer animation and effects, 4th ed., Hoboken, N.J.: John Wiley & Sons, 2009. Chapter 3, 4 2021/22 sem 1 3 Content  Ch3 Modeling Concepts  Ch4 Modeling Techniques  Geometric Primitives  Sweeping  Tutorial  Copy, Instance, Reference and Array  Editable Poly  Edge Ring, Edge Loop, Edge Connect  Cut  Chamfer  Relax  Bridge 4 Modeling Concepts  Modeling: the sculpting, spatial description, and placement of virtual 3-D objects, environments, and scenes with a computer system.  This chapter explores the basic concepts of the modeling process  Numerical description of objects  Moving and resizing objects in 3-D space 5 Space, Objects, and Structures  Fig 3.1.2 6 Space, Objects, and Structures  Workspace or scene: 3-D space with the boundaries  We can think of this space as our world or environment.  Objects that exist within the space are visible, those that fall outside are invisible.  The main point of reference in this world is called the world origin.  The origin is usually located in the center of the space, but it can also be placed elsewhere 7 Space, Objects, and Structures  Fig 3.1.3 8 Space, Objects, and Structures  All 3-D spaces have 3 basic dimensions: width, height, and depth.  Commonly represented by arrows or axes.  Commonly labeled width with X, height with Y and depth with Z.  But 3ds Max labeled width with X, height with Z and depth with Y.  The point where these 3 axes intersect is the world origin.  The rectangular coordinate system can be used to define specific locations and accurately position the points of objects in 3-D space.  Also referred to as the Catesian coordinate system 9 Space, Objects, and Structures  Right-handed coordinate system  Values on the X axis become larger to the right of the origin  Values on the Y axis increase as the move above the origin  Values on the Z axis grow as they get closer to us 10 Space, Objects, and Structures  The 3 axes can be paired with each other in 3 different ways to define a plane or a view.  XY axes: front plane  XZ axes: top plane  YZ axes: side plane  Fig 3.1.4 11 Space, Objects, and Structures  The spherical or azimuthal coordinate system is also widely used  Provides a simple method for placing objects in a 3D world in terms of their distance to the object, their angle around the point of interest, and their altitude angle above the point of interest  Especially useful for placing and moving cameras and light sources in a 3-D scene  Fig 3.4.8 The spherical or azimuthal coordinate system allows for orbiting or panning the camera around the subject 12 Vertices, Edges, and Facets  Points, lines, and facets are the basic elements that can be used to build 3-D objects.  Fig 3.3.1  The simple pyramid has 4 points or vertices, 6 lines or edges, and 4 planes or facets 13 Vertices, Edges, and Facets  A point can be easily defined by its XYZ position.  A line can be defined by the XYZ location of its two endpoints.  In 3-D geometry, a point is also referred to as a vertex, which is defined by the intersection of 2 or more edges.  An edge is defined by two adjacent surfaces.  A Facet is a planar surface that is defined by the position of its bounding lines.  A 3-D object is usually composed of several points, lines, and facets. 14 Vertices, Edges, and Facets  The facets or planar surfaces that defined most 3-D objects are also called polygons, which means “with many angles”  Polygons are closed planes bounded by straight lines  Can be regular or irregular  Can be used to create 3-D objects called polyhedral (Fig 4.3.1)  Fig 3.3.2 shows polygonal meshes in wireframe rendering style  Most modeling techniques focus on building surfaces that are hollow shells– this is called boundary geometry 15 16 Moving Things Around  Once we have built some objects, we can move them around  Sometimes needs to move some of an object’s components, e.g. a group of points, before the modeling is completed.  Geometric transformations: functions used for modifying the shape of objects, their size and proportions as well as their position in space  Most widely used geometric transformations:  Translation, rotation, scaling, perspective projection  Can also be applied to the camera and the lights 17 Concatenated transformations  A series of global transformations applied in sequence  Fig 3.4.2 18 Absolute or Relative Values  Common to use mouse to control the position, orientation, and size of the models in the environment  Sometimes necessary to type specific values for controlling the exact position, orientation, and size models  In 3ds Max, shortcut key for transform type-in: F12  Absolute values: exact position in space where the object must be relocated regardless of where the object was located in space before the transformation  Relative values: the number of units added or subtracted to the current position of the object (relative to an existing absolute position) 19 Translation  Move an object or group of objects in a linear way to a new location in 3-D space  Can occur along one axis or along several axes at the same time  Order of translations does not affect the final position (Fig 3.4.2)  Fig 3.4.3 20 Rotation  Move an element or group of elements around a specific center and axis  The amount of rotation is usually specified in terms of an angle of rotation (measured in degrees) and a direction of rotation  When rotating an object around its own center, it is possible to reposition that center (In 3ds Max, it is called “pivot”) 21 Scaling  Change the size and/or the proportion of an element or a group of elements  Can be applied in proportional or a non-proportional mode  Proportional scaling: resize an object along each axis in equal amounts  Non-proportional scaling: the object may be resized by different factors along each axis  Fig 3.4.7 22 Perspective Projection  Makes possible the representation of 3-D environments on the flat surface of the computer’s monitor or a sheet of paper  A perspective view of a 3-D scene is created by projecting each point of an object from the viewpoint onto the image plane  The points in 3-D object coordinate system are then transformed to the 2-D image coordinate system  Happens automatically in virtually all 3-D software EIE 3101 Computer Animation Modeling Techniques 23 Isaac Kerlow, The art of 3D computer animation and effects, 4th ed., Hoboken, N.J.: John Wiley & Sons, 2009. Chapter 4 25 Geometric Primitives  Virtually all 3-D modeling computer programs provide a collection of tools for creating simple shapes with a fixed structure known as geometric primitives.  The number and type of geometric primitives varies from program to program, but the following list is a representative selection:  Cubes, spheres, cylinders, cones, toruses, regular polyhedral, and 2-D polygons  Fig 4.3.1, 4.4.1 26 What are the standard primitives provided by 3ds Max? 27 Geometric Primitives  Geometric primitives are standard shapes that the modeling program can create and manipulate effortlessly and usually from a simple predefined mathematical description.  Can be used to represent simple shapes  Require almost no modification except for changes to their position in space, size, and proportion in some cases  Can be used as the basis for more complex, composite 3-D shapes  Build more complex objects with a variety of utility tools for trimming, attaching, and blending  Fig 10.2.4 28 Geometric Primitives 1. Cubes  Six-sided, closed, 3-D objects  All sides have the same length (the only variable) 2. Spheres  Symmetric, closed, 3-D objects  Variable of radius or diameter  Popular as the starting point for free-form modeling 3. Cylinders and Cones  Commonly defined as polygonal objects  May be shaped by the following variables: radius, height, number of longitudinal divisions, number of latitudinal divisions, and whether they are capped or not.  Capping determines whether the round sides of cones or cylinders are open or whether they are closed 29 Geometric Primitives 4. Toruses  A torus is a 3-D, closed shape that resembles a donut  Like a cylinder that has been bent and stretched so that the two bases touch each other  Modeling variables: size of exterior radius, size of interior radius, number of latitudinal divisions, and number of longitudinal divisions.  Can also be built with radial sweeping techniques (Fig 4.4.1) 30 Geometric Primitives 5. Regular Polyhedra A polyhedron refers to a 3-D object that is composed of polygons Common regular polyhedral: 4-sided tetrahedron, 8-sided octahedron, 12-sided dodecahedron,  20-sided icosahedron Fig 4.3.1 31 Geometric Primitives 6. 2-D Shapes  Usually include arcs, circles, spirals, triangles, squares, and other polygons 32 Sweeping  Sweeping is perhaps the most powerful derivative modeling technique  The basic idea behind all sweeping modeling techniques consists of defining a 2-D outline that is swept along a predefined path.  As the outline is swept, it defines a shape in 3-D space.  The resulting 3-D model depends largely on the complexity of the seed outline and the complexity of the path (Fig 4.4.2) 33 34 Sweeping The 3 most popular sweeping techniques: 1. Extrusion  Create 3-D shapes by starting with a 2-D outline and extruding or extending it along a straight path along one axis (Fig 4.4.2)  Sometimes called lofting because the 2-D outlines are duplicated and moved a level up 2. Free-form sweeps  Some programs also offer the ability to extrude objects along curved paths of any shape and along any axis or combination of axes.  An extrusion that takes place along several axes is sometimes called a sweep, an extrusion on a path, or a free-form extrusion (Fig 4.4.3) 35 Sweeping The 3 most popular sweeping techniques (con’t): 3. Lathe or revolve  The surfaces created with this technique are usually called surfaces of revolution.  The software-based lathe tool simulates a real lathe, which is a tool composed of a rotating base on which you place a cylinder of wood that is shaped by placing a steep blade on its surface as the base rotates around its vertical axis.  The software lathe sweeps a 2-D outline around one axis; the 2-D outline may be open or closed.  A new 3-D shape emerges as the 2-D outline is swept along a circular or radial path; it usually remains perpendicular to the sweeping path as they are swept.  The resulting 3-D object is defined by the areas enclosed with the revolved 2-D outline. 36 Sweeping The 3 most popular sweeping techniques (con’t): 3. Lathe or revolve (con’t)  2-D outlines that do not touch the axis of sweeping will result in 3-D objects with holes  In these cases, the resulting shapes can be capped or uncapped.  Fig 4.4.4