Lec03 Advanced Modeling_2122.pdf

EIE 3101 Computer Animation Lec 03 Modeling Techniques And Advanced Modeling 1 Isaac Kerlow, The art of 3D computer animation and effects, 4th ed., Hoboken, N.J.: John Wiley & Sons, 2009. Chapter 4, 5 2021/22 sem 1 2 Content  Ch4 Modeling Techniques  Curved Lines  Basic Modeling Utilities ...

EIE 3101 Computer Animation Lec 03 Modeling Techniques And Advanced Modeling 1 Isaac Kerlow, The art of 3D computer animation and effects, 4th ed., Hoboken, N.J.: John Wiley & Sons, 2009. Chapter 4, 5 2021/22 sem 1 2 Content  Ch4 Modeling Techniques  Curved Lines  Basic Modeling Utilities  Ch5 Advanced Modeling  Free-Form Curved Surfaces  Subdivision Surfaces  Logical Operators and Trimmed Surfaces  Advanced Modeling Utilities  Tutorial  ProBoolean Compound Object  Editable Spline 3 Curved Lines  Lines are used to define the shape of the object and many of its surface characteristics.  Lines are fundamental component of all 3-D objects.  Straight lines define the shortest distance between two points  Defined by 2 endpoints only; may have a slope but no change in angularity (slope is constant no curvature)  Sometimes called polygonal lines  Curves are about subtlety of change and elegance of design  Defined by several points; deviate from a straight path without any sharp breaks in angularity (slope is variable)  Sometimes called curve segments  Also called splines 4 Curved Lines  All splines are generated from a defining polygon  controlled curves  Each of the spline curves can be quickly characterized by the way in which it is controlled by the control points or control vertices  Control points can control the curvature or tension of a curved line  The structures that control the splines are invisible https://upload.wikimedia.org/wikipedia/commons/f/f2/Spline01.gif 5 Curved Lines  Five Popular Types of Curves: 1. Linear splines  Looks like a series of straight lines connecting the control points 2. Cardinal splines  Looks like a curve that passes through all of its control points 3. B-splines  Looks like a curved line that rarely passes through the control points 4. Bezier curves  Passes through all of its control points 5. NURBS (nonuniform rational b-splines)  Does not pass through all its control points 6 Bezier curve  The Bezier curve differs from the other splines because it has tangent points in addition to the control points.  Tangent points are used to fine– tune the degree of curvature on a line without modifying the control points.  Fig 4.2.4 7 NURBS  NURBS offer a high degree of local curve control by using weights and knots.  These controls allow a portion of the spline to be modified without affecting other parts of the spline.  The knots on a NURBS determine the distribution and local density of points on a curve.  One weight is attached to each control point, and they determine the distance between the control point and the apex of the curve.  Nonrational curve: all control vertices on a spline have the same weight factor  (B-splines are NURBS with equal weights)  Rational curve: when the values of the weights on the curve are modified  Manipulating weights on a NURBS curve may improve the subtle shaping of a line, but it usually also slows down the rendering of the final model. 8 Basic Modeling Utilities 1. Getting Information and Naming Objects  Objects can be named so that we can identify them faster  Get Information feature presents detailed information about the active object in numerical form (Fig 4.6.1) 2. Locking  Objects can be locked in a specific position, orientation, size, or spatial range.  Locking an object or an object’s element that is not supposed to move can help streamline the modeling process. 3. Setting a Face  2-D outlines are not really 3-D objects, they are just lines with a hole in the middle  In order for 2-D outlines to be rendered properly, it is necessary to turn them into planes  This process is called setting a face to an outline. 9 Basic Modeling Utilities 4. Setting the Center of Objects  By default, the centers of objects are automatically placed in the objects’ geometric centers.  Being able to interactively reposition this location is important because many modeling and animation operations are calculated based on the spatial position of the center of the object. 5. Duplicating and Instancing  Duplicating creates a single independent copy of the selected model or group of selected models.  The copy can be created in the same location or in a new position.  The values needed to create multiple copies of an object typically include the number of copies, and the XYZ values for translation, rotation, and scaling (Fig 4.6.2)  Instancing is an alternative to duplicating  Instancing—also called cloning in some systems—creates multiples of an original object by using its numerical description and cloning it elsewhere in the scene.  The multiples created with instancing continue to be related at all times to the original object. If the original changes shape or is scaled, its dependent instances are also transformed. 10 Basic Modeling Utilities 6. Setting Text  Text tools are capable of automatically producing 2-D outlines or 3-D objects extracted from the 2-D outlines of fonts (or typefaces) installed in the computer system. 7. Mirroring  Mirroring a 3-D model is a useful technique when building an object composed of 2 identical (or almost identical) halves. 8. Snapping to the Grid  By forcing the object’s or its components’ points to snap to a grid, 3-D modeling programs can help to simplify the construction of regular shapes or precise details within larger shapes. 11 Basic Modeling Utilities 9. Volume Calculation  Volume calculation tools allow users to find out the total volume and area of the inside, outside, or parts of any 3-D object.  Being able to unfold the planes that bound a 3D object can be quite useful when it is necessary to fabricate either a cardboard scale model or prototype of the 3-D object in more durable materials, such as plastic or sheet metal (Fig 15.8.1) 12 Basic Modeling Utilities 10. Bounding Box  When modeling a scene with multiple complex objects, many computer systems may slow down because of the huge number of calculations needed to redraw the image of the models on the screen.  Using bounding boxes to represent objects is a convenient technique for speeding up their display.  Bounding boxes are usually rectangular, and they are defined by the points most distant from the center of the model.  Fig 4.6.4 EIE 3101 Computer Animation Advanced Modeling 13 Isaac Kerlow, The art of 3D computer animation and effects, 4th ed., Hoboken, N.J.: John Wiley & Sons, 2009. Chapter 5 14 Free-Form Curved Surfaces  Curves are used to define free-form curved surfaces and to build meshes of curved surfaces.  There are many types of curves, and the most popular types include 1. Linear splines 2. Cardinal splines 3. B-splines 4. Bezier curves 5. NURBS (nonuniform rational b-splines)  Each of the curved surfaces can be characterized by the way in which its curvature or tension is controlled by the control points. 15 Curved Patches  A curved patch is a small curved area that can be created from curves. 16 Curved Patches  Complex free-form surfaces are created by merging 2 or more curved patches.  When curved patches that have the same number of rows and columns are merged, the results are fairly predictable.  But merging patches with different numbers of rows and/or columns requires the use of interpolation techniques that modify one of the 2 patches being merged (Fig 5.1.2) 17 Curved Patches  Merging patches is one of the most powerful modeling techniques that can yield detailed models with subtle shapes (Fig 5.1.3) 18 Fitting Curved Surfaces to Polygons  The techniques of fitting curved surfaces to polygonal meshes have gained popularity due to the increased use of 3-D scanners to capture physical models and maquettes.  Scanners usually capture 3-D geometry in the form of polygonal meshes, and specialized software has been developed to help convert the polygonal information into curved surfaces. (Fig 5.1.9) 19 3D Scanning Demonstration https://youtu.be/mdvyec06t1A 20 Subdivision Surfaces  Subdivision surfaces are popular as a flexible solution of modeling surfaces.  There are many ways to go about subdividing a surface: interpolation, averaging, approximation, and insertion of new points.  To be efficient, they are usually based on adaptive approximation (the surface will subdivide only where the topology of the surface requires additional detail). 21 Subdivision Surfaces Subdivision surfaces are defined algorithmically, and many of the algorithms that produce more polygons do so in 2 steps: 1. Split each surface into 4 facets 2. Reposition the vertices by doing local weight point averaging 22 Logical Operators  Logical operators are used to create models by adding and subtracting shapes in a variety of ways.  The most common logical operators include  Union  Intersection  Difference  Fig 5.3.1 23 Trimmed Surfaces  The difference logical operator is usually referred to as trimming  The surfaces created with it are called trimmed surfaces  This technique is especially useful for creating 3-D objects or surfaces with holes  Fig 5.3.2 24 Advanced Modeling Utilities 1. Beveling (3ds Max: Chamfer)  The edge between adjacent surfaces can be customized with great detail with a variety of beveling techniques.  Simple beveling usually works by truncating the hard edge between adjacent surfaces and replacing it with a slanted plane.  The amount of beveling can be controlled by a distance radius, or angle value 2. Rounding (3ds Max: Fillet) Rounding is a delicate form of beveling that literally rounds the straight edges or points of an object.  The degree of rounding is controlled by the number of segments or facets that are used to define the smooth transition between adjacent surfaces  25 Advanced Modeling Utilities 26 Fillet and chamfer in 3ds max https://youtu.be/GfWOn_GIdX4 27 Advanced Modeling Utilities 3. Blending  Special way of merging 2 surfaces.  Instead of merging 2 surfaces by first making them touch each other and then merging them, blending creates a new surface that extends from each of the 2 surfaces being blended.  The new surface created by blending connects the 2 surfaces, and the smoothness of the blending is controlled with a function curve or by manipulating the control points of the blended surface. 28 Advanced Modeling Utilities 29 Advanced Modeling Utilities 4. Purging Points (3ds Max: vertex weld)  Purging utilities are useful for automatically eliminating excessive vertices in complex 3-D models.  This is usually done by identifying pairs of points that are too close to each other – based on a minimum distance – and deleting one of them.  Manual point-editing is often used in conjunction with purging utilities to fine-tune and adjust the distribution of points in the model. 30 Advanced Modeling Utilities 5. Deformed and Randomized Surfaces  The technique of deformation with splines and patches consists of using a spline or a patch as the agent that deforms the object that is associated with them (Fig 5.4.5)  Refers to “Simple Deformations.pdf”  Interesting deformations can be achieved by offsetting the vertices of 3-D objects with functions or random values  The technique of random distortion is especially useful for creating models of terrains that have so many irregularities that it would be difficult to model them with other techniques. (Fig 5.4.4)  Random distortion can also be used to animate the effect of shaking by animating the displacement of points back and forth through time. 31 Randomized Surfaces 3ds Max Modeling Tips - Using the Noise Modifier https://youtu.be/fa0387BkBUM