CS408 Animation Software Design Sample Exam Questions (Second Half)

Transcription

1 CS408 Animation Software Design Sample Exam Questions (Second Half) 42. NEW QUESTION Consider the starting position of the following objects, and their desired end position and orientation as part of the pictured hierarchical model. You may make the following assumptions: All objects are perfectly symmetrical. Objects are defined with their point of rotation at the origin. Objects are defined in their default neutral orientation relative to their parent limb. No scaling of any object is required (all local models have the correct final sizes). Starting Positions: Hierarchical Object Tree:

2 Final Configuration of Object (picture may not be to scale): (Hint imagine that the point half way along the top of object 0 is labelled (15, 18); sorry no time to change diagram now.)

3 Given this information, perform the following: (a) determine all the transformations that are required for the object tree (specify the angle of rotation for R transformations and the 2D translation for T transformations). (b) not required for : construct all of the matrices that appear in the object tree (c) show the multiplication of transformations that is needed to to transform the point (5.0, 2.2) on object 2.1 to world coordinates (d) not required for : use the appropriate matrices to calculate the transformation of the point (5.0, 2.2) on object 2.1 to world coordinates. (Hint: for parts (a) and (b), you will need 9 transformations/matrices; for part (c) and (d) you will need (matrix) multiplication with the vector (5.0, 2.2) on the right hand side; for parts (c) and (d), (5.0, 2.2) is in the location coordinate system of object Need more questions on Hierarchical Kinematic Models b + c a 47. (15 marks) NEW QUESTION Use the cosine rule ( cos A = ) to 2bc determine the joint angles needed to solve the following simple inverse kinematics problem. Be sure to check that the desired position is within reach first Need more questions on Inverse Kinematics PARTICLE SYSTEMS 58. (4 marks) List four types of phenomena that might be modeled in an animation using particle systems. Describe the particles used in each case. 59. (10 marks) Describe the basic model for a particle system and its five major components. 60. (4 marks) What is a stochastic process? Describe one use of a stochastic process in an animation system.

4 61. (4 marks) Identify four properties that particles might have in a particle system. 62. (20 marks) Using particles with velocity and three other properties, write pseudocode or a code segment to generate 2 t particles at time step t. Have all four properties change in each time step. Use comments to describe how each property is changing. 63. (20 marks) Using code or pseudo-code write a function/constructor to initialize a particle system and another function to update it for the passing of time. The particle system should be initialized with a mean of 100 particles, uniformly distributed in the range 80 to 120 particles. The lifetimes of the particles should be a mean of 6 seconds, uniformly distributed in the range 4 to 8 seconds. The initial positions should be chosen randomly in the rectangular volume from (-100, -100, -100) to (100, 100, 100). The velocity of a particle should be initialized with a mean velocity of 10 units per second, uniformly distributed from 5 to 15 units per second. If a particle disappears, it should be replaced immediately with a new particle with random properties. Assume a random number generator function is available. Describe the range and type of values it returns. Hint for exam preparation: see ParticleGenerator code on Notes website : IGNORE QUESTIONS 64 TO 70 FLOCKING 64. (4 marks) What is emergent behavior? Describe one place in an animation system where emergent behavior might occur. 65. (5 marks) What are the two main tendencies that in flock behavior? Describe a method for resolving conflicts between these two tendencies. 66. (5 marks) Explain local control versus global control with respect to modeling flock behavior. Give one advantage of each type of control. 67. (4 marks) Flocking behavior has been described as needing an O(n 2 ) algorithm. Give an example of a phenomenon relevant to flocking that requires an O(n 2 ) algorithm and explain why. 70. (3 marks) Explain the issues related to splitting and rejoining when discussing flock behavior. PLANTS 71. (8 marks) Given the following L-system, give the current string and draw the corresponding tree for each of the first 3 iterations. Axiom: A Rules: A FF F F[+F][-F]F Angle: 45

5 72B. Given the following L-system, give the current string and draw the corresponding tree for each of the first 2 iterations (not including the axiom). Hint for exam preparation: do not draw just the F. The first drawing is after one substitution. Axiom: F Rules: F F[+F]F-F Angle: 30 72C. Give a bracketed L-system that will produce the three plants shown below in its first three iterations. The first two branches leave the trunk at a 30 angle from the trunk Hint for exam preparation: specify the axiom, the rule(s), and the angle. Hint for exam preparation: By default, assume the vocabulary includes at least F = forward while drawing, + = turn left, - = turn right, f = forward without drawing. Hint: write down a possible grammar and then draw the first two iterations. 72D. Given the following stochastic L-system, give the current string and draw the corresponding tree for each of the first 2 iterations (not including the axiom). Assume on the first iteration the first rule is always selected and on the second iteration the second rule is always selected. Axiom: F Rules: F 0.5 F[+F]F F 0.5 F[-F]F Angle: 45 72E. Given the following timed L-system, give the current string for each of the first 10 iterations. Assume that only the F terminal symbol causes drawing to occur and that nonterminal symbols such as A, B, C, and D are simply skipped when drawing. Draw the first two different trees that appear and state which iteration they appear for.

6 Axiom: A Rules: A B B BC C -FD D +F Angle: 45 [t+3] [t+2] [t+2] GAS SIMULATON 73. (6 marks) Identify and briefly describe the three main approaches used to model gas? 74. (10 marks) Explain how the grid-based method of animating gases works. Make sure to include a description of the circumstances under which the density of a cell is increased and decreased. How is the appearance of a cell determined? 74B (10 marks) Give code or pseudo-code to show how the outflow of gases works in a 2D grid-based animation model. Draw a diagram and mark it with the variables used for a typical cell of gases flowing to the maximum number of possible output cells. 74C (6 marks) Draw a diagram showing how several different input cells could all flow to the same output cell. Indicate the main properties of each cell. Hint for exam preparation: the main properties are mass and velocity. 74D (10 marks) Give code or pseudo-code to show how the inflow of gases works in a 2D grid-based animation model. Make sure that you show how the contents of one new cell is updated when gas from an old cell is added. Draw a diagram showing how several different input cells could all flow to the same output cell. 75. NEED SOME QUESTIONS ON SAND : IGNORE THE REMAINDER OF THE QUESTIONS 80. (5 marks) Explain how to use one or more particle systems to create the appearance of a fire. 83. (4 marks) Discuss the advantages and disadvantages of polygons versus splines for facial animation. 84. (5 marks) How is a subdivision surface model created? 85. (6 marks) Describe the three different ways of creating a model for facial animation. 86. (4 marks) What are phonemes and visemes and what are their roles in facial animation?

7 87. (5 marks) What is FACS? Discuss its advantages and disadvantages for facial animation. 88. (9 marks) Compare and contrast direct parameterized models, pseudomusclebased models, and muscle models. 89. (8 marks) Discuss Parke s model in depth. 90. (8 marks) What is involved in rotating the jaw (corresponding to changing parameter #4) in Parke s model? Use a diagram.