Past Midterm and Exam Questions (PDF) - Student.cs.uwaterloo.ca ...

66 CS488/688 Introduction to Computer Graphics
20 Short Answer
1. Suppose you are using Euler angle rotations to manipulate the orientation of an object by
rotating around the coordinate axes. Suddenly, you encounter Gimbal lock. Describe the
effect of Gimbal lock and state how you would “break the lock”.
2. Photon mapping traces rays from a light source into the scene in order to achieve forward ray
tracing affects such as caustics. One forward effect of light is the separation of white light into
a rainbow of colours by shining the white light through a prism due to different wavelengths
refracting different amounts. What difficulties would you encounter in trying to reproduce
this effect with photon mapping?
3. What is the mathematical difficulty associated with using piecewise cubic splines for animating
the path of a moving object at a constant speed?
4. Give one advantage and one disadvantage of using motion capture to create animation.
5. Name and describe two different styles of non-photorealistic rendering.
6. Name and describe two objectionable visual artifacts that are caused by aliasing.
7. Name and describe two advanced visual phenomena, other than antialiasing, that can be
computed using Monte Carlo techniques (that is, by averaging random samples).
8. The Blinn-Phong lighting model uses the half-vector ⃗ h = (⃗v + ⃗ l)/|⃗v + ⃗ l| and the expression
(⃗n ·⃗h) k in its specular term. Describe the motivation behind the use of the half-vector in this
lighting model.
9. Give at least one situation where a bounding box hierarchy would would decrease the performance
of a raytracer.
10. Name one visual effect that can be rendered with a photon mapping algorithm but not a
raytracer, and describe why a raytracer cannot render this effect.
11. How do we get shadows in ray traced images?
12. Physically-based lighting models should not emit more energy than they absorb. However,
some common lighting models, such as the Phong lighting model, do not satisfy this property.
Why can this be a problem for global illumination algorithms?
13. What does it mean for a polygon to be convex?
14. Is the intersection of two convex polygons necessarily convex? Why or why not?
15. Explain what homogeneous coordinates are and why we use them.
16. Explain what metamers are and say briefly what their existence implies about our perception
of colour.
17. Here are four steps in a typical 3D graphics pipeline:
(a) Apply a perspective projection