Computer Science 455
Quiz 7
April 13-14, 2009
Instructor: R. P. Burton

1. Why are rays traced backwards from the eye to a light source?
        a. because the eye looks “outward,” toward the light
        b. because photons, like electrons, actually transport information by traveling in the opposite direction
        c. to reduce the number of rays that need to be traced
        d. they aren’t; rays are traced from a light source to the eye
(c)

2. Raytracing may involve all of the following EXCEPT
        a. pixel rays
        b. illumination rays
        c. reflection rays
        d. transparency rays
        e. (no exceptions here)
(e)

3. Sooner or later, any ray sent into a scene will reach a light source, though it may be after several “bounces”
        a. true
        b. false
(b)

4. Why do wheels sometimes appear to be turning backwards?
        a. Because the eye samples discretely
        b. Because the image is presented discretely
(b)

5. “Missing” small objects occasionally in an animation has a minimal impact on the quality of the visual presentation.
        a. true
        b. false
(b)

6. Which of the following guarantee(s) a correct image?
        a. supersampling
        b. adaptive supersampling
        c. both
        d. neither
(d)

7. Stochastic ray tracing
        a. sends a random number of rays through each pixel
        b. sends a fixed number of rays through each pixel
(b)

8. A ray tracing package may include all of the following except
        a. determining where to send rays
        b. finding the intersection of rays and objects
        c. reflecting and refracting rays
        d. combining rays appropriately to determine pixel colors
        e. (no exceptions here)
(e)

9. In the context of ray tracing, mathematical elegance ______ computational efficiency.
        a. goes hand in hand with
        b. sometimes is at odds with
(b)

10. A sphere in a raytacing context typically is
        a. approximated by several small polygons
        b. just the (one-sided) skin of the sphere
        c. a true, solid sphere
(c)

11. A sphere in a raytracing context typically is represented
        a. explicitly
        b. implicitly
        c. parametrically
(b)

12. The simple checks to avoid some calculations (such as determining if a ray is pointing away from a sphere) can be made
        a. in the algebraic solution
        b. in the geometric solution
        c. in both
(c)

13. The geometric approach ______________ the calculation of square roots.
        a. avoids
        b. postpones
(b)

14. A ray whose origin lies inside a sphere will always hit the sphere.
        a. true
        b. false
(a)

15. A ray may strike a sphere in all but ___ place(s).
        a. 0
        b. 1
        c. 2
        d. 3
        e. (no exceptions here)
(d)

16. The spherical inverse mapping problem may be stated as
        a. convert an intersection point on a sphere to a longitude and a latitude
        b. find a point on a sphere from which an incoming ray will be reflected toward a light source
        c. given the parametric equation for an outgoing ray and a point of intersection, finding the parametric equation for the incoming ray
(a)

17. A ray and a polygon may not intersect, but a ray always intersects the plane in which the polygon resides.
        a. true
        b. false
(b)

18. The algebraic solutions to the ray/sphere intersection problem and the ray/plane intersection problem take _______ approaches.
        a. the same basic
        b. fundamentally different
(a)

19. A solution to the ray/plane intersection problem is equivalent to a solution to the ray/polygon intersection problem.
        a. true
        b. false
(b)

20. If a ray intersects a polygon in 3D, it intersects any correct projection of that polygon in 2D.
        a. true
        b. false
(a)

21. An ideal projection of the ray/polygon intersection problem (from 3D to 2D) is along a principal axis determined by the planar coefficient with
        a. the smallest positive value
        b. the largest positive value
        c. the largest absolute value
        d. the smallest absolute value
        e. any negative value
(c)

22. The solution to the ray/box intersection problem is useful for
        a. scenes that have boxes in them
        b. eliminating collections of objects
        c. both (a) and (b)
(c)

23. In the context of the ray/box intersection solution, what is the volume of a slab?
        a. the same as the volume of the box
        b. the same as the volume of a bounding box around an aligned or nonaligned box
        c. smaller than the volume of the box
        d. infinite
(d)

24. The solution to the ray/quadric problem
        a. cannot be obtained for quadrics in general
        b. of necessity takes a different and much more difficult approach than any of the other approaches discussed previously
        c. can be obtained using techniques discussed previously
(c)

25. Inverse mapping for a circle is mostly a problem of converting from Cartesian to polar coordinates.
        a. true
        b. false
(a)

26. Which inverse mapping is most straightforward?
        a. to a circle
        b. to a cylinder
        c. to a cone
(b)

27. How do photons “bounce” off surfaces?
        a. the frequency of the photon is incompatible with the frequencies of the atoms that constitute the surface, causing the photon to be repelled
        b. the frequency of the photon is compatible with the frequency of at least one atom in at the point where the photon strikes the surface, causing it to be repelled
        c. it isn’t “bounced;” the photon is absorbed and another photon with a similar frequency is generated
(c)

28. What are metamers?
        a. surfaces which accept photons of one frequency and generate photons of (sometimes very different) frequencies
        b. two (or more) spectra which yield perceptibly equivalent colors
        c. complementary colors
(b)

29. What color is the highlight on a copper kettle?
        a. copper colored
        b. the color of the incident light
        c. a combination of (a) and (b)
(c)

30. Fractal geometry dates approximately to the time
        a. Lehi left Jerusalem
        b. of the Reformation
        c. of the Restoration
        d. to the time when the Priesthood was made available to all worthy male members of the Church
(d)

31. The applications of fractals are limited to computer graphics.
        a. true
        b. false
(b)

32. The complexity of a fractal is
        a. given as its fractal dimension
        b. given as the fractional part of its fractal dimension
        c. indicated by the length of the shortest program that can be used to produce it
(c)

33. What is the length of the California coastline?
        a. between 100 and 300 miles
        b. between 300 and 1000 miles
        c. more than 1000 miles
        d. it depends on how you measure it
(d)

34. What is the length of the perimeter of the Koch snowflake, assuming it starts with an equilateral triangle with edges of length 1 each.
        a. between 3 and 6
        b. between 6 and 12
        c. more than 12
(c)

35. Why are fractal curves often generated with functions in the complex plane?
        a. to distinguish the x coordinate from the y coordinate
        b. because fractals have a real part and an imaginary part
        c. to map 3 dimensions onto 2 dimensions
(a)

36. The visual realism of shapes resulting from the random displacement method typically increases EXCEPT when
        a. the average displacement is zero
        b. the likelihood of a point being displaced falls off with distance from the midpoint
        c. the displacement is proportional to the length of the edge
        d. the number of recursive applications of the procedure is maximized
        e. (no exceptions here)
(e)

37. How does the fractal dimension compare to the Euclidean dimension?
        a. it is one greater
        b. it is fractionally greater
        c. they are unrelated
(b)

38. How does the number of big craters on the moon compare with the number of small craters?
        a. more little craters
        b. about the same
        c. more big craters
(a)

39. If you take a sphere and (iteratively) randomly slice through the center, displacing the hemispheres relative to each other, then after 10,000 iterations or so,
        a. you have pretty much uniformly distributed high spots and low spots
        b. distinct continents will form
        c. it’s impossible to predict what you will get in terms of distributions
(b)

40. What is the source of 1/fbeta noise?
        a. radiation pulsing from the sun
        b. radiation pulsing from outside our galaxy
        c. nobody knows
(c)

41. Mathematical expertise beyond the freshman level is needed to generate fractals.
        a. true
        b. false
(b)

42. Which of the following does not have a stable orbit?
        a. sqrt(x)
        b. sin(x) (x measured in radians)
        c. cos(x) (x measured in radians)
        d. (all have stable orbits)
        e. (none have stable orbits)
(d)

43. What is inverse iteration (for generating fractals)?
        a. starting with the fully specified fractal and reducing its complexity to something that can be rendered by computer
        b. taking square roots instead of squaring
        c. decrementing instead of incrementing in the for or while loop
(b)

44. Why are the Julia sets often painted black on the interior, but with all sorts of color bands around the outside?
        a. Because the Julia set consists of the border and the interior
        b. Because nothing on the interior is part of the Julia set
        c. Because points on the interior never escape
(c)

45. What is the relationship between the Mandelbrot set and the Julia sets?
        a. The Mandelbrot set is a Julia set
        b. The Mandelbrot set is a dictionary to the Julia sets
        c. There is no relationship; one was developed by Julia and the other by Mandelbrot
(b)