Computer Science 455

Instructor: R. P. Burton

Seventh Quiz

April 14-15, 2008

Name _________________________________________ Score ____________/xx

1. The colors around the top of the HSV hexacone are, in order, red, orange, yellow, green, blue, indigo, and violet.
1. true
2. false

(b)

2. Where are the pure hues in or on the HSV hexacone?
1. around the top
2. on the top surface
3. down the outside
4. on the inside
5. (there are no pure hues in or on the HSV hexacone)

(a)

3. Where are the tones in or on the HSV hexacone?
1. around the top
2. on the top surface
3. down the outside
4. on the inside
5. (there are no tones in or on the HSV hexacone)

(d)

4. The HLS color model contains ____ the HSV color model.
1. the same colors as
2. different colors relative to

(a)

5. Which of the following color selection techniques is best?
1. Select roughly equally from equivalent, nonintersecting volumes of the RGB or CMY color cubes
2. Select roughly equally from each face of the RGB or CMY color cubes
3. Select at roughly equal intervals along a straight line in or on the RGB or CMY color cube
4. (each of these techniques is equivalently good or bad)

(c)

6. Raytracing attempts to simulate how a camera records a physical scene onto film
1. true
2. false

(a)

7. In the raytracing model, a pixel on the display corresponds to a region of the film plane.
1. true
2. false

(a)

8. Why trace rays backwards rather than forwards?
1. to mimic the flow of electrons (which actually travel in a reverse direction)
2. to mimic the flow of photons (which actually travel in a reverse direction)
3. to reduce the number of rays that need to be traced
4. (rays are not traced backwards; they are traced forwards!)

(c)

9. An illumination ray can split into a reflection ray and a transparency ray when it strikes a surface. A reflection ray ____ after it strikes another surface
1. remains a reflection ray
2. becomes a pixel ray
3. can split into a reflection ray and a transparency ray

(c)

10. Pick an appropriate height range for a ray tree:
1. 0 or 1
2. 2 to 10
3. 11 to 100
4. 100 to °.

(b)

11. Why do wheel spokes sometimes appear to be turning backwards when the associated vehicle is moving forward?
1. the discrete sampling nature of the human eye
2. the discrete nature of the illumination information reaching the eye
3. because the owners of such vehicles have purchased special wheel covers
4. because the recording was ÒdoctoredÓ

(b)

12. How many rays must be sent through each pixel to guarantee than no objects are missed?
1. just 1
2. 5, the center and the corners
3. 9
4. 13
5. (itÕs never guaranteed)

(e)

13. Stochastic ray tracing
1. shoots rays through all pixel centers and corners
2. continues to send rays until no objects are missed
3. sends rays in randomized directions

(c)

14. Techniques which find the intersection of a ray with an object demonstrate that mathematically elegant techniques also are ______ computationally efficient techniques.
1. virtually always
2. sometimes
3. almost never

(b)

15. For ray-sphere intersection, the ray is represented ______ and the sphere is represented _____.
1. implicitly, explicitly
2. explicitly, parametrically
3. parametrically, implicitly
4. implicitly, implicitly
5. explicitly, explicitly

(c)

16. A ray always intersects a sphere in no points or in two points (which may be coincident points).
1. true
2. false

(b)

17. Every point on a sphereÕs exterior surface has a distinct normal (ignoring machine precision for the moment).
1. true
2. false

(a)

18. The advantages of the geometric solution to the ray-sphere intersection problem, relative to the algebraic solution can be characterized as simple geometric checks to avoid calculations.
1. true
2. false

(a)

19. A ray is guaranteed to hit a sphere (assuming no intervening object) unless
1. the ray starts inside the sphere
2. the ray passes within one Òsphere radiusÓ of the sphereÕs center
3. the ray starts outside the sphere and points away
4. (no exceptions here)

(c)

20. What is spherical inverse mapping?
1. determining a point (if it exists) on the surface of a sphere struck by a ray
2. mapping a longitude and latitude onto the surface of a sphere
3. mapping from a point on the surface of a sphere to a longitude and latitude
4. correcting the image inversion caused by a pin hole camera and by a raytracing method which emulates the pin hole camera

(c)

21. Given a ray, a plane not parallel to the ray, and no intervening objects, the ray is guaranteed to intersect the plane for some value of t > 0.
1. true
2. false

(b)

22. For ray-plane intersection, the ray is represented ______ and the plane is represented _____.
1. implicitly, explicitly
2. explicitly, parametrically
3. parametrically, implicitly
4. implicitly, implicitly
5. explicitly, explicitly

(c)

23. If a ray intersects a plane, to determine if a ray intersects a polygon in the plane, conventional Òinside/outsideÓ tests can be used, independent of the orientation of the plane.
1. true
2. false

(a)

24. For projection purposes (in the context of ray-polygon intersection), if the equation of the plane containing the polygon is 3x Ð 5y + 4z Ð 7 = 0, to which principal plane should the projection occur?
1. xy
2. yz
3. zx

(c)

25. Mapping from one convex quadrilateral (perhaps containing a pattern) onto another convex quadrilateral amounts to
1. nothing more than a scaling of the source to the destination
2. nothing more than a scaling of the destination to the source
3. more than a scaling

(c)

26. Triangle inverse mapping can be done using the quadrilateral inverse mapping techniques.
1. true
2. false

(a)

27. Given a collection of polygons defined by their vertices and a collection of spheres defined by their centers and radii, in general it would be
1. more efficient to find a bounding box
2. more efficient to find a bounding sphere
3. equivalently efficient to find a bounding box or a bounding sphere

(a)

28. Using the slab method for ray-box intersection, there must be a positive value of t for which the ray is inside _____ slab(s) in order for the ray to intersect the box.
1. one
2. two
3. three
4. more than three

(c)

29. The techniques for finding the intersection of a ray with a cylinder, cone, ellipsoid, paraboloid, or hyperboloid are fundamentally _________ the techniques for finding the intersection of a ray with a sphere or plane.
1. the same as
2. different from

(a)

30. A common inverse mapping for a circle amounts to converting from Cartesian to polar coordinates.
1. true
2. false

(a)

31. How much distortion is anticipated in an inverse mapping for a cylinder?
1. probably just a scaling
2. probably more than a scaling

(a)

32. How much distortion is anticipated in an inverse mapping for a cone?
1. probably just a scaling
2. probably more than a scaling

(b)

33. Ray tracing generally assumes the _____ model of light.
1. particle
2. wave

(a)

34. The angle of refraction depends on the wavelength of the incoming light.
1. true
2. false

(a)

35. White light shines on a copper kettle. The highlight on the copper kettle is
1. white
2. copper-colored

(b)

36. Fractal geometry dates back to
1. the ancient Egyptians
2. the ancient Greeks
3. the turn of the previous century (i.e. 1900)
4. approximately the time of your birth
5. the current millennium

(d)

37. The application of fractals is limited almost exclusively to the rendering of phenomena using computer graphics.
1. true
2. false

(b)

38. What is the fractal dimension of a plot of the Dow Jones Industrial average since 2001?
1. less than 1
2. 1
3. more than 1 but less than 2
4. 2
5. more than 2 but less than 3
6. infinite

(c)

39. Displacements (as in random point displacement methods) should reflect all of the following EXCEPT
1. the displacement should be proportional to the length of the line segment
2. an average displacement of zero
3. equal likelihood of any point along the line segment being displaced
4. (no exceptions here)

(c)

40. If the original quadrilateral triangle has length 3, what is the length of the ultimate von Koch snowflake curve
1. it remains 3
2. almost 6
3. almost 9
4. infinite

(d)

41. A magnified view of a section of the Koch snowflake curve would reveal the level (number of levels of recursion).
1. true
2. false

(b)

42. Pick the best statement: The number of craters on the moon of a particular area (i.e. the two-dimensional size of the crater) is
1. independent of the relative size of the area
2. proportional to the size of the area
3. inversely proportional to the area

(c)

43. If you take a sphere, divide it through the center in a random direction and displace the hemispheres relative to one another, and repeat this process on the evolving shape perhaps 10,000 times, elevations and depressions on the resulting surface
1. will be fairly uniformly distributed across the surface of the sphere
2. will form ÒcontinentsÓ and Òocean bottomsÓ

(b)

44. Which of the following would be an appropriate fractal dimension for a coastline or for a plot of the Dow Jones Industrial average?
1. 1.2
2. 1.5
3. 1.8

(a)

45. What is the source of 1/f^beta noise?
1. nuclear resonance
2. solar flares
3. the maximum cell division/disintegration rate
4. heaven may know; we donÕt

(d)

46. To compute a Julia set using the inverse iteration method and polar coordinates
1. take the positive square root of r and half the angle
2. take the positive square root of r and half the angle + ¹
3. either (a) or (b), as long as you are consistent
4. either (a) or (b), with no need for consistency in the choice

(d)

47. Even the casual passer-by would be able to distinguish fractal music from the music of a foreign culture.
1. true
2. false

(b)