Computer Science 455

Instructor: R. P. Burton

Fifth Quiz

March 14-15, 2005

Name _________________________________________ Score ____________/52

1. Pick the best technique for modeling a best friend’s face

   1. constructive solid geometry

   2. polygonal approximation

   3. fractals

   4. particle systems

   5. sweeping

(b)

2. Pick the best technique for modeling Mt. Timpanogos for a fly-by movie

   1. constructive solid geometry

   2. polygonal approximation

   3. fractals

   4. particle systems

   5. sweeping

(c)

3. Pick the best technique for modeling a fire on the west side of Mt. Timpanogos

   1. constructive solid geometry

   2. polygonal approximation

   3. fractals

   4. particle systems

   5. sweeping

(d)

4. Pick the best technique for modeling the gears inside a watch

   1. constructive solid geometry

   2. polygonal approximation

   3. fractals

   4. particle systems

   5. sweeping

(a)

5. Pick the best technique for modeling a curved, tapered rod

   1. constructive solid geometry

   2. polygonal approximation

   3. fractals

   4. particle systems

   5. sweeping

(e)

6. Which of the following is a quadric surface?

   1. an ellipse

   2. an ellipsoid

   3. a hyperellipsoid

   4. (all are quadric surface)

(b)

7. Which of the following is most likely to qualify as a “blobby” object?

   1. a basketball

   2. a medicine ball

   3. a bicep

   4. a chunk of snow frozen solid

(c)

8. Projection from 3D to 2D is a reversible transformation.

   1. true

   2. false

(b)

9. Brighter lines appear closer than fainter lines (assuming other characteristics are common to both sets of lines) to all users.

   1. true

   2. false

(b)

10. A line that is presented as a dashed line or as a colored line should not be referred to as a “hidden” line.

    1. true

    2. false

(b)

11. Parallel projection is preferable to perspective projection only because it is easier and less expensive to do.

    1. true

    2. false

(b)

12. In a parallel projection, the direction of projection is

    1. parallel to the screen

    2. perpendicular to the screen

    3. at almost any angle to the screen

(c)

13. It _____ possible to have a parallel, orthographic, axonometric, isometric projection.

    1. is

    2. is not

(a)

14. Which projection “looks” more realistic?

    1. cavalier

    2. cabinet

(b)

15. An image presented on a screen as a perspective projection is most realistic if the viewing coordinates are divided by

    1. the depths (z) of the corresponding points

    2. the distance to the corresponding point (which considers x, y, and z)

    3. the depths (z) and either x or y

(a)

16. Where MUST the origin of coordinates be in order to produce correct projections?

    1. at the eye

    2. at the center of the view plane

    3. either (a) or (b) works

(c)

17. Every set of parallel lines not parallel to the projection screen can produce a vanishing point.

    1. true

    2. false

(a)

18. Transforming from world coordinates to viewing coordinates is simply a special case of transforming from one coordinate system to another.

    1. true

    2. false

(a)

19. What is the shape of the view volume for parallel projection?

    1. a finite parallelepiped

    2. an infinite parallelepiped

    3. a finite frustum

    4. an infinite frustum

(b)

20. An oblique projection can be converted to an orthographic projection simply by shearing.

    1. true

    2. false

(a)

21. The sole purpose of near and far planes is to take cross sections (i.e. to eliminate some elements or parts of elements).

    1. true

    2. false

(b)

22. What is the shape of a normalized view volume? (pick the most specific, accurate answer)

    1. an infinite parallelepiped

    2. an infinite rectangular parallelepiped

    3. a finite parallelepiped

    4. a finite rectangular parallelepiped

    5. a cube

(e)

23. To convert from a perspective projection to an equivalent parallel projection,

    1. divide by depth

    2. (it can’t be done; there is no one-to-one correspondence)

(a)

24. All of the following extend easily to three dimensions except

    1. Cohen-Sutherland

    2. Liang & Barsky

    3. Nicholl Lee Nicholl

    4. (no exceptions here)

(c)

25. A parametric representation of a curve overcomes all of the following except

    1. multiple values of x for some values of y

    2. multiple values of y for some values of x

    3. self-intersection

    4. (no exceptions here)

(d)

26. Two curve sections with a common endpoint and common tangents at that endpoint exhibit ______ continuity.

    1. no

    2. zero-order

    3. first-order

    4. second-order

(c)

27. Parametric forms are suitable for curves, but not for surfaces (which extend in multiple dimensions).

    1. true

    2. false

(b)

28. All things considered, curves which _______ control points generally are preferred.

    1. approximate

    2. interpolate

(a)

29. Like the Bresenham formulation, the Bezier coordinate function is mathematically sound, but devoid of any obvious intuitive meaning.

    1. true

    2. false

(b)

30. Given 5 sets of 6 points, how many Bezier blending functions are needed?

    1. 4

    2. 5

    3. 6

    4. 7

    5. 30

(c)

31. If and only if the control points (taken in order) determine a convex polygon is there a convex hull for the corresponding Bezier curve.

    1. true

    2. false

(b)

32. Pick the most complete (and still true) of the following statements:

    1. A Bezier curve can be closed

    2. and the tangents at the point of closure can match.

(b)

33. Bezier curves exhibit _____ control; B-spline curves exhibit _____ control.

    1. local, local

    2. local, global

    3. global, local

    4. global, global

(c)

34. Pick the most complete (and still true) of the following statements:

    1. A B-spline curve can be closed

    2. and the tangents at the point of closure can match.

(b)

35. If Bezier techniques are used to model the surface of an automobile, it is impossible to change the shape of the hood without affecting the shape of the boot (the trunk).

    1. true

    2. false

(b)

36. If B-spline techniques are used to model the surface of an automobile, it is impossible to change the shape of the hood without affecting the shape of the boot (the trunk).

    1. true

    2. false

(b)

37. Ray casting is suitable for all of the following EXCEPT

    1. union

    2. intersection

    3. difference

    4. (no exceptions here)

(d)

38. To store information in an octree (assuming the same resolution in all directions) requires about ______ more memory than storing information in a quadtree.

    1. 50%

    2. 100%

    3. 200%

    4. n³-n² where n is the resolution in each direction

(d)

39. All of the following can occur during sweeping EXCEPT

    1. translation along a non-linear path

    2. rotation

    3. scaling

    4. shearing

    5. (no exceptions here)

(e)

40. Most contemporary hidden-element algorithms are _____-space algorithms.

    1. object

    2. image

(b)

41. For a scene composed of closed polyhedra, back-face elimination removes approximately _____ of the faces.

    1. 1/10

    2. 1/5

    3. ½

    4. ¾

    5. 90%

(c)

42. If the scene is represented in viewing coordinates, back-face removal requires (for each planar polygon)

    1. the planar coefficients

    2. the planar coefficients except D

    3. just one of the planar coefficients

    4. the sign of just one of the planar coefficients

(d)

43. The depth-buffer method ______ surfaces to be sorted before they are processed by the (remainder of the) algorithm.

    1. requires

    2. does not require

(b)

44. Calculating the depth of the second of two adjacent points (for the z-buffer algorithm) requires

    1. adding or subtracting a constant

    2. adding or subtracting the result of a division of constants unique to the adjacent point

    3. calculating planar coefficients for the adjacent point, and adding or subtracting the division of the planar coefficients

(a)

45. The scan-line method _____ surfaces to be sorted before they are processed by the (remainder of the) algorithm.

    1. requires

    2. does not require

(b)

46. What is the maximum number of surfaces that can be “on” for the purposes of the scan-line algorithm?

    1. one

    2. two

    3. unlimited

(c)

47. Since a polygon can have an arbitrary orientation (making it possible for polygons to overlap in x, y, and/or z), it is not possible to sort polygons by depth.

    1. true

    2. false

(b)

48. Suppose polygons can be ordered so that no two polygons overlap in z. If the polygons are scan-converted in order of decreasing depth, the resulting presentation will contain the visible surfaces (and visible portions of surfaces).

    1. true

    2. false

(a)

49. Suppose polygons can be ordered so that no two polygons overlap in x. If the polygons are scan-converted in ANY order, the resulting presentation will contain the visible surfaces (and visible portions of surfaces).

    1. true

    2. false

(a)

50. Which test is likely to be helpful for ordering polygons?

    1. Are all the vertices of one polygon further away than the plane of the other surface?

    2. Are all the vertices of the other surface closer than the plane of the one surface?

    3. (both (a) and (b) are helpful)

(c)

51. Painter’s algorithm sometimes requires dividing polygons, even when the polygons are planar.

    1. true

    2. false

(a)

52. Which of the following visible element techniques does not lend itself well to partially transparent surfaces?

    1. z-buffer

    2. scan-line

    3. depth-sorting

    4. (all lend themselves well to partially transparent surfaces)

(a)