Computer Science 455
Quiz 5
March 16-17, 2009
Instructor: R. P. Burton
1. Thicker/darker lines are perceived by all viewers as being closer than thinner/lighter lines.
a. true
b. false
(b)
2. Dashed lines are perceived by all viewers as being farther away than solid lines
a. true
b. false
(a)
3. Which is the better choice for lines on the back side of a solid object?
a. red
b. blue
c. (it doesn’t make any difference)
(b)
4. In a parallel projection, all of the following except ______ must be true
a. points project to the viewing surface along parallel lines
b. points project orthogonally to the viewing surface
c. the viewpoint is infinitely far away
d. (no exceptions here)
(b)
5. In a perspective projection all of the following except ______ must be true.
a. points project to the viewing surface along lines which typically are not parallel
b. all points project obliquely to the viewing surface
c. the viewpoint is not infinitely far away
d. (no exceptions here)
(b)
6. All of the following are common parallel, orthographic projections except
a. front elevations
b. side elevations
c. plan views
d. projections not parallel to a principal axis
e. (no exceptions here)
(e)
7. A parallel projection, parallel to a principal axis, can be represented in matrix form using the identity matrix with one of the elements changed to a zero.
a. true
b. false
(a)
8. An oblique parallel projection can be represented in a functionally effective matrix form.
a. true
b. false
(a)
9. _________ projection(s) produce(s) results which preserve measurements in a usable way.
a. A cavalier
b. A cabinet
c. Both (a) and (b)
(c)
10. A perspective projection can be represented in a functionally effective matrix form.
a. true
b. false
(b)
11. In what units should d, the distance of the viewer from the screen, be measured?
a. inches
b. pixels
c. world coordinates
(c)
12. Perspective is achieved by dividing by depth, but this is merely an approximation that does not work for long, narrow elements of the scene.
a. true
b. false
(b)
13. A scene can have not more than _____ vanishing points.
a. 2
b. 3
c. infinitely many
(c)
14. The viewing transformation is
a. Identical to the first several pieces of the transformation to rotate about an arbitrary axis
b. (a) + one more rotation
c. (a) + two more rotations
d. none of the above
(b)
15. A center of projection and a (probably rectangular) region of the display surface are sufficient to determine a view volume.
a. true
b. false
(a)
16. ______ can be achieved practically with matrix transformations.
a. Orthogonalization of an oblique view volume
b. Parallelization of a perspective view volume
c. Both (a) and (b)
(a)
17. What advantage(s) is/are there to orthogonalization of an oblique view volume?
a. none
b. easier clipping
c. more accurate projections
d. more freedom in choosing the viewpoint and viewing direction
e. (b) through (d)
(b)
18. What advantage(s) is/are there to near and far planes?
a. more precision
b. cross-sectioning
c. prevents some inversion
d. (all of the above)
(d)
19. All of the following techniques extend simply from 2D to 3D EXCEPT
a. Cohen Sutherland
b. Liang Barsky
c. Nicholl Lee Nicholl
d. (no exceptions here)
(c)
20. In general, points on a curve in 3D can be represented satisfactorily, and with arbitrary density, by finding functions f and g such that y = f(x) and z = g(x).
a. true
b. false
(b)
21. Hidden element removal is virtually a “brute force” activity. Each element must be considered individually, and relatively little can be done to increase the efficiency of the process.
a. true
b. false
(b)
22. Back-face removal takes care of approximately ____ of the faces in a typical scene.
a. 10%
b. 50%
c. 90%
(b)
23. A face can be determined to be a back face by considering, at a minimum,
a. the normal to the face
b. the value of the “C” component of the normal
c. the sign of the “C” component of the normal
(c)
24. Which group of algorithms is less likely to exploit the full precision with which the elements of the scene are defined?
a. object-space
b. image-space
c. (both are roughly equivalently likely)
(b)
25. Roberts’ algorithm is (or can be made) compatible with
a. parallel projection
b. perspective projection
c. both (a) and (b)
(c)
26. How does the depth-buffer method differ from the z-buffer method?
a. one is an image space method and the other is an object space method
b. one requires the surfaces to be sorted; the other does not
c. one requires a separate buffer; the other does not
d. all of the above
e. none of the above
(e)
27. For the depth-buffer method (and the z-buffer method), the calculation of the depth z of a surface of every position (x, y) requires a new division by C, the coefficient of z.
a. true
b. false
(b)
28. For the scan-line method, what is the maximum number of surfaces that can be active (i.e. “on”) at any one time?
a. one
b. two
c. more than two
(c)
29. Who of the following did NOT participate in developing the depth-sorting method?
a. Newell
b. Painter
c. Sancha
d. (no exceptions here)
(b)
30. Surfaces which are not perpendicular to the viewing direction cannot be sorted since they may overlap.
a. true
b. false
(b)
31. Using the depth-sorting method, it can be accurate to treat the surface which is closest to the viewer as being furthest from the viewer, even when there are several other surfaces and when all surfaces are visible.
a. true
b. false
(a)
32. The depth-sorting method sometimes requires the subdivision of surfaces.
a. true
b. false
(a)
33. The area subdivision algorithm may require subdivision
a. if all faces are outside the area
b. when only one surface intersects the area
c. when one surface surrounds the area
d. (none of these requires subdivision)
(c)
34. How many “practical” views are there of an octree?
a. one
b. more than one, but less than ten
c. ten or more, all equivalently practical
(b)
35. Which generally should be done first?
a. projection into the normalized view volume
b. hidden surface removal
c. (it doesn’t make much difference)
(a)
36. How “big” is a “point” light source?
a. infinitesimally small
b. a pixel or less in size
c. small compared to the objects in the scene
(c)
37. What is/are the source(s) of diffuse reflection?
a. light from point light sources
b. light from ambient light sources
c. light from light-reflecting surfaces
d. any of the above
e. none of the above
(d)
38. The intensity of ambient light reflected from a surface is independent of the angle of illumination.
a. true
b. false
(a)
39. The intensity of diffuse reflection is independent of the distance between the surface and the light source(s).
a. true
b. false
(b)
40. Specular reflections are
a. white (i.e. independent of the color of the surface and the color of the incident light)
b. usually the color of the surface
c. usually the color of the incident light
(c)
41. Two metals of identical colors (e.g. brass and gold) cannot be made to appear different in a graphic presentation without altering the base (RGB) color of one of the metals.
a. true
b. false
(b)
42. Which is more difficult to simulate?
a. translucency
b. transparency
c. (they represent the same phenomenon)
(a)
43. Why do the bricks on the interior of the classroom manifest texture?
a. the paint didn’t penetrate
b. the paint penetrated, but oxidized more on the surface than on the interiors of the indentations
c. light doesn’t strike the microsurfaces uniformily
(c)
44. How should texture NOT be achieved?
a. micropolygonization
b. alteration of normals
c. alteration of reflection coefficients
d. (all are practical for achieving texture)
(a)
45. How should surface patterns NOT be achieved?
a. mapping onto an object
b. placement of polygons infinitesimally close to the surface
c. (both are acceptable for achieving surface patterns)
(b)
46. Without consideration for the physics, how can a shadow be modeled?
a. by darkening the color of (the portion of) an object in “the shadow”
b. by refraining from adding light to (the portion of) an object “in the shadow”
c. either (a) or (b)
(c)
47. Hidden-element techniques are applicable to the calculation of shadows.
a. true
b. false
(a)