Computer Science 455
Quiz 4
March 2-3, 2009
Instructor: R. P. Burton
1. Translation, scaling, and reflection in 3D are straightforward extensions of the corresponding 2D transformations.
a. true
b. true except for translation
c. true except for scaling
d. true except for reflection
e. false
(a)
2. Translation, scaling, and reflection in 4D are straightforward extensions of the corresponding 3D transformations.
a. true
b. true except for translation
c. true except for scaling
d. true except for reflection
e. false
(a)
3. For counterclockwise rotation in 3D, the negative sign is consistently associated with the sine in the upper right corner of the “cos sin sin cos” quadrant.
a. true
b. false
(b)
4. In 3D, the basic translation matrix involves 3 translation factors, the basic scaling matrix involves 3 scaling factors, and the basic rotation matrix involves 3 sines and 3 consines.
a. true
b. false
(b)
5. Assume the x-axis points down, the z-axis points out, and the y-axis points right. To rotate clockwise about the x-axis, the negative sign on the sine should be in position _____. (assume that the upper-left corner is position (1,1))
a. (1,1)
b. (1,3)
c. (2,3)
d. (3,1)
e. (3,2)
(c)
6. In 2D, shearing is the scaling of one variable based on the value of another variable. In 3D, shearing is the scaling of one variable based on the
a. value of one of two other variables
b. value of either or both of two other variables
c. (neither (a) nor (b))
(b)
7. Rotation about a line in 3D can occur unless
a. the line is not a principal axis
b. the line is not parallel to a principal axis
c. the line does not pass through the origin
d. (no exceptions here)
(d)
8. How many transformation matrices are typically composed to rotate about an arbitrary line?
a. 3
b. 5
c. 7
d. 9
e. (none of the above)
(c)
9. The traditional window determines “what” will be seen, and the traditional viewport determines “where” it will be seen.
a. true
b. false
(a)
10. When the traditional viewport is enlarged in x, the contents of the viewport
a. enlarge in x
b. shrink in x
(a)
11. When the traditional window moves left, the contents of the viewport
a. move left
b. move right
(b)
12. The window-to-viewport transformation can be determined by finding a transformation that maps (a point on) the window onto (a corresponding point on) the viewport.
a. true
b. false
(b)
13. A point can be retained (as opposed to being clipped) if it’s x coordinate lies between the minimum and maximum x coordinates of the clipping region ___ it’s y coordinate lies between the minimum and maximum y coordinates of the clipping region.
a. and
b. (inclusive) or
c. (exclusive) or
(a)
14. One endpoint of a line segment lies above and to the right of the clipping region. The other endpoint lies below and to the left of the clipping region. The line segment ____ intersect the clipping region.
a. does
b. may
c. does not
(b)
15. One endpoint of a line segment lies above and to the right of the clipping region. The other endpoint lies above and to the left of the clipping region. The line segment ____ intersect the clipping region.
a. does
b. may
c. does not
(c)
16. The Cohen Sutherland line clipping algorithm first attempts a trivial acceptance of a line segment. If it cannot be accepted trivially, it is rejected.
a. true
b. false
(b)
17. Clipping generally is more efficient if done in __________ coordinates.
a. world
b. device
c. (it makes no difference)
(b)
18. Logical operations (such as AND, OR, XOR) can be used on line segment endpoint region codes by the Cohen Sutherland algorithm to determine trivial acceptability or trivial rejectability.
a. true
b. false
(a)
19. For the Liang Barsky algorithm, line segments are represented
a. by their endpoint region codes
b. explicitly
c. implicitly
d. parametrically
(d)
20. A person using the Liang Barksy algorithm and “minding his p’s and q’s” will be able to determine all of the following except
a. if a line segment is parallel to a window boundary
b. if an extended line segment proceeds from inside to outside (or outside to inside) an extended window boundary
c. the point of intersection of an extended window boundary with an extended line segment (if such an intersection exists)
d. (no exceptions here)
(d)
21. The Nicholl Lee Nicholl algorithm _______ intersections of line segments with window boundaries.
a. finds
b. can avoid needing to find
c. both (a) and (b)
(b)
22. In how many different types of regions can the endpoint of a line segment lie for the purposes of the Nicholl Lee Nicholl algorithm?
a. just one
b. three
c. nine
d. twenty-seven
(b)
23. To accommodate all possible locations for the endpoints of a line segment, the Nicholl Lee Nicholl algorithm must find the slopes of ____ lines from one endpoint through clipping window corners.
a. 1 x 4
b. 3 x 4
c. 9 x 4
d. infinitely many
(b)
24. The line algorithms discussed in class (Cohen Sutherland, Liang Barsky, Nicholl Lee Nicholl) are applicable to (and useful for) only windows whose edges are parallel to the principal axes (x and y).
a. true
b. false
(b)
25. If a polygon is rendered in outline form (i.e. only the border is presented), then the line clipping algorithms can be used satisfactorily for clipping such polygons.
a. true
b. false
(b)
26. A clipped set of n points results in a set of not more than n points. A clipped set of m line segments results in a set of not more than m line segments. A clipped set of p areas results in a set of not more than p areas.
a. true
b. false
(b)
27. The Sutherland Hodgman area clipping algorithm anticipates clipping against window boundaries
a. in counterclockwise order
b. in clockwise order
c. in any order at all
(c)
28. Which algorithm(s) always produce(s) correct results, even for concave polygons?
a. Sutherland Hodgman
b. Weiler Atherton
c. Both
d. Neither
(b)
29. For purposes of “all or nothing” string clipping, _______ of the bounding box can be clipped (i.e. processed by the clipper)
a. the major diagonal
b. the minor diagonal
c. either diagonal
d. both diagonals
e. (none of the above)
(c)
30. What is “exterior clipping”?
a. The attempt to trivially reject precedes the attempt to trivially accept, and then it proceeds as in conventional clipping.
b. The elements within the window are discarded
c. The window boundary is considered to be part of the window
(b)
31. Curve clipping can be achieved by
a. finding a parametric equation for the curve, and then determining the values of the parameter for which the curve is inside the clipping window
b. individually clipping the points that constitute the curve
c. individually clipping the line segments that approximate the curve
d. (any of the above)
(d)
32. Which variety of graphics applications is likely to require more sophistication?
a. analytic
b. synthetic
(b)
33. Why is computer graphics traditionally done in left-handed coordinates?
a. Because Ivan Sutherland was left-handed
b. So “z” points in
c. To permit normals to point out when vertices are selected in a counterclockwise manner
(b)
34. Virtually all graphics applications are done in Cartesian coordinates, even though the origin might be other than in the lower left corner.
a. true
b. false
(b)
35. ____ graphics presentations are on a 2D medium.
a. All
b. Almost all
c. About half of all
d. No
(b)
36. If you suffer from monocular vision, perception of depth is a lost cause (except in rare instances with extensive training).
a. true
b. false
(b)
37. The absence of lines which otherwise would be hidden unambiguously communicates front and back faces in a projection, at least for simple objects consisting of a few faces.
a. true
b. false
(b)
38. A point of view and viewing direction always exists so that a perspective projection and a parallel projection of the same 3D object yield identical results.
a. true
b. false
(b)
39. What is the minimum dimensionality of a hider in 2D?
a. 0
b. 1
c. 2
d. 3
(a)