Computer Science 455
Instructor: R. P. Burton
Fifth Quiz
November 8-9, 2004
Name _________________________________________ Score ____________/39
1. What is a principal advantage of an orthographic projection?
a. It produces realistic views
b. It is computationally easy
c. (both (a) and (b))
(b)
2. A ______ projection looks more realistic; a ______ projection is more accurate.
a. cavalier, cavalier
b. cavalier, cabinet
c. cabinet, cavalier
d. cabinet, cabinet
(c)
3. A perspective projection is division by the depth of _____
a. the view plane
b. the far plane
c. the average of all points
d. the average of all visible points
e. each point
(e)
4. A polyhedron has at most ______ vanishing point(s).
a. one
b. two
c. three
d. more than 3
(d)
5. Suppose your direction of view is perpendicular to a tall building. What makes
the building taper (in y) when the building is projected perspectively onto a (tall)
display surface?
a. division by y
b. division by z
c. (it doesn't taper in y as it is projected)
(c)
6. The viewing transformation ____ establish the field of vision.
a. does
b. does not
(b)
7. The viewing transformation can be derived by finding a transformation which
superimposes the _______ onto the _______.
a. viewer's coordinate frame, world coordinate frame
b. world coordinate frame, viewer's coordinate frame
(a)
8. For all practical purposes, a view volume is
a. finite
b. infinite
(a)
9. What is the purpose for establishing a "near plane" and a "far plane?"
a. to take cross sections
b. to accommodate the finite precision of the computer
c. both (a) and (b)
d. neither (a) nor (b)
(c)
10. All of the following can be realized as a practical (and usable) matrix transformation
EXCEPT
a. parallel orthographic projection
b. parallel oblique projection
c. perspective orthographic projection
d. (no exceptions here)
(c)
11. If the projection is perspective oblique, the best place to clip is
a. before the transformation to viewing coordinates
b. after the transformation to viewing coordinates
c. after projection to the window
(b)
12. All of the following can be converted to a regular parallelepiped EXCEPT the
view volume for
a. parallel orthographic projection
b. parallel oblique projection
c. perspective orthographic projection
d. perspective oblique projection
e. (no exceptions here)
(e)
13. Two curve sections with matching tangents at the joint exhibit ___-order
continuity.
a. zero
b. first
c. second
(b)
14. If a curve interpolates a collection of control points, then
a. it passes through the all the control points.
b. it passes through at least the first and last control points.
c. its shape is determined by the control points, but in need not pass through any of them.
(a)
15. If you have a collection of control points, each with an (x,y,z) coordinate triplet,
then the blending functions _____ for the x coordinates, the y coordinates, and the
z coordinates.
a. are the same
b. are different in general
(a)
16. The convex hull for a collection of (Bezier) control points
a. is the polygon passing through all the control points, in order.
b. is the polygon passing through all the control points, but not necessarily in order.
c. contains all the control points.
(c)
17. Bezier curves cannot be closed.
a. true
b. false
(b)
18. What is the maximum degree of a Bezier curve determined by 10 control points?
a. 9
b. 10
c. 11
d. 20
e. (Bezier curves are never defined by more than 4 control points.)
(a)
19. To produce 6 Bezier curves, each defined by four control points, you need ____
blending functions.
a. 4
b. 6
c. 10
d. 24
(a)
20. B-spline curves
a. are the same thing as Bezier curves, just with an American name
b. are similar to Bezier curves, but with a different blending function
c. are similar to Bezier curves, use the same blending function as Bezier curves, but allow a larger range for the parameter
(b)
21. What price do you typically pay for interpolation?
a. You lose the convex hull property
b. You lose the variation diminishing property
c. You lose both (a) and (b)
d. You lose neither (a) nor (b)
(c)
22. If you have a mesh of 4 x 3 control points for a Bezier surface, then the surface is
approximated by
a. 3 x 2 patches
b. 4 x 3 patches
c. 5 x 4 patches
d. 400 x 300 patches
e. any of the above that you choose
(e)
23. Suppose a rectangle is swept translationally to produce a 3D solid. How many
vertices are needed to describe the rectangle?
a. 4
b. 8
c. some multiple of 4 greater than 8
(b)
24. During a sweep, a polygonal shape can undergo all of the following
transformations EXCEPT
a. rotation
b. scaling
c. reflection
d. shearing
e. (no exceptions here)
(e)
25. Ray-casting is appropriate for all of the following constructive solid geometry
techniques EXCEPT
a. union
b. Intersection
c. difference
d. (no exceptions here)
(d)
26. Which of the following best describes the octants in an octree?
a. all are the same size
b. all are the same shape
c. both (a) and (b)
(b)
27. An octree representation for a 1000 x 1000 display takes about ____ times as much
storage as a quadtree representation for the same display.
a. 1.5
b. 2
c. 10
d. 100
e. 1000
(e)
28. Hidden surfaces should be determined relative to
a. world coordinates
b. viewing coordinates
c. normalized viewing coordinates
(c)
29. The Roberts hidden-line algorithm is a(n) _____-space method.
a. image
b. object
c. hybrid image/object
(b)
30. For a closed, convex polyhedron, the simplest test for a back face requires
consideration of
a. the sign of the (value of the) planar equation when the viewpoint is substituted into that equation
b. the dot product of the normal vector and the view vector
c. the sign of one of the components of the normal vector
(c)
31. The depth-buffer algorithm conveniently facilitates all of the following EXCEPT
a. processing of surfaces in any order
b. interpenetrating surfaces
c. transparent surfaces
d. (no exceptions here)
(c)
32. The z-buffer algorithm requires
a. consideration of every pixel on every surface
b. consideration only of the intersection of each scan line with each surface
c. consideration only of the vertices (and planar equation) of each surface
(a)
33. The scan-line visible surface method processes
a. one entire polygon at a time
b. one entire scan line at a time
c. parts of a scan line, one at a time
(c)
34. The depth-sorting method is a(n) _____-space method.
a. image
b. object
c. hybrid image/object
(c)
35. Since polygons need not be parallel to the viewing surface, it is not reasonable to
attempt to sort them by depth.
a. true
b. false
(b)
36. It is _____ for two surfaces to overlap in x, y, and z and not have all the vertices
of one polygon on one side of the plane of another polygon, or vice versa.
a. possible
b. impossible
(a)
37. The area subdivision algorithm anticipates
a. a BSP tree
b. a quadtree
c. an octree
d. a linear list
(b)
38. Which of the following is NOT "simple enough" for the area subdivision
algorithm (meaning no further subdivision is required)?
a. only one surface surrounds the area
b. two surfaces intersect the area, but do not intersect each other
c. no surface intersects the area
d. the area surrounds exactly one surface
e. all are "simple enough"
(b)
39. In general, hidden-line algorithms run much faster than hidden surface algorithms.
a. true
b. false
(b)