Computer Science 455

Instructor: R. P. Burton

Fifth Quiz

March 20-21, 2006

Name _________________________________________ Score ____________/46

1. Given 5 sets of control points (each with 4 control points), how many blending functions need to be determined?

   1. 4

   2. 5

   3. 9

   4. 20

(a)

2. Every Bezier curve has a convex hull?

   1. true

   2. true unless the (sequence of) control points form(s) a concavity

   3. false

(a)

3. What is the implication of multiple co-positional control points?

   1. the Bezier properties no longer can be guaranteed

   2. that position exerts a relatively strong influence on the shape of the curve

   3. none; it’s like putting the same element into a set more than once

(b)

4. What is the degree of a Bezier polynomial determined for 10 control points?

   1. 3

   2. at most 9

   3. at least 9

   4. at most 10

   5. at least 10

   6. more than 10

(b)

5. Renumbering the control points (for example, point 4 is called point 2 and point 2 is called point 4) ___________ change the shape of the Bezier curve.

   1. does

   2. does not

(a)

6. When Bezier curves are pieced together, ______ continuity can be achieved at the joint.

   1. no

   2. zero order

   3. first order

(c)

7. B-splines differ from Bezier curves in

   1. how control points are specified

   2. the blending functions

   3. how the control points and the blending functions are combined

   4. (all of the above)

(b)

8. A change to a B-spline control point affects _____ of the associated B-spline curve.

   1. some

   2. all

(a)

9. The “convex hull / variation diminishing property” is typically associated with curves which _______ control points.

   1. approximate

   2. interpolate

(a)

10. An n x m mesh of control points for a Bezier surface produces _____ (polygonal) surface patches.

    1. n-1 x m-1

    2. n x m

    3. m+1 x n+1

    4. (any of the above, and lots of other combinations, too)

(d)

11. What is the minimum dimensionality of a “hider” in 6 dimensions?

    1. 2

    2. 3

    3. 4

    4. 5

    5. 6

    6. 7

(d)

12. A quadrilateral swept translationally produces a(n efficient) polyhedron of ______ sides.

    1. 4

    2. 6

    3. lots more than 6

(b)

13. What is “super” about a super quadric?

    1. it is a combination of quadrics (e.g. a parabolic hyperboloid)

    2. it has a higher number of dimensions (e.g. four)

    3. it had additional features for adjusting shapes (e.g. more round or more pointed)

(c)

14. Which is the most descriptive statement for “blobby” objects.

    1. fixed volume, variable shape

    2. textured to give the illusion of softness

    3. composed of several distinct parts (a.k.a. blobs)

(a)

15. Ray casting would be most useful for

    1. superquadrics

    2. blobby objects

    3. union, intersection, and difference

(c)

16. Quadtrees would be most efficient for scenes with ______ homogeneous regions.

    1. large

    2. small

(a)

17. Octrees would be appropriate

18. for three-dimensional objects represented by their ____.

    1. shells

    2. shells and interiors

(b)

19. Octrees and quadtrees are

    1. balanced

    2. balanced and bushy

    3. complete

    4. full

    5. (all of the above)

    6. (none of the above)

(f)

20. Suppose M transforms coordinates x, y, and z. What transforms the associated coefficients A, B, C, and D?

    1. M

    2. M-inverse

    3. M-transpose

    4. Nothing

(b)

21. In a (properly designed and implemented) graphics setting, a “hidden” line is never displayed.

    1. true

    2. false

(b)

22. The Roberts hidden-line algorithm discussed in class is an _____-space algorithm.

    1. image

    2. object

(b)

23. In the Roberts algorithm it ____ necessary to determine, individually, the visibility of every point on every edge on every object.

    1. was

    2. was not

(b)

24. Which of the following can be used to enhance the efficiency of a visible surface algorithm?

    1. sorting

    2. coherence

    3. both

    4. neither

(c)

25. A backface is most efficiently detected by

    1. substituting the coordinates of the eye into the equation of the plane containing the potential backface, and then looking at the sign of the result

    2. considering the normal vector for the backface

    3. considering only one of the components of the normal vector of the backface

    4. (none of the above)

(c)

26. What is the fundamental distinction between the depth-buffer algorithm and the z-buffer algorithm?

    1. the z-buffer algorithm considers only the z coordinates of scene elements whereas the depth-buffer algorithm determines depth using x, y, and z coordinates

    2. the z-buffer algorithm handles only parallel orthographic projections

    3. (there is no fundamental distinction)

(c)

27. What is the minimum size of the depth buffer?

    1. the same as the frame buffer

    2. one “scan line”

    3. one “pixel”

(c)

28. For the purposes of the z-buffer algorithm, calculation of the depth of any point on a planar surface generally is done by solving the planar equation for z, which involves a division by C.

    1. always true

    2. infrequently true

    3. always false

(b - it’s usually done by adding or subtracting a constant)

29. The scan-line hidden surface method allows ______ polygons to overlap and determines which is closer/closest.

    1. two

    2. two or more

(b)

30. The scan-line hidden surface method requires the determination of the closer/closest polygon at _____ point(s) along the scan line.

    1. all

    2. typically only a few

    3. only one

(b)

31. The depth-sorting algorithm sorts surfaces by depth, as the name suggests.

    1. true

    2. false

(a)

32. Surface A spans surface B in depth, but the two surfaces do not overlap in x. Which should be the subject and which should be the neighbor?

    1. A should be the subject

    2. B should be the subject

    3. It doesn’t matter; either arrangement will produce correct results

(c)

33. The following two tests are equivalent: (1) the vertices of the surface of greatest depth are further away that the plane of the surface of next greatest depth, (2) the vertices of the surface of next greatest depth are closer than the plane of the surface of greatest depth.

    1. true

    2. false

(b)

34. The area subdivision algorithm uses ______ concepts.

    1. constructive solid geometry

    2. quadtree

    3. octree

    4. fractal

    5. particle system

(b)

35. The Warnock algorithm contemplates no further subdivision in all of the following cases except

    1. all surfaces are outside the area

    2. only one surface intersects the area

    3. two surfaces intersect the area, but are disjoint

    4. a surrounding surface is closer than all other surfaces which intersect the area

    5. (no exceptions here)

(c)

36. An octree representation lends itself more efficiently to visible element presentation by projecting octants

    1. back to front

    2. front to back

    3. (it doesn’t lend itself to visible element presentation)

(b)

37. All of the following lend themselves to hidden-line removal except

    1. z-buffer

    2. scan-line

    3. painter’s

    4. area subdivision

    5. (no exceptions here)

(e)

38. All of the following lend themselves to transparency except

    1. z-buffer

    2. scan-line

    3. painter’s

    4. area subdivision

    5. (no exceptions here)

(a)

39. Which of the following would be appropriate for a wireframe display with transparency?

    1. z-buffer

    2. scan-line

    3. painter’s

    4. area subdivision

    5. (all of the above)

    6. (none of the above)

(f)

40. What are the dimensions of a “point” light source in a computer graphics context?

    1. infinitesimally small

    2. one pixel (or voxel)

    3. small relative to the scene

(c)

41. Which of the following should NOT be treated as a light source?

    1. a light-emitting source

    2. a light-reflecting source

    3. a light-transmitting source

    4. (b) and (c)

    5. (none of the above)

(e)

42. Diffuse reflection is a function primarily of the

    1. light source

    2. the surface

(b)

43. Ambient light produces ______ reflection(s).

    1. diffuse

    2. specular

    3. both diffuse and specular

(a)

44. If a scene consists of ambient light and 10 point light sources (each with a red, green, and blue component), ____ components are summed to determine to total diffuse reflection.

    1. 2

    2. 11

    3. 31

    4. 33

(d)

43. Which of the following contribute(s) to the color of a specular reflection?

    1. the light source

    2. the surface

    3. both the light source and the surface

(c)

43. Why does gold look different from brass of the same color?

    1. because intensity falls off more rapidly (as a function of the angle between the ideal reflection and the viewer) for brass than for gold (or vice versa)

    2. because the curves representing how light falls off (as a function of the angle between the normal and the ideal reflector) are different

    3. it doesn’t and that’s why gold is almost impossible to distinguish from brass “of the same color”

(b)

43. Which is more costly to implement?

    1. translucency

    2. transparency

(a)

43. When light arrives at a convex angle theta from a less dense medium and enters a more dense medium, the direction traveled by the light in the more dense medium is

    1. more nearly perpendicular to the surface of the more dense medium

    2. less nearly perpendicular to the surface of the more dense medium

(b)