Computer Science 455
Instructor: R. P. Burton
Fourth Quiz

March 3-4, 2003

1. Which of the following would be most appropriate for curve clipping?
   • Cannon-Nydegger
   • Catmull-Rom
   • Standard point and line clipping algorithms
   (c)


2. The complexity of blanking is ________ the complexity of conventional clipping.
   • much less than
   • about the same as
   • much greater than
   (b)


3. Suppose you have a scene with 10 painted, but unposted segments along with 50 posted and painted segments. The scene is being refreshed 60 times per second. What should you do?
   • nothing
   • unpaint these segments
   • scan-convert only the posted segments
   • post the painted segments
   (c)


4. Opening an existing segment to add graphics primitives is
   • Conceptually easy and efficient
   • Conceptually easy, but inefficient
   • Conceptually difficult and inefficient
   • Conceptually difficult, but efficient
   (b)


5. Suppose you have a corporate facility which consists of X division complexes each of which consists of Y department complexes each of which consists of Z group complexes, each of which consists of W offices, each with 5 pieces of furniture. How many pieces of furniture are defined in master coordinates?
   • probably 5
   • 5 x W
   • 5 x W x Z x Y x X
   • W x Z x Y x X
   (a)

Continuing the preceding question, how many transformations likely are stored in the hierarchy representing the corporate complex?
• probably 5
• 5 x W
• 5 x W x Z x Y x X
• W x Z x Y x X
(c)

6. Suppose you wish to clip in master coordinates. Which approach clips most efficiently?
   • clip the diagonal of the bounding box of the object relative to the image of the viewport mapped back to master coordinates
   • clip the diagonal of the image of the viewport mapped back to master coordinates relative to the bounding box of the object
   • the results, and the efficiency of the operations are equivalent for (a) and (b)
   (a - since it permits a trivial accept)


7. The most important quality (from the following list) of a GUI is
   • the obvious good taste manifested in the colors, shapes, textures, and arrangement of the components of the GUI
   • its ability to draw (i.e. "pull") the user into the application with a minimum of distraction
   • it's ability to adapt to users with several different skill levels
   (b)


8. As a general rule, a user learns best when a GUI
   • handles erroneous input with a minimum of chastisement
   • punishes the user severely to discourage him from future erroneous input
   • substitutes default values for erroneous input so as not to delay processing
   • provides the user with immediate, detailed instructions for providing input to the GUI he/she is using
   (a)


9. All of the following EXCEPT __________are acceptable for determining whether the user is specifying the mosquito, or the sheet of glass on which it is resting, or the picture frame assembly which includes the sheet of glass, or the cabinet in which the picture frame assembly sits, or the …
   • highlighting each component in sequence until the user provides logical "button" input
   • highlighting each component in order of decreasing likelihood until the user provides a logical "button" input
   • providing a "hot point" on each component from which the user may select
   • allowing the user to specify a "bounding box" around the component of interest
   • projecting the user's pick device into the scene to determine which unique object it intersects
   • (no exceptions here)
   (e)


10. The user has clicked to specify one endpoint of a horizontal line. The system essentially pauses and awaits the x-coordinate of the other endpoint of the line. The system is in ____ mode.
    • request
    • sample
    • event
    (a)


11. The user has clicked within the gravity field and near the center of a line segment. The system is supposed to find the closest point on the line segment. The system is likely to make direct or indirect use of all of the following EXCEPT_____.
    • the slope of the line segment
    • the length of the line segment
    • the equation of the line segment
    • (no exceptions here)
    (b)


12. A "front elevation" (which is a parallel projection) of a home represents a camera view from
    • a standard 20 feet in front of the home
    • the property line
    • the center of the street in front of the home
    • (all of the above)
    • (none of the above)
    (e)


13. Lines (such as the edges on a line-drawn pyramid) which are darker and thicker appear ________ than lines which are lighter and thinner.
    • closer
    • farther away
    • perhaps closer or perhaps farther away, depending on the person,
    (c)


14. Stereo vision (i.e. two eyes) is required to perceive depth.
    • true
    • false
    (b)


15. The equations of planes (which contain polygons which are components of a scene) are used in all of the following EXCEPT
    • viewing transformations
    • shading models
    • removal of hidden surfaces
    • (no exceptions here)
    (d)


16. ANY three (noncoincident) points on a plane are sufficient to determine the equation of the plane. (Be careful)
    • true
    • false
    (b)


17. Suppose the equation of a plane is determined using the coordinates of three of its vertices. Suppose these vertices are transformed by a matrix M. The equation of the associated plane is
    • unchanged
    • computed by transforming the planar coefficients with the same matrix M
    • computed by transforming the planar coefficients by the inverse of the matrix M
    • uncomputable from the matrix M or its inverse; it must be determined directly from the new coordinates of points on the plane (such as the vertices)
    (c)


18. What is a superquadric?
    • The abstract parent class of all quadrics
    • a quadric of three or more dimensions
    • a quadric with an imaginary component
    • a quadric with additional parameters for adjusting its shape
    (d)


19. Which of the following is most likely to be a "blobby" object?
    • an object with a smooth (as opposed to polygonized) surface
    • an object with a fuzzy (as opposed to smooth) surface
    • an object with a fixed volume, but a variable ("fluid") shape
    • an object which seeks (and comes to rest in) a minimum potential energy position
    (c)


20. In a parametric equation, what does the parameter "u" represent?
    • height
    • width
    • depth
    • any one of height, width, or depth
    • (none of the above)
    (e)


21. What can it mean for some form of "continuity" to exist between two curve sections?
    • the curves meet at a common point
    • the curves have the same slope at a common point
    • the curves have the same curvature at a common point
    • (any of the above)
    (d)


22. More often than not, the control points used to determine curves and surfaces (for computer-aided design) are _________.
    • interpolated
    • approximated
    (b)


23. Bezier was a contemporary of
    • Ptolemy
    • Galileo
    • Napoleon
    • DeGaulle
    (d)


24. Suppose you have 5 sets, each with 4 control points, each with three coordinates (x, y, and z). How many distinct blending functions are needed to produce Bezier curves for each of the 5 sets?
    • 5
    • 4
    • 3
    • 4 x 3
    • 5 x 3
    • 5 x 4 x 3
    (b)


25. The convex hull for a Bezier curve is the polygon formed
    • with all of the control points as vertices, connected in order
    • will all of control points as vertices, not necessarily connected in order
    • with at least some of the control points as vertices
    • with vertices dictated by (but not always coincident with) the control points
    (c)


26. Bezier curves exhibit ____ control; B-splines exhibit ____ control.
    • local, local
    • local, global
    • global, local
    • global, global
    (c)


27. A Bezier curve ___ be a closed curve; a B-spline ___ be a closed curve.
    • can, can
    • can, cannot
    • cannot, can
    • cannot, cannot
    (a)


28. The maximum degree of a polynomial for a ______ is determined by the number of control points.
    • Bezier curve
    • B-spline
    • Bezier curve and a B-spline
    (a)


29. Suppose you have a Bezier surface determined by a 3x4 mesh. What is the minimum number of Bezier curves contained in the surface (meaning how many two-dimensional slices can you take through the surface that are guaranteed to produce Bezier curves)?
    • 0
    • 3
    • 4
    • 7
    • 3 x 4
    • infinitely many
    (c)


30. Continuing the previous question, how many surface patches result from the 3 x 4 mesh?
    • 3 x 3
    • 3 x 4
    • 4 x 4
    • arbitrarily many
    (d)


31. If the curve doesn't wiggle a lot, and if you can obtain the convex hull easily, the control points probably are
    • interpolated
    • approximated
    (b)