CS248 Final Review Practice Questions- Dec. 4, 1999
This page includes a few example problems for the cs248 Final.
Answers have been removed, if you want to test yourself before
looking at the answers. See also the
review notes page , which gives the answers to these
Disclaimer: These questions were designed to give you an idea of
what kinds of questions we might ask about the material.
This was not intended to be an exhaustive coverage
of all material you should know for the exam.
(by Lucas Pereira)
(I forgot to cover this at the review session. Even though this
class was the Thursday before the midterm, the material was not
covered in the midterm, and so will be fair game for the final,
although will not be heavily emphasized.)
(by Lucas Pereira)
- Where on earth can you walk forward 6219 miles (1/4 circumference),
turn right, walk forward 6219 miles, turn right,
walk forward 6219 miles, and be back where you started?
- When viewed by a perspective projection, which of the following
properties of a texture-mapped plane will be preserved:
lengths, angles, parallel lines, and straight lines?
- When rendering with OpenGL texture-mapping (GL_NEAREST, no mipmaps),
is this a forward-mapping or backward-mapping operation?
- Lucas wants to do rotatez(90), but he spilled coffee on his
keyboard and his z key no longer works. He decides instead
that he can do it with the following: rotatex(90) [
rotatey(angley) [ rotatex(-90) ]].
Is he right? What should (angley) be?
(by Sean Anderson)
- Can a 1-D texture map be applied to a 2-D surface? How?
- Can a 2-D texture map be applied to a 1-D line? How?
- What is minification? Magnification?
- What are the effects of using GL_NEAREST as your texture filter
when minifying? Magnifying? Explain.
- What are the effects of using GL_LINEAR as your texture filter
when minifying? Magnifying? Explain.
- What is the common OpenGL approach to avoid aliasing
while minifying? Will it have any effect on magnifying?
- What filter kernel does GL_NEAREST correspond to?
- What filter kernel does GL_LINEAR correspond to?
- How does mipmapping with tri-linear interpolation compute
the texture color for a vertex?
- To make things simpler, Lucas has turned his '89 Integra
Racing game into a drag-racing game. As such, he has his car
racing up the Y axis of a single texture-mapped ground
polygon. The viewer always looks orthographically straight
down on his car. In this orthographic view, the ground
texture is magnified (more pixels than texels). Because his
car goes so fast (many texels per frame), the ground plane
looks choppy, instead of smoothly motion-blurred. Since Prof.
Levoy is his advisor, he figures that all problems can be
solved with proper filtering. Could standard mipmapping solve
his problem? Why or why not?
- Give 2 reasons for clipping before homogenization.
- What is the condition used to determine if the x coordinate (xc) of a
non-homogeneous projected point is within the left and right walls (at
-1 and +1 on the near plane) of a perspective view frustum?
- What part of a 4x4 matrix tells you that it is a perspective
- Consider a view of a scene with 2 cubes oriented arbitrarily; how many
vanishing points could there be in the image?
- Where is the viewer's eye and what is the viewing direction when the
perspective transform is applied?
(by Dave Koller)
(by Szymon Rusinkiewicz)
- NASA wants to draw a picture of Mars to try to visualize the
landing site of the missing Mars Polar Lander probe, and so
they're trying to pick a good hidden-surface algorithm. They
have a high-powered supercomputer, with 1.7GB of RAM. They
want to draw a 3000x3000 pixel image. Unfortunately, their
Mars model consists of ten Billion polygons, and so they can
only load 2% of it in memory at a time. They want to minimize
disk accesses. Alas, they only have programmers who know how
to implement Watkin's algorithm, Weiler-Atherton, BSP trees,
and Z-buffering. Which algorithm should they use, and why?
(For each discarded algorithm, state why it's a bad choice.)
If they can load a million polygons per second off disk, how
long will it take before they will have a picture to show
A cs248 student is experiencing difficulties with his z-buffer,
so he sends email to the cs248tas. The problem, he says, is
that he's seeing really bad artifacts. Upon investigation,
they realize that he's setting the near clipping plane to
0.01, the far clipping plane to 20, and most objects are
about 10 units away. The TAs tell him that his problem is
lack of precision; different surfaces are getting mapped to the exact
same Z-value in his 16-bit Zbuffer.
What is the depth range of a single z "bucket"
at a distance of 10 units away? How could he fix his problem?
You may assume the following formula maps zwin into
the range 0 to 1:
zwin = [(znear + z) *
zfar] / [(zfar - znear) *
- You change the normal vectors of an OpenGL triangle, but don't change
the position of the vertices. Which components of the color seen
by the viewer (ambient, diffuse, and specular) might change?
- An object is sitting in a room with lights you can't turn off.
You want to take a picture of the object with only a single point light
source. You accomplish this by taking the object's picture with the
normal light in the room, and another picture with that light plus a
point light source. You then subtract the first picture from the second.
Will this work? Why or why not?
- You are in an empty room (just 4 walls, floor and ceiling),
with a single light bulb. You carefully measure the dimensions of the
room, the color of the paint on each wall, and the radiant intensity
of the light bulb. You use these measurements to construct an OpenGL
model of the room, and render the scene. Nevertheless, the rendering
will not look like a photograph of the room. Why not?
- In the table below, write "YES" or "NO" in each of the four squares,
to indicate whether a viewer might see a finite-sized specular
highlight (shiny spot) on a large flat plane. You may assume the
plane is made up of many tiny triangles, so that it is effectively
computing a normal for each pixel.
|| Directional Light (w=0)
|| Point Light (w=1)
| Orthographic Projection|
| Perspective Projection|
- Infinite Engine Motor Corp. (IEMC) introduces their new luxury
car, the W=0, with Seaborgium headlights. They advertise that
these headlights are only the size of a dime, but put out the
same power as their regular six-inch xenon headlights. Ralph
Nader, having lost his bid for governor, decides to sue IEMC,
claiming (a) that the radiance of the new headlights is
greatly increased, and will damage peoples' foveae. IEMC
counters that the headlights are safe, because (b) they emit
the same flux, and (c) provide the same irradiance. Which of
these claims (a, b, c) are right? Do you think these
headlights are more dangerous to oncoming drivers? Why or why
not? (You may assume that oncoming drivers view the headlights
close enough that the six-inch headlights get focused on many
cells of the fovea.)
- Lucas is still writing his '89 Integra Racing game. Since he
has spent all quarter hacking instead of washing his car, his
car is now an ideal dusty surface. He wants to capture this
appearance, but can't think of the right coefficients to model
this surface accurately. Is it possible to model this surface
with the Phong shading model? (in theory; ignore whether
OpenGL will allow these values.) Assuming his car is
completely coated (100% coverage) with ideal white dust, what
values of Kd, Ks, and n (the cos(a) exponent) should he pick?
Is such an "ideal dusty surface" physically possible?
(Consider the total flux falling on the car, and total flux
exiting the car.)
Copyright © 1999 Lucas Pereira, Sean Anderson,
David Koller, and Szymon Rusinkiewicz
December 9, 1999 07:04:32 PM