课程名称︰虚拟实境
课程性质︰选修
课程教师：欧阳明
开课学院：电资学院
开课系所︰资工所、网媒所
考试日期（年月日）︰2007.05.08
考试时限（分钟）：
试题 :
Virtual Reality Mid-term Exam, May 8, 2007
1. Augmented Reality (10%)
(a) (5%) What's Augmented Reality (AR) and Mixed Reality (MR)?
(b) (5%) Design an AR application. Please describe in detail about the
motivation, hardware/software system, and operating scenario of your
design.
2. (20%) Mr. Superplayer buys a Gundam model and uses a 3D scanner to digitize
it. He wants to make an animation about Gundam, but doesn't know how to
build it and let it stand on the floor. Please use OpenGL to help
Mr. Superplayer. The data is given below.
(a) (10%) How to combine each part to let Gundam stand? Write OpenGL code
to do that. (You should define any parameters that you need,
eg., "LeftLegLength" etc.)
(Hint: You have glPushMatrix(), glPopMatrix(), glRoatef(),
glTranslatef(), DrawBody(), DrawRightLeg(), DrawLeftLeg() etc).
(b) (10%) Only three parts (Body, LeftLeg, RightLeg) are not enough for
animation. By your experience, if the Gundam wants to shoot from a
kneeling position, how to split the model? (PS; coordinate system is
important here!) (Hint: You can simply draw "Line Segment with Label"
as split part, "Circle" as joint or origin).
Fig. http://i.imgur.com/Bqjt8zr.png
3. (15%) The goal of 3D sound is to simulate the direction and distance of a
sound source in a real world.
(a) (7%) The DVD (Digital Versatile Disk) standard uses the Dolby AC-3 as
its sound output, where AC-3 uses 5 speakers plus one bass speaker, as
shown in Figure 3. However, your PC has two speakers only. How would you
design your PC to play a DVD movie with a sound similar to Dolby AC-3?
Fig. http://i.imgur.com/ZDCT6NQ.png
(b) (8%) The following is the shape of your study room, and you want to hear
the music exactly as it was generated in the opera house in Paris,
France. Can it be done? How?
Fig. http://i.imgur.com/AgKjzQr.png
4. Term project (5%)
What is the term project you want to do for this semester? What kind of
technical problems will you encounter and have to be solved?
5. (5%) Please design a method to achieve the goal "smell real" in a movie
theater? Give at least one example.
6. Force-feedback devices (15%)
Agent Mulder build his 3D sculpting system with a force-feedback device.
The pseudo code of his main algorithm is following:
while(sculpting){
Do the "collusion detection" with current sculptor position
Calculate the "feedback force" and set it to force-feedback device
Modify the 3D scene
Render the 3D scene
}
(a) (5%) What are the parameters that the force feedback device needs to
send them back to the computer to simulate the force system? Can you
write down and explain the formula for simulating the force feedback
system with previous parameters?
(b) (5%) Let's simulate a "rock" wall (hard surface) using such a spring
system using a large spring constant K = 1000000 NT/m. Do you think it
is a good system design? What are the potential problems?
(c) (5%) For the problem in (b), can you think of ways to actually simulate
a hard surface in virtual reality?
7. (15%) In terms of graphics acceleration, there are at least two approaches
been proposed, namely (1) parallel processing or SIMD, such as in the
nVidia GeForce4 chip set, and (2) binary machines such as the PixelPlanes
chip set.
(a) (5%) Can you describe the basic idea of how these two approaches can
accelerate graphics and the major difference between them.
(b) (10%) There is a functon fast_calculate (A, B, C, x, y) which can be
evaluated in parallel, where fast_calculate() can calculate
A*x + B*y + C for each pixel position (x, y). For a triangle defined
by vertices (0, 6, 0), (0, 0, 0) and (8, 0, 0), please write a parallel
procedure using fast_calculate() to draw all the pixels inside this
triangle by Phong shading (vertex normal interpolation) with the shading
function (surface normal) dot_product (light_direction). The surface
normal at (0, 6, 0) is (1, 0, 0), at (0, 0, 0) is (0.6, 0.8, 0), and at
(8, 0, 0) is (0, 1, 0), and the light is at (0, 0, 15). We view this
triangle from Z axis above.
8. (15%) In order for objects in virtual environment to move realistically,
the response time of the system must be very short. However, in practice,
there is always system lag (latency). To solve the problem, many different
methods have been proposed to "predict" the future movement upon the past
motion path. One method is the simple extrapolation:
Time(ms) t-200 t-100 t t+100
Input X(n-2) X(n-1) X(n) X(n+1)
Value 1.2 1.3 1.5
(a) (3%) By first order linear interpolation, X(n+1) = ?
(b) (5%) By second order extrapolation, X(n+1) = ? How to formulate your
equation?
(c) (2%)Suppose the moving object has a mass M, will this fact help the
prediction?
(d) (5%) Do you think more data in the past will help? Why? Is there an
upper bound (number of past data) for the past data? If so, what are
the factors that will limit the past length?
(Hint: second order prediction: a curve passing through X(n), X(n-1),
X(n-2))