Computer Graphics I

4003-570-01 / 4005-761-01

Homework #2: 3D Viewing in OpenGL.

Date assigned: April 22, 2008
Date due: April 29, 2008 at 11:59 p.m.

Drop box available at myCourses

The goal of this homework is to provide you with some experience in 3D Viewing using OpenGL.

The exercises are based on the projection tutorial created by Nate Robbins. You can obtain this tutorial at the following places:

Source -- http://www.cs.rit.edu/usr/local/pub/ncs/graphics/OpenGL/SIGGRAPHTutorials
Executables for Sun -- http://www.cs.rit.edu/usr/local/pub/ncs/graphics/OpenGL/SIGGRAPHTutorials
Executables for PC - http://www.cs.rit.edu/usr/local/pub/ncs/graphics/OpenGL/SIGGRAPHTutorials/PCExecutables/
Executables for Mac OS X -- http://www.xmission.com/~nate/tutors.html

Download the projection tutorial app

Download the contents of the data directory (There is a data.zip file in the directory)

You can submit answers for the homework as many times as you like up to the due date. Your last submission will be graded.

I would suggest that you copy and paste the questions into some text editor and write the answers below each question.

Projections

Use your experimentation with the SIGGRAPH tutorial on projections and your textbook to answer the following questions: (BE SURE to reset the parameters between each question to isolate the cause and effects. This can be done using the menu that appears if the right mouse button is held down while over the textual area or by typing "r".)

For Perspective Projection using gluPerspective:
1. How does the image change if you make the fovy argument of the gluPerspective parameter list smaller? larger?
2. How does the image change if you make the aspect argument of the gluPerspective parameter list smaller? larger?
3. How does the image change if you make the zNear argument of the gluPerspective parameter list smaller? larger?
4. How does the image change if you make the zFar argument of the gluPerspective parameter list smaller? larger?
5. How does the image change of the x component of the eye triplet is made larger? smaller?
6. How does the image change of the y component of the eye triplet is made larger? smaller?
7. How does the image change of the z component of the eye triplet is made larger? smaller?
8. How does the image change of the x component of the center triplet is made larger? smaller?
9. How does the image change of the y component of the center triplet is made larger? smaller?
10. How does the image change of the z component of the center triplet is made larger? smaller?
11. How does the image change of the x component of the up triplet is made larger? smaller?
12. How does the image change of the y component of the up triplet is made larger? smaller?
13. How does the image change of the z component of the up triplet is made larger? smaller?
For Perspective Projection using glFrustum
1. How does the image change if the left parameter of the glFrustum call is made larger? smaller?
2. How does the image change if the right parameter of the glFrustum call is made larger? smaller?
3. How does the image change if the bottom parameter of the glFrustum call is made larger? smaller?
4. How does the image change if the top parameter of the glFrustum call is made larger? smaller?
5. How does the image change if the near parameter of the glFrustum call is made larger? smaller?
6. How does the image change if the far parameter of the glFrustum call is made larger? smaller?
7. Do the gluLookAt parameters affect the image in the same way using glFrustum as they do using gluPerspective? If not, in what way do the causes and effects differ?
8. Why do the zNear and zFar parameters have different effects on the image when using glFrustum and gluPerspective?
For Parallel or Orthographic Projection:
1. How does the image change if the left parameter of the glOrtho call is made larger? smaller?
2. How does the image change if the right parameter of the glOrtho call is made larger? smaller?
3. How does the image change if the bottom parameter of the glOrtho call is made larger? smaller?
4. How does the image change if the top parameter of the glOrtho call is made larger? smaller?
5. How does the image change if the near parameter of the glOrtho call is made larger? smaller?
6. How does the image change if the far parameter of the glOrtho call is made larger? smaller?
7. Which of the following has a different effect in parallel projection than it does in perspective projection? If the effect is the same, indicate so. If it is different, tell how.
  - How does the image change of the x component of the eye triplet is made larger? smaller?
  - How does the image change of the y component of the eye triplet is made larger? smaller?
  - How does the image change of the z component of the eye triplet is made larger? smaller?
  - How does the image change of the x component of the center triplet is made larger? smaller?
  - How does the image change of the y component of the center triplet is made larger? smaller?
  - How does the image change of the z component of the center triplet is made larger? smaller?
  - How does the image change of the x component of the up triplet is made larger? smaller?
  - How does the image change of the y component of the up triplet is made larger? smaller?
  - How does the image change of the z component of the up triplet is made larger? smaller?
For all types of projections:
1. The three triplets of the gluLookAt call specify which coordinate system?
2. The eye triplet represents what in this coordinate system?
3. The center or point to triplet represents what in this coordinate system?
4. The up triplet represents what in this coordinate system?
5. Which entity does gluPerspective, glFrustum, and glOrtho specify?
6. What is the main difference between parallel and perspective projection?