Assignment 3
CSCI-4965: Three-Dimensional Computer Graphics
Fall 2000

Announcements

Here are some clarifications and announcements regarding Assignment 3.
  1. Not using the proper array index can cause your program to crash. The pixel member of the RGBpixmap class is an array that stores the color values at each pixel. pixel[0] corresponds to the lower left pixel of the image, and pixel[numrows*numcols - 1] corresponds to the upper right pixel of the image.

    Assume the origin of the XY coordinate system is placed at the lower left corner of the image, with the X axis being horizontal and the Y axis being vertical. Then the pixel at (x, y) corresponds to pixel[y*numcols + x], where x varies from 0 to (numcols - 1) and y varies from 0 to (numrows - 1).

  2. Converting from (x, y) coordinates to polar coordinates (r, theta):
    r = square_root[(x-cx)^2 + (y-cy)^2]
    theta = inverse_tangent[(y-cy)/(x-cx)]
    where (cx, cy) is the coordinates of the image center.
    Using atan2(ycomponent, xcomponent) to compute the inverse tangent of (ycomponent/xcomponent) should return an angle specified in radians in the interval [-pi, pi].
    Note that using atan(ycomponent/xcomponent) gives an answer in the range [-pi/2, pi/2]. So both atan(ycomponent/xcomponent) and atan(-ycomponent/-xcomponent) will give you the same answer, which is probably not what you want.

  3. Converting from polar coordinates (r, theta) to (x, y) coordinates:
    x = r*cosine(theta) + cx
    y = r*sine(theta) + cy
    where (cx, cy) is the coordinates of the image center.

  4. If you need to access an image pixel outside the bounds of the image array for an image transformation, one solution is to consider the image to be wrapped around so that the left edge of the image is joined to the right edge of the image, and the bottom edge is joined to the top edge. So the image pixel value can be obtained from the corresponding pixel in the wrapped image.

  5. Be sure to list the image files (from the set we provided) that your program uses in your README file. Hopefully the problem with the submission script due to the size of the image files has now been fixed. Knowing the set of files your program uses will be helpful in case you are unable to include the image files in your submission. Please email us if you have trouble submitting your image files using the submit script.

  6. If your assignment implementation deviates from the specifications, be sure to document this in your README file.
The above announcements and clarifications list was last updated at 1:30pm, November 7, 2000.

Description

Code for BMP files

Code for TIFF files

If you prefer, you can also use the libtiff software library to read and write TIFF files.

Lab

You can use the Sun Ultra10 machines with Elite3D graphics in the Sparc Lab in Amos Eaton 217. The OOT Lab in Amos Eaton 117 has a cluster of 16 Sun Ultra10 machines with Creator3D graphics that you can use.

Note on Lab Timings: The Sparc Lab and OOT Lab are usually open Monday-Saturday from 9am-5pm. You can enter and use the labs at any other time if you are able to get in. (There usually are some students working in the Sparc lab late at night.) If you are the last person to leave the lab after hours, please lock the door behind you.

Handin Instructions

You will submit your assignment by running a script that tars files in the source directory, gzips and tars them, and emails the uuencoded file. You will automatically receive an email acknowledgment of your submission (sent to your CS account).

To submit your assignment, follow these steps:
1. You must be on a CS machine running unix. The Ultras in the Sparc lab will do fine.
2. Go to the directory in which all your source code (source and header files), Makefile, and README file are placed.
3. Type "submit compgraph" at the prompt.
This script will automatically tar, gzip, uu-encode and email the entire directory contents. It tries to be smart about not including executable and object files, core files, etc.
4. You will receive an automatic email reply showing all the files that were submitted, along with a timestamp. This email is sent to your CS account, so be sure to check there or forward email from there to your RCS account.

Note that you can send in multiple submissions. We will use the most recent one for evaluation of your assignment. The corresponding timestamp will serve to determine the penalty for late submissions.

Let us know if you have any problems with this submission procedure.

Important: Please save your submitted assignment files until your assignment has been graded.

Back to the course home page

Xianfeng Zhao
Email: zhaox3@cs.rpi.edu

Srinivas Akella
Email: sakella@cs.rpi.edu