Selection in 3D Graphics Environments
Christine Albert and Lindsey Press

This week, we began to move from the eye space to the frustum space. We divided by the w-coordinate, which was 20 for the hand and 25 for the box corners in our examples. This resulted in the normalized coordinates shown below, and the w-coordinate is dropped because it is 1 and no longer necessary for further transformations. Although the numbers may not initially look accurate, it is important to remember that after moving the camera the coordinate system is now relative to the camera and no longer centrally located. We then scaled the normalized coordinates to adjust for a screen size of 512x512. To do this, we used the formula (w(x+1)/2, h(-y+1)/2), where w represents the height and h represents the width. In this step we remove the z coordinate because the image that we are now viewing is in two dimensions, rather than three.The results of our calculations are shown below.

Box Divide by w:

Box Scaled:

Hand Divide by w:

Hand Scaled:




Resources:

http://www.ntu.edu.sg/home/ehchua/programming/opengl/cg_basicstheory.html