Subject: sp4 correction

(This message is being sent to CPSC 215 Students and TA's)

The x-coord mapping from pixel to world space should actually look like:

   *(world + 0) = x / (proj->win_size_pixel[0] - 1) *
                                    proj->win_size_world[0];

   *(world + 0) -=  proj->win_size_world[0] / 2.0;

The -1 is needed because, for example, a pixmap that is 5
pixels in width  consists of pixels 0, 1, 2, 3, 4 and thus has
a width of 4 (instead of 5) in pixel space.

The sample output in sp4data has been updated to reflect this
correction.

mw