IMAGE COORDINATES
                
        Several files in the dataset express data in image coordinates,
i.e., X-Y pairs.  All such values are expressed in pixels in X-Y format
(*not* row-column), with the origin in the upper left corner of the
image.
Pictorially:


                 _______________________
                | -----> X              |
                | |                     |
                | |                     |
                | |                     |
                | v Y                   |
                |                       |
                |_______________________|