Cartesian Coordinate Systems - 3D Math Primer for Graphics and Game Development - page 9

axis which direction we consider to be positive. For example, when working
with images on a computer screen, it is customary to use the coordinate
system shown in Figure 1.6. Notice that the origin is in the upper left-hand
corner, +x points to the right, and +y points down rather than up.

Unfortunately, when Cartesia was
being laid out, the only mapmak-
ers were in the neighboring town of
Dyslexia. The minor-level functionary
who sent the contract out to bid ne-
glected take into account that the
dyslectic mapmaker was equally likely
to draw his maps with north pointing
up, down, left, or right. Although he
always drew the east-west line at right
angles to the north-south line, he often
got east and west backwards. When his
boss realized that the job had gone to
the lowest bidder, who happened to live
in Dyslexia, many hours were spent in
committee meetings trying to figure out
what to do. The paperwork had been
done, the purchase order had been is-
sued, and bureaucracies being what they are, it would be too expensive
and time-consuming to cancel the order. Still, nobody had any idea what
the mapmaker would deliver. A committee was hastily formed.
The committee fairly quickly decided that there were only eight possi-
ble orientations that the mapmaker could deliver, shown in Figure 1.7. In

Figure 1.6
Screen coordinate space

Figure 1.7. Possible map axis orientations in 2D