An application can rotate the flag counterclockwise through 90ø, by applying:

x' = x cos 90 - y sin 90

y' = x sin 90 + y cos 90

Because cos 90 = 0 and sin 90 = 1, these equations become:

x' = - y

y' = x

The original five points are transformed: (0,0) Ä (0,0)
(0,4) Ä (-4,0)
(0,6) Ä (-6,0)
(2,4) Ä (-4,2)
(2,6) Ä (-6,2)

The following figure shows the effect of rotating the flag 90ø.

Rotation Counterclockwise through 90ø