Vector orientation is defined for an ordered pair of vectors in an oriented plane.
For two nonzero vectors, let
be the directed angle measured in the positive
rotation sense from the first vector
to the second. If
,
the pair is positively oriented. If
, the pair is negatively oriented.
Two vectors with coordinates in a positively oriented basis
are positively oriented iff the determinant
and are negatively oriented iff the determinant .