In the special case of orthogonal projectors, 
.
Nonorthogonal projectors transform vectors to 
by
``casting the shadow'' at a different angle from the perpendicular to the
plane 
.
If P is a projector onto 
, so that PX=X, then
for all possible values of 
. For this reason, all projections of y
onto 
are linear unbiased estimators of 
,
differing according to the direction the projectors go along. The OLS
estimator is the orthogonal projection of y. In
the figure above
we illustrate nonorthogonal projection.
