  An effective strategy for accelerating the calculation of convex hulls for
point sets is to filter the input points by discarding interior points. In this
paper, we present such a straightforward and efficient preprocessing approach
by exploiting the GPU. The basic idea behind our approach is to discard the
points that locate inside a convex polygon formed by 16 extreme points. Due to
the fact that the extreme points of a point set do not alter when all points
are rotated in the same angle, four groups of extreme points with min or max x
or y coordinates can be found in the original point set and three rotated point
sets. These 16 extreme points are then used to form a convex polygon. We check
all input points and discard the points that locate inside the convex polygon.
We use the remaining points to calculate the expected convex hull. Experimental
results show that: when employing the proposed preprocessing algorithm, it
achieves the speedups of about 4x ~5x on average and 5x ~ 6x in the best cases
over the cases where the proposed approach is not used. In addition, more than
99% input points can be discarded in most experimental tests.
