//! Helper member function.
SIFTDescriptor operator()(const OERegion& f,
const Image<Vector2f>& gradPolar) const
{ return this->operator()(f.x(), f.y(), f.scale(), f.orientation(), gradPolar); }
//! Helper member function.
descriptor_type operator()(const OERegion& f,
const Image<Vector2f>& grad_polar_coords) const
{
return this->operator()(f.x(), f.y(), f.scale(), f.orientation(), grad_polar_coords);
}