Circular kernel with sectors as subregions opencv

edit

I am an opencv newbie . I need to create a circular kernel with 8 sectors as subregions to perform kuwahara filter on an image . I am creating the kernel using opencv as

"Mat kernel=getStructuringElement(CV_SHAPE_ELLIPSE,Size(3,3),Point(-1,-1));"

I need to obtain the sectors and subsequently apply the filter to it. Any ideas on how to get the sectors will be greatly appreciated .