Before revision: {\rm Kernel }_{\theta}(P) while \theta varies in [-\frac{\pi}{2},\frac{\pi}{2}), obtaining the angular intervals where the \{0^{o\}}  -{\rm Kernel }_{\theta}(P) is not empty and (ii) for orthogonal polygons P, computing the orientation \theta\in 0, \frac{\pi{2}) such that the area and/or the perimeter of the \{0^{o},90^{o}\}}  -{\rm Kernel }_{\theta}(P) are maximum or minimum.
After revision: {\rm Kernel }_{\theta}(P) while \theta varies in [-\frac{\pi}{2},\frac{\pi}{2}), obtaining the angular intervals where \}} -{\rm Kernel }_{\theta}(P) is not empty and (ii) for orthogonal polygons P, computing the orientation \theta\in 0, \frac{\pi{2}) such that the area and/or the perimeter of the \{0^{o},90^{o}\}} -{\rm Kernel }_{\theta}(P) are maximum or minimum.