Centers and keep the aspect ratio in a 3D representation.
        
        Created to help higher classes to manage cascade representation
        of multiple lower objects.
        
        :param ax: Axes to apply the method.
        :type ax: mplot3d.Axes3D
        :returns: None

def center_plot(self, ax):
        """
        Centers and keep the aspect ratio in a 3D representation.
        
        Created to help higher classes to manage cascade representation
        of multiple lower objects.
        
        :param ax: Axes to apply the method.
        :type ax: mplot3d.Axes3D
        :returns: None
        """
        
        # Domain
        domain = self.get_domain()
        bound = np.max(domain[1]-domain[0])
        centroid = self.get_centroid()
        pos = np.vstack((centroid-bound/2, centroid+bound/2))

        # Axis limits
        ax.set_xlim3d(left=pos[0,0], right=pos[1,0])
        ax.set_ylim3d(bottom=pos[0,1], top=pos[1,1])
        ax.set_zlim3d(bottom=pos[0,2], top=pos[1,2])