def computeRR(self):
    """
    Compute the rectangularity ratio (RR) of the max-tree nodes. RR is defined as the 
    area (volume) of a connected component divided by the area (volume) of its bounding-box. 
    """
    xmin,xmax = self.node_array[6,:], self.node_array[7,:] + 1
    ymin,ymax = self.node_array[9,:], self.node_array[10,:] + 1
    area = self.node_array[3,:]

    if self.node_index.ndim == 2:
        return 1.0*area/((xmax-xmin)*(ymax-ymin))
    else:
        zmin,zmax = self.node_array[12,:], self.node_array[13,:] + 1
        return 1.0*area/((xmax-xmin)*(ymax-ymin)*(zmax-zmin))