Stores the distance between the centres of C1 and C2
double C1C2 = Math . sqrt ( ( C [ 1 ] . x - C [ 0 ] . x ) * ( C [ 1 ] . x - C [ 0 ] . x ) + ( C [ 1 ] . y - C [ 0 ] . y ) * ( C [ 1 ] . y - C [ 0 ] . y ) ) ;