the symmetric values about the imaginary axis of zero-poles which the unstable process lies in the open and closed right-half plane are defined as their mirror-injection.
非稳定过程在开右半平面的零极点关于虚轴的对称值称为该零极点的镜像映射。
the geometrical concept is to make a lot of parallel lines of the imaginary axis in the complex plane, and to decide the points which satisfy both the root loci and the parallel lines by the computer.