How to check the 90 degree angle on the route

Hi all

      I have a problem at work. I use virtuoso 6.1.6-64b.

      As shown below. How can I use skill to check the 90 degree angle on the path (or pathSeg、polygon、rect).

      Hope you can give me some ideas, or some skill functions. 

      Or use other methods or tools to check. 

Thank All.