Geometry view 2D

Hello all,

I have been working with the Geometry view 2D and I was wondering how to do the following (if it is possible):

Currently I have drawn various shapes based on coordinates. Now I want to define the length of a shape, see the schetched red arrow line. How do I do this?

You can always write a function that converts length(s) to coordinates.

ps. The SquareBeam class actually uses lengths.