Assume that we have two coordinates (a) and (b). I want to draw a line which is a parallel translation of the line which connects (a) and (b).
I would like to have something like \drawparallel{a}{b}{dist} which will draw a line parallel to the one connecting (a) and (b) at (signed!) distance dist.
I tried many things both based on \newcommand and on \tikzset but could not make it work.
Edit: To make it clearer, I want the the four points (two of the original line segment, and two of its translated copy) will form a rectangle.

\draw ([xshit=dist]a)--([xhsift=dist]b);enough? – Ignasi May 31 '13 at 10:52