What makes the following expression produce a wrong rotated point?

Question

I want to rotate point B 30 degrees counterclockwise about A to produce a new point C. However, I failed to get the correct C as illustrated below. The red circle helps us to notice the issue easily.

\documentclass[pstricks,border=12pt]{standalone}
\usepackage{pst-eucl}
\psset{saveNodeCoors}
\begin{document}
\begin{pspicture}[showgrid](6,6)
    \pstGeonode
        (1,1){A}
        (5,3){B}
        (!N-B.y N-A.y sub 2 exp  N-B.x N-A.x sub 2 exp add sqrt N-B.y N-A.y sub N-B.x N-A.x sub atan 30 add PtoC){C}
    \pstCircleOA[linecolor=red]{A}{B}
\end{pspicture}
\end{document}

Notes

Don't suggest me to use \pstRotation as I already know it and it is not my interest. You might suggest me to use ([angle=30,nodesep=]{B}A), but the problem is that nodesep must be assigned with an absolute value. It might be a good idea to add a new key, for example, relnodesep to ([angle=30,...]{B}A) syntax so we can solve this problem by just writing ([angle=30,relnodesep=1]{B}A).

Answer 1

You only rotate the difference vector between node A and B, but at the end you must add the coordinates of the 'origin' A:

\documentclass[pstricks,border=12pt]{standalone}
\usepackage{pst-eucl}
\psset{saveNodeCoors}
\begin{document}
\begin{pspicture}[showgrid](6,6)
    \pstGeonode
        (1,1){A}
        (5,3){B}
        (!N-B.y N-A.y sub 2 exp  N-B.x N-A.x sub 2 exp add sqrt 
          N-B.y N-A.y sub N-B.x N-A.x sub atan 30 add PtoC 
          N-A.y add exch N-A.x add exch % this was missing
        ){C}
    \pstCircleOA[linecolor=red]{A}{B}
\end{pspicture}
\end{document}