Declare the point for incomming arrows on nodes

Question

is there a way to tell the a node, where the arrow shall arrive?

At this example, the Arrow from Node B to A should arrive exactly in the middle of the "D" from "Dies". It should start on top-center of B's text.

Hope this is understandable.

\documentclass[11pt, halfparskip,toc=flat,numbers=noendperiod]{scrartcl}
\usepackage[utf8]{inputenc}
\usepackage{ngerman} % deutsche Silbentrennung, Deutsche Ausdrücke

\usepackage[T1]{fontenc}
\usepackage{lmodern,textcomp}


\usepackage{pstricks-add}

\begin{document}
\begin{center}
\psset{xunit=1cm,yunit=1cm,runit=1cm}
\begin{pspicture}(10,5)
    %\psgrid(0,0)(0,0)(10,5)


    \rput[t](5, 5){
        \rnode{A}{
            \parbox[c]{3cm}{
                \centering
                Dies ist Node A
            }
        }
    }

    \rput[t](0, 2.5){
        \rnode{B}{
            \parbox[c]{3.5cm}{
                \centering
                Dies ist der Text\\
                zu Node B
            }
        }
    }

    \rput[t](10,2.5){
        \rnode{C}{
            \parbox[c]{3cm}{
                Mein Name ist C, Node C
            }
        }
    }

    \rput[t](5,0){
        \rnode{D}{
            \parbox[c]{3cm}{
                Ich bin Node D\\
                Ich stehe ganz unten
            }
        }
    }

    \psset{linewidth=.05cm}
    \psset{nodesep=0.1cm}
    \psset{arcangle=45}

    \ncarc{->}{B}{A}
    \ncarc{->}{A}{C}
    \ncarc{->}{C}{D}
    \ncarc{->}{D}{B}

\end{pspicture}

\end{center}

\end{document}

Answer 1

There is a way. \nccurve for example allows to specify connection angles and offsets. If less precision were sufficient you could go with a one-liner; since you're looking for exact placement, you need some more code:

%calculate offset
\newlength\labellength
\newlength\dlength
\newlength\offset
\settowidth{\labellength}{Dies ist Node A}
\settowidth{\dlength}{D}    
\setlength{\offset}{\dimexpr-.5\labellength+.5\dlength\relax}

%draw curve
\nccurve[angleA=90,angleB=90,offsetB=\offset,ncurvA=.67,ncurvB=.67]{->}{B}{A}

The ncurv parameters, set to their defaults here, allow you to adjust the curve's shape. A and B, not to be confused with your node names, refer to the start and end node. For more details see the manual linked by @MarcoDaniel; several other options to connect two nodes are presented there as well.

Answer 2

With your current settings it can't be done. The node specifier \rnode has an optional argument to specify the refpoint but only once. The specifier is equal to \rput.

However the package pst-node offers an other way. You can use the new command \psDefBoxNodes{node name }{text } whereby the displayed refpoints will be defined:

The example is taken from the manual:

\documentclass[]{scrartcl}
\usepackage{pst-node}
\begin{document}

\psset{xunit=1cm,yunit=1cm,runit=1cm}
\begin{pspicture}(-1,-2)(10,6)
\psscalebox{15}{\psDefBoxNodes{Age}{\color{red!50}\sffamily \"Age}}%
\pspolygon[fillstyle=solid,
fillcolor=blue!30,opacity=0.3](Age:tl)(Age:tr)(Age:br)(Age:bl)%
\psline[linestyle=dashed](Age:Bl)(Age:Br)%
\psdots(Age:tl)(Age:tC)(Age:tr)(Age:Cl)(Age:C)(Age:Cr)%
(Age:Bl)(Age:BC)(Age:Br)(Age:bl)(Age:bC)(Age:br)%
\pcline[arrows=<->,linecolor=blue,arrowscale=1.25](Age:tC)(Age:Br)
\uput[180](Age:tl){tl}\uput[180](Age:Cl){Cl}\uput[180](Age:Bl){Bl}\uput[180](Age:bl){bl}
\uput[90](Age:tC){tC} \uput[0](Age:C){C}
\uput[0](Age:BC){BC} \uput[-90](Age:bC){bC}
\uput[0](Age:tr){tr} \uput[0](Age:Cr){Cr} \uput[0](Age:Br){Br} \uput[0](Age:br){br}
\end{pspicture}
\end{document}