Placing node right after end of path in Tikz

Question

I'd like to place a label (most of the times a single letter) right after the end of a line. That is, the node should be moved into the direction of the line from its endpoint, just as far that is doesn't overlap with the line.

I know that I could do

\tikz (a)--node[pos=1.1]{b}(b);

but I don't want the distance of the node from the line end to depend on the length of the line. Also I'd like this to work for arbitrary curved paths, not just straight lines.

What is the easiest way to do this in Tikz?

Answer 1

(this is the first time I add another answer --- if it's not the correct thing to do, please tell me; but this is so different from my first one that... should I mark it community wiki?)

You can use a transform on a decoration, thanks to the fact that the coordinate system in a decoration is along the path; that will shift the node after the end of the path by a distance specified as the second argument:

\documentclass[border = 2mm]{standalone}
\usepackage{tikz}
\usetikzlibrary{decorations.markings}
\begin{document}
\begin{tikzpicture}[
    endnode/.style n args={2}{
        decoration={
        markings,
        % transform={xshift=0.1*\pgfdecoratedpathlength}, % relative to lenght
        transform={xshift=#2},                            % absolute 
        % maybe add a endnodestyle like in Torbjørn T.'s answer
        mark=at position 1 with {\node[draw=red] {#1};}   % just to debug 
        },
     postaction={decorate},
  },
]
\foreach \Ang/\Len in {0/1,45/1.2,90/1.4,135/1.6,180/1.8,225/2,270/2.2,315/2.4}
{
    \draw [endnode={A}{2mm}] (0,0) -- (\Ang:\Len);
    \draw [endnode={B}{4mm}] (6,0) to[bend right]  ++(\Ang:\Len);
}
\end{tikzpicture}
\end{document}

This makes the node centered at a fixed distance from the end of the path, along the path. It doesn't change the node anchors, unfortunately... and auto is not working here.

Thanks to: Length of curve in TikZ, Torbjørn T.'s answer, \tikzset key with multiple arguments.

Answer 2

You can put the node at pos=1 and then left (or right, depending on where) align it:

\documentclass[border=10pt]{standalone}
\usepackage{tikz}
\begin{document}
\begin{tikzpicture}[every node/.style={draw=red},
    ]
         \draw (0,0) -- (1,0) node[right]{a} ;
         \draw (1,0.5) --node[pos=1, left]{b}  (0,0.5) ;
         \draw (0,-1) -- node[pos=1,  right]{c} (1, -2)  ;
         \draw (0,-1.3) -- node[pos=1,  sloped, right]{d} (1, -2.3)  ;
         \draw (0,-2) .. controls (0,-1) and (0.5,-1.5) .. node[pos=1,  right]{e} (1, -1)  ;
\end{tikzpicture}
\end{document}

Answer 3

One can get somewhat close using the decorations.markings library. The code below makes use of the fact that a markings decoration has an internal coordinate system where the x-axis is parallel to the path, so I made a short path along the y-axis, and placed an auto node along it.

It's not perfect, and I can't guarantee that it will always work. For the bent to paths in the example below, I had to rotate the nodes by -90 degrees, and I'm not exactly sure why. You can also see that the position of the nodes is perhaps not perfect.

\documentclass[border = 2mm]{standalone}
\usepackage{tikz}
\usetikzlibrary{decorations.markings}
\begin{document}
\begin{tikzpicture}[
  endnode style/.style={},
  endnodestyle/.style={endnode style/.append style={#1}},
  endnode/.style={
    decoration={
     markings,
     mark=at position 1 with {
       \path (0,-1pt) -- node[auto,swap,endnode style] {#1} (0,1pt);
     }
    },
    postaction={decorate}
  }
]
\foreach \Ang in {0,45,...,350}
{
  % works fine for straight lines
  \draw [endnode=a] (0,0) -- (\Ang:2cm);
  % needs a rotation for these curved paths
  \draw [endnodestyle={rotate=-90},endnode=foo] (6,0) to[bend right] ++(\Ang:2cm);
}
\end{tikzpicture}
\end{document}

Better output, less convenient to use

You could save two coordinates on the path, one very close to the end (I randomly used pos=0.97 here, but I suspect the ideal value will depend on the path), one at the end (pos=1). Then in a separate path, calculate the angle between those two coordinates with the let operation (manual section 14.15), and use that to set the anchor of a node. This does not have the problem the decorations.markings version above suffered, of failing at larger bend angles, but is as mentioned less convenient to use.

\documentclass[border = 2mm]{standalone}
\usepackage{tikz}
\usetikzlibrary{decorations.markings, calc}
\newcommand{\addnode}[2][tmp]{%
\path let
  \p1=($(#1-A)-(#1-B)$),\n1={atan2(\y1,\x1)}
  in
  node[anchor=\n1] at (#1-B) {#2};
}

\begin{document}
\begin{tikzpicture}
\foreach \Ang in {0,45,...,350}
{
  % works fine for straight lines
  \draw (0,0) -- 
        coordinate[pos=0.97] (tmp-A) % near end
        coordinate[pos=1]    (tmp-B) % at end
  (\Ang:2cm); % close the path
  \addnode{a} % add node in separate step


  \draw (6,0) to[bend right=80]
       coordinate[pos=0.97] (tmp-A)
       coordinate[pos=1]    (tmp-B)
    ++(\Ang:2cm);
  \addnode{foo}
}
\end{tikzpicture}
\end{document}

Answer 4

Here is another answer using decorations.markings that should work without manual tweaking : place the node node right after the end of the line, without rotation and with the right anchor.

The trick is to place first one node that is used as reference to determine the right anchor position.

\documentclass[tikz,border=7pt]{standalone}
\usetikzlibrary{decorations.markings,calc}
\begin{document}
\begin{tikzpicture}[
  endnode/.style={
    decoration={
     markings,
     mark=at position .999 with {
      \path (0,0) node[overlay](refnode){}
        let \p1=(refnode.west), \n1={-atan2(\y1,\x1)} in {
          node[anchor=\n1, draw=red] {#1}
        };
     }
    },
    postaction={decorate}
  }
]
\foreach \Ang in {0,20,...,350}
{
  \draw [endnode=a] (0,0) -- (\Ang:2cm);
  \draw [endnode=foo] (6,0) to[bend right=77] ++(\Ang:2cm);
}
\end{tikzpicture}
\end{document}

EDIT : As @Torbjørn T. suggest in his comment I replaced pos=1 with pos=.999 to avoid disappearing due to rounding tex errors. I also added overlay to the reference node to avoid bounding box surprises.