[Tex/LaTex] Differences between paths drawn between nodes and coordinates in tikz

coordinatesnodestikz-pgf

Referencing this very helpful posts and the Tikz manual, which states:

Whenever TikZ encounters a whole node name as a “coordinate,” it tries to “be smart” about the anchor that it should choose for this node. Depending on what happens next, TikZ will choose an anchor that lies on the border of the node on a line to the next coordinate or control point.

I can see the difference in the way the following two paths are drawn:

Paths between nodes vs. coordinates

The second path is the preferred one. My question is if there is a better way to integrate this into fewer commands. I cannot seem to get a "point" drawn using the shape=coordinate inside node[], and instead am drawing the actual points using filldraw.

\documentclass[border=5pt]{standalone}
\usepackage{tikz}
\usetikzlibrary{arrows,backgrounds,patterns,shapes.geometric,calc,positioning}

\begin{document}
\begin{tikzpicture}[scale=1,auto]
[bend angle=45]

\node[name=f,shape=ellipse,draw, thick, minimum width=50, minimum height=75] at (0,0) {};
\node[name=g,shape=ellipse,draw, thick, minimum width=50, minimum height=75] at (2,0) {};

\coordinate(f1) at ($(f.center) + (0,1)$);
\coordinate(g1) at ($(g.center) + (0,1)$);

\node at ($(f.center) + (0,-1)$) (f3) {};
\node at ($(g.center) + (0,-1)$) (g3) {};

\filldraw   
        (f1) circle (1pt)
        (f3) circle (1pt)
        (g1) circle (1pt)
        (g3) circle (1pt);  

\draw[->, >=stealth,bend left] (f1) to (g1);
\draw[->, >=stealth,bend left] (f3) to (g3);

\end{tikzpicture}
\end{document}

Best Answer

If you daw the nodes you made you will understand that in one case you connect points in the other one you connect "boxes" aka nodes :

\documentclass[border=5pt]{standalone}
\usepackage{tikz}
\usetikzlibrary{arrows,backgrounds,patterns,shapes.geometric,calc,positioning}

\tikzset{small dot/.style={fill=black,circle,scale=0.25}}

\begin{document}
\begin{tikzpicture}[scale=1,auto]
[bend angle=45]

\node[name=f,shape=ellipse,draw, thick, minimum width=50, minimum height=75] at (0,0) {};
\node[name=g,shape=ellipse,draw, thick, minimum width=50, minimum height=75] at (2,0) {};

\coordinate(f1) at ($(f.center) + (0,1)$);
\coordinate(g1) at ($(g.center) + (0,1)$);

\node[small dot] at ($(f.center) + (0,-1)$) (f3) {};
\node[small dot,outer sep=3pt] at ($(g.center) + (0,-1)$) (g3) {};

\filldraw   
        (f1) circle (1pt)
        %(f3) circle (1pt)
        (g1) circle (1pt)
        %(g3) circle (1pt)
        ;  

\draw[->, >=stealth,bend left] (f1) to (g1);
\draw[->, >=stealth,bend left] (f3) to (g3);

\end{tikzpicture}
\end{document}

enter image description here

Related Solutions

[Tex/LaTex] Rotate a node but not its content: the case of the ellipse decoration

The source of the difficulty is that ellipses are constructed in a particular way in TikZ. They are paths that start from the x-axis and proceed counter-clockwise around their centre. The vast majority of the time, the exact parametrisation doesn't matter. You appear to have found the one situation where it does!

In the actual question, you only want to be able to mirror the ellipse, and so draw it starting from the negative x-axis (the title of the question suggests a more flexible approach). That's actually not too hard since we can exploit the symmetry of the ellipse. The key is to provide it with a negative x-radius, since then it will start from the negative x-axis (and proceed clockwise, but we could correct for that by negating the y-radius as well). To do this, we interrupt the call from the node shape to the drawing command and flip the sign of the x-radius. The simplest way to do this is to redefine the \pgfpathellipse macro to do the negation and then call the original macro. The following code does this.

\documentclass{article}
\usepackage{tikz}
\usetikzlibrary{decorations,shapes,decorations.markings}
\makeatletter
\let\origpgfpathellipse=\pgfpathellipse
\def\revpgfpathellipse#1#2#3{%
  #2%
  \pgf@xa=-\pgf@x
  \origpgfpathellipse{#1}{\pgfqpoint{\pgf@xa}{0pt}}{#3}}
\makeatother

\tikzset{
  reversed ellipse/.style={
    ellipse,
    reverse the ellipse%
  },
  reverse the ellipse/.code={
    \let\pgfpathellipse=\revpgfpathellipse
  }
}
\begin{document}
\begin{tikzpicture}
\node[ellipse,
  draw,
  postaction={
    decorate,
    decoration={
      markings,
      mark=at position 1 with {
        \arrow[line width=5pt,blue]{>}
      }
    }
  }
] at (0,0) {hello world};

\node[reversed ellipse,
  draw,
  postaction={
    decorate,
    decoration={
      markings,
      mark=at position 1 with {
        \arrow[line width=5pt,blue]{>}
      }
    }
  }
] at (0,-2) {hello world};
\end{tikzpicture}

\end{document}

Here's the result:

rotated ellipse

(the arrow got clipped, but you can see where it lies)

[Tex/LaTex] Increase the thickness of node border in TikZ

The node’s border is a path, you can use the same options for a \path, e.g. ultra thin, thick, very thick, and so on:

\node[circle, draw=blue!80, thick, inner sep=0pt, minimum size=12pt] (1) at (0,0) {1};

The line width key works as well:

\node[circle,draw=blue!80, line width=1mm, inner sep=0pt,minimum size=12pt] (1) at(0,0) {1};

All predefined line widths are

\tikzset{
    ultra thin/.style= {line width=0.1pt},
    very thin/.style=  {line width=0.2pt},
    thin/.style=       {line width=0.4pt},% thin is the default
    semithick/.style=  {line width=0.6pt},
    thick/.style=      {line width=0.8pt},
    very thick/.style= {line width=1.2pt},
    ultra thick/.style={line width=1.6pt}
}

Code

\documentclass[tikz]{standalone}
\begin{document}
\begin{tikzpicture}[
   every node/.append style={circle, draw=blue!80, inner sep=0pt, minimum size=12pt}]
\node                 (1) at (0,0) {1};
\node[thick]          (2) at (1,0) {2};
\node[line width=1mm] (3) at (2,0) {3};
\end{tikzpicture}
\end{document}

Output