Does one need an invisible node to make edge split among nodes?

Question

I am learning how to make flow chart in tikz. In this MWE

\documentclass[crop,tikz]{standalone}
\usepackage{amsmath}
\usepackage{tikz}
\usetikzlibrary{shapes.geometric, arrows}
\begin{document}
\tikzstyle{NODE} = [rectangle, rounded corners, minimum width=3cm, minimum height=1cm, draw=black, fill=red!10]
\begin{tikzpicture}[node distance=2cm]
\node (A1) [NODE]  {my first node};
\node (A2) [NODE,below of=A1]  {my second node};
\node (A3) [NODE,below of=A2]  {is it true?};
\node (A4) [NODE,left of=A3,yshift=-2cm]   {we get here if true};
\node (A5) [NODE,right of=A3,yshift=-2cm]   {we get here if false};
\draw [->,thick] (A1.south) -|   (A2.north);
\draw [->,thick] (A2.south) -| (A3.north);
\draw [->,thick] (A3.south) -| node[anchor=south] {YES} (A4.north);
\draw [->,thick] (A3.south) -| node[anchor=south] {NO} (A5.north);
\end{tikzpicture}
\end{document}

It gives

I am not sure what is the correct way to produce this instead (which I did using paint.exe for illustration)

Do I need to make a hidden node below A3 first? in order to make the edges as shown? Or is there a better and canonical way to do this? I do not want the edges to be sloping, I like to use straight edges only. I know I could do this

\draw [->,thick] (A1.south) -|   (A2.north);
\draw [->,thick] (A2.south) -| (A3.north);
\draw [->,thick] (A3.south) -- node[anchor=south] {YES} (A4.north);
\draw [->,thick] (A3.south) -- node[anchor=south] {NO} (A5.north);

And get

But I like the straight edges more.

Can one make a node in tikz that has no size and do not show, and use it just as place holder to in order to make edges to it?

Answer 1

Adaptations

• use relative positioning to move to the point below the node: (A3.south) -- ++(0,-5mm)
• save that point as coordinate(a) (this is the invisible node without a size you mention)
• reuse it to draw the other line (a) -| ...
  • I left out the first part ((A3.south) -- (a)) because it would just draw a second line over the already existing one. You would only need this, if you use curved edges or colored arrows.
• use tikzset instead of tikzstyle (see Should \tikzset or \tikzstyle be used to define TikZ styles?)

See Also

• Vertical and horizontal lines in pgf-tikz

Code

\documentclass[crop,tikz]{standalone}
\usepackage{tikz}
\usetikzlibrary{shapes.geometric, arrows}
\begin{document}
\begin{tikzpicture}[
    node distance=2cm,
    NODE/.style={rectangle, rounded corners, minimum width=3cm, minimum height=1cm, draw=black, fill=red!10}
]
    \node (A1) [NODE]  {my first node};
    \node (A2) [NODE,below of=A1]  {my second node};
    \node (A3) [NODE,below of=A2]  {is it true?};
    \node (A4) [NODE,left of=A3,yshift=-2cm]   {we get here if true};
    \node (A5) [NODE,right of=A3,yshift=-2cm]   {we get here if false};
\draw [->,thick] (A1.south) -|   (A2.north);
\draw [->,thick] (A2.south) -| (A3.north);
\draw [->,thick] (A3.south) -- ++(0,-5mm) coordinate(a) -| node[anchor=south] {YES} (A4.north);
\draw [->,thick] (a) -| node[anchor=south] {NO} (A5.north);

\end{tikzpicture}
\end{document}

Result

Answer 2

Here is an alternative using forest.

\documentclass{article}
\usepackage{forest}
\useforestlibrary{edges}
\begin{document}
\begin{forest}
for tree={rounded corners, minimum width=3cm, minimum height=1cm, draw=black, fill=red!10,
  l sep=1cm, fork sep=5mm, s sep=1cm,
  forked edge, edge={thick, ->}
}
[my first node
  [my second node
    [is it true?
      [we get here if true, edge label={node[midway, above]{YES}}]
      [we get here if false, edge label={node[midway, above]{NO}}]
    ]
  ]
]
\end{forest}
\end{document}