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如何使用 TikZ 和 LaTeX 将节点绘制为实心圆圈（点）来指示连接？

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如何使用 TikZ 和 LaTeX 将节点绘制为实心圆圈（点）来指示连接？

我在使用 TikZ 绘制控制系统框图时遇到了一些麻烦。我希望某个节点显示为一个点，表示连接。但是，这个点不是位于节点的中心，而是位于其上方。我该如何解决这个问题？

从该 LaTeX 文档生成的 PS 或 PDF 中可以明显看出这个问题：

\documentclass{article}

\usepackage{tikz}
\usetikzlibrary{shapes,arrows}
\begin{document}

\pagestyle{empty}

\tikzstyle{block} = [draw, rectangle, minimum width = 0.75cm, minimum height = 0.75cm]
\tikzstyle{sum} = [draw, circle, minimum size=.5cm, node distance=1.75cm]
\tikzstyle{input} = [coordinate]
\tikzstyle{output} = [coordinate]

\begin{tikzpicture}[node distance=2cm,auto,>=latex']
    \node [input, name=input] {};
    \node [sum, right of=input] (sum) {};
    \node [block, right of=sum] (a1) {$A_1(s)$};
    \node [block, right of=a1] (a2) {$A_2(s)$};
    \node [block, right of=a2] (k) {$K$};
    \node [output, right of=k] (output) {}; 

    \draw [->] (a1) -- (a2);
    \draw [->] (a2) -- node [name=vout] {$V_o$} (k);

   \node [block, below of=a2] (a3) {$A_1(s)$};

   \draw [draw,->, node] (input) -- node {$V_\mathrm{ref}$} node[pos=0.95] {{\tiny $+$}} (sum);
   \draw [->] (sum) -- (a1);
   \draw [->] (k) -- node[name=vl]  {$V_L$} (output);
   \draw [->] (vl) |- (a3);
   \draw [->] (a3) -| node[pos=0.99, right] {{\tiny $-$}} (sum);

   \fill (vl) circle [radius=2pt];
\end{tikzpicture}
\end{document}

答案1

您可以使用

   \fill (vl.south) circle [radius=2pt];

或者更好的是，

   \fill (vl|-k) circle [radius=2pt];

完整示例：

\documentclass{article}

\usepackage{tikz}
\usetikzlibrary{shapes,arrows}
\begin{document}

\pagestyle{empty}

\tikzstyle{block} = [draw, rectangle, minimum width = 0.75cm, minimum height = 0.75cm]
\tikzstyle{sum} = [draw, circle, minimum size=.5cm, node distance=1.75cm]
\tikzstyle{input} = [coordinate]
\tikzstyle{output} = [coordinate]

\begin{tikzpicture}[node distance=2cm,auto,>=latex']
    \node [input, name=input] {};
    \node [sum, right of=input] (sum) {};
    \node [block, right of=sum] (a1) {$A_1(s)$};
    \node [block, right of=a1] (a2) {$A_2(s)$};
    \node [block, right of=a2] (k) {$K$};
    \node [output, right of=k] (output) {}; 

    \draw [->] (a1) -- (a2);
    \draw [->] (a2) -- node [name=vout] {$V_o$} (k);

   \node [block, below of=a2] (a3) {$A_1(s)$};

   \draw [draw,->] (input) -- node {$V_\mathrm{ref}$} node[pos=0.95] {{\tiny $+$}} (sum);
   \draw [->] (sum) -- (a1);
   \draw [->] (k) -- node[name=vl]  {$V_L$} (output);
   \draw [->] (vl) |- (a3);
   \draw [->] (a3) -| node[pos=0.99, right] {{\tiny $-$}} (sum);

   %\fill (vl.south) circle [radius=2pt];
   \fill (vl|-k) circle [radius=2pt];
\end{tikzpicture}
\end{document}

在此处输入图片描述

另一种选择是先V_L在适当的位置设置一个坐标，然后使用该坐标放置圆圈：

\documentclass{article}

\usepackage{tikz}
\usetikzlibrary{shapes,arrows}
\begin{document}

\pagestyle{empty}

\tikzstyle{block} = [draw, rectangle, minimum width = 0.75cm, minimum height = 0.75cm]
\tikzstyle{sum} = [draw, circle, minimum size=.5cm, node distance=1.75cm]
\tikzstyle{input} = [coordinate]
\tikzstyle{output} = [coordinate]

\begin{tikzpicture}[node distance=2cm,auto,>=latex']
    \node [input, name=input] {};
    \node [sum, right of=input] (sum) {};
    \node [block, right of=sum] (a1) {$A_1(s)$};
    \node [block, right of=a1] (a2) {$A_2(s)$};
    \node [block, right of=a2] (k) {$K$};
    \node [output, right of=k] (output) {}; 

    \draw [->] (a1) -- (a2);
    \draw [->] (a2) -- node [name=vout] {$V_o$} (k);

   \node [block, below of=a2] (a3) {$A_1(s)$};

   \draw [draw,->] (input) -- node {$V_\mathrm{ref}$} node[pos=0.95] {{\tiny $+$}} (sum);
   \draw [->] (sum) -- (a1);
   \draw [->] (k) -- coordinate[label=above:$V_L$] (vl)  (output);
   \draw [->] (vl) |- (a3);
   \draw [->] (a3) -| node[pos=0.99, right] {{\tiny $-$}} (sum);

   \fill (vl) circle [radius=2pt];
\end{tikzpicture}
\end{document}

另一个选择是使用坐标（如上面最后一个例子所示），然后使用*->箭头类型，并为 指定一个方便的值shorten，如

\draw [->] (k) -- coordinate[label=above:$V_L$] (vl)  (output);
\draw [*->,shorten <= -2pt] (vl) |- (a3);

完整示例：

\documentclass{article}

\usepackage{tikz}
\usetikzlibrary{shapes,arrows}
\begin{document}

\pagestyle{empty}

\tikzstyle{block} = [draw, rectangle, minimum width = 0.75cm, minimum height = 0.75cm]
\tikzstyle{sum} = [draw, circle, minimum size=.5cm, node distance=1.75cm]
\tikzstyle{input} = [coordinate]
\tikzstyle{output} = [coordinate]

\begin{tikzpicture}[node distance=2cm,auto,>=latex']
    \node [input, name=input] {};
    \node [sum, right of=input] (sum) {};
    \node [block, right of=sum] (a1) {$A_1(s)$};
    \node [block, right of=a1] (a2) {$A_2(s)$};
    \node [block, right of=a2] (k) {$K$};
    \node [output, right of=k] (output) {}; 

    \draw [->] (a1) -- (a2);
    \draw [->] (a2) -- node [name=vout] {$V_o$} (k);

   \node [block, below of=a2] (a3) {$A_1(s)$};

   \draw [draw,->] (input) -- node {$V_\mathrm{ref}$} node[pos=0.95] {{\tiny $+$}} (sum);
   \draw [->] (sum) -- (a1);
   \draw [->] (k) -- coordinate[label=above:$V_L$] (vl)  (output);
   \draw [*->,shorten <= -2pt] (vl) |- (a3);
   \draw [->] (a3) -| node[pos=0.99, right] {{\tiny $-$}} (sum);

\end{tikzpicture}
\end{document}

答案2

这里最好使用坐标来区分节点和交叉点

   \draw [draw,->, node] (input) -- node {$V_\mathrm{ref}$} node[pos=0.95] {{\tiny $+$}} (sum);
   \draw [->] (sum) -- (a1);
   \draw [->] (k) -- node[name=vl]  {$V_L$} (output);
   \draw [->] (vl) |- (a3);
   \draw [->] (a3) -| node[pos=0.99, right] {{\tiny $-$}} (sum);

   \fill (vl) circle [radius=2pt];

答案3

这里和有所不同coordinate。node我修改了代码。我使用了/.style和，并且用不同的方法放置{\tiny $+$}。我认为符号的位置更好。

\documentclass{article}
\usepackage{tikz}
\usetikzlibrary{shapes,arrows}
\begin{document}

\pagestyle{empty}

\begin{tikzpicture}[%
    node distance = 2 cm,auto,>=latex',
    block/.style  = {draw, rectangle, minimum width = 0.75cm, minimum height = 0.75cm},
    sum/.style    = {draw, circle, minimum size=.5cm, node distance=1.75cm},
    input/.style  = {coordinate},
    output/.style = {coordinate},
    dot/.style    = {anchor=base,fill,circle,inner sep=1pt}]

    \node [input, name=input] {};
    \node [sum, right of=input] (sum) {};
    \node [block, right of=sum] (a1) {$A_1(s)$};
    \node [block, right of=a1] (a2) {$A_2(s)$};
    \node [block, right of=a2] (k) {$K$};
    \node [output, right of=k] (output) {}; 
    \node [block, below of=a2] (a3) {$A_1(s)$};

    \draw [->] (a1) -- (a2);
    \draw [->] (a2) -- node [name=vout] {$V_o$} (k);
    \draw [draw,->] (input) -- node {$V_\mathrm{ref}$} (sum); 
    \draw [->] (sum) -- (a1);
    \draw [->] (k) -- coordinate[dot](vl) node  {$V_L$} (output); 
    \draw [->] (vl) |- (a3);
    \draw [->] (a3) -| (sum);

    \node [shift=({145:12pt})] at (sum.center)  {\tiny $+$}; % I removed {}
    \node [shift=({-45:12pt})] at (sum.center)  {\tiny $-$}; 
\end{tikzpicture} 

\end{document}

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