在 Tikz 中命名两条路径的交点

Question

考虑下面的椭圆，它有两个标记点，红色和绿色，使用 TikZ 的交叉点库计算。

\documentclass[margin=5mm]{standalone}
\usepackage{tikz}
\usetikzlibrary{calc}
\usetikzlibrary {intersections} 
\usetikzlibrary{calc}
\usetikzlibrary{math}
\usetikzlibrary{shapes}

\makeatletter
\newcommand{\gettikzxy}[3]{%
  \tikz@scan@one@point\pgfutil@firstofone#1\relax
  \edef#2{\the\pgf@x}%
  \edef#3{\the\pgf@y}%
}
\makeatother

\begin{document}
\begin{tikzpicture}
  \coordinate (CTRL)     at (0,0) ;
  \node[draw, black, thick, ellipse,
  minimum height=3cm, minimum width=2cm,
  name=ctrl,
  name path=ctrl] at (CTRL) {Control};

  \gettikzxy{(ctrl.south)}{\csx}{\csy}
  \gettikzxy{(ctrl.north)}{\cnx}{\cny}
  
  \coordinate (C1) at ($(\csx,\csy) + 1/7*(0,\cny-\csy)$) ;
  \path[name path=lev1] ($(C1)+(-2,0)$) -- ($(C1) + (2,0)$);

  \coordinate (C2) at ($(\csx,\csy) + 2/7*(0,\cny-\csy)$) ;
  \path[name path=lev2] ($(C2)+(-2,0)$) -- ($(C2) + (2,0)$);

% how do I name this intersection as I1?
  \fill [red,name intersections={of=ctrl and lev1}] (intersection-2) circle (2pt) node {}; 
 % how do I name this intersection as I2?
  \fill [green,name intersections={of=ctrl and lev2}] (intersection-2) circle (2pt) node {};
\end{tikzpicture}
\end{document}

我想将红点命名为 ，I1将绿点命名为I2，以便稍后在代码中绘制路径时使用它们。我该怎么做？

我尝试查看给出的交叉点的文档这里；使用by选项几乎似乎回答了这个问题，但是当我尝试在选项中使用如下方法时\fill

  \fill [red,name intersections={of=ctrl and lev1},by={a,b}] (b) circle (2pt) node {}; 

我收到错误

! Package pgfkeys Error: I do not know the key '/tikz/by', to which you passed 
'a,I1', and I am going to ignore it. Perhaps you misspelled it.

See the pgfkeys package documentation for explanation.
Type  H <return>  for immediate help.
 ...                                              
                                                  
l.34 ...ntersections={of=ctrl and lev1},by={a,I1}]
                                                   (I1) circle (2pt) node {}...

Answer 1

编辑：

• 路径交叉点的命名在包文档中有描述tikz，第 13.3.2 节 任意路径的交点，第 145 页。
• 你的 MWE 编译没有任何错误或警告，但如果你想更改交叉点名称，你需要在命令中声明，例如像这样

\fill [name intersections={of=..., by=I1}, red]  (I1) circle[radius=2pt];

• C1通过使用不同的坐标方式、C2计算和定义交点，您的 MWE 可以变得更短（更简单）：

\documentclass[margin=5mm]{standalone}
\usepackage{tikz}
\usetikzlibrary{calc,
                intersections,
                shapes}

\begin{document}
    \begin{tikzpicture}[
E/.style = {ellipse, draw, thick, 
            minimum height=3cm, minimum width=2cm}
                        ]
% elipse
\node[E, name path=C] (ctrl)  {Control};

\coordinate (C1) at ($ (ctrl.south)!1/7!(ctrl.north) $);
\coordinate (C2) at ($ (ctrl.south)!2/7!(ctrl.north) $);

\path[name path=A] (C1) -- ++ (1,0);  % changed
\path[name path=B] (C2) -- ++ (1,0);  % changed
% intersections
\fill [name intersections={of=C and A, by=I1}, red]  (I1) circle[radius=2pt)];
\fill [name intersections={of=C and B, by=I2}, teal] (I2) circle[radius=2pt)];

\end{tikzpicture}
\end{document}