只需从椭圆中的焦点处画一条线即可形成一个角度

Question

我想通过画一条线（$r$ 和 $\theta$）来表示角度。我想绘制下图。

平均能量损失

\documentclass{article}
\usepackage{tikz}
\begin{document}
\begin{center}
\begin{tikzpicture}
\draw (0,0) ellipse (2cm and 1cm);
\draw[](-2,0) -- (2,0);
\draw[](0,-1) -- (0,1);
% \draw[fill=black](0,0) circle (1 pt) node [above, right]{$O$};
\draw[fill=black](1,0) circle (1 pt);
\draw [<->] (-1.9,-0.1) -- (0.9,-0.1) node [midway,below]{$r_\text{max}$};
\draw [<->] (1.1,-0.1) -- (1.9,-0.1) node [midway,below]{$r_\text{min}$};
\draw [<->] (0,1.1) -- (2,1.1) node [midway,above]{$a$};
\draw [<->] (2.1,1.1) -- (2.1,0) node [midway,right]{$b$};
\draw [<-] (-0.1,0.1) -- (-1.5,1) node [end,left]{geometrical center};
\draw [<-] (1,-0.1) -- (1.4,-1) node [end,right]{centre of attraction};
\end{tikzpicture}
Elliptical Orbit
\end{center}
\end{document}

我的输出

Answer 1

您可以在定义角度的点处定义三个坐标：椭圆上的点、焦点（引力中心）和 x 轴的右端。

然后，作为奎伯比尔贝尔建议，您可以使用Ti\pic中定义的angles钾Z 库绘制指定这些点的角度。使用 quotes 库也可以轻松添加标签。

例如（我删除了end未定义的节点的样式）：

\documentclass{article}
\usepackage{amsmath} % for \text
\usepackage{tikz}
\usetikzlibrary{angles,quotes}

\begin{document}
\begin{center}
\begin{tikzpicture}
\draw (0,0) ellipse (2cm and 1cm);
\draw[](-2,0) -- (2,0) coordinate (A); % <-- a coordinate here
\draw[](0,-1) -- (0,1);
% \draw[fill=black](0,0) circle (1 pt) node [above, right]{$O$};
\draw[fill=black] (1,0) coordinate (F) circle (1 pt); % another coordinate at the focus (angle vertex)
\draw [<->] (-1.9,-0.1) -- (0.9,-0.1)  node [midway,below]{$r_\text{max}$};
\draw [<->] (1.1,-0.1)  -- (1.9,-0.1)  node [midway,below]{$r_\text{min}$};
\draw [<->] (0,1.1)     -- (2,1.1)     node [midway,above]{$a$};
\draw [<->] (2.1,1.1)   -- (2.1,0)     node [midway,right]{$b$};
\draw [<-]  (-0.1,0.1)  -- (-1.5,1)    node [left]{geometrical center};
\draw [<-]  (1,-0.1)    -- (1.4,-1)    node [right]{centre of attraction};
% LINE AND ANGLE
\draw (F) -- (40:2cm and 1cm) node[midway,above] {$r$} coordinate (P); % <-- and the last coordinate
\pic[draw,"$\theta$",angle radius=0.4cm,angle eccentricity=1.4] {angle={A--F--P}};
%            label                         label position
\end{tikzpicture}

Elliptical Orbit
\end{center}
\end{document}