使用 pgfplots 连接三维图中的坐标

Question

我正在尝试使用 连接 3d 图内的两个坐标（节点）pgfplots。我面临的问题是连接线甚至没有接触端点。我猜这条线被投影到某个平面上，但我该如何解决这个问题？

这是 MWE，其中洋红色的线说明了问题：

\documentclass[tikz]{standalone}
\usepackage{pgfplots}
\pgfplotsset{compat = newest}
\begin{document}

\begin{tikzpicture}
\begin{axis}
    
%   s(t) curve
    \addplot3 [
        mesh,
        color=blue,
        domain=-0.7:0.7
    ] (x, x, -{2/5}*x^2);
    
%   dots on s(t)
    \addplot3 [
        color=blue,
        draw=none, 
        mark=*, 
        mark size=1.5
        ] table [row sep=crcr] {%
         0    0    0    \\
        } node (S) [at start,above] {$s(t)$};
    
%   r(t)
    \addplot3 [
        mesh,
        color=blue,
        domain=-0.7:0.707
    ] (x, {0.5*(5*0.3-(-4*x^2+20*0.2-20*x*0.3+25*0.3^2)^0.5)}, {-0.2+0.5*0.3*(2*x-5*0.3+(-4*x^2+20*0.2-20*x*0.3+25*0.3^2)^0.5)});
    
%   dots on r(t)
    \addplot3 [
        color=blue,
        draw=none, 
        mark=*, 
        mark size=1.5
        ] table [row sep=crcr] {%
        0   -0.5        -0.05\\
        } node (R) [at start,below] {$r(t)$};
        
    \draw[thick,magenta] (R) -- (S);
    
\end{axis}
\end{tikzpicture}

\end{document}

Answer 1

为什么要连接节点？您应该通过坐标进行连接。因为正如您所指定的，节点实际上位于坐标的上方和下方（node (S) [at start,above] {$s(t)$}和node (R) [at start,below] {$r(t)$}）：

\documentclass[tikz]{standalone}
\usepackage{pgfplots}
\pgfplotsset{compat = newest}
\begin{document}

\begin{tikzpicture}
\begin{axis}
    
%   s(t) curve
    \addplot3 [
        mesh,
        color=blue,
        domain=-0.7:0.7
    ] (x, x, -{2/5}*x^2);
    
%   dots on s(t)
    \addplot3 [
        color=blue,
        draw=none, 
        mark=*, 
        mark size=1.5
        ] table [row sep=crcr] {%
         0    0    0    \\
        } node (S) [at start,above] {$s(t)$};
    
%   r(t)
    \addplot3 [
        mesh,
        color=blue,
        domain=-0.7:0.707
    ] (x, {0.5*(5*0.3-(-4*x^2+20*0.2-20*x*0.3+25*0.3^2)^0.5)}, {-0.2+0.5*0.3*(2*x-5*0.3+(-4*x^2+20*0.2-20*x*0.3+25*0.3^2)^0.5)});
    
%   dots on r(t)
    \addplot3 [
        color=blue,
        draw=none, 
        mark=*, 
        mark size=1.5
        ] table [row sep=crcr] {%
        0   -0.5        -0.05\\
        } node (R) [at start,below] {$r(t)$};
        
    \draw[thick,magenta] (0,0,0) -- (0,-0.5,-0.05);
    
\end{axis}
\end{tikzpicture}

\end{document}