如何在单个绘图上绘制矢量场和曲线

Question

我正在尝试使用以下代码绘制矢量场和圆。按照原样使用代码，蓝色圆圈看起来偏离中心。如果我注释掉该绘制命令并取消注释另一个命令，蓝色圆圈根本就不会绘制。为什么会发生这种情况？如何修复？我觉得我错过了一些非常简单的东西。

\usepackage{pgfplots}
\usepackage{tikz-3dplot}
\usetikzlibrary{3d}
\begin{document}
\def\length{sqrt(1+(x+y)^2)}
\begin{tikzpicture}[>=latex,x=1.5cm,y=1.5cm,scale=1.85,font=\footnotesize]
    \begin{axis}[
        axis lines=middle,
        view={0}{90},
        domain=-2.5:2.5,
        samples=18,
        axis equal image,
        ticklabel style = {font=\tiny}
        ]
        \addplot3[
        gray,
        quiver={u={1/(\length)},
        v={(x+y)/(\length)},
        scale arrows=0.2,
        every arrow/.append style={-latex}}
        ] (x,y,0);
        % \draw (axis cs:0,0) circle [blue, radius=1];
    \end{axis}
    \draw[thick,blue] (0,0) circle (1);
\end{tikzpicture}
\end{document}

Answer 1

添加以使环境\pgfplotsset{compat=newest}内的坐标系与宏（以及和类似宏）同步。这样，您可以省略：axis\path\draw\fillaxis cs

\documentclass[border=10pt]{standalone}
\usepackage{pgfplots}
\pgfplotsset{compat=newest}

\begin{document}
\begin{tikzpicture}[>=latex, x=1.5cm, y=1.5cm, scale=1.85, font=\footnotesize]
    \def\length{sqrt(1+(x+y)^2)}
    \begin{axis}[
        axis lines=middle,
        view={0}{90},
        domain=-2.5:2.5,
        samples=18,
        axis equal image,
        ticklabel style={font=\tiny}
    ]
    \addplot3[
        gray,
        quiver={u={1/(\length)},
        v={(x+y)/(\length)},
        scale arrows=0.2,
        every arrow/.append style={-latex}},
    ] (x,y,0);
    \draw[blue] (0,0) circle[radius=1];
    \end{axis}
\end{tikzpicture}
\end{document}