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在 PGFplots 轴环境中计算 TikZ 注释的坐标

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在 PGFplots 轴环境中计算 TikZ 注释的坐标

TikZ我正在尝试通过节点在轴环境中进行一些注释PGFplots。但是，节点的放置总是出错，请参见下面的最小工作示例。我该如何解决这个问题？如何TikZ正确计算注释的坐标？

梅威瑟：

\documentclass[margin=1cm]{standalone}
\usepackage{pgfplots}
\pgfplotsset{compat=newest}
\usetikzlibrary{calc}
\begin{document}
    \begin{tikzpicture}
        \begin{axis}
        [
            xtick={-0.1,0,1,1.1},xmin=-0.1,xmax=1.1,xlabel=$x$,
            ytick={-0.2,0,2,2.2},ymin=-0.2,ymax=2.2,ylabel style={rotate=-90},ylabel=$y$,
            unit vector ratio=2 1 1,
        ]
            \addplot[blue,domain=0:1] {x};
            \addplot[red,domain=0:1] {2*x};

            % Annotation.
            \coordinate (SW) at (axis cs:-0.1,-0.2); % (S)outh (w)est.
            \coordinate (SE) at (axis cs:1.1,-0.2); % (S)outh (e)ast.
            \coordinate (NE) at (axis cs:1.1,2.2); % (N)orth (e)ast.
            \coordinate (NW) at (axis cs:-0.1,2.2); % (N)orth (w)est.

            \coordinate (A) at (axis cs:1,0);
            \fill[black] (A) circle (1pt) node[anchor=south]{A};

             % ??? WHY IS THIS NOT WORKING. SHOULD BE THE SAME AS NODE A. ???
            \coordinate (B) at ($(SE)+(axis cs:-0.1,0.2)$); % ??? WHY IS THIS NOT WORKING. SHOULD BE THE SAME AS NODE A. ???
            \fill[black] (B) circle (1pt) node[anchor=south east]{B}; % ??? WHY IS THIS NOT WORKING. SHOULD BE THE SAME AS NODE A. ???
             % ??? WHY IS THIS NOT WORKING. SHOULD BE THE SAME AS NODE A. ???

        \end{axis}
    \end{tikzpicture}
\end{document}

答案1

画布区域的原点与绘图区域的原点不同。calc 表达式中的绘图坐标对 (-0.1, 0.2)($(SE) + (-0.1, 0.2)$)被转换为画布坐标并添加到 的画布坐标中SE。但由于原点不匹配，结果会因绘图原点到画布原点的位移而移动。实际上您想添加“相对”坐标：

($(SE) + (-0.1, 0.2) - (0, 0)$)

下面的例子试图说明这一点：

\documentclass[margin=1cm]{standalone}
\usepackage{pgfplots}
\pgfplotsset{compat=newest}
\usetikzlibrary{arrows.meta}
\usetikzlibrary{calc}
\begin{document}
    \begin{tikzpicture}
        \begin{axis}
        [
            xtick={-0.1,0,1,1.1},xmin=-0.1,xmax=1.1,xlabel=$x$,
            ytick={-0.2,0,.5,.7},
            ymin=-0.2,ymax=.7,
            ylabel style={rotate=-90},
            ylabel=$y$,
            unit vector ratio=2 1 1,
        ]
            % \addplot[blue,domain=0:1] {x};
            % \addplot[red,domain=0:1] {2*x};

            % Annotation.
            \coordinate (SW) at (axis cs:-0.1,-0.2); % (S)outh (w)est.
            \coordinate (SE) at (axis cs:1.1,-0.2); % (S)outh (e)ast.
            \coordinate (NE) at (axis cs:1.1,2.2); % (N)orth (e)ast.
            \coordinate (NW) at (axis cs:-0.1,2.2); % (N)orth (w)est.

            \coordinate (A) at ($(1,0)$);
            \fill[black] (A) circle (1pt) node[anchor=south]{A};

            \coordinate (CO) at (0pt, 0pt);% canvas origin
            \coordinate (PO) at (0, 0);% plot origin
            \coordinate (D) at (-0.1, 0.2);% displacement as plot point

            \begin{scope}[
              -{Triangle[]},
              node font=\footnotesize,
              inner sep=.15em,
            ]
              % Show canvas origin
              \draw
               (CO) ++(1em, .4em) node[above right] (tmp) {Canvas origin (CO)}
               (tmp.west) -- (CO);

              % Show plot origin
              \draw
                (PO) ++(1em, .4em) node[above right] (tmp) {Plot origin (PO)}
                (tmp.west) -- (PO);

              % Show displacement as absolute plot point
              \draw
                (D) ++(1em, .4em) node[above right] (tmp) {D}
                (tmp.west) -- (D);

              % Show SE
              \draw
                (SE) ++(-1.5em, .4em) node[above left] (tmp) {SE}
                (tmp.east) -- (SE);

               % Show SE + D
               \draw
                 ($(SE) + (D)$) coordinate (SE_D)
                 ++(-1em, .4em) node[above left] (tmp) {SE + D}
                 (tmp.east) -- (SE_D);

               % Show SE + D - plot origin
               \draw
                 ($(SE) + (D) - (PO)$) coordinate (SE_D_PO)
                 ++(-1em, 0em) node[left] (tmp) {SE + D - PO}
                 (tmp.east) -- (SE_D_PO);

               \draw[red, very thick, <->, >={latex[]}]
                 (CO) -- (D);
               \draw[red, very thick, <->, >={latex[]}]
                 (SE) -- (SE_D);

               \draw[blue, thick, <->, >={latex[]}]
                 (PO) -- (D);
               \draw[blue, thick, <->, >={latex[]}]
                 (SE) -- (SE_D_PO);
            \end{scope}
        \end{axis}
    \end{tikzpicture}
\end{document}

结果

更清晰的符号是使用cs axis direction如下坐标系回答的 esdd。

答案2

您必须使用axis direction cs：

\coordinate (B) at ($(SE)+(axis direction cs:-0.1,0.2)$);

在此处输入图片描述

代码：

\documentclass[margin=1cm]{standalone}
\usepackage{pgfplots}
\pgfplotsset{compat=1.12}
\usetikzlibrary{calc}
\begin{document}
    \begin{tikzpicture}
        \begin{axis}
        [
            xtick={-0.1,0,1,1.1},xmin=-0.1,xmax=1.1,xlabel=$x$,
            ytick={-0.2,0,2,2.2},ymin=-0.2,ymax=2.2,ylabel style={rotate=-90},ylabel=$y$,
            unit vector ratio=2 1 1,
        ]
            \addplot[blue,domain=0:1] {x};
            \addplot[red,domain=0:1] {2*x};

            % Annotation.
            \coordinate (SW) at (-0.1,-0.2); % (S)outh (w)est.
            \coordinate (SE) at (1.1,-0.2); % (S)outh (e)ast.
            \coordinate (NE) at (1.1,2.2); % (N)orth (e)ast.
            \coordinate (NW) at (-0.1,2.2); % (N)orth (w)est.

            \coordinate (A) at (1,0);
            \fill[black] (A) circle (1pt) node[anchor=south]{A};

             % ??? WHY IS THIS NOT WORKING. SHOULD BE THE SAME AS NODE A. ???
            \coordinate (B) at ($(SE)+(axis direction cs:-0.1,0.2)$);??? WHY IS THIS NOT WORKING. SHOULD BE THE SAME AS NODE A. ???
            \fill[red,fill opacity=.5] (B) circle (2pt) node[anchor=south east]{B}; % ??? WHY IS THIS NOT WORKING. SHOULD BE THE SAME AS NODE A. ???
             % ??? WHY IS THIS NOT WORKING. SHOULD BE THE SAME AS NODE A. ???

        \end{axis}
    \end{tikzpicture}
\end{document}

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