折线图——放置水平截止线

Question

\documentclass{article}
\usepackage{pgfplotstable}
\title  {Hydrogen Breath Test Report}
\begin{document}
\maketitle
\begin{tikzpicture}
    \begin{axis}[
        xlabel=min,
        ylabel=Hydrogen ppm]
    \addplot[color=black,mark=x] coordinates {
        (0,  2)
        (15,4)
        (30, 15)
        (60, 20)
        (90, 25)
        (120, 30)
        (180, 45)
    };
    \addplot[color=black!10] coordinates{
        (0,  13)
        (15,13)
        (30, 13)
        (60, 13)
        (90, 13)
        (120, 13)
        (180, 13)
    };
    \end{axis}
\end{tikzpicture}
\end{document}

你好，请看一下这段代码。我画了一条灰色的水平线来表示截止水平。有没有更好的方法？x 轴上的“0”是基线值。我怎样才能用“基线”标签代替“0”？问候

Answer 1

所以这可能是您正在寻找的内容...
（有关更多详细信息，请查看代码的注释。）

\documentclass[border=5pt]{standalone}
\usepackage{pgfplots}
    \pgfplotsset{
        % to place the axis labels better
        compat=1.3,
    }
\begin{document}
    \begin{tikzpicture}
        \begin{axis}[
            % define the axis limits
            xmin=0,
            xmax=200,
            ymin=0,
            ymax=50,
            % improved a bit the axis labels
            xlabel=time in min,
            ylabel=Hydrogen concentration in ppm,
            % -----------------------------
            % add extra labels at x = 0 and y = 13
            extra x ticks={0},
            extra y ticks={13},
            % define the style for the extra ticks
            extra tick style={
                % to not draw an extra tick set the width to 0
                tickwidth=0pt,
                % write "baseline" as extra x tick label
                xticklabels={baseline},
                % so the 0 of the normal ticks isn't seen any more ...
                xticklabel style={
                    % ... fill the extra tick label white ...
                    fill=white,
                    % ... and adjust the "sep"s of the node so the 0 of the
                    % y tick label isn't overdrawn
                    % to do so just exchange the default values of the inner
                    % and outer sep
                    inner sep=0pt,
                    outer sep=0.3333em,
                },
                % to not draw an extra y tick label give an empty argument
                yticklabels={},
                % instead a grid line should be drawn
                ymajorgrids=true,
            },
        ]
            \addplot [mark=x] coordinates {
                (  0,  2)
                ( 15,  4)
                ( 30, 15)
                ( 60, 20)
                ( 90, 25)
                (120, 30)
                (180, 45)
            };
        \end{axis}
    \end{tikzpicture}
\end{document}