具有指定坐标的 tikz 图片中的中心点

Question

我试图通过在图表上画一个点来注释图表。我指定了点中心的准确坐标，但显然这不是点的中心...

有没有办法在不改变坐标的情况下改变这种情况？

\documentclass[11pt, a4paper]{article}

\usepackage[latin1]{inputenc} % niet-ASCII-tekens gebruiken
\usepackage{tikz} % geavanceerde figuren maken
\usepackage[Gray,squaren,thinqspace,thinspace]{SIunits} % elegant eenheden zetten
\usepackage[dutch]{babel} % Nederlands als taal instellen
\usepackage[small,bf,hang]{caption} % bijschriften invoegen
\usepackage{pgfplots} % data plottenf
\pgfplotsset{compat=newest} % meest recente versie pgfplots gebruiken
\usepackage{pgfplotstable} % tabellen uit .csv laden
\usepackage{amsmath} % uitgebreide wiskundige mogelijkheden
\usepackage{pgf} %meer mooie plots
\usepackage{subcaption} %figuren naast elkaar
    \usetikzlibrary{arrows,automata} %mooie pijlen

\begin{document}
\begin{figure}[ht]
\centering
\begin{subfigure}{0.48\linewidth}
\centering
\begin{tikzpicture}
\begin{loglogaxis}[
xlabel=frequentie $f (\hertz)$,
ylabel=transferfunctie $T\ (\frac{\volt}{\volt})$,
grid=both, 
minor grid style={gray!25}, 
major grid style={gray!25},
no marks,
width=\linewidth]
\draw[*-,color=red!50] (axis cs:3e4,1) -- (axis cs:10e4,0.5) node[right,color=black] {$f_\text{\unit{3}{dB}}$};
\addplot [color=red] coordinates {(1e3, 1)
(3e4, 1) % breekpunt
(3*1e5, 0.1)};
\end{loglogaxis}
\end{tikzpicture}
\subcaption{Amplitude bode-plot.\label{BodeAmplitudeTweedeTrap}}
\end{subfigure}%
\hspace{5pt}
\begin{subfigure}{0.48\linewidth}
\centering
\begin{tikzpicture}
\begin{axis}[
xmode=log,
ymode=normal,
xlabel=frequentie $f (\hertz)$,
ylabel=fase $\phi (\degree)$,
ytick={-90,-45,0,45,90},
grid=both, 
minor grid style={gray!25}, 
major grid style={gray!25},
width=\linewidth,
no marks]
\addplot [color=red] coordinates {(1e3, 0)
(3e3,0)
(3e4, -45) % breekpunt
(3e5,-90)
(1e6,-90)};
\end{axis}
\end{tikzpicture}
\subcaption{Fase bode-plot.\label{BodeFrequentieTweedeTrap}}
\end{subfigure}%
\caption{Bode-diagram transferfunctie tweede trap.\label{BodeEersteTrap}}
\end{figure}
\end{document}

Answer 1

您使用的语法-*是用于箭头的。如果您想要一个实心圆，那么最好将其放置为：

\draw[<options>] (axis cs:3e4,1) circle (2pt) ....

笔记：

• 第二个图似乎与问题无关，所以我在下面的 MWE 中将其注释掉了。

代码：

\documentclass[11pt, a4paper]{article}

\usepackage[latin1]{inputenc} % niet-ASCII-tekens gebruiken
\usepackage{tikz} % geavanceerde figuren maken
\usepackage[Gray,squaren,thinqspace,thinspace]{SIunits} % elegant eenheden zetten
\usepackage[dutch]{babel} % Nederlands als taal instellen
\usepackage[small,bf,hang]{caption} % bijschriften invoegen
\usepackage{pgfplots} % data plottenf
\pgfplotsset{compat=newest} % meest recente versie pgfplots gebruiken
\usepackage{pgfplotstable} % tabellen uit .csv laden
\usepackage{amsmath} % uitgebreide wiskundige mogelijkheden
\usepackage{pgf} %meer mooie plots
\usepackage{subcaption} %figuren naast elkaar
    \usetikzlibrary{arrows,automata} %mooie pijlen

\begin{document}
\begin{figure}[ht]
\centering
\begin{subfigure}{0.48\linewidth}
\centering
\begin{tikzpicture}
\begin{loglogaxis}[
xlabel=frequentie $f (\hertz)$,
ylabel=transferfunctie $T\ (\frac{\volt}{\volt})$,
grid=both, 
minor grid style={gray!25}, 
major grid style={gray!25},
no marks,
width=\linewidth]
\draw[color=red!50,fill=blue!50, fill opacity=0.5] (axis cs:3e4,1) circle (2pt) -- (axis cs:10e4,0.5) node[right,color=black] {$f_\text{\unit{3}{dB}}$};
\addplot [color=red] coordinates {(1e3, 1)
(3e4, 1) % breekpunt
(3*1e5, 0.1)};
\end{loglogaxis}
\end{tikzpicture}
\subcaption{Amplitude bode-plot.\label{BodeAmplitudeTweedeTrap}}
\end{subfigure}%
%\hspace{5pt}
%\begin{subfigure}{0.48\linewidth}
%\centering
%\begin{tikzpicture}
%\begin{axis}[
%xmode=log,
%ymode=normal,
%xlabel=frequentie $f (\hertz)$,
%ylabel=fase $\phi (\degree)$,
%ytick={-90,-45,0,45,90},
%grid=both, 
%minor grid style={gray!25}, 
%major grid style={gray!25},
%width=\linewidth,
%no marks]
%\addplot [color=red] coordinates {(1e3, 0)
%(3e3,0)
%(3e4, -45) % breekpunt
%(3e5,-90)
%(1e6,-90)};
%\end{axis}
%\end{tikzpicture}
%\subcaption{Fase bode-plot.\label{BodeFrequentieTweedeTrap}}
%\end{subfigure}%
%\caption{Bode-diagram transferfunctie tweede trap.\label{BodeEersteTrap}}
\end{figure}
\end{document}