[Tex/LaTex] How to fill area under plot using a color map

pgfplotstikz-pgf

I have one diagram showing a function f(x,y) like imshow does, and a second diagram that shows the probability distribution P(f). Find below an image of the situation. The code for the plot at the bottom is basically

\addplot[const plot,fill=black!20,very thin] file{hist.dat} \closedcycle;

To increase the visual connection between both images, I'd like to use the colormap from the first diagram in the second diagram: The currently gray area below the histogram plot should be filled with the colormap's gradient in x direction.

I tried to achieve that with stuff like fill=mapped color and different plot types like ycomb and ybar interval, but it seems that, out of the box, only mesh and scatter support colormaps, and both are unsuitable for my scenario.

Here is an image of the situation.

EDIT: For completeness, here is my solution, derived from the accepted answer.

\def\defcolormapshading#1#2{%
 \pgfplotscolormaptoshadingspec{#2}{50pt}\tempa%
 \def\tempb{\pgfdeclarehorizontalshading{#1}{\paperheight}}%
 \expandafter\tempb\expandafter{\tempa}%
 \let\tempa\undefined\let\tempb\undefined%
}%

Put this in your preamble. Then, before the tikzpicture environment, say

\defcolormapshading{myshading}{mymap}

(replace "mymap" by the colormap name, and "myshading" by a descriptive name for the shading). Then give the key shading=myshading to \addplot. The use of \pgfplotscolormaptoshadingspec like in this snippet is detailed in the pgfplots manual.

Best Answer

You could just define an appropriate shading using \pgfdeclarehorizontalshading and use that to fill your plot. The colour at position 25bp of the shading is the leftmost visible color, that at 75bp is the rightmost visible colour.

\documentclass{article}
\usepackage{pgfplots}
\usepgfplotslibrary{colormaps}

\begin{document}
\begin{tikzpicture}
\pgfdeclarehorizontalshading{stefan}{100bp}{
color(0bp)=(blue!50!black);
color(25bp)=(blue!50!black);
color(50bp)=(blue);
color(55bp)=(green);
color(60bp)=(yellow);
color(65bp)=(orange);
color(70bp)=(red);
color(75bp)=(red!50!black);
color(100bp)=(red!50!black)
}

\begin{axis}[enlargelimits=false,domain=-2.63:1.39,point meta=x]
\addplot [shading=stefan] coordinates {(-2.63,0.2) (-0.5,0.4) (-0.2,0.5) (-0.1,2.6) (0,0.8) (0.1,0.7) (0.2,0.8) (0.4,2.2) (0.5,0.4) (1.39,0.3)} \closedcycle;
\end{axis}
\end{tikzpicture}
\end{document}

Related Solutions

[Tex/LaTex] Draw box around plot or fill plot area in tikz/pgfplots

You can use the \pgf@pathminx and \pgf@pathmaxy commands, which hold the current path's minimum and maximum x and y coordinates, to draw a rectangle around the plot. Here's a macro \drawplotbox that can be called at the end of the \addplot command. The style of the box is controlled by a key called plot box, the padding of the box can be set using plot box padding:

\documentclass{standalone}
\usepackage{tikz,pgfplots}

\makeatletter
\newcommand{\drawplotbox}{
(\pgf@pathminx,\pgf@pathminy) coordinate (current plot south west)
            (\pgf@pathmaxx,\pgf@pathmaxy) coordinate (current plot north east);
            \draw [plot box] ([shift={(-135:1.41*\pgfkeysvalueof{/tikz/plot box padding})}]current plot south west) rectangle ([shift={(45:1.41*\pgfkeysvalueof{/tikz/plot box padding})}]current plot north east);
}

\tikzset{
    plot box/.style={
        thick, rounded corners, orange
    },
    plot box padding/.initial=5pt
}

\begin{document}
    \begin{tikzpicture}
        \begin{axis}
            \addplot coordinates{
                (0,0)
                (2,1)
                (1,1)
                (2,2)
                (0,2)
            } \drawplotbox;
            \addplot +[plot box/.append style=black, plot box padding=10pt] coordinates{
                (3,3)
                (5,4)
                (4,4)
                (5,5)
                (3,5)
            } \drawplotbox;
        \end{axis}
    \end{tikzpicture}
\end{document}

[Tex/LaTex] Pgfplots: how to fill bounded area under a curve using addplot and fill

This can be done by means of the fillbetween library which has been introduced in pgfplots 1.10 :

enter image description here

\documentclass{standalone}

\usepackage{pgfplots}

\pgfplotsset{compat=1.10}

\usepgfplotslibrary{fillbetween}

\begin{document}
\begin{tikzpicture} 
    \begin{axis}[enlargelimits=0.1]
    \addplot[name path=f,domain=-.15:1.05,blue] {x^2};

    \path[name path=axis] (axis cs:0,0) -- (axis cs:1,0);

    \addplot [
        thick,
        color=blue,
        fill=blue, 
        fill opacity=0.05
    ]
    fill between[
        of=f and axis,
        soft clip={domain=0:1},
    ];

    \node [rotate=48] at (axis cs:  .7,  .59) {$y=x^2$};
    \node [rotate=90] at (axis cs:  1.05,  .25) {$x=1$};
    \end{axis}
\end{tikzpicture}  
\end{document}

The basic idea is to have two labelled input paths, in our case the function as such and the path which resembles the other boundary (in our case the part of the axis from 0 to 1). Then, \addplot fill between can draw the area between these two input paths.

The fill between library can also draw intersection segments individually. This would allow you to fill only the area between y=0.2 and the function:

enter image description here

\documentclass{standalone}

\usepackage{pgfplots}

\pgfplotsset{compat=1.10}

\usepgfplotslibrary{fillbetween}

\begin{document}

\begin{tikzpicture} 
    \begin{axis}[enlargelimits=0.1]
    \addplot[name path=f,domain=-.15:1.05,blue] {x^2};

    \path[name path=axis] (axis cs:0,0.2) -- (axis cs:1,0.2);

    \addplot [
        thick,
        color=blue,
        fill=blue, 
        fill opacity=0.05
    ]
    fill between[
        of=f and axis,
        split,
        every segment no 0/.style={
            %fill=none,
            yellow,
        },
    ];

    \node [rotate=48] at (axis cs:  .7,  .59) {$y=x^2$};
    \node [rotate=90] at (axis cs:  1.05,  .25) {$x=1$};
    \end{axis}
\end{tikzpicture}  
\end{document}

In this example, the second path (labelled axis) is at y=0.2 and we fill between f and axis. Clearly, this results in two segments. I told fillbetween to fill the first segment in yellow, but you can easily use fill=none to make it invisible.

In case you want to show the boundaries of the filled region, you can easily add draw to the option list of \addplot fill between.

Best Answer

Related Solutions

[Tex/LaTex] Draw box around plot or fill plot area in tikz/pgfplots

[Tex/LaTex] Pgfplots: how to fill bounded area under a curve using addplot and fill

Related Question