[Tex/LaTex] Common colorbar over groupplot

graphicsgroupplotspgfplotstikz-pgf

I have results that I want to present in a groupplot that share a common result range. Naturally, I don't want to show multiple colorbar next to each picture next to each individual picture but one colorbar

over or under the groupplot spanning from left to right of the groupplot or
left or right of the groupplot spanning from top to bottom of the groupplot

I got the groupplot working thanks to this thread. I tried several things for the colorbar but I was not successful so far:

Solution try 1

Based on this answer. But the height is not correct:

\documentclass{standalone}

\usepackage{pgfplots}
\usepgfplotslibrary{groupplots}
\usepackage{tikz}
\usetikzlibrary{positioning}

\begin{document}

\begin{tikzpicture}
\pgfmathsetmacro{\xmin}{0}
\pgfmathsetmacro{\xmax}{1.64}
\pgfmathsetmacro{\ymin}{0}
\pgfmathsetmacro{\ymax}{1}
\begin{groupplot}[
  group style={
    group name=my plots,
    group size= 2 by 4,
    vertical sep=1.5cm
  },
  width=7cm,
  hide axis,
  enlargelimits=false,
  axis equal image,
]
  \nextgroupplot
\addplot graphics [xmin=\xmin,xmax=\xmax,ymin=\ymin,ymax=\ymax]
          {example-image-a};
  \nextgroupplot[
    point meta min=0.0,
    point meta max=1.0,
    colormap/bluered,                     % Colormap preset
    colorbar sampled,                     % Steps in colorbar
    colorbar right,
    colorbar style={
      separate axis lines,
      samples=256,                        % Number of steps
    },
    every colorbar/.append style={
      height=2*\pgfkeysvalueof{/pgfplots/parent axis height}+
               \pgfkeysvalueof{/pgfplots/group/vertical sep}
    }
  ]
\addplot graphics [xmin=\xmin,xmax=\xmax,ymin=\ymin,ymax=\ymax]
          {example-image-a};
  \nextgroupplot
\addplot graphics [xmin=\xmin,xmax=\xmax,ymin=\ymin,ymax=\ymax]
          {example-image-a};
  \nextgroupplot
\addplot graphics [xmin=\xmin,xmax=\xmax,ymin=\ymin,ymax=\ymax]
          {example-image-a};
\end{groupplot}
% Labels
\node[below = 0.5cm of my plots c1r1.south] {(a) Timestep 25};
\node[below = 0.5cm of my plots c2r1.south] {(b) Timestep 35};
\node[below = 0.5cm of my plots c1r2.south] {(c) Timestep 45};
\node[below = 0.5cm of my plots c2r2.south] {(d) Timestep 55};
\end{tikzpicture}

\end{document}

Giving this result:

Defining a fixed height does not change anything regarding the result. Interestingly I can change the colorbar height with point meta max=2 option

Solution try 2

Based on this answer I tried using node relative positioning:

\documentclass{standalone}

\usepackage{pgfplots}
\usepgfplotslibrary{groupplots}
\usepackage{tikz}
\usetikzlibrary{positioning}

\begin{document}

\begin{tikzpicture}
\pgfmathsetmacro{\xmin}{0}
\pgfmathsetmacro{\xmax}{1.64}
\pgfmathsetmacro{\ymin}{0}
\pgfmathsetmacro{\ymax}{1}
\begin{groupplot}[
  group style={
    group name=my plots,
    group size= 2 by 4,
    vertical sep=1.5cm
  },
  width=7cm,
  hide axis,
  enlargelimits=false,
  axis equal image,
]
  \nextgroupplot
    \addplot graphics [xmin=\xmin,xmax=\xmax,ymin=\ymin,ymax=\ymax]
          {example-image-a};
    \coordinate (top) at (rel axis cs:0,1);% coordinate at top of the first plot
  \nextgroupplot
    \addplot graphics [xmin=\xmin,xmax=\xmax,ymin=\ymin,ymax=\ymax]
          {example-image-a};
  \nextgroupplot
    \addplot graphics [xmin=\xmin,xmax=\xmax,ymin=\ymin,ymax=\ymax]
          {example-image-a};
  \nextgroupplot
    \addplot graphics [xmin=\xmin,xmax=\xmax,ymin=\ymin,ymax=\ymax]
          {example-image-a};
    \coordinate (bot) at (rel axis cs:1,0);% coordinate at bottom of the last plot
\end{groupplot}
% Labels
\node[below = 0.5cm of my plots c1r1.south] {(a) Timestep 25};
\node[below = 0.5cm of my plots c2r1.south] {(b) Timestep 35};
\node[below = 0.5cm of my plots c1r2.south] {(c) Timestep 45};
\node[below = 0.5cm of my plots c2r2.south] {(d) Timestep 55};
% Colorbar
\path (top|-current bounding box.north)--
                    coordinate(legendpos)
                    (bot|-current bounding box.north);
\begin{axis}[%
  hide axis,
  scale only axis,
  %height=.6\linewidth,
  %width=.9\linewidth,
  at={(top.north)},
  anchor=north west,
  point meta min=0.0,
  point meta max=2.0,
  colormap/bluered,                     % Colormap preset
  colorbar horizontal,                  % Active colorbar
  colorbar sampled,                     % Steps in colorbar
  colorbar style={
    separate axis lines,
    samples=256,                        % Number of steps
  },
]
  \addplot [draw=none] coordinates {(0,0)};
\end{axis}
\end{tikzpicture}

\end{document}

This gives me a colorbar but it is not nearly where I would expect it and the width is not from left to right of two subplots:

Any ideas how to fix the colorbar?

Best Answer

Ok, I basically got what I want with the second attempt. But the solution is not as automated as I would like it to have concerning width and position of the colorbar

\documentclass{standalone}

\usepackage{pgfplots}
\usepgfplotslibrary{groupplots}
\usepackage{tikz}
\usetikzlibrary{positioning}

\begin{document}

\begin{tikzpicture}
\pgfmathsetmacro{\xmin}{0}
\pgfmathsetmacro{\xmax}{1.64}
\pgfmathsetmacro{\ymin}{0}
\pgfmathsetmacro{\ymax}{1}
\begin{groupplot}[
  group style={
    group name=my plots,
    group size= 2 by 4,
    vertical sep=1.5cm
  },
  width=7cm,
  hide axis,
  enlargelimits=false,
  axis equal image,
]
  \nextgroupplot
    \addplot graphics [xmin=\xmin,xmax=\xmax,ymin=\ymin,ymax=\ymax]
          {example-image-a};
    \coordinate (top) at (rel axis cs:0,1);% coordinate at top of the first plot
  \nextgroupplot
    \addplot graphics [xmin=\xmin,xmax=\xmax,ymin=\ymin,ymax=\ymax]
          {example-image-a};
  \nextgroupplot
    \addplot graphics [xmin=\xmin,xmax=\xmax,ymin=\ymin,ymax=\ymax]
          {example-image-a};
  \nextgroupplot
    \addplot graphics [xmin=\xmin,xmax=\xmax,ymin=\ymin,ymax=\ymax]
          {example-image-a};
    \coordinate (bot) at (rel axis cs:1,0);% coordinate at bottom of the last plot
\end{groupplot}
% Labels
\node[below = 0.5cm of my plots c1r1.south] {(a) Timestep 25};
\node[below = 0.5cm of my plots c2r1.south] {(b) Timestep 35};
\node[below = 0.5cm of my plots c1r2.south] {(c) Timestep 45};
\node[below = 0.5cm of my plots c2r2.south] {(d) Timestep 55};
% Node position middle right groupplot
\path (top-|current bounding box.east)--
                    coordinate(legendposright)
                    (bot-|current bounding box.east);
% Node position middle above groupplot
\path (top|-current bounding box.north)--
                    coordinate(legendposabove)
                    (bot|-current bounding box.north);
% Node markers
%\node [circle,fill=black,minimum size=10pt] at (legendposright){};
%\node [circle,fill=black,minimum size=10pt] at (legendposabove){};
%Colorbar above
\begin{axis}[%
  hide axis,
  scale only axis,
  height=.01\linewidth,
  width=0.975\linewidth,
  at={(legendposabove.south)},
  yshift=1.25cm,
  anchor=south,
  point meta min=0.0,
  point meta max=2.0,
  colormap/bluered,                     % Colormap preset
  colorbar horizontal,                  % Active colorbar
  colorbar sampled,                     % Steps in colorbar
  colorbar style={
    separate axis lines,
    samples=256,                        % Number of steps
    xticklabel pos=upper
  },
  %every colorbar/.append style={
  %  width=\pgfkeysvalueof{/pgfplots/parent axis width}%+
  %             %\pgfkeysvalueof{/pgfplots/group/vertical sep}
  %}
]
  \addplot [draw=none] coordinates {(0,0)};
\end{axis}
%Colorbar right
\begin{axis}[%
  hide axis,
  scale only axis,
  %height=0.975\linewidth,
  %width=0.01\linewidth,
  at={(legendposright.east)},
  anchor=east,
  xshift=0.25cm,
  point meta min=0.0,
  point meta max=2.0,
  colormap/bluered,                     % Colormap preset
  colorbar right,                  % Active colorbar
  colorbar sampled,                     % Steps in colorbar
  colorbar style={
    separate axis lines,
    samples=256,                        % Number of steps
  },
  every colorbar/.append style={
    height=\pgfkeysvalueof{/pgfplots/parent axis height}%+
               %\pgfkeysvalueof{/pgfplots/group/vertical sep}
  }
]
  \addplot [draw=none] coordinates {(0,0)};
\end{axis}
\end{tikzpicture}

\end{document}

Result:

Any improvements ideas?

Related Solutions

[Tex/LaTex] Common scale for pgfplots groupplot

You can use the every plot/.style key to enter the common settings in that group

\documentclass{article}
\usepackage{pgfplots}
\usepgfplotslibrary{groupplots}
\begin{document}
\begin{tikzpicture}
\begin{groupplot}[group style={group size=2 by 2,
                               every plot/.style={
                                        xmin=-1,
                                        xmax=2,
                                        enlargelimits=true
                                 }
                             }]
\nextgroupplot
\addplot coordinates{(0,0)(1,1)(2,2)};
\nextgroupplot
\addplot coordinates{(0,2)(1,1)(2,0)};
\nextgroupplot
\addplot coordinates{(0,2)(1,1)(2,1)};
\nextgroupplot
\addplot coordinates{(0,2)(1,1)(1,0)};
\end{groupplot}
\end{tikzpicture}
\end{document}

enter image description here

[Tex/LaTex] Common colorbar for groupplot

You simply need to adjust the height of the color bar plot.

This can easily be accomplished by doing:

every colorbar/.append style={height=<height specification>}

However, often you will use different heights for different groupplots. Therefore a more general approach would be:

every colorbar/.append style={height=
    2*\pgfkeysvalueof{/pgfplots/parent axis height}+
    \pgfkeysvalueof{/pgfplots/group/vertical sep}
}

The first key /pgfplots/parent axis height is the height of the actual contour plot (of which you attach the colorbar).

The second key /pgfplots/group/vertical sep is the spacing in between the two group plots. This needs to be adjusted by the number of lower lying plots, in this case only one.

So the above takes and makes the colorbar plot have a height equal to 2 plots plus the vertical separation of the plots. Furthermore it is generic if you change height and vertical sep, etc. However, notice that if the plots have different heights the above approach will not work.

Ok, so one thing is that you only need to plot the colorbar once. Groupplots ensure that each statement in the groupplot environment will be added to every sub-plot. Hence you simply need to put the colorbar in the top \nextgroupplot. The colorbar is aligned at the top right corner of the parent axis, hence you should do it to the top plot.
So:

\nextgroupplot[colorbar right,
   every colorbar/.append style={height=
      2*\pgfkeysvalueof{/pgfplots/parent axis height}+
      \pgfkeysvalueof{/pgfplots/group/vertical sep}}]

A thing to be very careful about when attaching colorbars to several contours is to ensure the bounds of the contour to be the same for both, hence I would recommend you to also add point meta min=<value> and point meta max=<value>. Please do remember this! :)

Ok, so the final groupplots is something like this:

\begin{tikzpicture}
  \begin{groupplot}[view={0}{90},
    xlabel=$x$,
    ylabel=$y$,
    height=3cm,
    point meta min=-1.5,
    point meta max=1.5,
    group/xlabels at = edge bottom,
    group style = {group size = 1 by 2,
        xlabels at = edge bottom
    }]
    \nextgroupplot[colorbar right,
    every colorbar/.append style={height=
        2*\pgfkeysvalueof{/pgfplots/parent axis height}+
        \pgfkeysvalueof{/pgfplots/group/vertical sep}}]
    \addplot3[surf] {sin(36*x)};
    \nextgroupplot
    \addplot3[surf] {cos(36*y)};
  \end{groupplot}
\end{tikzpicture}

This will result in: