# [Tex/LaTex] draw a grid in the foreground

tikz-pgf

I'm trying to follow this example on how to draw a background grid so I can easily connect arrows, but it draws the (non-transparent) picture on top of the grid making it hard to use. I want to draw the grid in the foreground, how can I do that?

You can temporarily use opacity=.5 for the node where you insert the picture:

\node [inner sep=0pt,above right,opacity=.5]   %%% <--- here
{\includegraphics[width=4cm]{example-image}};


When you are done, simply make opacity = 1 or delete it.

Full code:

\documentclass{beamer} %
\usepackage{tikz}
\usepackage{verbatim}

\usetikzlibrary{arrows,shapes,backgrounds}

\begin{document}
% For every picture that defines or uses external nodes, you'll have to
% apply the 'remember picture' style. To avoid some typing, we'll apply
% the style to all pictures.
\tikzstyle{every picture}+=[remember picture]
\tikzstyle{na} = [baseline=-.5ex]

\begin{frame}

\frametitle{Daniell's pile, saline bridge version}

\begin{columns}
\begin{column}{0.4\paperwidth}
% define source coordinates
\begin{itemize}
\item Anode \tikz[na] \coordinate (s-anode);
\item Cathode \tikz[na] \coordinate (s-cathode);
\item Saline bridge \tikz[na] \coordinate (s-bridge);
\end{itemize}

\end{column}
\begin{column}{0.45\paperwidth}
% Use a background grid to make it easier to find coordinates
% When the coordinates have been found, remove the
% 'show background grid' option.
\tikzstyle{background grid}=[draw, black!50,step=.5cm]
\begin{tikzpicture}[show background grid]
% Put the graphic inside a node. This makes it easy to place the
% graphic and to draw on top of it.
% The above right option is used to place the lower left corner
% of the image at the (0,0) coordinate.
\node [inner sep=0pt,above right,opacity=.5]
{\includegraphics[width=4cm]{example-image}};
% show origin
\fill (0,0) circle (2pt);
% define destination coordinates
\path (0.7,2) coordinate (cathode)
(2,1.8) coordinate (bridge)
(2.75,2.5) coordinate (anode);
\end{tikzpicture}
\end{column}
\end{columns}

% define overlays
% Note the use of the overlay option. This is required when
% you want to access nodes in different pictures.
\begin{tikzpicture}[overlay]
\path[->,red,thick] (s-anode) edge [bend left] (anode);
\path[->,blue,thick] (s-cathode) edge [bend left] (cathode);
\path[->,red,thick] (s-bridge) edge [out=0, in=-90] (bridge);
\end{tikzpicture}

\end{frame}

\end{document}


Or using a scope to draw them after including image.

       \begin{tikzpicture}
\node [inner sep=0pt,above right]
{\includegraphics[width=4cm]{example-image}};
\path (0.7,2) coordinate (cathode)
(2,1.2) coordinate (bridge)
(2.75,2.5) coordinate (anode);
\begin{scope}
\draw (current bounding box.south west)
grid [step=0.5cm] (current bounding box.north east);
\end{scope}
\end{tikzpicture}


PS: I have used example-image from mwe package. Change it with your picture.