scatter plot in datavisualization with extra draw

Question

In this question, it seems like adding an extra \draw to a datavisualization should be relatively straightforward. But I'm baffled:

\begin{figure}[h]
\begin{tikzpicture}

\datavisualization [scientific axes, visualize as scatter]
data [format=named] {
x={0,...,10}, y={0,...,10}
}; 
\draw [dashed] (0,1) -- (1,0);
\end{tikzpicture}
\end{figure}

As one can see in the picture, I definitely don't see any line connecting (1,0) or (0,1) here, but instead one that seems to connect (2,0) and (0,pi) (?).

Now the reference manual is, as we all know, not quite as user-friendly as may be hoped. It took me forever to figure out how to get other markers for this ... and if you remove scientific axes then most of the markers disappear.

Anyway, that's just a rant - is this somehow related to some "absolute" coordinates that are mysteriously cropping up? Why does the other question seem to work fine?

(Note: what I really want is just a grid of lattice points with a Matlab-style labeling, but for some reason that seems to be nontrivial.)

Answer 1

Drawing after \datavisualization is done using TikZ units. If you want to draw something into the plot using plot coordinates, it has to be done in info (drawing on top of the plot) orinfo' (drawing below the plot) using the visualization coordinate system.

\documentclass{article}
\usepackage{tikz}
\usetikzlibrary{datavisualization}
\begin{document}
\begin{tikzpicture}

\datavisualization [scientific axes, visualize as scatter]
data [format=named] {
    x={0,...,10}, y={0,...,10}
}
% add objects on top of the plot
info {
    % uses TikZ units
    \draw [blue] (0,1) -- (1,0);
    % use visualization coordinates
    \draw [dashed] (visualization cs: x=0,y=1) -- (visualization cs: x=1,y=0);
    % center as visualization coordinates, radius in TikZ units
    \fill [red] (visualization cs: x=3,y=3) circle (0.1);
}
% add objects below the plot
info' {
    \fill [red] (visualization cs: x=6,y=6) circle (0.1);
};
% uses TikZ units, visualization coordinates are not available here
\draw [red] (0,0) circle (0.1);
\end{tikzpicture}
\end{document}