Center align two scopes (horizontally, vertically)

Question

Imagine I have two quite unrelated scopes:

• Scope 1: A geometric drawing with exact dimensions in millimeters and an overall scaling factor
• Scope 2: A circuittikz drawing using the normal dimensionless grid

Now I would like to place both scopes on top of each other, but vertically and horizontally aligned. I tried to use the local bounding box of the first scope, but as the second scope does not have a mid/center anchor point I don't know how to align the two scopes.

Please assume:

• The scaling factor of the first scope is arbitrary and should not be used
• I do know the coordinate of the center point of the second scope

Do you know how I could shift the inner coordinate system of the second scope, so the origin lies in the center? Or is it somehow possible to determine the center of the second scope automatically and use it for alignment?

MWE

\documentclass{article}

\usepackage{tikz}

\begin{document}

\begin{tikzpicture}

\begin{scope}[scale=2, local bounding box = scope1]
\draw[fill=blue, opacity = 0.5] (0,0) rectangle (1,1);
\end{scope}

\begin{scope}[scale=1.5, shift={(scope1.center)}]
\draw[fill=red, opacity = 0.5] (0,0) rectangle (1,1);
\end{scope}

\end{tikzpicture}

\end{document}

What I get

What I want

Thank you very much for your help!

More complex MWE

Imagine I would like to center the resistor inside the rectangle:

\documentclass{article}

\usepackage{tikz}
\usepackage{circuitikz}
\usetikzlibrary{calc}

\begin{document}

\begin{tikzpicture}

\begin{scope}[scale=1.5, local bounding box = scope1]
    % These are real dimensions of a more complex geometry
    \filldraw[thin, fill = gray!20!white] (0mm,0mm) 
    -- ++(0mm, 7mm) 
    -- ++(22mm, 0mm)  
    -- ++(0mm, -7mm) 
    -- cycle;
\end{scope}

\begin{scope}[scale=1.2]
    \draw
    (0,0) to [R=$R$] (2,0)
    ;
\end{scope}

\end{tikzpicture}

\end{document}

Answer 1

In order to shift the second drawing appropriately, you need to now its dimensions. One trick that allows you to position the second drawing where you want is to store it in a pic, and then use a matrix to position it because a matrix "measures" what's inside before drawing it.

\documentclass{article}

\usepackage{tikz}

\begin{document}

\begin{tikzpicture}

\begin{scope}[scale=2, local bounding box = scope1]
\draw[fill=blue, opacity = 0.5] (0,0) rectangle (1,1);
\end{scope}

\tikzset{pics/centered/.style={code={
\draw[fill=red, opacity = 0.5] (0,0) rectangle (1,1);
}}}

\matrix[at={(scope1.center)}] {
\pic[scale=1.5] {centered};\\
};

\end{tikzpicture}

\end{document}

There are limitations. For instance, the inner drawing cannot contain a matrix.

Answer 2

Here's a solution using a recent update to tikzmark (link to github as it isn't yet on CTAN) which introduces code for positioning a scope at an internally defined anchor which is evaluated after the scope is constructed. It uses tikzmark to remember locations which means that it needs two complications to work.

\documentclass{article}
% \url{https://tex.stackexchange.com/q/517894/86}
\usepackage{tikz}
\usetikzlibrary{tikzmark}
\begin{document}
\begin{tikzpicture}
\begin{scope}[scale=2, local bounding box = scope1]
\draw[fill=blue, opacity = 0.5] (0,0) rectangle (1,1);
\end{scope}
\begin{scope}[
  scale=1.5,
  shift={(scope1.center)},
  anchor=center,
  scope anchor,
]
\draw[fill=red, opacity = 0.5] (0,0) rectangle (1,1);
\end{scope}
\end{tikzpicture}
\end{document}

(Note: this is new code so I'm still ironing out some bugs - on the first compilation then it complains about coordinates but it works on the second.)