Tikz coordinates relative to one node

Using both calc and |- would be a convenient way to refer to "inner, relative coordinates" of a node, with

• (0, 0) meaning node.center,
• (0, 1) meaning node.east and
• (.3, -.5) meaning somewhere precise (but relative) in the south east quarter.

However, as described here and there, the following coordinate is not parsed:

($(node.center)!.3!(node.east)$ |- $(node.center)!-.5!(node.north)$)

So the following convenience macro does not work:

\newcommand{\relativeToNode}{($(#1.center)!#2!(#1.east)$ |- $(#1.center)!#3!(#1.north)$)}

How nice would it be to write:

\node (inner) at (\relativeToNode{outer}{.3}{-.5}) {hey!};

Is there any chance to get this working?
Any workaround that would not involve defining intermediate macros or coordinates (whose names would have to be picked etc.)?

• tikz doesn't enable calculation of coordinates on the way as you desired. you should defined one auxiliary coordinate: \coordinate (aux) at ($(node1.south) + (1,0)$); \draw ($(node1.south) + (1,0)$) to (aux |- node2.north); – Zarko Aug 27 '18 at 9:52
• @Zarko Well, it seems that it is finally possible like this :) – iago-lito Aug 27 '18 at 12:15

For your use case you don't even need the calc library. You can define style relative to node=<node name> that shifts and scales the coordinate system accordingly:

\tikzset{
relative to node/.style={
shift={(#1.center)},
x={(#1.east)},
y={(#1.north)},
}
}

Then you can place your node with

\path[relative to node=outer] (-0.4,-0.5) node {Hello};

MWE:

\documentclass[tikz,margin=2mm]{standalone}

\tikzset{
relative to node/.style={
shift={(#1.center)},
x={(#1.east)},
y={(#1.north)},
}
}

\begin{document}
\begin{tikzpicture}
\node[minimum width=2cm,minimum height=3cm,draw=red] (outer) at (3,3) {};

% Only for the grid
\begin{scope}[relative to node=outer]
\foreach \ratio in {-1,-0.8,...,1}{
\draw[help lines] (-1,\ratio) -- (1,\ratio);
\draw[help lines] (\ratio,-1) -- (\ratio,1);
}
\draw (-1,0) -- (1,0);
\draw (0,-1) -- (0,1);
\end{scope}

\path[relative to node=outer] (-0.4,-0.5) node {Hello};

\end{tikzpicture}
\end{document}

Resulting in • Awesome, thanks :) Since this is not my core problem, but the core problem has no solution according to Zarko, I'll edit the OP so it matches your answer best. – iago-lito Aug 27 '18 at 9:59