Relative positioning in 3D

Question

I am trying to position a node in 3D according to the (x, y) coordinates of a node previously defined on another z level. However, I can't figure out how to make it work:

\documentclass{article}
\usepackage{tikz}
\usepackage[utf8]{inputenc}
\usepackage[pdftex, active, tightpage]{preview}
\usetikzlibrary{calc, 3d, backgrounds, positioning}
\setlength\PreviewBorder{2mm}
\begin{document}
\pgfdeclarelayer{background}
\pgfdeclarelayer{foreground}
\pgfsetlayers{background,main,foreground}
\begin{preview}
\begin{tikzpicture}[scale = 1, x  = {(-0.2cm, -0.5cm)},
    y  = {(0.9659cm, -0.05882cm)},
    z  = {(0cm, 1cm)}]
    \begin{scope}[canvas is yx plane at z = 0]
        \draw (2, 3) node[inner sep = 0pt, outer sep = 0pt, color = black!60, circle, minimum size = 0.2pt] (1) {};
        \draw (3, 3) node[inner sep = 0pt, outer sep = 0pt, color = black!60, circle, minimum size = 0.2pt] (2) {};
        \draw (3, 2) node[inner sep = 0pt, outer sep = 0pt, color = black!60, circle, minimum size = 0.2pt] (3) {};
        \draw (1.center) -- (2.center) -- (3.center) -- cycle;
    \end{scope}
    \begin{scope}[canvas is yx plane at z = 1.5]
        \draw (2, 3) node[inner sep = 0pt, outer sep = 0pt, color = red!60, circle, fill, text width = 0.2pt] {};
        \draw node[inner sep = 0pt, outer sep = 0pt, color = blue!60, circle, fill, text width = 0.2pt] at (1) {};
    \end{scope}
\end{tikzpicture}
\end{preview}
\end{document}

The red node is where he is supposed to be, with the explicit (x, y) coordinates (just ''above'' the first node), but the blue node is at z = 0

What is an efficient way to make this work, i.e. to have the blue node cover the red node ? (is it possible to avoid using the second scope and just use at (1) ++ some magic relative displacement in 3D here or even some hidden(*) zshift parameter ?)

(*) I couldn't find this in the manual

Answer 1

I'm not sure I understand your code. I made some modifications but if I going in the wrong direction, I will update my answer.

Firstly minimum size = 0.2pt is not large enough to see a circle. The line width is by default 0.4 pt, if you want to see the nodes you need to increase the width! Then you can avoid some repetition and use styles for the nodes. When you create the second scope, if you use (2,3) to place a node, you use the canvas and the node is correctly placed. However, when you want to place the blue one at (1), you place the node at coordinates defined (1), which is defined outside this scope, so the coordinates of (1) don't change!

I don't understand text width = 0.2pt in your code. Is it a mistake?

Here is perhaps the simplest code:

\documentclass{article}
\usepackage{tikz}
\usetikzlibrary{calc, 3d, backgrounds, positioning}
\begin{document}

\begin{tikzpicture}[scale = 1, 
    x  = {(-0.2cm, -0.5cm)},
    y  = {(0.9659cm, -0.05882cm)},
    z  = {(0cm, 1cm)},
    every node/.style ={draw,
                       circle, minimum size = 1.8pt,
                       inner sep = 0pt, outer sep = 0pt}] 

    \begin{scope}[canvas is yx plane at z = 0,
                  every node/.append style ={ color = black!60}]
        \node (1) at  (2, 3)   {};
        \node (2) at  (3, 3)   {};
        \node (3) at  (3, 2)   {};
        \draw (1.center) -- (2.center) -- (3.center) -- cycle;
    \end{scope}

    \begin{scope}[every node/.append style ={ color = blue} ]
        \node[yshift=1.5 cm]  at  (1)   {};
        \node[yshift=1.5 cm]  at  (2)   {};
        \node[yshift=1.5 cm]  at  (3)   {};   
    \end{scope}
\end{tikzpicture}
\end{document}