Layered graph by tikz lib graphdrawing: rotate & minimize manual adjustments

Question

I was trying to recreate following graphviz graph with tikz (from https://graphs.grevian.org/example)

graph {
    rankdir=LR;
    a -- { b c d }; b -- { c e }; c -- { e f }; d -- { f g }; e -- h;
    f -- { h i j g }; g -- k; h -- { o l }; i -- { l m j }; j -- { m n k };
    k -- { n r }; l -- { o m }; m -- { o p n }; n -- { q r };
    o -- { s p }; p -- { s t q }; q -- { t r }; r -- t; s -- z; t -- z;
    { rank=same; b, c, d }
    { rank=same; e, f, g }
    { rank=same; h, i, j, k }
    { rank=same; l, m, n }
    { rank=same; o, p, q, r }
    { rank=same; s, t }
}

To replicate the setting rankdir=LR; I have followed the advice from Rotate tikz "Layered Layout" and have added grow=right, components go down left aligned:

%! TEX program = lualatex
\documentclass[tikz]{standalone}
\usetikzlibrary{graphs,graphdrawing,shapes}
\usegdlibrary{layered}
\begin{document}
\tikz \graph [layered layout,
    nodes={ellipse, minimum width=25pt, draw},
    % https://tex.stackexchange.com/q/390417/rotate-tikz-layered-layout
    grow=right, components go down left aligned
    ] {
    { [same layer] b, c, d };
    { [same layer] e, f, g };
    { [same layer] h, i, j, k };
    { [same layer] l, m, n };
    { [same layer] o, p, q, r };
    { [same layer] s, t };

    a[nudge left=25mm] -- { b, c, d }; b -- { c, e };c -- { e, f };
    d -- { f, g }; e -- h; f[nudge down=10mm] -- { h, i, j, g };
    g[nudge down=10mm] -- k; h --[bend left=-30] o; h -- l;
    i -- { l, m, j }; j -- { m, n, k }; k -- { n, r }; l[nudge up=10mm] -- { o, m };
    m[nudge up=10mm] -- { o, p, n }; n -- { q, r }; o -- { s, p }; p -- { s, t, q };
    q -- { t, r }; r -- t; s -- z; t -- z;
};
\end{document}

I have removed unnecessary edge crossings by 'nudging' node a to the left. To fill the empty space left by the moved node a, I have moved g and f downwards. Also I had to adjust m and l upwards and bend the edge h--o downwards.

Without these modifications the graph looks like

In particular the edge h--o is completely misleading.

Does anyone know how to recreate the graphviz result, i.e. orient the layered graph horizontally (in contrast to the default) and avoid so many manual adjustments?

UPDATE

placing a on an own layer already fixed nudging a, f and g:

{ [same layer] a };

The remaining problem is apparently the crossing minimization algorithm which does not know the 'easy' solution to move m and l up and add the kink into the other direction:

Note: answer by marmot suggests to add those edges manually which connect nodes of two different layers with at least one additional layer between them. Maybe this could be a rule of thumb for other graphs as well.

Answer 1

I do not know if that's helpful, but if I

• remove all nudges,
• create a layer for a,
• change grow=right to grow'=right, and
• move a single command "out of the graph": \draw (h) to[bend left=40] (o);,

I get

\documentclass[tikz]{standalone}
\usetikzlibrary{graphs,graphdrawing}
\usetikzlibrary{shapes}
\usegdlibrary{layered}
\begin{document}
\begin{tikzpicture}
\graph [layered layout,
    nodes={ellipse, minimum width=25pt, draw},
    % https://tex.stackexchange.com/q/390417/rotate-tikz-layered-layout
    grow'=right, components go down left aligned
    ] {
    { [same layer] a }; %<- added
    { [same layer] b, c, d };
    { [same layer] e, f, g };
    { [same layer] h, i, j, k };
    { [same layer] l, m, n };
    { [same layer] o, p, q, r };
    { [same layer] s, t };
    a -- { b, c, d }; 
    b -- { c, e };
    c -- { e, f };
    d -- { f, g }; 
    e -- h; 
    f -- { h, i, j, g };
    g -- k; 
    h -- l;
    i -- { l, m, j }; 
    j -- { m, n, k }; 
    k -- { n, r }; 
    l -- { o, m };
    m -- { o, p, n }; 
    n -- { q, r }; 
    o -- { s, p }; 
    p -- { s, t, q };
    q -- { t, r }; 
    r -- t; 
    s -- z; 
    t -- z;
};
\draw (h) to[bend left=40] (o);
\end{tikzpicture}
\end{document}

To an ordinary marmots eye, this looks already close to the desired result.

If I, in addition, move one more connection "out of the graph", \draw (k) -- (r);, this gives me

\documentclass[tikz]{standalone}
\usetikzlibrary{graphs,graphdrawing}
\usetikzlibrary{shapes}
\usegdlibrary{layered}
\begin{document}
\begin{tikzpicture}
\graph [layered layout,
    nodes={ellipse, minimum width=25pt, draw},
    % https://tex.stackexchange.com/q/390417/rotate-tikz-layered-layout
    grow'=right, components go down left aligned
    ] {
    { [same layer] a }; %<- added
    { [same layer] b, c, d };
    { [same layer] e, f, g };
    { [same layer] h, i, j, k };
    { [same layer] l, m, n };
    { [same layer] o, p, q, r };
    { [same layer] s, t };
    a -- { b, c, d }; 
    b -- { c, e };
    c -- { e, f };
    d -- { f, g }; 
    e -- h; 
    f -- { h, i, j, g };
    g -- k; 
    h -- l;
    i -- { l, m, j }; 
    j -- { m, n, k }; 
    k -- { n }; 
    l -- { o, m };
    m -- { o, p, n }; 
    n -- { q, r }; 
    o -- { s, p }; 
    p -- { s, t, q };
    q -- { t, r }; 
    r -- t; 
    s -- z; 
    t -- z;
};
\draw (h) to[bend left=40] (o);
\draw (k) -- (r);
\end{tikzpicture}
\end{document}

which is arguably even closer to the desired result.