Control layout using graphviz twopi

Question

I am trying to draw a graph showing search prefixes using twopi. I have a simple input file and am getting this output:

alt text http://www.freeimagehosting.net/uploads/th.ac6cd51528.png (full image)

Here is the input file:

digraph search {

// ordering=out;
// color=blue;
// rank=same;
// overlap=scale;
 rankdir=LR;
 root=root;
 ranksep=1.25;
 overlap=true;

"root";

a [color=none,fontsize=12];
b [color=none,fontsize=12];
c [color=none,fontsize=12];
d [color=none,fontsize=12];
e [color=none,fontsize=12];
f [color=none,fontsize=12];
#g [color=none,fontsize=12];
h [color=none,fontsize=12];
i [color=none,fontsize=12];
j [color=none,fontsize=12];
k [color=none,fontsize=12];
l [color=none,fontsize=12];
m [color=none,fontsize=12];
n [color=none,fontsize=12];
o [color=none,fontsize=12];
p [color=none,fontsize=12];
q [color=none,fontsize=12];
r [color=none,fontsize=12];
s [color=none,fontsize=12];
t [color=none,fontsize=12];
u [color=none,fontsize=12];
v [color=none,fontsize=12];
w [color=none,fontsize=12];
x [color=none,fontsize=12];
y [color=none,fontsize=12];

#ga [color=none,fontsize=12];
gb [color=none,fontsize=12];
gc [color=none,fontsize=12];
gd [color=none,fontsize=12];
ge [color=none,fontsize=12];
gf [color=none,fontsize=12];
gg [color=none,fontsize=12];
gh [color=none,fontsize=12];
gi [color=none,fontsize=12];
gj [color=none,fontsize=12];
gk [color=none,fontsize=12];
gl [color=none,fontsize=12];
gm [color=none,fontsize=12];
gn [color=none,fontsize=12];
go [color=none,fontsize=12];
gp [color=none,fontsize=12];
gq [color=none,fontsize=12];
gr [color=none,fontsize=12];
gs [color=none,fontsize=12];
gt [color=none,fontsize=12];
gu [color=none,fontsize=12];
gv [color=none,fontsize=12];
gw [color=none,fontsize=12];
gx [color=none,fontsize=12];
gy [color=none,fontsize=12];

gaa [color=none,fontsize=12];
gab [color=none,fontsize=12];
gac [color=none,fontsize=12];
gad [color=none,fontsize=12];
gae [color=none,fontsize=12];
gaf [color=none,fontsize=12];
gag [color=none,fontsize=12];
gah [color=none,fontsize=12];
gai [color=none,fontsize=12];
gaj [color=none,fontsize=12];
gak [color=none,fontsize=12];
gal [color=none,fontsize=12];
gam [color=none,fontsize=12];
gan [color=none,fontsize=12];
gao [color=none,fontsize=12];
gap [color=none,fontsize=12];
gaq [color=none,fontsize=12];
#gaz [color=none,fontsize=12];
gas [color=none,fontsize=12];
gat [color=none,fontsize=12];
gau [color=none,fontsize=12];
gav [color=none,fontsize=12];
gaw [color=none,fontsize=12];
gax [color=none,fontsize=12];
gay [color=none,fontsize=12];

gaza [color=none,fontsize=12];
gazb [color=none,fontsize=12];
gazc [color=none,fontsize=12];
gazd [color=none,fontsize=12];
gaze [color=none,fontsize=12];
#gazf [color=none,fontsize=12];
gazg [color=none,fontsize=12];
gazh [color=none,fontsize=12];
gazi [color=none,fontsize=12];
gazj [color=none,fontsize=12];
gazk [color=none,fontsize=12];
gazl [color=none,fontsize=12];
gazm [color=none,fontsize=12];
gazn [color=none,fontsize=12];
gazo [color=none,fontsize=12];
gazp [color=none,fontsize=12];
gazq [color=none,fontsize=12];
gazr [color=none,fontsize=12];
gazs [color=none,fontsize=12];
gazt [color=none,fontsize=12];
gazu [color=none,fontsize=12];
gazv [color=none,fontsize=12];
gazw [color=none,fontsize=12];
gazx [color=none,fontsize=12];
gazy [color=none,fontsize=12];

root -> a  [minlen=2];
root -> b  [minlen=2];
root -> c  [minlen=2];
root -> d  [minlen=2];
root -> e  [minlen=2];
root -> f  [minlen=2];
root -> g  [minlen=2];
root -> h  [minlen=2];
root -> i  [minlen=2];
root -> j  [minlen=2];
root -> k  [minlen=2];
root -> l  [minlen=2];
root -> m  [minlen=2];
root -> n  [minlen=2];
root -> o  [minlen=2];
root -> p  [minlen=2];
root -> q  [minlen=2];
root -> r  [minlen=2];
root -> s  [minlen=20];
root -> t  [minlen=2];
root -> u  [minlen=2];
root -> v  [minlen=2];
root -> w  [minlen=2];
root -> x  [minlen=2];
root -> y  [minlen=2];
root -> 0  [minlen=2];
root -> 1  [minlen=2];
root -> 2  [minlen=2];
root -> 3  [minlen=2];
root -> 4  [minlen=2];
root -> 5  [minlen=2];
root -> 6  [minlen=2];
root -> 7  [minlen=2];
root -> 8  [minlen=2];
root -> 9  [minlen=2];
root -> "."  [minlen=2];

g -> ga  ;
g -> gb  ;
g -> gc  ;
g -> gd  ;
g -> ge  ;
g -> gf  ;
g -> gg  ;
g -> gh  ;
g -> gi  ;
g -> gj  ;
g -> gk  ;
g -> gl  ;
g -> gm  ;
g -> gn  ;
g -> go  ;
g -> gp  ;
g -> gq  ;
g -> gr  ;
g -> gs  ;
g -> gt  ;
g -> gu  ;
g -> gv  ;
g -> gw  ;
g -> gx  ;
g -> gy  ;

ga -> gaa  ;
ga -> gab  ;
ga -> gac  ;
ga -> gad  ;
ga -> gae  ;
ga -> gaf  ;
ga -> gag  ;
ga -> gah  ;
ga -> gai  ;
ga -> gaj  ;
ga -> gak  ;
ga -> gal  ;
ga -> gam  ;
ga -> gan  ;
ga -> gao  ;
ga -> gap  ;
ga -> gaq  ;
ga -> gaz  ;
ga -> gas  ;
ga -> gat  ;
ga -> gau  ;
ga -> gav  ;
ga -> gaw  ;
ga -> gax  ;
ga -> gay  ;

gaz -> gaza  ;
gaz -> gazb  ;
gaz -> gazc  ;
gaz -> gazd  ;
gaz -> gaze  ;
gaz -> gazf  ;
gaz -> gazg  ;
gaz -> gazh  ;
gaz -> gazi  ;
gaz -> gazj  ;
gaz -> gazk  ;
gaz -> gazl  ;
gaz -> gazm  ;
gaz -> gazn  ;
gaz -> gazo  ;
gaz -> gazp  ;
gaz -> gazq  ;
gaz -> gazr  ;
gaz -> gazs  ;
gaz -> gazt  ;
gaz -> gazu  ;
gaz -> gazv  ;
gaz -> gazw  ;
gaz -> gazx  ;
gaz -> gazy  ;

gazo -> "Blue Tuesday" ;
"Blue Tuesday" [ fontsize=10];

// Layout engines: circo dot fdp neato nop nop1 nop2 osage patchwork sfdp twopi 

}

This output is generated with:

twopi -os1.png -Tpng s1.dot

I'm posting here because the printout is pretty dreadful. All of the nodes hung of "gaz" are overlapping; I've tried specifying nodesep and it is simply ignored. I would like to see the lines from root to the single letters further apart, but again, I can't control that.

This seems to be a bug in twopi. The documentation says it should clearly follow these directives, but it doesn't seem to.

My questions:

1. Is there any way to make twopi behave?
2. Failing that, is there a better layout engine to use?

Thanks.

Answer 1

I have found twopi to be the most difficult to work with of all the graphviz layout engines.

I made a few small changes to your original dot file. The rendered graph is shown below.

Here are the diffs:

graph attributes:

• size="7.75,10.25"; // ensures that entire graph fits on a single 8.5 x 11 page;

• orientation="landscape";

• ranksep=3.0; nodesep=2.0;

• deleted: "root=root"; and "overlap=true"

edge attributes:

• i set the edge weight equal to 0.1 for all edges: [weight=0.1]

---

Reducing the edge weight by 90% for all edges has the net effect of increasing the edge length (or more precisely relaxing the constraint on edge length); obviously, this helps the nodes to "fan out". Doing this also increases the distance between "g" and "root", giving the child nodes of "root" more room.

I also tweaked a few purely aesthetic attributes--not having any effect on the layout, but that to me, seem to matter when you need to draw even a moderately dense graph on a single page:

graph attributes:

fontname="Helvetica"; fontsize=13

node attributes:

"root" [color="goldenrod4", shape="diamond", style="filled"]

"g" [color="lightsteelblue2", shape="diamond", style="filled"]

"ga" [color="darkorange", shape="diamond", style="filled"]

"gaz" [color="bisque4", shape="diamond", style="filled"]

edge attributes:

[arrowsize=0.4, penwidth=1.2]