Here is a stored procedure that can be user to create a GraphViz input file from a pgRouting edge table. It create a text output that can be copied to myfile.gv, then can be converted to an image using ``neato -Tpng -O myfile.gv`` and the image will be in ``myfile.gv.png``.

pgr_graphviz.sql

create or replace function pgr_graphviz(edge_table text, 
                                        eid text default 'id', 
                                        source text default 'source', 
                                        target text default 'target',
                                        oneway text default '',
                                        ft text[] default array['FT']::text[],
                                        tf text[] default array['TF']::text[],
                                        where_clause text default 'true',
                                        nodepos bool default false)
returns text as
$body$
declare
    txt text;
    sql text;
    rec record;
    r record;
    
begin
    -- setup the file header information
    txt := '
/*
    generated by: select pgr_graphviz('''||edge_table||''', '''||eid||''', '''||source||''', '''||target||''', 
                                      '''||oneway||''', ''array['||array_to_string(ft, ',')||']'',
                                      ''array['||array_to_string(tf, ',')||']'',
                                      '''||where_clause||''','||nodepos||');
';

    if oneway = '' then
        txt := txt || '    save result as: graph.gv
    run: neato -Tpng -O graph.gv
    generates: graph.png
';
    else
        txt := txt || '    save result as: digraph.gv
    run: neato -Tpng -O digraph.gv
    or run: dot -Tpng -O digraph.gv
    generates: digraph.png
';
    end if;

    txt := txt || '
*/
';
    if oneway = '' then
        txt := txt || 'graph {
';
    else
        txt := txt || 'digraph {
';
    end if;

    if nodepos then
        select * from pgr_getTableName(edge_table||'_vertices_pgr') INTO r;
        if r.tname is null then
            raise notice 'Table % does not exist can not position nodes!', quote_literal(edge_table||'_vertices_pgr');
        else
            sql := 'select id, st_x(the_geom) as x, st_y(the_geom) as y 
                      from ' || pgr_quote_ident(edge_table||'_vertices_pgr') ||
                      ' order by id';
            for rec in execute sql loop
                txt := txt || rec.id || ' [pos="' || rec.x || ',' || rec.y ||'"];
';
            end loop;
        end if;
    end if;

    sql := 'select ' || quote_ident(eid)    || ' as eid, ' ||
                        quote_ident(source) || ' as source, ' ||
                        quote_ident(target) || ' as target';
    if oneway != '' then
        sql := sql || ', ' || quote_ident(oneway) || '::text as oneway';
    end if;
    
    sql := sql || ' from '||pgr_quote_ident(edge_table)||' where '||where_clause;

    for rec in execute sql loop
        if oneway != '' then
            if tf @> ARRAY[rec.oneway] then
                txt := txt || rec.target || ' -> ' || rec.source || ' [weight="1.0" label="' || rec.eid || '"];
';
            elsif ft @> ARRAY[rec.oneway] then
                txt := txt || rec.source || ' -> ' || rec.target || ' [weight="1.0" label="' || rec.eid || '"];
';
            else
                txt := txt || rec.source || ' -> ' || rec.target || ' [weight="1.0" label="' || rec.eid || '"];
';
                txt := txt || rec.target || ' -> ' || rec.source || ' [weight="1.0" label="' || rec.eid || '"];
';
            end if;
        else
            txt := txt || rec.source || ' -- ' || rec.target || ' [weight="1.0" label="' || rec.eid || '"];
';
        end if;
    end loop;

    txt := txt || '}';

    return txt;
end;
$body$
language plpgsql volatile strict;

/*
select pgr_graphviz('edge_table');
select pgr_graphviz('edge_table', oneway:='dir');
select pgr_graphviz('network', nodepos:=true);

*/