[postgis-users] Merge Lines

[Stefan Wagner]

Hi,

I'm sorry, if my question was answered already, but i couldn't find a
similar post.

I'm using mapnik with PostGIS to render a map of Austria's capital Vienna.
Everything worked fine so far, but now i want to add the public transport
lines. Would be no problem, these are simple LINESTRINGs, but as on some
streets, different lines come together respectively are congruent, this
sometimes looks awful, because the lines are drawn on top of each other and
the captions are not placed well because of different starting points of the
lines.

So what i would need is: only have one line, if there come together several
lines (so merge different lines to one, on parts where they are congruent)
and have the type and name put together like with group_concat (e.g. line 40
and 41 share the same line, have a field with "40,41" or "bus,tram,tram" if
there are 1 bus- and 2 tramlines).
I tried to group by the geom Column, and use group_concat (rather a
equivalent to group_concat found somewhere on the net) to put together the
captions. This sometimes worked, but in most cases it didn't (would be to
easy, right? :-) )

So do you see an solution for this, or do i have to split all linestrings
into simple 2point lines and group by that?

TIA.

Greetings from Austria,
Stefan Wagner
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