* Steve Bennett stevag...@gmail.com [2013-03-19 10:52 +1100]:
One way to fudge this is to render the way, then render the route
relation over the top, obscuring it. But that doesn't work if you want
to use line smoothing (eg, line-smooth:0.6). The route relation will
form a smooth bezier curve the intersection of two ways, but the way
rendering will form a sharp point.
So I'm just wondering if there is a way around this - some setting in
osm2pgsql, some SQL magic I could play with.
I do something very similar with my highway shield rendering, which is
driven by route relations. I go through the planet_osm_rels table that's
created by osm2pgsql's slim mode, which is considered cheating in some
circles.
My rendering has code at https://launchpad.net/osm-shields , but the meat
of what you're interested in is the following two functions:
-- osm2pgsql stores tags in PostgreSQL arrays, where even-numbered array
-- members are tags and odd-numbered members are the tags' values. This
-- is a convenience function to go through such an array and retrieve the
-- value for a given tag.
CREATE OR REPLACE FUNCTION osm_get_tag_value(tags TEXT[], tag TEXT)
RETURNS TEXT
IMMUTABLE
RETURNS NULL ON NULL INPUT
LANGUAGE plpgsql
AS $$
DECLARE
tag_index INTEGER;
BEGIN
SELECT i INTO tag_index
FROM (SELECT generate_subscripts(tags, 1) AS i) AS indices
WHERE i % 2 = 1 AND tags[i] = tag;
RETURN tags[tag_index + 1];
END;
$$;
CREATE OR REPLACE FUNCTION
shields_get_route_memberships(planet_osm_rels.id%TYPE)
RETURNS fullref[]
STABLE
RETURNS NULL ON NULL INPUT
COST 5000
LANGUAGE SQL
AS $$
SELECT
shields_replace_groups(array_agg(ROW(shields_sanitize_text(network),
shields_sanitize_text(ref))::fullref))
FROM (SELECT osm_get_tag_value(tags, 'route') route,
UPPER(osm_get_tag_value(tags, 'network')) network,
UPPER(COALESCE(NULLIF(osm_get_tag_value(tags, 'ref'), ''),
osm_get_tag_value(tags, 'name'))) AS ref
FROM planet_osm_rels
WHERE parts ARRAY[$1]
AND parts[way_off:array_upper(parts, 1)] ARRAY[$1]) AS
ref_inner
WHERE route = 'road' AND network IS NOT NULL AND ref IS NOT NULL;
$$;
There's a lot of shield-rendering-specific code in there. A more succinct
query might be the following (where $1 is the OSM ID of the way for which
you want to determine route membership):
SELECT *
FROM (SELECT osm_get_tag_value(tags, 'route') route,
osm_get_tag_value(tags, 'network') network,
osm_get_tag_value(tags, 'ref') ref,
osm_get_tag_value(tags, 'name') name
FROM planet_osm_rels
WHERE parts ARRAY[$1]
AND parts[way_off:array_upper(parts, 1)] ARRAY[$1]) AS
ref_inner
WHERE route IS NOT NULL;
Obviously, you can add your own parameters in the statement.
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