On 12/20/2011 08:45 AM, Peter Wendorff wrote:
I'm working on the look-and-listen-map (toolserver project lalm), a web
map portal for the Blind and Visually Impaired.
That is not a rendering application like the several mapnik stylesheets
running on the toolserver, but I agreed with the Admins, that it might
be worth in respect of capacities of the toolserver to use the mapnik
Today I finally got database access and looked deeper into the schema.
Most queries in my application rely on the osm_id present in all tables
(and index, too), so that's not a problem.
Some queries will later on require geometric queries, but here I can
combine the postprocessed tables (planet_nodes, planet_line,
planet_polygon...) for filtering and the non-processed ones for fetching
the values - so that's okay, too.
My problem lies, where mapnik does ugly tricks for rendering: I have a
node-id and want to get all ways this node is part of.
That would be possible, querying planet_ways, as planet_ways contains a
field nodes, that is a integer-array; but as far as I know there is no
performant way to query an array-field of a database on containing a
Currently my code is based on a different database schema, but I have a
query with the following characteristics, that I need with the
IN: node_id (int)
OUT: a list of way_id, where the corresponding way contains the node
with id node_id.
The mapnik updater has to do that as well. As a moved node needs to
recreate the geometry of the way that contains that node.
There is a GIN index on the planet_ways table that allows to do this.
The query osm2pgsql runs for this is "UPDATE %p_ways SET pending = true
WHERE nodes && ARRAY[$1] AND NOT pending;"
You don't want the update or pending part, but the "WHERE nodes &&
ARRAY[osm_id]" should work for you.
A second question would be, if errors would occur, when I combine e.g.
planet_ways with planet_line in a query, and a matching row in
planet_ways is pending. Usually the intermediate tables are only
accessed by the import tool, so I would do unconventional things here,
but am I right? If the planet_ways-row is pending, the data of this
table is not in sync with the data in planet_line.
Yes, that is correct. But that should only be for a fairly short period
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