[OSM-dev] osmosis, bounding boxes and updating

[David Paleino]

On Tue, 22 Mar 2011 15:55:03 +0100, Martijn van Exel wrote:

> I think I found the answer to my own question:
> 
> http://www.mail-archive.com/dev@openstreetmap.org/msg03530.html
> 
> In short: it's not possible to combine change streams with bounding 
> boxes / polygons.
> 
> Right?

No.

With some hackery, I did it once :)

1. download an initial complete dump of the area you want, and call it
"complete.osm"

2. in a crontab, to be run each minute (if you want minutely diff):
   $ osmosis \
        --read-replication-interval workingDirectory=... \
        --simplify-change \
        --write-xml-change changes.osc.gz
   $ osmosis \
        --read-xml-change changes.osc.gz \
        --read-xml file=complete.osm \
        --ac \
        --bounding-polygon file=yourpolygon.poly \
        --write-xml complete_new.osm
    $ osm2pgsql \
        --merc \
        --extra-attributes --style $BASE/osm2pgsql.style \
        complete_new.osm && \
        mv complete.osm complete.osm.bak && \
        mv complete_new.osm complete.osm

Check the manpage/web/--help for what to put in the workingDirectory=
parameter of --read-replication-interval.

Also, the last osm2pgsql acts on "complete_new.osm", which is renamed to
"complete.osm" (so that it's ready for the next crontab run) only if everything
goes well. In case of errors, there's always "complete.osm.bak" :)

This worked one month ago. I didn't check now, because I shut my app down, so
can't tell if anything changed; but I don't think so.
Also, my app originally had two (or more) different polygons imported and
rendered, and the script put in crontab is a bit more complicated (and
generalized) than this. But this should be sufficient to do what you want :)

Kindly,
David

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