[OSM-dev] Geofabrik downloads to change multipolygon handling

Frederik Ramm frederik at remote.org
Mon Jan 16 22:35:35 UTC 2017


Hi,

  this is just a small heads-up. The Geofabrik downloads (regional
.osm.pbf extracts for various continents, countries etc) will switch to
a different software stack later this month. We currently use
osm-history-splitter which is based on an older version of Osmium, and
will in the future use a new feature offered by the osmium command line
tool and the newest Osmium version instead.

This will enable us to change the handling of relations in the extracts.

Currently, relations are included in the extracts if one of their
members lies (partially) inside the area; but members of the relation
that lie fully outside the area are not considered.

This has adverse effects when large multipolygons cross the border, for
example Lake Constance not be fully contained in any of the Germany,
Austria, or Switzerland extracts.

In the future we will be able to include all members of multipolygon
relations that have at least one member (partially) inside the area.
This will only be done for multipolygons and not for other relations
(like boundaries or routes). Therefore, water bodies, forests etc. that
cross the boundary should in the future be fully contained in the extracts.

This comes at a price of a slightly larger extract but the difference is
negligible. On the day we make the switch, all regional .osc files will
have a slight size bump becasue all the missing bits and pieces required
to complete the multipolygons will be contained in them.

Bye
Frederik

-- 
Frederik Ramm  ##  eMail frederik at remote.org  ##  N49°00'09" E008°23'33"



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