On 11/14/2012 12:33 PM, Brett Henderson wrote:
>
It sounds good to me. Osmosis typically tries to maintain data accuracy
with no surprises, so I'm not particularly happy with the current
situation of dropping ways even if they are invalid.
Jochen Topf was the one who originally introduced the checks in
WayGeometryBuilder to ensure a Way contained at least two nodes. He
might have some thoughts on whether we can remove the checks. Perhaps
it was simply introduced to avoid the additional overheads of having to
do st_isvalid() checks?
Based on my experience with processing geometry for OSM objects I'd
strongly discourage having any invalid geometries in the database. This
leads to very unpleasant surprises with ST_Union, ST_Intersection and
other spatial functions. Upgrading the GEOS library (which PostGIS uses)
helps a bit but still many operations can behave very strangely and
after hours/days of debugging you find yourself hitting the "invalid
geometry" wall.
Whether Osmosis should be responsible for maintaining valid geometries
is kind of a different question I think - depends on policy. But
whatever you decide, it needs to be communicated front and center in
documentation what geometry is created.
Paweł
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