[osmosis-dev] Single node ways

[Shaun McDonald]

On 14 Nov 2012, at 11:48, Paweł Paprota <ppawel at fastmail.fm> wrote:

> 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.

The problem is that if you are using Osmosis to shunt the data into a database that you use to find and highlight these invalid geometries for the community to go and fix in the source data.

I think that Osmosis could have a filter to drop invalid data, or even the inverse of only outputting the invalid data.

Shaun