[Tilesathome] Handling of multipolygons large than Z12 tile

[Rob Reid]

Adam Schreiber wrote the following on 22/05/2009 06:22:
> Has there been any work in osmarender/tiles at home on handling
> multipolygons larger than a Z12 tile?  There's been an effort to
> import US NHD data for water ways and bodies of water and often rivers
> or lakes will cross tile boundaries causing problems like [1] [2].
>
> Cheers,
>
> Adam
>
> [1] http://informationfreeway.org/?lat=34.782449752666295&lon=-82.76998792819016&zoom=13&layers=B0000F000F
> [2] http://informationfreeway.org/?lat=34.596345710140696&lon=-82.8900650353609&zoom=12&layers=B0000F000F
>
>   
So far I've only looked at the first example above, but as far as I can 
tell the problem is that osmarender does not currently support 
multipolygons with multiple outer ways.
In the first example above the river has 5 waterway=riverbank ways with 
a role of outer. Osmarender just sees these as 5 unclosed ways which is 
why the results are a bit haphazard.

I note that there is an open trac ticket to add support for multiple 
outer ways to osmarender  :
http://trac.openstreetmap.org/ticket/1435

A possible interim solution would be to split the river into more than 
one multipolygon each with a single outer way. As this is how situations 
like this were handled prior to the advanced multipolygon proposal its 
is more likely to be supported in all renderers and editors.

rcr