[OSM-talk] Best way to draw areas with holes?
Chris Hill
chillly809 at yahoo.co.uk
Fri Dec 21 12:22:57 GMT 2007
> Alex Mauer wrote:
> > Chris Hill wrote:
> >
> > I have used the multipolygon relation to draw islands in rivers.
> >It
>
>is specifically intended for drawing holes in areas and worked
> very
>
>well for me.
> >
>
> I've tried to use it for this, but I run into problems when the river
> bank is too large for a single way. (I split the ways at 129
> nodes,
>
but
> the exact number doesn't matter)
>
> Here is the result:
>
> http://www.informationfreeway.org/?lat=46.381337247472786&lon=-90.25169857324616
> &zoom=8&layers=B000F000
>
> It appears to me that it mostly works, but then the renderer randomly
> decides to treat one of the islands with an "inner" role as if it had a
> role of "outer" instead of following the ring of "outer" ways.
>
>
I too broke a river into chunks, though it's smaller than your river.
Each chunk has an area drawn with a clockwise way marked as waterway=riverbank. The chunks butt up
to one another. The islands have a way drawn anticlockwise, which is
important for the Osmarender renderer. They are also tagged with waterway=riverbank.
You can take a look at:
http://www.openstreetmap.org/?lat=53.7207&lon=-0.7214&zoom=12&layers=0BF
I modified Jon Burgess's step by step list from his email and added it to the relation Wiki page:
http://wiki.openstreetmap.org/index.php/Relations/Multipolygon
This renders well at zoom 12 and higher, but lower zooms do not seem to render.
cheers,Chris
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