[OSM-dev] Advice sought on polygon-with-hole drawing

bvh bvh-osm at irule.be
Fri Mar 14 11:39:14 GMT 2008


On Fri, Mar 14, 2008 at 10:43:54AM +0000, Robert (Jamie) Munro wrote:
> Yes. That is what I am saying. 1 simple rule:
> 
> *All* areas should be colour on the right (i.e. clockwise)
> 
> It's simple, it's validatable (albeit the current JOSM validator get's
> it wrong), it means that coastline is not an exception, it makes the
> maths simpler. It might even mean that you don't need relationships to
> associate inner and outer -  Any system that gets 1 segment of an area
> should be able to know which side of that segment the feature is on.
> 
> | Also, my idea would allow a way to serve as an "inner" member of one
> | multipoly at the same time as as an "outer" member of another; I think
> | you couldn't get that with evenodd.
> 
> That's really ugly. There should be 2 ways. They can share nodes if that
> ~ is wanted. If you really want to use only one way, then you could put a
> direction=-1 tag or something in the relationship that defines the
> tagging for the inner area, but I still don't like that. I think that if
> the edge of an area crosses through something you should know what is on
> each side of it without having to consider special tags for exceptional
> cases.

I disagree. Requiring mappers to add two ways that overlap
completly is with the goal of making the math simpler is
shifting the burden from software to users.

Could you elaborate on your last sentence? What problem can we
now not solve because it is more difficult to find out at
which edge a feature lies? Maybe there are others to achieve it?

cu bart




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