[josm-dev] Clockwise coastline, anti-clockwise water

[Matthias Julius]

Dirk Stöcker <openstreetmap at dstoecker.de> writes:

> On Mon, 7 Jul 2008, Martijn van Oosterhout wrote:
>
>>> http://wiki.openstreetmap.org/index.php/Tag:natural=coastline
>>> States as anti-clockwise, but regarding the land surrounded by water
>>
>> Coastline doesn't have to be a single closed way.
>>
>>> http://wiki.openstreetmap.org/index.php/Tag:natural=water
>>> States clockwise, but regarding the water itself and not the land.
>>
>> And natural=water does.
>>
>> (Or at least, if the rules have changed then the rendering for mapnik
>> will be wrong).
>>
>> Which, as far as I'm concerned makes the test completely useless for
>> natural=water. Does anything actually rely on it? The wiki page says
>> its important but doesn't say *why*?
>
> I thought the same. But the check anyway only tests closed ways (there is 
> no real useable way to determine this issue for non-closed ways. Think of 
> e.g. a U or J shaped way. How will you determine on which side water is 
> (You can probably detect minimum distances to 100% land related 
> structures and assume the side with these structures is land, but this 
> will be a big effort).

Neighboring coastlines need to go in opposite direction.  It is an
error if they don't.

Didn't somebody implement a test for that?

>
> To make it a bit more useful, I will an an check, which tests for unclosed 
> ways in case of "natural=". That will be helpful.

At least coastlines don't need to be closed.  And it would be good if
we could drop that requirement for other areas as well.

Matthias