[OSM-talk] buildings

Robert (Jamie) Munro rjmunro at arjam.net
Mon Aug 13 18:30:54 BST 2007


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Martijn van Oosterhout wrote:
> On 7/24/07, Iván Sánchez Ortega <ivansanchez at escomposlinux.org> wrote:
>> The second problem is more grave IMHO: according to the actual standards,
>> there is no way to correctly *draw* three touching (adjacent) ways.
> 
> I didn't see a response to this, so I'm bringing it up again...
> 
>> I'll explain myself: the current data model (and validator rules) encourage
>> the following:
>>
>> - Reuse data (reuse a node if possible)
>> - Reuse a segment if you really, really need to
>> - Closed ways "areas" must be ordered. Either it draws a clockwise polygon, or
>> a counter-clockwise polygon.
> 
> In my original validator I made an exception for this: if a way is
> looped (so that it is an area) then the the arrows don't have to face
> the same way. They still need to be ordered, just the arrows don't
> have all face the same way.

That seems evil. Polygons must go clockwise(*) - the fill is on the
right. All renderers should assume polygons go clockwise. Otherwise
chaos will ensue.

Robert (Jamie) Munro

* Coastlines may appear to be an exception as they go anticlockwise
around land, but they aren't. They actually go clockwise around the sea.
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