[GeoJSON] polygon orientation, trying number 2

[Keith Jenkins]

And exterior-ring-clockwise is how PostGIS interprets the right-hand
rule as well:
    http://postgis.net/docs/manual-2.2/ST_ForceRHR.html

Keith

On Sat, Jul 16, 2016 at 1:25 PM, Jukka Rahkonen
<jukka.rahkonen at latuviitta.fi> wrote:
> Hi Sean,
>
> Would you mind to check also if what is written about the right-hand rule is
> correct:
>
>
> "Polygon rings MUST follow the right-hand rule for orientation
>       (counter-clockwise external rings, clockwise internal rings)"
>
> At least the ESRI shapefile specification defines the right-hand rule in an
> opposite way:
>
> "The order of vertices or orientation for a ring indicates which side of the
> ring
> is the interior of the polygon. The neighborhood to the right of an observer
> walking along
> the ring in vertex order is the neighborhood inside the polygon. Vertices of
> rings defining
> holes in polygons are in a counterclockwise direction. Vertices for a
> single, ringed
> polygon are, therefore, always in clockwise order."
>
> For me it seems that GeoJSON specification is following the left-hand rule,
> not the right-hand rule.
>
> -Jukka Rahkonen-
>
>
>
> Sean Gillies kirjoitti 2016-07-16 03:38:
>>
>> Hi Anna,
>>
>> Thanks for letting us know about this! I've updated the examples in
>> our GitHub repo and sent a patch along to the RFC Editor. When the
>> GeoJSON standard is published, the examples will have the correct
>> orientation: exterior rings that wind counter-clockwise and interior
>> rings that wind clockwise.
>>
>> See https://github.com/geojson/draft-geojson/issues/231 for the
>> specific changes.
>>
>> Yours,
>>
>> On Thu, Jul 14, 2016 at 4:56 AM, Anna Eivazi
>> <Anna.Eivazi at sharpershape.com> wrote:
>>
>>> Hello geojson-gurus,
>>>
>>> First of all, thank you for all your good work about geojson, we
>>> love to use it!;)
>>>
>>> I’ve got a question after trying to figure out which orientation
>>> to use for polygons.
>>>
>>> So I’ve read your latest specs:
>>>
>>> https://datatracker.ietf.org/doc/draft-ietf-geojson/?include_text=1
>>>
>>> Here it is said:
>>>
>>> Polygon rings MUST follow the right-hand rule for orientation
>>>
>>> (counter-clockwise external rings, clockwise internal rings).
>>>
>>> (clear answer to my question, right?)
>>>
>>> But a bit upper in the same doc Polygon section:
>>>
>>> A.3.  Polygons
>>>
>>> Coordinates of a Polygon are an array of LinearRing (see
>>>
>>> Section 3.1.6) coordinate arrays.  The first element in the
>>> array
>>>
>>> represents the exterior ring.  Any subsequent elements represent
>>>
>>>
>>> interior rings (or holes).
>>>
>>> No holes:
>>>
>>> {
>>>
>>> "type": "Polygon",
>>>
>>> "coordinates": [
>>>
>>> [
>>>
>>> [100.0, 0.0],
>>>
>>> [100.0, 1.0],
>>>
>>> [101.0, 1.0],
>>>
>>> [101.0, 0.0],
>>>
>>> [100.0, 0.0]
>>>
>>> ]
>>>
>>> ]
>>>
>>> }
>>>
>>> That would mean clockwise orientation…?
>>>
>>> So, which one u are planning to use in future? So we will stick to
>>> it too!
>>>
>>> Thanks a lot!
>>>
>>> Best regards,
>>>
>>> Anna Eivazi
>>>
>>> _______________________________________________
>>> GeoJSON mailing list
>>> GeoJSON at lists.geojson.org
>>> http://lists.geojson.org/listinfo.cgi/geojson-geojson.org
>>
>>
>> --
>> Sean Gillies
>> _______________________________________________
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>> GeoJSON at lists.geojson.org
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>
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