Re: [Geojson] [Technical Errata Reported] RFC7946 (5069)

[Martin Thomson <[e-mail]>]

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On 15 July 2017 at 03:57, James Winterbottom
<[e-mail]> wrote:
> +1 for Martin's position
>
> Sent from my iPhone
>
>> On 15 Jul 2017, at 3:42 am, Martin Thomson <[e-mail]> wrote:
>>
>> My understanding is that the polygon definition follows the accepted
>> norms for point order. GML defines the shape this way.  Section 5.1 of
>> RFC 5491: https://tools.ietf.org/html/rfc5491#section-5.1 also uses
>> counter-clockwise point order: the upward normal points up!  See also
>> Appendix B of RFC 7459 https://tools.ietf.org/html/rfc7459#appendix-B
>>
>> My understanding of the right hand rule being curled fingers on the
>> right hand follow the points and the thumb becomes the upward normal.
>>
>> I think that we should reject this erratum, but can someone else
>> double-check that I'm not off base?
>>
>>> On 15 July 2017 at 01:44, RFC Errata System <[e-mail]> wrote:
>>> The following errata report has been submitted for RFC7946,
>>> "The GeoJSON Format".
>>>
>>> --------------------------------------
>>> You may review the report below and at:
>>> http://www.rfc-editor.org/errata/eid5069
>>>
>>> --------------------------------------
>>> Type: Technical
>>> Reported by: Clark Archer <[e-mail]>
>>>
>>> Section: 3.1.6
>>>
>>> Original Text
>>> -------------
>>> 3.1.6.  Polygon
>>>
>>>   To specify a constraint specific to Polygons, it is useful to
>>>   introduce the concept of a linear ring:
>>>
>>>   o  A linear ring is a closed LineString with four or more positions.
>>>
>>>   o  The first and last positions are equivalent, and they MUST contain
>>>      identical values; their representation SHOULD also be identical.
>>>
>>>   o  A linear ring is the boundary of a surface or the boundary of a
>>>      hole in a surface.
>>>
>>>   o  A linear ring MUST follow the right-hand rule with respect to the
>>>      area it bounds, i.e., exterior rings are counterclockwise, and
>>>      holes are clockwise.
>>>
>>>   Note: the [GJ2008] specification did not discuss linear ring winding
>>>   order.  For backwards compatibility, parsers SHOULD NOT reject
>>>   Polygons that do not follow the right-hand rule.
>>>
>>>   Though a linear ring is not explicitly represented as a GeoJSON
>>>   geometry type, it leads to a canonical formulation of the Polygon
>>>   geometry type definition as follows:
>>>
>>>   o  For type "Polygon", the "coordinates" member MUST be an array of
>>>      linear ring coordinate arrays.
>>>
>>>   o  For Polygons with more than one of these rings, the first MUST be
>>>      the exterior ring, and any others MUST be interior rings.  The
>>>      exterior ring bounds the surface, and the interior rings (if
>>>      present) bound holes within the surface.
>>>
>>>
>>> Corrected Text
>>> --------------
>>> 3.1.6.  Polygon
>>>
>>>   To specify a constraint specific to Polygons, it is useful to
>>>   introduce the concept of a linear ring:
>>>
>>>   o  A linear ring is a closed LineString with four or more positions.
>>>
>>>   o  The first and last positions are equivalent, and they MUST contain
>>>      identical values; their representation SHOULD also be identical.
>>>
>>>   o  A linear ring is the boundary of a surface or the boundary of a
>>>      hole in a surface.
>>>
>>>   o  A linear ring MUST follow the right-hand rule with respect to the
>>>      area it bounds, i.e., exterior rings are clockwise, and holes are
>>>      counterclockwise.
>>>
>>>   Note: the [GJ2008] specification did not discuss linear ring winding
>>>   order.  For backwards compatibility, parsers SHOULD NOT reject
>>>   Polygons that do not follow the right-hand rule.
>>>
>>>   Though a linear ring is not explicitly represented as a GeoJSON
>>>   geometry type, it leads to a canonical formulation of the Polygon
>>>   geometry type definition as follows:
>>>
>>>   o  For type "Polygon", the "coordinates" member MUST be an array of
>>>      linear ring coordinate arrays.
>>>
>>>   o  For Polygons with more than one of these rings, the first MUST be
>>>      the exterior ring, and any others MUST be interior rings.  The
>>>      exterior ring bounds the surface, and the interior rings (if
>>>      present) bound holes within the surface.
>>>
>>>
>>> Notes
>>> -----
>>> This is only for the bullet point describing the right-hand rule for linear rings. It seems like the clockwise/counterclockwise descriptions are the opposite of the right-hand rule. Walking an exterior ring in a counterclockwise direction would have the exterior of the ring to the right of the observer.
>>>
>>> Instructions:
>>> -------------
>>> This erratum is currently posted as "Reported". If necessary, please
>>> use "Reply All" to discuss whether it should be verified or
>>> rejected. When a decision is reached, the verifying party
>>> can log in to change the status and edit the report, if necessary.
>>>
>>> --------------------------------------
>>> RFC7946 (draft-ietf-geojson-04)
>>> --------------------------------------
>>> Title               : The GeoJSON Format
>>> Publication Date    : August 2016
>>> Author(s)           : H. Butler, M. Daly, A. Doyle, S. Gillies, S. Hagen, T. Schaub
>>> Category            : PROPOSED STANDARD
>>> Source              : Geographic JSON
>>> Area                : Applications and Real-Time
>>> Stream              : IETF
>>> Verifying Party     : IESG
>>
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