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

[James Winterbottom <[e-mail]>]

+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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