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

[Martin Thomson <[e-mail]>]

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