[GeoJSON] erratum 5069

[John Herring]

Hi,

The history of the the "counter-clockwise" rotation of an outer boundary 
(and the opposite for interior boundaries, is from Green's Theorem 
<https://en.wikipedia.org/wiki/Green%27s_theorem> which calculates the 
surface area (of a polygon in Euclidean 2 space) as an integral on the 
boundary. The term "right hand rule" reference the "moving vector frame 
of the curve in Euclidean 3-space" of the curve (tangent, normal and 
binormal is a right-handed vector frame matching the orientation of the 
"x y z" axes of 'right-handed' Euclidean 3-space).

Any engineering student who got to 3^rd year multivariate calculus 
should recognize this. I do also probably because I taught some of the 
those engineers at Penn State in the late 1970's, but maybe because I 
was there when we wrote Simple Features in the 1990's.

Regards,
John


On 2018-06-19 11:31 AM, Jukka Rahkonen wrote:
> Hi,
>
> This topic was discussed in this gdal-dev thread 
> https://urldefense.proofpoint.com/v2/url?u=http-3A__osgeo-2Dorg.1560.x6.nabble.com_gdal-2Ddev-2DTime-2Dfor-2Da-2Dnew-2DGeoJSON-2Ddriver-2Dtd5278061.html&d=DwIGaQ&c=RoP1YumCXCgaWHvlZYR8PZh8Bv7qIrMUB65eapI_JnE&r=DOuE8PC0dVIPkFJAHd8u_Po6cDEyqqQ1vxmdZfe0eHc&m=11UKl--0Yg98UQMHN2L2-gvq7w7byDFKmsHyKzwxO84&s=SPokLHy1kM7RC-4O-Lcasj3_LxUloS4iOr0mmF7GoiU&e=.
>
> Conclusion: the mathematical right hand rule is what the GeoJSON 
> specification implements (winding as fingers of the right hand wind, 
> so counterclockwise). Unfortunately another well known specification, 
> the ESRI shapefile one, calls the opposite winding order with 
> clockwise outer ring also as a right hand rule even a better name 
> could have been "right arm rule" - when you walk along the rings your 
> right arm points to the interior.
>
> The erratum is incorrect.
>
> -Jukka Rahkonen-
>
> Martin Raifer kirjoitti 2018-06-19 18:01:
>> I'm wondering about the following reported erratum on rfc7946
>> https://urldefense.proofpoint.com/v2/url?u=https-3A__www.rfc-2Deditor.org_errata_eid5069&d=DwIGaQ&c=RoP1YumCXCgaWHvlZYR8PZh8Bv7qIrMUB65eapI_JnE&r=DOuE8PC0dVIPkFJAHd8u_Po6cDEyqqQ1vxmdZfe0eHc&m=11UKl--0Yg98UQMHN2L2-gvq7w7byDFKmsHyKzwxO84&s=lUOsFimY5EHi8TF93F-uA5px4E1Y6F8E0Hhi0OF-YiM&e= 
>> about section 3.1.6.:
>>
>>> 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.
>>
>> I believe that this erratum is incorrect and that the given
>> interpretation of the "right hand rule" in rfc7946 – exterior ring
>> have counterclockwise winding order – is actually the intended one. Is
>> that correct?
>>
>> I'm not very familiar with RFC errata (and their statuses [1]), but it
>> looks to me like it was reported, but not yet verified or rejected. It
>> would certainly be nice to have the status of this erratum clarified
>> (for example so that the rfc7946 page no longer IMHO falsely states
>> that "Errata Exist"). Or is the verification process already in
>> progress?
>>
>> Best,
>> Martin Raifer
>>
>> [1] 
>> https://urldefense.proofpoint.com/v2/url?u=https-3A__www.rfc-2Deditor.org_errata-2Ddefinitions_&d=DwIGaQ&c=RoP1YumCXCgaWHvlZYR8PZh8Bv7qIrMUB65eapI_JnE&r=DOuE8PC0dVIPkFJAHd8u_Po6cDEyqqQ1vxmdZfe0eHc&m=11UKl--0Yg98UQMHN2L2-gvq7w7byDFKmsHyKzwxO84&s=6pfjYG-iDR7R_JmyWK1CaQH2-vp-u1S7Kvi_KROSbIw&e=
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>>
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