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<p>Hi,</p>
<p>The history of the the "counter-clockwise" rotation of an outer
boundary (and the opposite for interior boundaries, is from <a
moz-do-not-send="true"
href="https://en.wikipedia.org/wiki/Green%27s_theorem">Green's
Theorem</a> 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). <br>
</p>
<p>Any engineering student who got to 3<sup>rd</sup> 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.<br>
</p>
<p>Regards,<br>
John <br>
</p>
<br>
<div class="moz-cite-prefix">On 2018-06-19 11:31 AM, Jukka Rahkonen
wrote:<br>
</div>
<blockquote type="cite"
cite="mid:8f83e07d1c331ef487aaecfb807c5d0a@latuviitta.fi">Hi,
<br>
<br>
This topic was discussed in this gdal-dev thread
<a class="moz-txt-link-freetext" href="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=">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=</a>.<br>
<br>
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.
<br>
<br>
The erratum is incorrect.
<br>
<br>
-Jukka Rahkonen-
<br>
<br>
Martin Raifer kirjoitti 2018-06-19 18:01:
<br>
<blockquote type="cite">I'm wondering about the following reported
erratum on rfc7946
<br>
<a class="moz-txt-link-freetext" href="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=">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=</a>
about section 3.1.6.:
<br>
<br>
<blockquote type="cite">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.
<br>
</blockquote>
<br>
I believe that this erratum is incorrect and that the given
<br>
interpretation of the "right hand rule" in rfc7946 – exterior
ring
<br>
have counterclockwise winding order – is actually the intended
one. Is
<br>
that correct?
<br>
<br>
I'm not very familiar with RFC errata (and their statuses [1]),
but it
<br>
looks to me like it was reported, but not yet verified or
rejected. It
<br>
would certainly be nice to have the status of this erratum
clarified
<br>
(for example so that the rfc7946 page no longer IMHO falsely
states
<br>
that "Errata Exist"). Or is the verification process already in
<br>
progress?
<br>
<br>
Best,
<br>
Martin Raifer
<br>
<br>
[1]
<a class="moz-txt-link-freetext" href="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=">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=</a><br>
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