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RE: RFC 5870 - A Uniform Resource Identifier for Geographic Locations ('geo' URI)

From: Little, Chris <chris.little@metoffice.gov.uk>
Date: Tue, 4 Aug 2015 15:02:25 +0000
To: Ed Parsons <eparsons@google.com>, Joshua Lieberman <jlieberman@tumblingwalls.com>, "simon.cox@csiro.au" <simon.cox@csiro.au>
CC: "public-sdw-wg@w3.org" <public-sdw-wg@w3.org>
Message-ID: <3DAD8A5A545D7644A066C4F2E82072883E1789E7@EXXCMPD1DAG4.cmpd1.metoffice.gov.uk>
And another cautionary example – meteorologists routinely publish Mean Sea Level Pressure maps, even over the Tibetan plateau, and the geodetic details have been routinely ignored for decades.

From: Ed Parsons [mailto:eparsons@google.com]
Sent: Wednesday, July 22, 2015 10:16 AM
To: Joshua Lieberman; simon.cox@csiro.au
Cc: public-sdw-wg@w3.org
Subject: Re: RFC 5870 - A Uniform Resource Identifier for Geographic Locations ('geo' URI)

Yes matters sometimes.. to some people.. It is equally a generalisation to say that geodetic details are relevant to everyone using global coordinates on the web !

Ed


On Wed, 22 Jul 2015 at 03:01 Joshua Lieberman <jlieberman@tumblingwalls.com<mailto:jlieberman@tumblingwalls.com>> wrote:
An excellent cautionary tale. For example, the 3D default coordinate system is cited as EPSG:4979, with optional elevation relative to the WGS84 geoid. However, 4979 elevation is relative to the WGS84 ellipsoid, not the geoid the RFC cites. There is a defined WGS84 gravimetric geoid (EGM96) that varies from the ellipsoid by around +/-100m over the earth, and is approximated by a coarse coverage in most modern GPS units while neglected in older ones. Unfortunately the geodetic details matter.

-Josh


On Jul 21, 2015, at 8:08 PM, simon.cox@csiro.au<mailto:simon.cox@csiro.au> wrote:


Just became aware of this (via the GeoJSON list)

https://tools.ietf.org/html/rfc5870#section-3.4.5


I’ve added it to the BP ref list https://www.w3.org/2015/spatial/wiki/BP_References


Simon

--

Ed Parsons
Geospatial Technologist, Google

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www.edparsons.com<http://www.edparsons.com> @edparsons
Received on Tuesday, 4 August 2015 15:02:55 UTC

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