My understanding of his response is that this is a non-issue for the EM
domain. In terms of transformations, treated like any other CRS
transformation.
Cheers
Carl
ITRS is the International Terrestrial Reference System, which is a dynamic
reference system (we live on a dynamic earth). In principle every year a
'snapshot' is taken, freezing the Datum and Coordinate System (in ISO 19111
terms). These "snapshots" are called ITRFyyyy, where 'F' means 'Frame' and
'yyyy' is the year (realization epoch). You can transform from e.g. IRTF1992
to ITRF2005 in the same way as transform between any other two datums. See
the EPSG database for those transformations.
ITRS is a more rigorous solution than WGS 84, which was never defined to
deal with a dynamic earth surface. However, we know that the earth is
dynamic, so how does WGS 84 deal with that?
WGS 84 is periodically corrected to bring it in-line with ITRS, the
'tolerance' being 10 cm.
It means that if you would have an accurate GPS receiver on your roof you
would see the coordinates 'drift away' slowly over time, with a periodic
jump as well when WGS 84 is brough in line with ITRS.
Best regards,
Roel
----- Original Message -----
From: "Dawson, Martin" <Martin.Dawson@andrew.com>
To: "Thomson, Martin" <Martin.Thomson@andrew.com>; "Carl Reed"
<creed@opengeospatial.org>; "Alexander Mayrhofer"
<alexander.mayrhofer@nic.at>; "GEOPRIV" <geopriv@ietf.org>;
<vcarddav@ietf.org>
Sent: Wednesday, June 03, 2009 11:28 PM
Subject: RE: [Geopriv] [VCARDDAV] The "geo" URI draft
> Does it really matter what Galileo, or any other GNSS, "uses"?
>
> If I buy a Garmin receiver that has GPS internally and it displays a
> particular location, I would not expect the quantity displayed to be any
> different on a model that is identical other than using Galileo
> internally.
>
> The "secret business" between the receiver and the satellites is not the
> same as the application/presentation. I believe the discussion is around
> a simplified encoding for Internet applications. Why can't we settle,
> for now, on a single reference system for Internet applications?
>
> Cheers,
> Martin
>
> -----Original Message-----
> From: geopriv-bounces@ietf.org [mailto:geopriv-bounces@ietf.org] On
> Behalf Of Thomson, Martin
> Sent: Thursday, 4 June 2009 11:18 AM
> To: Carl Reed; Alexander Mayrhofer; GEOPRIV; vcarddav@ietf.org
> Subject: Re: [Geopriv] [VCARDDAV] The "geo" URI draft
>
> I can verify. Galileo will _NOT_ use WGS84, but for all practical
> purposes, the CRS that they intend to use will be the same. Differences
> are likely to be in the order of a centimetre.
>
> Conversion is in theory necessary, but only for extreme cases. In most
> cases, coordinates will be close enough that the difference has no
> practical impact.
>
>> -----Original Message-----
>> From: geopriv-bounces@ietf.org [mailto:geopriv-bounces@ietf.org] On
>> Behalf Of Carl Reed
>> Sent: Thursday, 4 June 2009 1:25 AM
>> To: Alexander Mayrhofer; GEOPRIV; vcarddav@ietf.org
>> Subject: Re: [Geopriv] [VCARDDAV] The "geo" URI draft
>>
>> I can check.
>>
>> Carl
>>
>> ----- Original Message -----
>> From: "Alexander Mayrhofer" <alexander.mayrhofer@nic.at>
>> To: "GEOPRIV" <geopriv@ietf.org>; <vcarddav@ietf.org>
>> Sent: Wednesday, June 03, 2009 7:18 AM
>> Subject: Re: [Geopriv] [VCARDDAV] The "geo" URI draft
>>
>>
>> >
>> >
>> >> Also, the forthcoming Galileo system:
>> >>
>> >> <http://en.wikipedia.org/wiki/Galileo_positioning_system>
>> >>
>> >> will not, I understand, use WGS84.
>> >
>> > I don't claim to be an expert in reference systems / geopotential
>> models
>> > etc. so please take the following information with caution (Carl? ;)
>> >
>> > I couldn't find any information about the reference system that
>> Galileo
>> > uses on the wikipedia page. However, a bit of research shows that
>> > Galileo seems to use ITRF ("International Terrestrial Reference
>> Frame"),
>> > which, however, seems to be practically identical to WGS84,
> according
>> to
>> > http://www.dqts.net/wgs84.htm (web site by EUROCONTROL). Also, this
>> >
>>
> http://www.cambridgeconference.com/2007_conference_information/Conferen
>> c
>> > e%20proceedings/w2_5_cross.pdf presentation notes on slide 15 that
>> > "WGS84 and IRTF are aligned".
>> >
>> > Which means that Galileo will use a reference system that is
>> practically
>> > identical to WGS84.
>> >
>> > Again, Disclaimer: i'm not an expert in this field.
>> >
>> > Alex
>> > _______________________________________________
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>> > Geopriv@ietf.org
>> > https://www.ietf.org/mailman/listinfo/geopriv
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