I agree with what you're saying, but the actions implied aren't clear.
Do you think we should go ahead and define a datum parameter, or just
not preclude one? If we do, do we define values, and are clients
required to process it?
--Richard
Ted Hardie wrote:
> At 8:24 AM -0700 6/3/09, Carl Reed wrote:
>> I can check.
>>
>> Carl
>
> Both Galileo and GLONASS use datums which are distinct from
> WGS84. PZ-90, which is the datum used by GLONASS, does differ
> from WGS84, though the difference is minor (Wikipedia puts
> it as "less than 40cm in any given direction").
>
> In some applications, 40cm is significant, and if you can eliminate
> an error by noting that the reference datum was PZ-90 rather
> than WGS84, it seems useful to me personally to do so.
>
> To back up a step, I have to ask what we think we're getting
> by using a URI here. This is clearly not a URI intended to be
> used to trigger protocol processing; it is instead a way of
> capturing the context of the data. For those of us who use
> GPS and systems designed to work with GPS, lat, long, altitude
> and WGS84 are the syntax and context for location. This
> group could agree to mint a URI scheme that works only
> in that context and it would have a very simple syntax.
>
> It could instead have a slightly more general syntax and
> mechanism for indicating context (the parameter indicating
> datum). I think the latter is more in keeping with the purpose
> of URIs. Shorn of even the possibility of using new or different
> datums, I think we will either see other URI schemes,
> the same URI schemes used with different datums (thus introducing
> invisible differences in reference coordinates). Though I
> usually fall into the "strings are cheap" view of URI schemes,
> having a URI proliferation like geo:, geoGLONASS:, geoWGS84-2009:
> etc strikes me as unlikely to be a long term win. And having
> folks use the same URI scheme with different but unmarked
> datums makes me very concerned indeed.
>
> The parameter method suggested before is easy to specify,
> relatively cheap to parse, and it meets my personal test
> for simplicity. I understand it doesn't meet others, but
> speaking personally, I think the resistance to it doesn't
> match the real likelihood of problems. Unless someone
> builds a parser without reading the spec or referring to
> a standard URI library, there's a fair chance they'll get it
> right.
>
> My two cents,
> Ted
>
>
>
>> ----- 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/Conferenc
>>> 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
>>> _______________________________________________
>>> Geopriv mailing list
>>> Geopriv@ietf.org
>>> https://www.ietf.org/mailman/listinfo/geopriv
>> _______________________________________________
>> Geopriv mailing list
>> Geopriv@ietf.org
>> https://www.ietf.org/mailman/listinfo/geopriv
>
> _______________________________________________
> Geopriv mailing list
> Geopriv@ietf.org
> https://www.ietf.org/mailman/listinfo/geopriv
>
_______________________________________________
Geopriv mailing list
Geopriv@ietf.org
https://www.ietf.org/mailman/listinfo/geopriv
