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Re: geo:lat owl:samePropertyAs vcard:latitude? (vCard/RDF)

From: Norman Gray <norman@astro.gla.ac.uk>
Date: Thu, 23 Nov 2006 15:54:37 +0000
Message-Id: <1AAE6EDA-25B9-4439-80F1-5320F10416CC@astro.gla.ac.uk>
Cc: semantic-web@w3.org
To: Dan Connolly <connolly@w3.org>


Greetings.

On 2006 Nov 21 , at 15.51, Dan Connolly wrote:

> Wikipedia cites a NIMA tech report... eek... it's only good
> thru 2010?!? I wonder if the process for the next version is
> rolling yet.

It'll be good for a good long while after that, for all practical  
purposes (given that your personal practical purposes don't include  
dropping cruise missiles on folk -- guess why the various WGSxx  
specifications were originally associated with the US DoD and GPS).   
The earth neither changes shape, nor nutates, quickly enough for most  
of us to notice datum errors.

As a more general point, it does seem slightly eccentric for <http:// 
www.w3.org/2003/01/geo/> to privilege WGS84 over all other possible  
datums.  WGS84 is what the GPS uses, but no-one writing a geographic  
mashup is likely to have to care about that.

The issue isn't just one of obsolescence (how many internet years ago  
is 1984?), but parochialism.  Galileo has been launched, and is due  
to come on-stream around 2010: it uses its own datam (as far as I can  
tell), which is distinct from, but based on, the ITRS (International  
Terrestrial Reference System).  Thus if you were, at some point in  
the future, to add to your FOAF file a position taken from a  
navigation system tuned in to Galileo (without making the Galileo- 
 >GPS corrections), it would be formally incorrect to call them a  
wgs84_pos (and you could be as much as a metre adrift of your correct  
position -- quel horreur!).

Quite independently, quoting positions with reference to a particular  
datum is like quoting your height to the nearest nanometre: the extra  
apparent precision is probably spurious, for everyone except all  
those folk surveying telescope mountings, or -- well -- aiming  
missiles, who probably aren't the most urgent targets for mashup- 
facilitation (and who already know all this stuff in more detail than  
gives them pleasure).

Thus rather than

>  I suggest obsoleting 2006/vcard/ns#latitude
> in favor of 2003/01/geo/wgs84_pos#lat

...it would probably be more sensible to go in the other direction,  
and say

>  geo:lat rdfs:subPropertyOf vcard:latitude

and nothing more.  In particular, it would probably be best to leave  
the vCard lat/long as informally specified, and let WGS84, and ITRS,  
and ..., coordinates to be subProperties of them, for those few  
specialists who care.

All the best,

Norman


-- 
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Norman Gray  /  http://nxg.me.uk
eurovotech.org  /  University of Leicester, UK
Received on Thursday, 23 November 2006 15:54:54 GMT

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