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RE: UCR issue: phrasing of CRS requirement(s)

From: Svensson, Lars <L.Svensson@dnb.de>
Date: Mon, 18 May 2015 11:43:56 +0000
To: Ed Parsons <eparsons@google.com>, "janowicz@ucsb.edu" <janowicz@ucsb.edu>
Cc: SDW WG Public List <public-sdw-wg@w3.org>
Message-ID: <24637769D123E644A105A0AF0E1F92EF010CF6B6DB@dnbf-ex1.AD.DDB.DE>
On Monday, May 18, 2015 12:24 PM, Ed Parsons wrote:

> In most cases I don't think they actually do mean WGS84 as in the ellipsoid and
> datum.
> 
> I would guess it is usually shorthand for the the full spatial reference system
> defined by EPSG4326 or more likely on the web EPSG:3857

My fear is that in some cases the data providers don't really know what their coordinates mean in terms of ellipsoid, datum and reference system. They have some coordinates taken from geonames, Wikipedia or some other source and haven’t really thought of that (geographic) coordinates are not just coordinates but that there is a context to that, too. To what extent we can assume that they mean CRS84, I don't know.

So I think I'm on the same page as Linda on this.

Best,

Lars
 
> On 16 May 2015 at 04:02, Krzysztof Janowicz <janowicz@ucsb.edu> wrote:
> right, so how can they be sure they mean WGS84?
> 
> Here is a funny example how this can go wrong and went wrong in the past:
> http://stko.geog.ucsb.edu/location_linked_data (See the Copernicus crater)
> 
> Best,
> Krzysztof
> 
> 
> 
> 
> On 05/15/2015 04:27 AM, Peter Baumann wrote:
> right, so how can they be sure they mean WGS84? if I copy-past coordinates
> from web info about Germany then in the past this used to be Gauss-Krüger,
> and several strips = sub-systems. Now let's talk about height and SI vs imperial
> units etc - what default could we agree on?
> 
> With a default, all coordinate info out there on the Web (flat, height/depth,
> time, pressure, ...) will often be interpreted wrongly. IMHO we should rather
> encourage, for m2m communication, that we achieve informational
> completeness.
> 
> my 2 cents,
> Peter
> 
> On 05/15/15 13:21, Linda van den Brink wrote:
> Hi all,
> 
> OK, that could be the consensus within OGC, but the GeoJSON spec does
> describe a default CRS and I can understand this very well. Non-experts, i.e.
> people from outside the geospatial domain who are using or want to use
> geospatial data, often have no idea that there even *are* multiple coordinate
> reference systems.
> 
> Linda
> 
> Van: Peter Baumann [mailto:p.baumann@jacobs-university.de]
> Verzonden: vrijdag 15 mei 2015 13:01
> Aan: Linda van den Brink; Frans Knibbe; SDW WG (public-sdw-wg@w3.org)
> Onderwerp: Re: UCR issue: phrasing of CRS requirement(s)
> 
> Hi all,
> 
> FYI, there has been a vivid discussion in OGC on default CRSs on the occasion of
> JSON coming up with such an idea, and OGC very much and strongly agreed
> that this is not a good idea.
> 
> In general, a coordinate tuple should have exactly one CRS referenced which
> may include
> - spatial horizontal (such as Lat/Long)
> - time (possibly using different calendars)
> - elevation
> - anything else (eg, atmospheric sciences like to use pressure as a proxy for
> height)
> - finally, planetary CRSs are more and more coming into play as well.
> I sense that this is very much in alignment with the ideas that we are discussing
> here.
> 
> OTOH, it is indeed important to have one common mechanism of describing
> CRSs. As mentioned earlier, OGC has such mechanisms in place through CRS
> WKT plus the CRS Name Type Specification (maybe quite misleading in its title,
> it allows to describe CRSs by composing them from other ones, such as flatland
> + time, flatland + pressure, flatland + depth, flatland + geological time).
> 
> So definitely supporting Linda's observation on referencing vs describing.
> 
> -Peter
> 
> On 05/15/15 09:40, Linda van den Brink wrote:
> Hi Frans,
> 
> I noticed that a requirement related to this is in the spreadsheet but not (yet?)
> in the UCR document. It is this requirement:
> 
> “There should be a default CRS that is assumed when nog CRS is specified”
> (s/nog/no)
> 
> WGS84/lat lng is the de facto standard CRS for spatial data on the web. Both
> publishing and using spatial data on the web should be easy for non-experts, so
> this requirement of having a default CRS makes a lot of sense to me. The most
> common cases become more easy that way. I think this should be added to par.
> 5.6 of the UCR.
> 
> In this light (i.e. usability for non-expert users), the best practice should have
> information about how data owners should describe, how users can recognize
> and what tools they can use to transform non-WGS84 coordinate systems to the
> coordinate system they need.
> 
> A second point I’d like to make is that CRS should be suitable also for non-
> geographical reference systems (for non-Earth oriented applications).I think
> this is covered by 5.14, but the text of that paragraph is not completely clear to
> me. )“Standards for spatial data on the web should be independent on the
> reference systems that are used for data.”)
> 
> Finally, to answer the question in the issue, as I read it, req A is not replaceable
> by req B. Req A is about *referencing* a CRS, while req B is about *describing*
> a CRS – i.e. the description you get about the CRS when you dereference  a CRS
> reference.
> 
> Linda
> 
> Van: Frans Knibbe [mailto:frans.knibbe@geodan.nl]
> Verzonden: woensdag 13 mei 2015 14:20
> Aan: SDW WG Public List
> Onderwerp: UCR issue: phrasing of CRS requirement(s)
> 
> Hello all,
> 
> I have raised an issue for the UCR document: ISSUE-10.
> All help in getting this issue resolved is very welcome.
> 
> Regards,
> Frans
> 
> 
> --
> Frans Knibbe
> Geodan
> President Kennedylaan 1
> 1079 MB Amsterdam (NL)
> 
> T +31 (0)20 - 5711 347
> E frans.knibbe@geodan.nl
> www.geodan.nl
> disclaimer
> 
> 
> --
> Dr. Peter Baumann
>  - Professor of Computer Science, Jacobs University Bremen
>    www.faculty.jacobs-university.de/pbaumann
>    mail: p.baumann@jacobs-university.de
>    tel: +49-421-200-3178, fax: +49-421-200-493178
>  - Executive Director, rasdaman GmbH Bremen (HRB 26793)
>    www.rasdaman.com, mail: baumann@rasdaman.com
>    tel: 0800-rasdaman, fax: 0800-rasdafax, mobile: +49-173-5837882
> "Si forte in alienas manus oberraverit hec peregrina epistola incertis ventis
> dimissa, sed Deo commendata, precamur ut ei reddatur cui soli destinata, nec
> preripiat quisquam non sibi parata." (mail disclaimer, AD 1083)
> 
> 
> 
> 
> --
> Dr. Peter Baumann
>  - Professor of Computer Science, Jacobs University Bremen
>    www.faculty.jacobs-university.de/pbaumann
>    mail: p.baumann@jacobs-university.de
>    tel: +49-421-200-3178, fax: +49-421-200-493178
>  - Executive Director, rasdaman GmbH Bremen (HRB 26793)
>    www.rasdaman.com, mail: baumann@rasdaman.com
>    tel: 0800-rasdaman, fax: 0800-rasdafax, mobile: +49-173-5837882
> "Si forte in alienas manus oberraverit hec peregrina epistola incertis ventis
> dimissa, sed Deo commendata, precamur ut ei reddatur cui soli destinata, nec
> preripiat quisquam non sibi parata." (mail disclaimer, AD 1083)
> 
> 
> 
> --
> Krzysztof Janowicz
> 
> Geography Department, University of California, Santa Barbara
> 4830 Ellison Hall, Santa Barbara, CA 93106-4060
> 
> Email: jano@geog.ucsb.edu
> Webpage: http://geog.ucsb.edu/~jano/

> Semantic Web Journal: http://www.semantic-web-journal.net


Received on Monday, 18 May 2015 11:44:26 UTC

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