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

From: <Simon.Cox@csiro.au>
Date: Mon, 18 May 2015 21:56:42 +0000
To: <Kerry.Taylor@csiro.au>, <L.Svensson@dnb.de>, <eparsons@google.com>, <janowicz@ucsb.edu>
CC: <public-sdw-wg@w3.org>
Message-ID: <2A7346E8D9F62D4CA8D78387173A054A601738CE@exmbx04-cdc.nexus.csiro.au>
> For the *description" of a CRS, I would vote to defer that to the OGC by its existing methods, and I see no reason why that description needs to have a linked data representation, beyond an ontology that permits its use.
	
Thanks Kerry - that's essentially the way I see it, if by "linked data representation" you are implying RDF. I would like to ask those people advocating a new CRS encoding in RDF, what this would be useful for? The main use for a CRS _description_ (as opposed to denotation) is to support _coordinate transformation_, which is a very mathematical operation. Not really what RDF is good at. I can't think of a compelling _reasoning_ application for CRS. Let's not get carried away with RDF applications. There are boundaries past which reasoning/RDF are not the main application, so we should try not to step over them. 

Simon


-----Original Message-----
From: Kerry.Taylor@csiro.au [mailto:Kerry.Taylor@csiro.au] 
Sent: Tuesday, 19 May 2015 12:40 AM
To: L.Svensson@dnb.de; eparsons@google.com; janowicz@ucsb.edu
Cc: public-sdw-wg@w3.org
Subject: [ExternalEmail] RE: UCR issue: phrasing of CRS requirement(s)

WGS84 is certainly widely used for linked data in practice, probably  heavily influenced by this http://www.w3.org/2003/01/geo/, commonly called "geo".

Oddly, perhaps, schema.org seems not to care about CRS at all: http://schema.org/GeoCoordinates 

Can we take inspiration from the former one  (geo)  and admit alternative CRSs that must be identified by virtue of the ontology (and therefore namespace, assuming a 1-1 relationship) that is used?  We could perhaps develop a couple ourselves (perhaps a WGS84-like one, and another for a relative 3D system), and then allow any other to be used by virtue of reference to the intended vocabulary (as our best practice advice)?

Maybe this is a cop-out but it is a way of dealing with the common cases blindly, yet requiring a CRS to be implicitly identified, and also enabling the use of more complex or niche CRS whenever needed. We won't stop people making mistakes, whatever we do.

This could do for  *referencing* a  CRS without ever needing a "default". For the *description" of a CRS, I would vote to defer that to the OGC by its existing methods, and I see no reason why that description needs to have a linked data representation,  beyond an ontology that permits its use.




Krzysztof, why is Java such a hot bed of linked data?!?

Kerry


> -----Original Message-----
> From: Svensson, Lars [mailto:L.Svensson@dnb.de]
> Sent: Monday, 18 May 2015 9:44 PM
> To: Ed Parsons; janowicz@ucsb.edu
> Cc: SDW WG Public List
> Subject: RE: UCR issue: phrasing of CRS requirement(s)
> 
> 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 21:57:42 UTC

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