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

Hello Ed,

Yes, we could recommend using the EPSG descriptions in the BP. That is
future work. But looking ahead to that, I think the EPSG registry has some
issues: CRS are not identified with a URI, it is hard to automatically
process CRS data, and CRS do not have the same axis order. I think CRS
registries like those made available by the OGC and IGN France are an
improvement, at least in those respects.

Do you agree with the proposed requirement?


Greetings,
Frans

2015-05-27 15:29 GMT+02:00 Ed Parsons <eparsons@google.com>:

> Describing CRS attributes is a "can of worms" for is, I would rather we
> just point to the EPSG repository for simplicity. Perhaps we could in the
> BP point out a few well used CRS and their EPSG descriptions.
>
> Ed
>
> Ed Parsons
> Geospatial Technologist, Google
>
> Mobile: +44 (0)7825 382263
> www.edparsons.com @edparsons
> On 27 May 2015 13:49, "Frans Knibbe" <frans.knibbe@geodan.nl> wrote:
>
>> Hello all,
>>
>> It is nice to see a good discussion with lots of outside references and
>> proposals for meeting the requirements. But I would like to get back to the
>> issue of phrasing the requirements.
>>
>> Linda was right in noting that the requirement for a default or canonical
>> has not been listed in the UCR document yet. I will add it. It will be very
>> interesting to see if we can succeed in finding such a CRS. But that is
>> something that will become clear when we work on the Best Practices.
>>
>> As for the phrasing of the CRS requirement, I would like to propose the
>> following:
>>
>> "There should be a standard for publishing data about coordinate
>> reference systems (CRS). It should be applicable to any 2D or 3D CRS,
>> not only geographical reference systems. CRS descriptions should be
>> referencable by HTTP URIs."
>>
>> I think that given the context of this WG (spatial data on the web), the
>> requirement that things should be referencable goes without saying, but
>> I have made it explicit nonetheless.
>>
>> I should note that when put this way, there is no requirement for having
>> a registry of CRSs - anyone can publish a CRS defintion anywhere.
>>
>> Would it be sensible to add some information about what kind of data we
>> would expect when a CRS is described? There could be a need for having
>> complete descriptions that allow automatic coordinate transformation. Or we
>> could try to list a few CRS attributes that we consider essential for
>> common usage (like axis order, units, whether it is spherical or flat
>> plane, spatial coverage....)
>>
>> Greetings,
>> Frans
>>
>>
>> 2015-05-26 21:12 GMT+02:00 Krzysztof Janowicz <janowicz@ucsb.edu>:
>>
>>> Krzysztof, why is Java such a hot bed of linked data?!?
>>>>
>>>
>>> Good question. If you look at the detailed map here
>>> http://stko.geog.ucsb.edu/pictures/lstd_map.png you will see massive
>>> data errors. Based on our 14+ million sample, it looks like about 10% of
>>> all linked geographic data has some issues related to it. In many cases
>>> those issues were systematic and we notified the data providers, e.g.,
>>> DBpedia. For instance, the dense block-like areas in China are in fact
>>> places from the US east coast. I will look into the data from Java and will
>>> let you know if I find something interesting.
>>>
>>> Anyway, the systematic list of errors may turn out to be useful for our
>>> sdw group as it illustrates what typically goes wrong.
>>>
>>> Best,
>>> Krzysztof
>>>
>>>
>>>
>>>
>>> On 05/18/2015 07:39 AM, Kerry.Taylor@csiro.au wrote:
>>>
>>>> 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
>>>>>>
>>>>>
>>>
>>> --
>>> 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
>>>
>>>
>>>
>>
>>
>> --
>> 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 <http://www.geodan.nl/disclaimer>
>>
>>


-- 
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 <http://www.geodan.nl/disclaimer>