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
> <http://www.w3.org/2015/spatial/track/issues/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 <mailto:frans.knibbe@geodan.nl>
>
> www.geodan.nl <http://www.geodan.nl>
>
> disclaimer <http://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)