RE: [SDWWG] CRS Issues [SEC=UNCLASSIFIED]

I will not participate in these discussions for a while because of my holiday. But just for the record:

+1 to the benefits of a default CRS, as long as any such default is well documented and understood.

Van: SDWWG [mailto:sdwwg-bounces+l.vandenbrink=geonovum.nl@lists.opengeospatial.org] Namens Ed Parsons via SDWWG
Verzonden: donderdag 2 juli 2015 11:16
Aan: Peter Baumann; Bruce Bannerman; SDW WG Public List; sdwwg@lists.opengeospatial.org
Onderwerp: Re: [SDWWG] CRS Issues [SEC=UNCLASSIFIED]

This issue addresses only how your reference the details of a CRS detailed at a different location on the web. I think it is beyond our scope to define new spatio-temporal CRS's.

As to the dangers of a default CRS, as long as any such default is well documented and understood, there is great benefit. I look forward to continued debate on this issue :-)


Ed


On Thu, 2 Jul 2015 at 09:55 Peter Baumann <p.baumann@jacobs-university.de<mailto:p.baumann@jacobs-university.de>> wrote:
+1 from my side, plus an extra issue:

it is pretty clear that today we need CRSs for height and time just as much as
we need it for Lat and Long. Technically IMHO this means we need to come up with
CRSs being able to hold _all_ such axes. Having all these CRSs separate and with
individual mechanisms is a nightmare. Therefore, I'd propose a

Requirement:
It must be possible in location information item (such as coordinates) to
express all spatio-temporal location information in one CRS. This implies that
CRSs can have a different number of dimensions, depending on the dimensions
captured (such as 1-D time, 2-D Lat/Long, 3-D Lat/Long/time or Lat/Long/height
or Lat/Long/Pressure, or 4-D Lat/Long/height/time).

Furthermore:

On 07/01/15 23:34, Bruce Bannerman wrote:
> Sorry that I was not able to participate in the call.
>
> Two CRS issues:
>
> _CRS Definition_
>
> Most of the discussion to date on this thread appears to have related to just horizontal CRS. Issues relating to both vertical and temporal CRS have also been discussed in a number of emails.
>
> Are these CRS also covered by 1. Below.
>
>
>
> _Default CRS_
>
> Issues relating to the assumption that data is based on a default CRS have been raised from memory. For many use cases, this assumption can be quite dangerous and can have unforeseen consequences.
>
> See also my related post on 'misuse of spatial data'.
>
> I'm trying to find some citable references that effectively illustrate the issue of 'misuse', but have limited time. I'll keep going though, as this is an important, but typically overlooked issue, as people just strive for a map as a 'pretty picture'.

I had sent around an example where an Austrian municipality publishes its
coordinates - without CRS. And the silently assumed CRS is not WGS84. So
locating this town under the assumption of WGS84 would lead you maybe into the
ocean.

-Peter

>
> Bruce
>
>
>
> ________________________________
> From: Ed Parsons <eparsons@google.com<mailto:eparsons@google.com>>
> Sent: Thursday, 2 July 2015 12:14 AM
> To: SDW WG Public List; sdwwg@lists.opengeospatial.org<mailto:sdwwg@lists.opengeospatial.org>
> Subject: CRS Issues
>
> Thanks for you input everyone on the call today.. Here is where we stand on the combined issues raised by Frans.
>
> 1)The CRS Definition requirement<http://w3c.github.io/sdw/UseCases/SDWUseCasesAndRequirements.html#CRSDefinition> currently in the UCR document should be rephrased. This is what ISSUE-10<https://www.w3.org/2015/spatial/track/issues/10> is about. The proposal for new wording is "There should be a recommended way of referencing a CRS with a HTTP URI, and to get useful information about the CRS when that URI is dereferenced."
>
> Agreed and accepted slight modified wording removing "recommended".
>
> 2)In the course of discussing CRS requirements a new BP requirement was introduced: Default CRS<http://w3c.github.io/sdw/UseCases/SDWUseCasesAndRequirements.html#DefaultCRS>. No issues have been raised with regard to this requirement yet.
>
> New issue created but not a new formal requirement.
>
> 3)In the course of discussing CRS requirements a possible new BP requirement has come up. ISSUE-29 (Add a requirement for linking geometry to CRS)<https://www.w3.org/2015/spatial/track/issues/29> was raised to enable further discussion and/or decision-making.
>
> Agreed a new requirement
>
> 4)Whether 'a recommend way' is the best expression to be used in requirements is something that is discussed in the thread Use of the word 'standard' in the UCR document<https://lists.w3.org/Archives/Public/public-sdw-wg/2015Jun/0211.html>.
>
> Agreed that the appropriate term should be "Advice", rather than recommended way or standard, so the BP should offer Advice as needed.
>
>
> Ed
>
>
> --
> Ed Parsons
> Geospatial Technologist, Google
> Mobile +44 (0)7825 382263
> www.edparsons.com<http://www.edparsons.com><http://www.edparsons.com> @edparsons
>

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