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Re: Wanted: feedback on UCR requirements

From: matthew perry <matthew.perry@oracle.com>
Date: Thu, 14 Jul 2016 09:42:35 -0400
To: public-sdw-wg@w3.org
Message-ID: <9ad402d0-a2f4-91a3-7dcc-a48aa9e7e984@oracle.com>

Thanks for making the change. You make a good point about another 
requirement. I would personally like such a requirement. Something like 
"When possible, spatial data should be made available in commonly used 
spatial reference systems (e.g., CRS84) to allow for easier integration 
with spatial data from different sources". I guess my wording is more of 
a recommendation than requirement.

I'm not sure if we would have majority support for this requirement 
though since it's getting close to a default CRS.


On 7/14/2016 5:13 AM, Frans Knibbe wrote:
> Thank you Matt. I will solve issue 28 by changing the requirement to 
> the suggested wording. And I will search for other use cases that have 
> the same requirement.
> So you don't think that next to the requirement for always being able 
> to determine the CRS another requirement is needed, calling for (a) 
> best practice(s) for avoiding coordinate transformations when 
> combining geometric data from different sources?
> Regards,
> Frans
> On 13 July 2016 at 20:08, matthew perry <matthew.perry@oracle.com 
> <mailto:matthew.perry@oracle.com>> wrote:
>     Hi Frans,
>     I agree that the core requirement from issue 28 is that users
>     should always be able to determine what CRS is used. Without such
>     information, there's not much hope for integration. I am fine with
>     this new wording.
>     I think suggestion #1 from Jon is a good way to promote a
>     "default" CRS without trying to assert that data without an
>     explicit CRS should be interpreted as CRS84.
>     Thanks,
>     Matt
>     On 7/13/2016 12:33 PM, Jon Blower wrote:
>>     Hi Frans,
>>     I haven’t followed the previous discussions in detail I’m afraid,
>>     but in my mind a “Best Practice” around CRS might look like this:
>>     1.If your goal is to make data available to mass-market web
>>     users, make it available in CRS84, but be aware (and perhaps
>>     publish) the limitations of doing so.
>>     2.If your goal is high accuracy, choose the best CRS for your data.
>>     3.Publishing data in multiple CRSs is fine, and may help users to
>>     combine your data with other sources, as well as serving multiple
>>     types of user.
>>     4.Always explicitly state which CRS(s) you are using. [I don’t
>>     think a default CRS should be recommended]
>>     If multiple CRS are used we may need a mechanism to communicate
>>     which CRS is “preferred” in terms of accuracy.
>>     Does this help? I’ve deliberately been neutral about the
>>     mechanism by which the above could be communicated, because users
>>     might get such information in multiple ways.
>>     Cheers,
>>     Jon
>>     *From: *Frans Knibbe <frans.knibbe@geodan.nl>
>>     <mailto:frans.knibbe@geodan.nl>
>>     *Date: *Wednesday, 13 July 2016 15:13
>>     *To: *Linda van den Brink <l.vandenbrink@geonovum.nl>
>>     <mailto:l.vandenbrink@geonovum.nl>, matthew perry
>>     <matthew.perry@oracle.com> <mailto:matthew.perry@oracle.com>
>>     *Cc: *SDW WG Public List <public-sdw-wg@w3.org>
>>     <mailto:public-sdw-wg@w3.org>
>>     *Subject: *Re: Wanted: feedback on UCR requirements
>>     *Resent-From: *<public-sdw-wg@w3.org> <mailto:public-sdw-wg@w3.org>
>>     *Resent-Date: *Wednesday, 13 July 2016 15:14
>>     Hello Linda, Matt,
>>     Thanks to the BP editors for taking time to look at these issues.
>>     The solution to issue 28 looks sensible to me, but I would like
>>     to ask Matt if he agrees with the change. The requirement for a
>>     default/canonical CRS comes directly from the use case Combining
>>     spatial RDF data for integrated querying in a triplestore
>>     <http://w3c.github.io/sdw/UseCases/SDWUseCasesAndRequirements.html#CombiningSpatialRDFDataForIntegratedQueryingInATriplestore>,
>>     which Matt contributed. It seems to me that if the requirement in
>>     its new wording is met, the problem of having to do coordinate
>>     transformations (for instance in federated SPARQL queries) still
>>     exists. So I wonder if the new wording does justice to the use case.
>>     I think the problem of having to perform coordinate
>>     transformation when combining datasets could also be solved by
>>     recommending using multiple CRSs in data publications. A
>>     procedure for combining data from two data sets would then have a
>>     higher chance of finding a CRS that both data sets have in
>>     common. Having good standards for making the CRS known of course
>>     would help a lot in that process, and the requirement in its new
>>     wording would help there.
>>     Another way of mitigating the problem of having to transform
>>     coordinates would be to have a more general lat-lon CRS than the
>>     likes of ETRS89 and WGS84, which could not be used for high
>>     precision data but could aid interoperabilty.
>>     So if we acknowledge that there could be different solutions for
>>     the problem of having to perform coordinate transformation when
>>     combining data, would that mean there is room for a new
>>     requirement that specifies the problem and does not hint at
>>     possible solutions? For example "Recommendations or standards are
>>     needed to avoid having to transform coordinates when data from
>>     different sources are combined"?
>>     Regards,
>>     Frans
>>     On 12 July 2016 at 16:17, Linda van den Brink
>>     <l.vandenbrink@geonovum.nl <mailto:l.vandenbrink@geonovum.nl>> wrote:
>>         Hi Frans,
>>         We (the BP editors) have discussed the BP issues and concluded:
>>         -issue 23: We think this issue can be closed because in our
>>         view the wording as it currently is for this requirement in
>>         the UCR is fine. We will try to address the questions that
>>         are raised in the issue in the BP. I created an issue in
>>         Github so we don’t forget. https://github.com/w3c/sdw/issues/298
>>         -issue 28: The requirement according to us three is: “that
>>         clients or users must always be able to determine what CRS is
>>         used.” This could be because it’s present in the data in some
>>         form, or because it’s determined by the spec (and this could
>>         be that if unspecified in the data, there’s some default). 
>>         In the BP we will go into the question of when a more precise
>>         CRS than WGS84 is needed. We hope this helps us resolve the
>>         issue.
>>         Linda
>>         *Van:*Frans Knibbe [mailto:frans.knibbe@geodan.nl
>>         <mailto:frans.knibbe@geodan.nl>]
>>         *Verzonden:* woensdag 6 juli 2016 15:01
>>         *Aan:* Jeremy Tandy; Linda van den Brink; Payam Barnaghi;
>>         Simon Cox; Chris Little; Krzysztof Janowicz; Armin Haller;
>>         danh.lephuoc@deri.org <mailto:danh.lephuoc@deri.org>; Bill
>>         Roberts; Kerry Taylor
>>         *CC:* SDW WG Public List
>>         *Onderwerp:* Re: Wanted: feedback on UCR requirements
>>         Dear editors,
>>         I haven't had much response to my question so far. So as an
>>         aid, here is a list of the open issues marked in the current
>>         UCR draft:
>>         <https://www.w3.org/2015/spatial/track/issues/20>
>>         ISSUE-20 <https://www.w3.org/2015/spatial/track/issues/20> (SSN)
>>         ISSUE-23 <https://www.w3.org/2015/spatial/track/issues/23>
>>         (Best Practices)
>>         ISSUE-24 <https://www.w3.org/2015/spatial/track/issues/24> (SSN)
>>         ISSUE-26 <https://www.w3.org/2015/spatial/track/issues/26> (Time)
>>         ISSUE-28 <https://www.w3.org/2015/spatial/track/issues/28>
>>         (Best Practices)
>>         Wouldn't it be nice if we can resolve these issues before the
>>         next and final PWD of the UCR document this month?
>>         Regards,
>>         Frans
>>         2016-06-22 13:12 GMT+02:00 Frans Knibbe
>>         <frans.knibbe@geodan.nl <mailto:frans.knibbe@geodan.nl>>:
>>         Dear editors of the BP/Time/SSN/Coverage deliverable,
>>         In preparation of a next public working draft of the UCR
>>         document I would like to ask you for feedback on the
>>         requirements for your deliverable as specified in the UCR
>>         document. Section 6
>>         <http://w3c.github.io/sdw/UseCases/SDWUseCasesAndRequirements.html#RequirementsByDeliverable>
>>         list requirements grouped by deliverable. By now you will
>>         have stared long & hard at those requirements, and perhaps
>>         you concluded that some or not clear yet, or that something
>>         else is wrong. Perhaps requirements or even important use
>>         cases are missing?
>>         While we are working on a new batch of publications before
>>         TPAC, it would be nice if the requirements in the UCR
>>         document are (among) the ones you are actually working with.
>>         I think the public we are writing for deserves that
>>         coherence. I presume your deliverables will link back to the
>>         UCR document and explain how requirements are met or why
>>         requirements are not met. So if you think any changes are
>>         required in the UCR document resulting from your work on your
>>         deliverable, please inform me.
>>         Thanks,
>>         Frans
Received on Thursday, 14 July 2016 13:43:15 UTC

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