Re: UCR ISSUE-70: add a requirement for avoiding coordinate transformations?

Hi Jon,

I try to phrase the requirements in such a way that meeting them is not
steered in any direction, and to allow creative freedom in solving the
problem. Of course in this case providing data with multiple CRSs meets the
requirement, but I assume our deliverable editors are smart enough to be
aware of that option. However, in this case having some kind of generally
applicable common CRS and recommending its use could also be viewed as a
solution to the problem. And perhaps there are more options...

Regards,
Frans



On 29 July 2016 at 11:59, Jon Blower <j.d.blower@reading.ac.uk> wrote:

> Hi Frans,
>
>
>
> That seems reasonable to me. Another alternative might be to make it more
> specific:
>
>
>
> “Data providers should provide their data in multiple coordinate reference
> systems, to assist consumers in using their data without further
> transformation”
>
>
>
> Best wishes,
> Jon
>
>
>
> *From: *Frans Knibbe <frans.knibbe@geodan.nl>
> *Date: *Thursday, 28 July 2016 16:59
> *To: *Chris Little <chris.little@metoffice.gov.uk>, Jon Blower <
> sgs02jdb@reading.ac.uk>, SDW WG Public List <public-sdw-wg@w3.org>
>
> *Subject: *Re: UCR ISSUE-70: add a requirement for avoiding coordinate
> transformations?
>
>
>
> Thank you Jon and Chris, for confirming the sensibility of the candidate
> requirement.
>
>
>
> Let's take it a step further and think about how the requirement could
> take form. Here is a proposal:
>
>
>
> *Requirement:* "Data consumers should be helped in avoiding coordinate
> transformations when spatial data from multiple sources are combined"
>
> *Related delirables:* Best Practices, Coverage in Linked Data
>
>
>
> Could this work?
>
>
>
> Regards,
>
> Frans
>
>
>
>
>
>
>
> On 26 July 2016 at 18:10, Little, Chris <chris.little@metoffice.gov.uk>
> wrote:
>
> Hi Frans,
>
>
>
> Just to expand on your bullet point:
>
>    - more?
>
> Surely, one class of requirements is to perform calculations on data to
> make realistic valid comparisons. E.g. areas, distances, bearings, stats.
> Not just visualisations on a map.
>
>
>
> HTH, Chris
>
>
>
> *From:* Jon Blower [mailto:j.d.blower@reading.ac.uk]
> *Sent:* Monday, July 25, 2016 4:39 PM
> *To:* Frans Knibbe; SDW WG Public List
> *Subject:* Re: UCR ISSUE-70: add a requirement for avoiding coordinate
> transformations?
>
>
>
> Hi Frans,
>
>
>
> Just to add a data point to this. In the Climate and Forecast conventions
> for NetCDF, it’s considered good practice to provide lat-lon coordinates
> even if the data are on a projected grid. (In other words, you should
> provide the projected coordinates, the projection parameters **and** the
> transformed lat-lon coordinates.)
>
>
>
> The reason for this is that most client tools for NetCDF will understand
> lat-lon but won’t understand many map projections (although that situation
> is changing). There was some debate about this recommendation, because the
> information is redundant, but was thought to be sufficiently useful to
> allow the “no redundancy” rule to be bent.
>
>
>
> It’s also worth pointing out that CF-NetCDF has a history in global
> simulation data, in which precise georeferencing is not a top priority
> (hence the “lat-lon” I’m talking about is actually a spherical lat-lon, not
> even WGS84). But recently there has been a shift towards using CF-NetCDF
> for “properly georeferenced” data, which has caused some lively debate!
>
>
>
> So, in conclusion, I would say that your recommendation is sensible and
> has precedent. It’s probably worth highlighting the implications of the
> recommendation (i.e. the redundancy and the need to check consistency of
> the different expressions of the data).
>
>
>
> In the coverage world, if we want to provide information with more than
> one CRS, that will probably mean we need to model them as different
> coverages, but link them somehow (maybe with an equivalent of “seeAlso”).
>
>
>
> Cheers,
>
> Jon
>
>
>
> *From: *Frans Knibbe <frans.knibbe@geodan.nl>
> *Date: *Monday, 25 July 2016 16:19
> *To: *SDW WG Public List <public-sdw-wg@w3.org>
> *Subject: *UCR ISSUE-70: add a requirement for avoiding coordinate
> transformations?
> *Resent-From: *<public-sdw-wg@w3.org>
> *Resent-Date: *Monday, 25 July 2016 16:20
>
>
>
> Hello all,
>
>
>
> This message is to make a thread dedicated to ISSUE-70
> <https://www.w3.org/2015/spatial/track/issues/70>
>
>
>
> The need to perform coordinate transformations occurs when spatial data
> (geometries and coverages) from different sources need to be combined and
> the data use different coordinate reference systems.
>
>
>
> There can be several reasons for wanting to combine spatial data from
> different sources:
>
>    - visualisation in a desktop app or web app
>    - storage in a data store that is configured for a single CRS
>    - federated SPARQL queries
>    - more?
>
> Coordinate transformations take time and could introduce errors in the
> output, so it is preferable to avoid them. A requirement could call for
> recommendations for publishing spatial data on the web in such a way that
> there is less chance of data consumers having to perform coordinate
> transformations.
>
>
>
> Questions I would like to put to you:
>
>    - Is this a sensible requirement?
>    - To which deliverables should the requirement be related? Best
>    Practices and Coverages too?
>    - Does the requirement follow from other use cases besides Combining
>    Spatial RDF Data For Integrated Querying In A Triplestore
>    <http://w3c.github.io/sdw/UseCases/SDWUseCasesAndRequirements.html#CombiningSpatialRDFDataForIntegratedQueryingInATriplestore>
>    ?
>
> Regards,
>
> Frans
>
>
>
>
>