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
>
>
>