Hi Frans,

 

I think this looks good in principle. My only doubt is that I’m not sure people will know what it is getting at. I know that you don’t want to prescribe a particular solution, and in general I think that’s a good goal. But in this case, is there any logical conclusion to this other than for data providers to provide data in multiple CRSs? What other action could someone take to implement this?

 

If there is only one logical conclusion from this recommendation then we might as well state it explicitly IMHO, even if only as an example.

 

Cheers,
Jon

 

 

 

From: Frans Knibbe <frans.knibbe@geodan.nl>
Date: Wednesday, 31 August 2016 16:52
To: SDW WG Public List <public-sdw-wg@w3.org>
Subject: Re: UCR ISSUE-70: add a requirement for avoiding coordinate transformations?
Resent-From: <public-sdw-wg@w3.org>
Resent-Date: Wednesday, 31 August 2016 16:53

 

OK, time to take this a bit further. Here is a complete proposal for a new requirement. I hope it can make it to the version of the UC&R document that will be evaluated at and before TPAC.

 

Requirement: Data consumers should be helped in avoiding coordinate transformations when spatial data from multiple sources are combined. 

When geometric data from different sources have no shared Coordinate Reference System (CRS), a data consumer will have to transform the coordinates of at least one data source to another CRS to spatially combine the data. Such a transformation takes time and could introduce errors in the output, so it is preferable to avoid it.

 

Related deliverable(s): Best Practices, Coverage in Linked Data

 

Related use cases:

 

Consuming Geographical Data In A Web Application

Harvesting Local Search Content

Enabling Publication, Discovery And Analysis Of Spatiotemporal Data In The Humanities

Using Spatial Data During Emergency Response Operations

Combining Spatial RDF Data For Integrated Querying In A Triplestore

Dutch Base Registry

Bushfire Response Coordination Centre

Marine Observations - Data Consumers

Crop Yield Estimation Using Multiple Satellites

 

Are there objections to putting it in the UC&R doc this way? If not, I will do it next week.

 

Thanks,

Frans

 

 

 

 

On 31 July 2016 at 10:53, Jon Blower <j.d.blower@reading.ac.uk> wrote:

Hi Frank,

 

Fair enough, understood. My concern was that the original requirement might be a bit too vague, and implementers may be confused about what it really means in terms of implementation. But I don’t feel strongly about it – if others prefer your wording then it’s fine with me.

 

Best wishes,
Jon

 

From: Frans Knibbe <frans.knibbe@geodan.nl>
Date: Friday, 29 July 2016 11:14
To: Jon Blower <sgs02jdb@reading.ac.uk>
Cc: Chris Little <chris.little@metoffice.gov.uk>, SDW WG Public List <public-sdw-wg@w3.org>


Subject: 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

 

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:

Regards,

Frans