FW: Coverage subgroup - document for discussion

From: Kerry Taylor
Sent: Thursday, 19 May 2016 12:50 AM
To: 'Little, Chris' <chris.little@metoffice.gov.uk>
Subject: RE: Coverage subgroup - document for discussion

Chris,
I think what you want was in the datacube model in an early draft --- a “subslice” but did not make it through to the final version.  I used it in a climate data project. However, relying on the beautiful W3C processes – you might be able to understand the why from here https://www.w3.org/2011/gld/track/issues/34. I think we need something like this for the coverage deliverable if we do go ahead with a qb model.

As I get it, the main reason for dropping it is that it is not defined in SDMX (the stats agency standard) and also (Dave Reynolds)
> The use case you mention is perfectly reasonable, but it can be addressed by a property in an extension namespace, and can be easily re-added in a future version.

So maybe that is something we should do? It makes sense to me.  Surely it can be used to define appropriately granular “extracts” even outside the original data publication. Does this do what you want? I’m not well enough aware of the relevant WCS2.0 capability.

--Kerry
From: Little, Chris [mailto:chris.little@metoffice.gov.uk]
Sent: Wednesday, 18 May 2016 11:49 PM
To: Rob Atkinson <rob@metalinkage.com.au<mailto:rob@metalinkage.com.au>>; Bill Roberts <bill@swirrl.com<mailto:bill@swirrl.com>>; Jon Blower <j.d.blower@reading.ac.uk<mailto:j.d.blower@reading.ac.uk>>
Cc: public-sdw-wg@w3.org<mailto:public-sdw-wg@w3.org>; Roger Brackin <roger.brackin@envitia.com<mailto:roger.brackin@envitia.com>>
Subject: RE: Coverage subgroup - document for discussion

Hi Rob,

This is a bit of a diversion and probably does not help finish this SDW WG  topic, but is a direction I want to go:

The QB model of dimensions and slices stops short of what is in OGC WCS2.0 – where any slice can be trimmed (a form of sub-setting) to a bounding box aligned with the dimension axes. So far, so what.

I am interested in the wholesale tiling of a data cube, as a one-off process, to enable a wider range of sub-setting and supporting scalability and reuse (if each tile given a persistent enough id). This is not really anything new, and some would argue is only an implementation detail. I am still interested. The tiles may not contain just single values from a simple scalar data cube, but may contain point clouds, vector geometry or other stuff – whatever the contents of the original data cube were.

There are a variety of applicable uses cases, such as archive granule retrieval, data dissemination to a very large number of low powered devices, boundary conditions for a large number of local weather prediction models.

Whether the tiles are treated as a single multi-dimensional coverage or a collection of a large number of lower dimensional coverages, I do not mind, but it seems to me that this a simple and straightforward addition to the QB model.

Is it?

Chris
From: Rob Atkinson [mailto:rob@metalinkage.com.au]
Sent: Wednesday, May 18, 2016 1:50 PM
To: Bill Roberts; Jon Blower
Cc: public-sdw-wg@w3.org<mailto:public-sdw-wg@w3.org>
Subject: Re: Coverage subgroup - document for discussion

Hi,
I've put some detail on the page https://www.w3.org/2015/spatial/wiki/Data_cube_for_coverage to identity different possible directions for this aspect.

FYI My project with OGC is concerned with UC1 and UC2, which seems complementary to the other activites supporting this thread.

Cheers
Rob Atkinson


On Wed, 18 May 2016 at 20:45 Bill Roberts <bill@swirrl.com<mailto:bill@swirrl.com>> wrote:
Thanks Jon, that's a useful perspective.  Certainly we talk about making discovery and retrieval of the data easier, working nicely with web-based technology etc - so we need to be clear about 'easier for whom'.  Inevitably different people will want different things so we will have to be explicit about our priorities.

The existing use cases cover quite a few of the scenarios you have sketched out, but they don't yet link those to these kind of user personas.  That might be worth doing - it probably wouldn't take long.





On 18 May 2016 at 11:35, Jon Blower <j.d.blower@reading.ac.uk<mailto:j.d.blower@reading.ac.uk>> wrote:
Hi Bill, all,

Just some initial thoughts in advance of our telecon. There is lots of good stuff in here, and it’s all relevant to the general area of “Coverages”. Some of these issues are of course very complex and I don’t think we’ll solve them all – and in fact this group might not be the best place to do so.

I wonder if it would help to structure the document and our thinking around the different audiences we might aim at. For example:

 * A “web developer” might need some explanation of what a coverage is (“dummies’ guide”). He/she would probably like a simple API to access them, and some simple formats with which he/she is familiar. The applications are likely to be reasonable simple and visualisation-oriented, rather than “deep” analysis.

 * A “spatial data publisher” might already be familiar with the terminology, but might want to know how to make his/her data more discoverable by mass-market search engines, or how best to make use of Linked Data and semantic stuff. He/she is probably going to be keen to describe coverage data very precisely (e.g. using the “right” CRS and full-res geometries), but is also interested in the cost/benefit tradeoff.

 * A “data analyst/scientist” might be interested in quality and uncertainty, and how to bring coverage data into his/her tools (e.g. GIS, Python scripts). This kind of person may just want to download the data files in an unmodified form, although data-extraction services can be useful in some circumstances (and hosted processing is increasingly popular).

 * An “environmental consultant” may have very limited time to perform some kind of analysis to form part of a report. If a dataset is hard to find, access or understand it will probably simply be omitted from the analysis. Often interested in a very specific geographic area. Needs to quickly establish that a dataset is trustworthy,

 * An “IT provider” might be interested in scalable and maintainable web services for high-volume data that can be made part of his/her organisation’s operational procedures. He/she probably has a low tolerance for high-complexity or “bleeding edge” technology.

This is just off the top of my head, and there are certainly more, and there will also be lots of overlap. And I’m sure there’s lots to argue about there. But this helps me, at least, put some structure on the Big List. For each of these kinds of user, what would be the most useful thing that we could do to help them (maybe a new technology, or a recommendation to use something existing, or an admission that the problem remains unsolved), in the context of this group?

(Am I just reinventing the Use Cases here, or is this still useful for the Coverage requirements?)

Cheers,
Jon



From: Bill Roberts <bill@swirrl.com<mailto:bill@swirrl.com>>
Date: Tuesday, 17 May 2016 23:44
To: "public-sdw-wg@w3.org<mailto:public-sdw-wg@w3.org>" <public-sdw-wg@w3.org<mailto:public-sdw-wg@w3.org>>
Subject: Coverage subgroup - document for discussion
Resent-From: <public-sdw-wg@w3.org<mailto:public-sdw-wg@w3.org>>
Resent-Date: Tuesday, 17 May 2016 23:44

Hi all

I've made some initial notes on requirements in this wiki page:

https://www.w3.org/2015/spatial/wiki/Coverage_draft_requirements


I'd like to go through this on the call tomorrow (we probably won't get all the way through it as there is quite a lot there).  If you are joining the call it would be great if you could look at it in advance.

Comments also welcome via this mailing list.

Cheers

Bill