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Re: Request for help: BP 9 "How to describe relative positions"

From: Jeremy Tandy <jeremy.tandy@gmail.com>
Date: Wed, 31 Aug 2016 11:42:54 +0000
Message-ID: <CADtUq_1YrBrtBEY5tTCAuMSDKM9topv55zw2vvhWtJBgTO-nxg@mail.gmail.com>
To: Joshua Lieberman <jlieberman@tumblingwalls.com>, Simon.Cox@csiro.au
Cc: eparsons@google.com, public-sdw-wg@w3.org
I take from the discussion so far:

* GML 3.3 does LR by defining a CRS
* LR is pretty specialised
* General GIS tooling does not typically support it; although specific
domains may (e.g. transport networks, hydrology, geology, navigation)

I think that @eparsons is inferring that LR is too niche to be considered a
"best practice" for spatial data on the web; if data publishers _do_ use LR
in their systems, then they should publish the information using a geometry
that is computed from their domain-specific specialised tools.

That would certainly give me less to write :-) ... but before concluding
this particular topic I'd like to see consensus from the group.

So ...

PROPOSAL: Linear Referencing is too niche to be considered a "best
practice" for spatial data on the web; if data publishers _do_ use LR in
their systems, then they should publish the information using a geometry
that is computed from their domain-specific specialised tools.

Voting please:
+0 (I lack the hands on experience to judge)


Finally, I also note that I still need help on the "spatial relations"
topic that was second in my original email. More help required please.


Jeremy

On Wed, 31 Aug 2016 at 12:18, Joshua Lieberman <jlieberman@tumblingwalls.com>
wrote:

> It's also a part of stream hydrology, which is mainly there is a version
> of it in sdwgeo.
>
> Josh
>
> Joshua Lieberman, Ph.D.
> Principal, Tumbling Walls Consultancy
> Tel/Direct: +1 617-431-6431
> jlieberman@tumblingwalls.com
>
> On Aug 31, 2016, at 06:23, <Simon.Cox@csiro.au> <Simon.Cox@csiro.au>
> wrote:
>
> Well you do see it in navigation systems. Time & distance.
>
>
>
> *From:* Ed Parsons [mailto:eparsons@google.com <eparsons@google.com>]
> *Sent:* Wednesday, 31 August 2016 7:49 PM
> *To:* Jeremy Tandy <jeremy.tandy@gmail.com>; SDW WG Public List <
> public-sdw-wg@w3.org>
> *Subject:* Re: Request for help: BP 9 "How to describe relative positions"
>
>
>
> I still question the need to include linear referencing, it's another very
> specialised way to model spatial data and one which is not widely seen on
> the web ?
>
>
>
> ed
>
>
>
>
>
> On Wed, 31 Aug 2016 at 10:26 Jeremy Tandy <jeremy.tandy@gmail.com> wrote:
>
> Hi-
>
>
>
> BP doc section § 10.5.1 "Describing location" [1] is where we intend to
> provide all the guidance that explains how you should encode location
> information in a web-friendly way.
>
>
>
> This includes BP 8 "Provide geometries on the Web in a usable way" [2] and
> BP 9 "How to describe relative positions" [3].
>
>
>
> (I think it's likely that we will also need a BP to help people choose the
> right CRS too ...)
>
>
>
> We editors envisage BP 9 covering:
>
>
>
> (1) Linear referencing
>
> (2) Use of spatial relations [4]
>
>
>
> ...
>
>
>
> (1)
>
> From a quick scan, I see that ISO 19148:2012 covers the topic of Linear
> Referencing. I don't have access to the ISO document itself, so I've not
> been able to read the standard ... but reviewing the UML model (accessible
> here [5]) it seems VERY complicated.
>
>
>
> I also note that the INSPIRE Generic Network Model has a simpler
> implementation of Linear Referencing.
>
>
>
> Questions:
>
> a) are we limited to GML implementations for Linear Referencing?
>
> b) has anyone converted the GML Application Schemas from ISO 19148 and
> INSPIRE GNM into other formats ... particularly an RDF / OWL ontology?
>
> c) are there any other mechanisms in use for Linear Referencing? e.g. can
> LR be done with GeoJSON?
>
> d) are people really using ISO 19148:2012 given it's complexity?
>
>
>
> INSPIRE's Transport Network specification v3.2 §10.3 "Linear Referencing"
> states:
>
>
>
> “In general it is expected that linear referencing will be used to model
> the relationships of objects that are associated with an network, but where
> the position of those associated objects is not known (or required) to a
> very high level of absolute accuracy ~ better than 1-3m at local level
> (e.g. traffic accidents, planned works, restrictions).
>
>
>
> Where absolute accuracy is required (e.g. the location of drain covers,
> excavations, line side signalling equipment, masts etc) such objects should
> be reused, and referenced, if they already exist e.g. as topographic
> features.”
>
>
>
> This seems like the basis of some guidance about when one might use Linear
> Referencing.
>
>
>
> What I need (please!) are some worked examples for Linear Referencing of a
> point along a linear feature and for Linear Referencing of a length along a
> linear feature. In the flooding scenario, this might be:
>
> * Location of flotsam / debris (point) blocking a drainage channel that
> needs to manually cleared
>
> * Location of a flooded section (length) of a road
>
>
>
> (2)
>
> We also want to demonstrate how spatial relations are used. There are
> obvious examples of topological relationships such as "this administrative
> unit _touches_ that administrative unit" (or contains etc.).
>
>
>
> I recall that we were going to get the set of topological relationships
> added to the IANA Link Relations registry [7]. I am not even sure which set
> of topological relations we should be recommending? GeoSPARQL has me
> somewhat confused with "Simple Features Relation", "Egenhofer Relation" and
> "RCC8 Relation". Then there's D9-EIM too ...
>
>
>
> Can someone provide me some worked examples using the preferred set of
> topological relationships?
>
>
>
> We also need to illustrate use of _directional_ (e.g. "left", "in front
> of" and "astern") and _distance_ relations (e.g. "at", "nearby" and "far
> away"). I don't know of any formalised vocabulary for expressing these
> things. If there is one, should we be seeking to add these to the IANA Link
> Relations registry too?
>
>
>
> Again, worked examples requested! If you can related them to an urban
> environment / flooding scenario all the better. (e.g. someone might assert
> "the flooding is near my house")
>
>
>
> Finally, we also need to show people how to express "fuzzy" spatial
> things. Examples we have elsewhere in the BP doc are "the American West"
> and "Renaissance Italy". These are spatial things were there is not general
> agreement about the exact geographic extent, so it is not possible to use a
> geometry to describe it. What is the best way to describe things like this?
> Should we use spatial relations e.g. "downtown" _contains_ city districts
> A, C, D, and G (because "everyone" agrees this) - but we're not saying it's
> exact geometry because it's a colloquial term used by citizens of our
> fictional Nieuwhaven.
>
>
>
> Again, I'd like to see a worked example.
>
>
>
> ...
>
>
>
> There's a lot of questions wrapped up in this email. I'm looking for help
> to resolve them ... preferably with someone in the WG taking the lead to
> coordinate a response.
>
>
>
> I'm also aware that we need to avoid an RDF bias, so it would be good to
> have examples in other formats too.
>
>
>
> Volunteers, please step forward!
>
>
>
> Thanks in advance. Jeremy
>
>
>
> [1]: http://w3c.github.io/sdw/bp/#bp-expr-geo
>
> [2]: http://w3c.github.io/sdw/bp/#describe-geometry
>
> [3]: http://w3c.github.io/sdw/bp/#relative-position
>
> [4]: http://w3c.github.io/sdw/bp/#spatial-relations
>
> [5]: https://github.com/ISO-TC211/HMMG
>
> [6]:
> http://inspire.ec.europa.eu/documents/Data_Specifications/INSPIRE_DataSpecification_TN_v3.2.pdf
>
>
> [7]: http://www.iana.org/assignments/link-relations/link-relations.xhtml
>
>
> --
>
> *Ed Parsons *FRGS
> Geospatial Technologist, Google
>
> Google Voice +44 (0)20 7881 4501
> www.edparsons.com @edparsons
>
>
Received on Wednesday, 31 August 2016 11:43:40 UTC

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