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

From: Frans Knibbe <frans.knibbe@geodan.nl>
Date: Wed, 31 Aug 2016 14:54:53 +0200
Message-ID: <CAFVDz40A+q=8HGgVoQH9=Nn8WKqfwrke-H1UT64j3EQ=f9Qgdg@mail.gmail.com>
To: Jeremy Tandy <jeremy.tandy@gmail.com>
Cc: Joshua Lieberman <jlieberman@tumblingwalls.com>, Simon Cox <Simon.Cox@csiro.au>, Ed Parsons <eparsons@google.com>, SDW WG Public List <public-sdw-wg@w3.org>
I wonder if Linear Referencing can be seen as a version of the more general
case of expression location in terms of a well defined CRS. For 3D data, we
use two numbers (latitude and longitude) to place a location on a funnily
shaped 3D geometry (a model of the surface of the Earth). In LR, we use a
single number to place locations on a funnily shaped 2D geometry (e.g. a
model of a road or a river). We can use topological relationships to make
assertions about those locations and to filter data: Is there an essential
difference between asking whether two polygons on Earth touch each other or
if two sections of road touch each other?

Now if our spatial ontology allows the definition of any kind of CRS in two
or three dimensions, and clearly associating that CRS with geometry, and
the use of topological relationships, then it could very well be that there
is no need to make special arrangements for LR.

I do think that organisations that naturally work with LR data, e.g.
organisations in the transportation sector, should be able to publish their
data on the web and let them be used by whomever it pleases.

Regards,
Frans


On 31 August 2016 at 13:42, Jeremy Tandy <jeremy.tandy@gmail.com> wrote:

> 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 12:55:32 UTC

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