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