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

@frans

> 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

This is certainly how I interpret GML doing it. I mentioned today that I
anticipate a new BP about Coordinate Reference Systems - I'll consider how
to add this in there.

@josh

> There is another way of looking at linear reference measurements, which
is that they are observations made directly on a linear feature.

I'm somewhat uncomfortable with _always_ having to take on observation
semantics for LR; I might just want to say the 30 mph speed limit starts
55m from intersection "x" along road "y". e.g. it's an assertion, not an
observation.

> it is a compact way of recording where some additional measurement has
been made, such as a water level ...

True

> ... that eventually gets converted to a linear reference point based on
an LRS, and from there to an (x,y) point.

Indeed. BUT are we saying "if you want to share your data on the web in an
easy to use format please use (x,y) point rather than (or in addition to)
LR because very few tools can understand LR".

Jeremy

On Wed, 31 Aug 2016 at 15:53 Jeremy Tandy <jeremy.tandy@gmail.com> wrote:

> @phila - the editor of POWDER-DR must be weeping ...
>
> On Wed, 31 Aug 2016 at 15:35 Phil Archer <phila@w3.org> wrote:
>
>> Just on the IANA registry point, all that's needed is a list of those
>> relationships. This might be in their own section or an appendix,
>> something so that each term can be referenced and provide a definition.
>> That may be copied from elsewhere (if credited of course). HTML5 defines
>> a bunch of them [1] but you can also do it as seen at the very bottom of
>> https://www.w3.org/TR/powder-dr/#appD - a spec so cruelly overlooked by
>> so many people except for that one definition.
>>
>> Then we write to IANA (actually Mark Nottingham) and ask that they're
>> added. As long as the doc is stable, he'll be happy. So I'd say that
>> once we go down this road, we need to be sure that we only want to add
>> new relationships as the doc evolves, not remove them. Thus they can use
>> the short URL (https://www.w3.org/TR/sdw-bp/#foo).
>>
>> HTH
>>
>> Phil.
>>
>> [1] https://www.w3.org/TR/html5/links.html#linkTypes
>>
>> On 31/08/2016 10:25, Jeremy Tandy 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
>> >
>>
>> --
>>
>>
>> Phil Archer
>> W3C Data Activity Lead
>> http://www.w3.org/2013/data/
>>
>> http://philarcher.org
>> +44 (0)7887 767755
>> @philarcher1
>>
>