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Re: Area of spatial objects

From: Frans Knibbe <frans.knibbe@geodan.nl>
Date: Thu, 8 Nov 2018 10:30:37 +0100
Message-ID: <CAFVDz41-xu_XBm9UEu4WMn43RtXxA4CxoMy8TDtvz+S5whbkng@mail.gmail.com>
To: Nicholas.Car@csiro.au
Cc: public-sdwig@w3.org
Hello Nick,

I don't think it would be problem if the coordinates of the geometry are
unknown. In that case the property with the coordinates (e.g.
geosparql:asWKT) would be absent. Features with a point geometry and an
area could be published as a feature having two geometries: one with
coordinates and one with an area. The other examples you mentioned could be
dealt with the same way. For instance, have a feature with three geometries
- one with only an area, one with an area and a CRS and one with just
coordinates. There would then be a future option to specify that some of
those geometry representations are actually the same thing.

I am not saying this way of publishing your data is better than another,
but I do think it is possible. And perhaps this method can be used together
with another method, leaving it up to the data consumer how she/he/it wants
to query the data.

Regards,
Frans



Op wo 7 nov. 2018 om 13:55 schreef Car, Nicholas (L&W, Dutton Park)
<Nicholas.Car@csiro.au>:

> Hi Frans,
>
>
>
> What if I wanted to publish Features’ areas without also publishing
> geometries? What about features with a point geometry and an area, no
> polygon. Also, I have data where an area is given and also a polygon but I
> don’t know for sure if the area was calculated from the polygon. In fact I
> have data with an area and an Albers area and a geometry and don’t really
> know what happened to make which.
>
>
>
> So, I want to be able to represent area as a spatial property of a
> feature, independently of any geometry. For this I will try using
> Observations and Measurements-style mechanics for this.
>
>
>
> I think I might use subclassing of a sosa:ObservableProperty (
> https://www.w3.org/TR/vocab-ssn/#SOSAObservableProperty) to express
> spatial properties such as area and then relate then to a geo:Feature which
> would also, by SOSA logic, be a sosa:FeatureOfInterest. I may invent
> modelling to relate that spatial property to a geometry, but this wouldn’t
> be required, just nice to have if known.
>
>
>
> Cheers,
>
>
>
> Nick
>
>
>
> *From:* Frans Knibbe <frans.knibbe@geodan.nl>
> *Sent:* Monday, 5 November 2018 6:22 PM
> *To:* public-sdwig@w3.org
> *Subject:* Re: Area of spatial objects
>
>
>
> Hi Nick,
>
>
>
> I wonder: Doesn't the fact that multiple areas for a single spatial thing
> are published mean that the areas are calculated from different geometric
> representations of that spatial thing? That would logically make the area a
> property of a geometry. Besides, the geometry instance could be used to
> link to the CRS (e.g. Albers), ideally by URI.
>
>
>
> CRS data linked to a geometry could also give access to the basic unit of
> the CRS (e.g. meter) and through that provide information on the units of
> properties derived from the geometry (like the area), but that would demand
> a fair amount of reasoning on the part of the data consumer.
>
>
>
> Regards,
>
> Frans
>
>
>
Received on Thursday, 8 November 2018 09:31:13 UTC

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