Re: Clarification required: BP5 "describing properties that change over time" [SEC=UNCLASSIFIED]

Thanks Bruce. Good points ... I was thinking in terms of the simplest
situation and there are, of course, these other cases you've reminded me
of.

The question remains for wider discussion: should we add timeseries
coverage as a "possible implementation" for BP 5?

Thanks.
On Wed, 24 Aug 2016 at 01:45, Bruce Bannerman <B.Bannerman@bom.gov.au>
wrote:

> Hi Jeremy,
>
>
> wrt: '(time-series are one-dimensional coverages)'
>
>
> I suspect that I'm missing the intent here, IMO this is but one type
> of time-series.
>
>
>
> I believe that we can have n-dimensional time-series of traditional
> coverages as well, e.g.:
>
>    - ​a time-series of climate grids representing the distribution of
>    maximum temperature across a continent;
>    -
>    - ​​a time-series of n-dimensional climate models across a continent,
>    or the globe;
>    - a time-series of n-dimensional satellite observations (i.e.
>    multi-spectral images along a swathe over multiple passes over a given
>    region); and
>    - a time-series of derived data across a region, e.g. a time-series of
>    NDVI analyses derived from multi-spectral satellite imagery.
>
>
> And of course in many instances we need to relate the observed property of
> the areal coverage time-series back to the type of one-dimensional
> time-series that you have referred to.
>
> Bruce
>
>
> ------------------------------
> *From:* Jeremy Tandy <jeremy.tandy@gmail.com>
> *Sent:* Wednesday, 24 August 2016 12:50 AM
> *To:* SDW WG Public List
> *Subject:* Clarification required: BP5 "describing properties that change
> over time"
>
> All-
>
> BP5 [1] addresses the situation where the properties of a spatial thing
> are updated due to some new measurement or assertion. For example, the
> boundary geometry of flooded area will change as the flood levels rise and
> fall, or the details of a land parcel may be updated due to a new survey.
>
> In this case, the resource is a spatial thing whose properties are
> captured as a series of discrete snapshots through time. Those snapshots
> may be created on a fixed schedule (e.g. as a result of an annual survey)
> or ad-hoc (e.g. some one notices that things have changed).
>
> There is a second case where properties change over time: when the
> property is a time dependent variable that is being measured or estimated
> according to some sampling regime. In this case, the resource seems to be a
> "time-series" of property values. For example, the water level of a canal,
> the wind speed measured at routine intervals by an anemometer, or the GPS
> position of a fishing vessel.
>
> (time-series are one-dimensional coverages)
>
> So in the example case of the canal and its water-level, the canal (a
> spatial object) has a property "water-level" that refers to a water-level
> time-series coverage. As coverages are themselves features (so says OGC et
> al) then we can also say that our water-level time-series coverage is also
> a spatial thing (albeit a conceptual spatial thing that you can't trip over
> in the real world).
>
> Is this second case a valid "possible approach to implementation" that
> should be added to BP 5? If so, please can someone in the working group
> suggest some criteria as when to use the "property snapshot" pattern (case
> 1) or the "time-series coverage" pattern (case 2).
>
> (for me it's subjective, but seems to be related to the intent to
> establish a coherent sampling regime for a property value as opposed to an
> ad-hoc update)
>
> Jeremy
>
> BTW, I've deliberately skipped over the "value assignment" concern (e.g.
> how values are assigned to properties) as described in ISO 19109 §7.4.10
> ValueAssignment - for example, how OM_Observation can be used to relate the
> "observed value" to a "feature of interest" with all the metadata about the
> observation or measurement process. I don't think this is relevant for this
> BP.
>
>
> [1]: http://w3c.github.io/sdw/bp/#desc-changing-properties
>