[QGIS-Developer] QGIS WFS3 Server temporal intervals

[Even Rouault]

On vendredi 18 octobre 2019 12:28:12 CEST Alessandro Pasotti wrote:
> Hi,
> 
> I was thinking about how to better implement this feature for QGIS server
> (but it does not need to be restricted to the server).
> 
> The WFS3 specs covers pretty much all use cases: you can have features with
> a single date/datetime temporal property and a set of date/datetime
> properties, the latter case can (not "must"!)  be used to define one (or
> many) date/datetime intervals.
> 
> Now, the specs say that it's up to the server to decide if only a single
> property has to be considered when querying or if multiple properties have
> to be combined together to create one (or many) intervals. But since we
> code the server it means that it's up to us to decide how to handle it.
> 
> Note that the conditions need to be AND(ed) and unless properties values
> are equal this does make sense only when multiple properties are combined
> to form intervals.
> 
> So, the question is how to model this in QGIS?
> 
> Since this information may spread over multiple fields, I think it should
> go into the QgsVectorLayer class (or some separate temporal settings
> companion class/struct).

Hi Alessandro,

Are you thinking to scenarios like a layer would have an "eventStart" and 
"eventEnd" timestamps and you would want them to be considered together when 
an incoming request with a datetime=request_begin/request_end interval 
arrives, so as to only select features whose eventStart <= request_end and 
eventEnd >= requestbegin ?

Your above proposal makes sense, but involves complication. I think it might 
be wise to wait a bit before designing this, beause filtering is going to be 
the main topic of the next OAPIF Hackathon in November (
https://www.opengeospatial.org/events/191105apisprint ), so an extension with 
more complex/complete filtering (probably similar to what FES offers) is 
likely to be created. So I can imagine that it would offer the possibility to 
explicitly filter on multiple datetime properties. Yet that wouldn't solve the 
issue with the datetime filtering capability of OAPIF core, but perhaps for 
core, we could adopt a simple solution, like use the first datetime field of 
the layer by default, unless the user (QGIS server admin) selects another one. 
And if more complex behaviour is desired, then OAPIF clients would use the 
filter extension to be able to combine filters on several fields.

Even

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