Hi Bill,
I guess perhaps you could calculate the
PointOnSurface (don't the centroids) for every single feature received.
The PointOnSurface (available on spatialite for example)
Will Allow you to understand if a new Features received is the same or
is another.
Another technics should be calculate the UUID of every feautre received.
I guess this technics should allow to understand almost pretty well if a
feature is repeated or not.
Regards,
Andrea.
Il 09/01/2012 15:29, Bill Clay ha scritto:
> All,
>
> Thanks to Andrea Peri, I have just discovered that WFS 1.0.0 apparently
> does NOT require a WFS server to report a unique feature ID with every
> feature it transmits (a typical newbie misconception?).
>
> The OGC specs are so nested and versioned, it's hard to be certain I've
> understood them correctly. Could someone be kind enough to enlighten me
> on the following?
>
> 1. Can you confirm or correct the following understandings:
>
> a. Every WFS server (versions 1.0.0 and 1.1.0) must have a permanent
> unique identifier for every feature.
>
> b. WFS GetFeature responses version 1.0.0 may or may NOT provide a
> unique "fid" attribute with each <feature> element, provided the layer
> is not editable (WFS-T).
>
> c. WFS GetFeature responses version 1.1.0 MUST provide a unique "fid"
> attribute with each <feature> element.
>
> 2. Are you aware of any common implementation of WFS 1.0.0 that does NOT
> always report a "fid" attribute with every <feature> element? (I
> understand TinyOFS can be configured not to do so.)
>
> 3. Do you believe that WFS services that do not always provide a "fid"
> with every feature are unusual enough that the QGIS WFS client can
> simply disable all feature caching for such servers?
>
> The proposal at item 3 would require GetFeatures to be requested for the
> entire canvas extent every time any previously un-fetched area is
> exposed on the canvas. Practically speaking, this means potentially long
> delays on every pan and zoom-out on maps containing WFS layers with many
> features that are hosted by such servers.
>
> Doubtless this is old news to everyone but me. Sorry for the static.
>
> Bill Clay
>
>
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