[Qgis-developer] Re: WFS feature IDs: when required, when not?

[aperi2007]

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
 >
 >