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

[Andrea Peri]

Hi Bill,

I must correct me.

more preferable (better) then using the UUID should be use the MD%.

You could calculate the MD5 of the single record (or of the single
geometry).
And when you retry a new record with same MD5 you can understand that it
is the same record.

Regards.


2012/1/9 aperi2007 <aperi2007 at gmail.com>

> 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
> >
> >
>
>


-- 
-----------------
Andrea Peri
. . . . . . . . .
qwerty àèìòù
-----------------
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://lists.osgeo.org/pipermail/qgis-developer/attachments/20120110/99682912/attachment.html