[Users] DescribeLayer and DescribeFeatureType

[Bart van den Eijnden (OSGIS)]

Hi Matt,

this is exactly the purpose of the DescribeLayer request. If there is no 
WFS associated, the DescribeLayer response will be an empty root 
element. If there is a WFS, the DescribeLayer response will give you the 
URL of the associated WFS and the name of the typename.

For ESRI I now use a hack [1], but it won't work if the admin has 
changed the urls, as you point out. There is nothing much we can do in 
that case, maybe let the application developer provide the associated 
WFS url and typename somehow.

Best regards,
Bart

[1]
// do a hack for ArcGIS Server since it does not support DescribeLayer
// 1) replace WMSServer with WFSServer in the url
// 2) the typename is the title of the WMS layer, normally with a prefix 
but requests without a prefix also succeed.

Matt Priour wrote:
> I think these requests have merit and make automatic configuration of 
> the underlying feature store easier.
> However:
> How would we know if WFS was available and its URL?
> ESRI ArcGIS Server & ArcIMS both have different URLs for WMS & WFS, 
> which depending on how the admin has configured it may or may not be 
> decipherable from the WMS url.
> Also, many servers don't have WFS turned on.
>
> Are these things that the LayerStore would guess at or would they be 
> required configuration options for this functionality to be accessible?
>
> Matt Priour
> Kestrel Computer Consulting
> www.kestrelcomputer.com
> --------------------------------------------------
> From: "Bart van den Eijnden (OSGIS)" <bartvde at osgis.nl>
> Sent: Tuesday, February 17, 2009 12:37 PM
> To: <users at geoext.org>
> Subject: [Users] DescribeLayer and DescribeFeatureType
>
>> Hi list,
>>
>> today Andreas and I had an interesting discussion about WMS
>> DescribeLayer and WFS DescribeFeatureType.
>>
>> Let me first give a bit of background for people not familiar with these
>> requests.
>>
>> WMS DescribeLayer is currently part of the SLD WMS spec, and is meant to
>> tie a WMS layer to a WFS typename or WCS coverage. Not all WMS services
>> implement this though, Mapserver and Geoserver do, but e.g. ArcGIS
>> Server currently does not. There are plans to move the DescribeLayer
>> request from SLD WMS to mainstream WMS in WMS 1.4. A simple parser for
>> WMS DescribeLayer response is in [1].
>>
>> Currently a lot of applications by-pass WMS DescribeLayer and assume WMS
>> OnlineResource = WFS OnlineResource and WMS layer name = WFS typename.
>> Although this will work in some cases, it will fail in others, but it
>> saves a trip to the server. So a question for GeoExt is: do we want to
>> follow the OGC way in this? I would be in favour of using WMS
>> DescribeLayer even if this is an extra round-trip to the server. But
>> what do others think?
>>
>> WFS DescribeFeatureType is a way to get an XML Schema back describing
>> the structure of a typename, to put it more simple it will return a list
>> of attributes from a layer. This can be used then to e.g. fill combo
>> boxes for layer attributes, for a querybuilder component for instance.
>> Btw a WFS DescribeFeatureType parser was just committed to OpenLayers
>> trunk this weekend by Andreas [2].
>>
>> The solution to integrate this into GeoExt that Andreas just came up
>> with is everytime a WMS layer is added to the LayerStore, we will
>> perform a DescribeLayer and subsequently a WFS DescribeFeatureType
>> request and store this information in the LayerStore.
>>
>> Does this approach make sense? Thoughts?
>>
>> Best regards,
>> Bart & Andreas
>>
>> [1] http://trac.openlayers.org/ticket/1201
>> [2] http://trac.openlayers.org/ticket/1202
>>
>> -- 
>> Bart van den Eijnden
>> OSGIS, Open Source GIS
>> bartvde at osgis.nl
>> http://www.osgis.nl
>>
>> _______________________________________________
>> Users mailing list
>> Users at geoext.org
>> http://www.geoext.org/cgi-bin/mailman/listinfo/users 
>
>
>


-- 
Bart van den Eijnden
OSGIS, Open Source GIS
bartvde at osgis.nl
http://www.osgis.nl