Discovering layer type

[Etienne Labuschagne]

Hi Bart,

Ok, so there is a light at the end of the tunnel :)  Luckily, the client
I am designing will need WFS anyway, so I will have access to a WFS
server.

Does WFS DescribeFeatureType "guarantee" that the geometry type will be
returned, or is that once again optional and dependant on the WFS server
implementation?

Groetnis
Etienne

On Tue, 2005-10-25 at 12:16 +0200, Bart van den Eijnden wrote:
> Hi Etienne,
> 
> there is no specific reason I guess, but WMS is intended for visualisation, so it mostly ends there. That's why they invented a DescribeLayer request in the SLD WMS spec to get more detailed info of the data underneath the WMS (linkage to another OGC interface).
> 
> Your basic route should be:
> 
> -WMS DescribeLayer
> -WFS DescribeFeatureType
> 
> But this means the data should be available on both a WMS and a WFS.
> 
> Best regards,
> Bart
> 
> Bart van den Eijnden
> Syncera IT Solutions
> Postbus 270
> 2600 AG  DELFT
> 
> tel.nr.: 015-7512436
> email: BEN at Syncera-ITSolutions.nl
> 
> >>> Etienne Labuschagne <elabuschagne at GMAIL.COM> 25-10-2005 12:10 >>>
> Bart,
> 
> Thanks for the prompt reply, even though this is exactly what I didn't
> want to hear ;)
> 
> Am I missing something or is this just plain silly?  I come from an ESRI
> ArcIMS environment and I expected that getting the layer's geometry type
> should be one of the basic easy things to do.
> 
> I understand that some implementations does give this info, but surely
> this should be part of the basic OGC standard?  Maybe there is a good
> reason that this is not included and would love to hear it!
> 
> Anyway, thanks for the trouble.
> Etienne
> 
> On Tue, 2005-10-25 at 11:22 +0200, Bart van den Eijnden wrote:
> > Hi,
> > 
> > it depends with the implementation, but it is a difficult theory anyway already :-)
> > 
> > WMS can be coupled to a WFS (on the same data) using a DescribeLayer WMS request. This is part of the SLD WMS spec.
> > The response of a WMS DescribeLayer is:
> > 
> > a) the onlineresource of a WFS (or WCS for raster layers)
> > b) the name of the typename
> > 
> > With this info, you could request more info from the associated WFS, mostly WFS DescribeFeatureType will be useful for that. It will give you all the attributes and most likely (depending on the implementation) also an idea of the geometry type. Note that something was changed in Mapserver 4.6 which makes it ouput a gml abstract featuretype by default, which won't give you an idea of the geometry type.
> > 
> > Note also that WMS GetFeatureInfo could give you a rough guess of the geometry type, and the list of attributes in the GML returned. But it is specific to a point clicked in the map. Mapserver also gives back a geometry on the WMS GetFeatureInfo (which you could check for point, polygon or line in the string), but most WMS's don't give back the geometry on WMS GetFeatureInfo.
> > 
> > Anyway, you can see it's not straightforward.
> > 
> > Best regards,
> > Bart
> > 
> > Bart van den Eijnden
> > Syncera IT Solutions
> > Postbus 270
> > 2600 AG  DELFT
> > 
> > tel.nr.: 015-7512436
> > email: BEN at Syncera-ITSolutions.nl 
> > 
> > >>> Etienne Labuschagne <elabuschagne at GMAIL.COM> 25-10-2005 10:13 >>>
> > Hi all,
> > 
> > I'm a newbie to MapServer and OGC in general.
> > 
> > I can discover the layer names with a WMS getCapabilities call.  The other
> > thing I need to discover is what type each layer is (Point, line, polygon)
> > and also what attribute fields there are available on each layer.
> > 
> > Is there an OGC way to get this information from any OGC compliant map
> > server?  The reason I say "OGC" is that my client program that I am writing
> > need to adhere to that standard and not nescessarily only MapServer.
> > 
> > Although I use MapServer predominantly, I may have to use other map servers
> > later and do not want to be bound by MapServer proprietary code.
> > 
> > Thanks
> > Etienne
> > 
>