[Fwd: Re: [webmap-discuss] zoomlevels in OWSContext?]

[Kralidis,Tom [Burlington]]

(Thanks Daniel for forwarding this to me, I'm now a part of this list
again :))


> 
> Steven M. Ottens wrote:
> > 
> > Currently we store out layers in a WMC document, but we're 
> switching 
> > to OWSContext to allow for more types of layers then just 
> WMS layers. 
> > Since the zoom levels are depending on the server, it makes 
> sense to 
> > me to store these levels in OWSContext. Are there any OWSContext 
> > experts around who can tell me if that's already in the standard,
> 
> No, that's not part of the OWSContext schema. I participated 
> in the OWS Context IE and don't remember the question of 
> storing multiple zoom levels even being raised at all. Note 
> that WMS doesn't support the concept of fixed zoom levels 
> either, so before multiple zoom levels can be added to OWS 
> Context some work will be required upstream in WMS.
> 

Correct.  Since OWSContext is based on OGC specifications, this doesn't
apply.

> > if not, what would be a proper place and name
> > for such a thing?
> > 
> 
> If I remember correctly an extension mechanism was included 
> in the schema that could possibly be used for that. I think 
> Tom Kralidis would be the best one to answer on this. I CC'd 
> him in case he is not on this list.
> 

There is an extension element in the OWSContext schemas (schema chunk
below) which allows this:

	<xs:complexType name="ExtensionType">
		<xs:annotation>
			<xs:documentation>This allows additional
elements to be added to support non WMS Layer
services.</xs:documentation>
		</xs:annotation>
		<xs:sequence>
			<xs:any namespace="##any"
processContents="lax"/>
		</xs:sequence>
	</xs:complexType>

Yes, fairy dust :)

The basic approach is to define your own namespace in the root element
of the OWSContext instance doc (i.e. xmlns:foo="http://foo/foo"), and
then use that prefix within the document when applying your own
constructs, i.e.:

<foo:zoomLevels>1,2,4,8,16,32,64</foo:zoomLevels>

Having said this, if you are going to be adding extensions, I would
suggest that these be agreed upon in some way, so at the least the
extensions are defacto; so it's great that it's being discussed here.

..Tom


> Daniel
> -- 
> Daniel Morissette
> http://www.mapgears.com/
> 
>