SRS handling questions

[Silke Reimer]

On Mon, Mar 22, 2004 at 10:24:57AM +0100, Martin Schulze wrote:
> Moin!
> 
> Jan-Oliver Wagner wrote:
> > > I wonder how I should interpret the WMS specification with regards to
> > > SRS handling.
> > > 
> > > The specification [OGC 01-068r3, §7.1.4.5.5, page 26] says about
> > > inheritance of SRS:
> > > 
> > >  - Every layer shall have at least one SRS element that is either
> > >    stated explicitly or inherited from a parent layer.
> > > 
> > >  - Layers may optionally add to the global SRS list, or to the list
> > >    inherited from a parent layer.
> > > 
> > > Since the specs don't lose a word how these two cases are
> > > distinguished, I'd consider them clashing.
> > 
> > I do understand the first rule and the syntax should be clear.
> > To understand the second rule I would like to see an example to
> > understand how this rule is to be expressed in the syntax.
> 
> *smile*  If I had an example and a different syntax, I wouldn't have
> to ask.

Perhaps you could have a look on the deegree-exapmles [1] how the
lat-lon people interpretate the spec. They are rather involved in
the development of the OGC-specifications.

> 
> > > Does anybody feel I should not implement the first rule and skip the
> > > latter?
> > 
> > Are you talking about the 2 rules or the 2 cases of the second rule?
> 
> Since I don't know when which of these rules may apply since I don't
> know how to distinguish between <SRS>-replace and <SRS>-addtoinherit
> I'm talking about the two rules.
> 
> I guess the two cases of the second rules could be aggregated to
> 'add SRS to inherited list'.  However, it's not very clear in the
> document as well.
> 
> > > Also, since the XML response has both <SRS>foo</SRS> and
> > > <BoundingBox SRS="foo" minx=...> elements, I wonder if it wouldn't be
> > > wiser to extract information about availibl SRS from the <BoundingBox>
> > > element, except for the root layer.
> > > I'd say yes, but I'd better ask if somebody sees a problem with this.
> > 
> > Are you talking about XML responses that came from the frida demo wms?
> > If yes, please note that it is an older UMN MapServer and not
> > necessarily 100% compliant with WMS specification.
> 
> I already noticed.  According to the specs the root layer SRS is wrong.
> However, applying the programming paradigma below it doesn't matter
> to our implementation.

Please have in mind that the UMN MapServer is implementing WMS
version 1.1.0 while you are referring to WMS version 1.1.1. I don't
no whether there is a difference in the handling of SRS between
these two versions but it is at least possible.

Many greetings,

	Silke

[1] http://deegree.sourceforge.net/

-- 
Silke Reimer

Intevation GmbH                      http://intevation.de/
FreeGIS                                http://freegis.org/

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