Question about ogrlayerinfo and wfslayerinfo (layer inheritance needed)

[Tamas Szekeres]

Daniel,

I am posting this thread to the mapserver-dev, and also waiting for any
comments from the other folks.


I can see the problem by now. WFS layer extends the functionality of the OGR
layer and each of them should maintain separate layer information.

In fact the problem could be solved if we could establish a similar concept
like inheritance in the OO design. WFS layer should be inherited from the
OGR layer by adding the WFS specific layer information.

I am thinking of a solution targeting this problem that could allow a layer
provider to extend the functionality of another provider. The recently added
vtable architecture makes a good foundation to achieve this. It could also
bring in great additions of the functionality in other areas.
For example:

- we could implement a provider independent feature caching system to
increase the rendering speed of the applications that can maintain the layer
object state between the drawings. By reducing the access to the providers
could decrease the thread interaction of the application as well.
- we could implement various provider independent data filters.
- by creating a "layer extender" we could increase the rendering area at the
provider side to allow drawing of the annotations falling onto the map
borders (see the related kamap label splitting issue)
- and many more...

By maintaining the vtables hierarchically we could easily invoke the methods
of the "base" layer. The main problems for now is the addition of the
specific parameters and the required mapfile representation. It would be
desirable if the provider specific information could be handled uniquely to
the various existing implementations (for example inside the vtable
structure)


Best Regards,

Tamas Szekeres


     
-----Original Message-----
From: Daniel Morissette [mailto:dmorissette at mapgears.com] 
Sent: Wednesday, May 17, 2006 9:14 PM
To: Tamas Szekeres
Subject: Re: Question about ogrlayerinfo and wfslayerinfo

Tamas Szekeres wrote:
> Daniel,
> 
> Do we have a specific reason to use provider specific ogrlayerinfo and
> wfslayerinfo in the
> layer object instead of using the common layerinfo parameter. I have
> also asked Frank, but
> he pointed me to you with this question.
> 
> 

Hi Tamas,

There is no good reason to keep ogrlayerinfo around, we actually 
discussed taking it out a while ago but that fell in a crack, see:
http://mapserver.gis.umn.edu/bugs/show_bug.cgi?id=331

Note that we need to be careful with wfslayerinfo since WFS layers use 
an OGR connection to read the GML data.

I'll have another look at that one now.

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

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