Re: [ZMapServer-Developers] bbox attribute container

[Sean G. <sgi...@fr...>]

On Feb 23, 2005, at 9:48 AM, Moisan Yves wrote:

> Hi Sean,
>
> I've been playing around lately with ZCO and I would like to share some
> thoughts.  The context is that I am trying to find a way to override 
> the
> default bbox values sent to the getMap script (demo/index_html),
> specifically bbox values to implement zooming.
>
> First, the layer object.  Looking at the attributes sequentially :
>
> - datastore : OK since the layer is a sort of ZCO wrapper or 
> abstraction
> of the DataStore
> - geometryType, srs : those really are attributes of the DataStore 
> (??),
> except maybe for srs which can be thought of as the datastore srs or 
> the
> "desired" srs for map viewing (which points to a view object IMO, at
> least comceptually)
> - bbox (e.g. the layers/line object in the ZCO demo) : IMO this is an
> attribute for some other object; in fact, I've been creating layers for
> a personal demo and I never put any bbox (if it had been a necessary
> attribute, I would have been brought naturally to add a bbox attribute
> to my layers).
>
> So in short I view the Layer object as a Python/Zope wrapper object to 
> a
> DataStore and a container for style variants.
>
> Now, the bbox attribute.  Considering the width/height invariant,
> zooming/panning and providing default views really are just bbox
> arithmetic stuff.  I was wondering where the bbox attribute would find
> its best home (Zope object).
>
> Use Case : I have users in city X and other is city Y.  Those
> geographical attributes are mimicked in a zope hierarchy, e.g.
> country/province/city.  Upon entering the cityX folder, I would like my
> map portlet to display a predetermined zone of my layers, which would
> call for some object holding the bbox (or a folder property ??).  Since
> I'll be reusing the same layers, I wouldn't want to define a Layer to
> hold my bbox attribute corresponding to predefined views.
>
> I don't know where bbox should be held.  I think isolating it in some
> sort of view object to allow one to set specific views in the current
> context is interesting.  I wonder if a bbox container in the current
> context could be used to write user-specified zooms?  E.g. a box asking
> the user for a zoom level (potentially float) the contetn of which 
> would
> be stored in the current mapper context and somehow hooked to before 
> the
> call to getMap.  We could probably think of objects to allow for bbox
> arithmetic first on the client side (combination of zoom and pan
> requests from the user) that would not call MapServer, then once the
> user is ready after playing around, he can send the request.
>
> Cheers,
>
> Yves Moisan
>

Yves,

Sorry it's taken me a while to respond.  The bbox property that I am 
using the demo isn't really an attribute of any ZCO object.  It's 
purely an application property that is used by the getmap Python 
Script.  I chose the name "bbox" to keep the getmap script's parameters 
as close as possible to those of a WMS GetMap request, but I haven't 
planned to reserve the name specifically for any one ZCO object.

I've been putting off work on programming specific property sheets for 
the ZCO objects, but maybe the time is now.  If anybody has experience 
and interest in helping out on this, please let me know.

cheers,
Sean

--
Sean Gillies
sgillies at frii dot com
http://users.frii.com/sgillies