[Thuban-list] Further work on extensibility

Jan-Oliver Wagner jan at intevation.de
Fri Jun 21 14:41:08 CEST 2002


Hi Tom,

On Thu, Jun 20, 2002 at 06:42:04PM -0500, nym wrote:
> I'm not sure if this is the case, but is this intended to help extend 
> thuban to allow objects from an application-ontop-thuban, such as 
> postgis server connectivity?

no, the application GREAT-ER I mentioned as an example is a simulation
system for chemicals in rivers and its functions should be kept
separate from Thuban since they are not directly related to GIS.

Features like a PostGIS connection should be an integral part
of Thuban.

> I'm trying to pick up as much as I can as 
> quickly as possible on this, but I'm still a bit fuzzy. I'm in the process 
> of going through the code to understand it all. At the moment I'm 
> imagining a layer that supports dynamic objects, such as data from 
> postgis. Obviously there are certain design issues at play here, and 
> I'd like to know where this would best be implemented.

We are not in favour of big-design-upfront and therefore Thuban only abstracts
where it was really needed. Further abstraction should follow once
it is clear what needs to be incorporated.

For adding PostGIS I suggest you make a copy of Model/layer.py:Layer
and make it a PostGIS Layer. We can later discuss on how a base class
should look like. We'll learn a lot comparing the PostGIS
and Shapefile Layer.

Furthermore you will need to make modifications to UI/renderer.py.
Some abstraction would make sense there, so feel free to implement
something to adapt to the PostGIS layer.

You might need to sligthly modifiy UI/view.py, but this module
is already quite generic.

> For example, 
> what about refreshing? Is this something we should do just on 
> specific layers, or does it have to be done on the whole map?

Thuban has a message system where information on changes are forwarded.
Please have a look at it.

Hope the hints help. Please don't hesitate to discuss your
implementation ideas here on this list.

All the best

	Jan

-- 
Jan-Oliver Wagner               http://intevation.de/~jan/

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




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