[udig-devel] uDig "pre-filtering" for WFS layers...

[Jody Garnett]

Christopher Stolte wrote:
> Hello,
>
> I am a software engineer in the geoscience community that has spent 
> time working with GeoServer and uDig, among other technologies, to 
> find interoperable and scalable ways of displaying map-based 
> scientific data to research scientists.  My working group has created 
> and deployed proof-of-concept WMS/WFS services, which provide some 
> very useful functionality.  I would like to find out more about the 
> [possible] existence of client features that would apply a filter when 
> adding a WFS layer (for example), so that only a subset of the layer 
> is actually
> loaded/rendered up front?
We have set this up for one project already; we will need to check if it 
is in the core uDig codebase or not.

Here is how it works:
- an additional Filter is placed on the Layer BlackBoard
- when the layer resolves to a FeatureSource the above Filter is used 
with the DataStore.getView( Filter ) method

The resulting content *is* read-only; but that is all we needed for display.

We also experimented with using this same Filter with WMS to great effect.
> We deal with datasets that are sometimes quite large, and are 
> particularly interested in finding a way to limit the layer according 
> to the properties it represents.  Note that while applying a filter 
> after the layer has loaded is also a nice [currently existing] 
> feature, I'm wondering about applying the filter before it loads, to 
> limit which points load at all.
See above workflow :-)

Note that you can do this sort of thing in your own application just 
using uDig extension points. Another option is to define your own 
renderer, that makes use of information you have placed on the 
blackboard to limit the information loaded.
> I have looked through the documentation and email archives, and have 
> found references to programming solutions (i.e. extending or modifying 
> the codebase).  Does uDig have any plans to incorporate this kind of 
> functionality into a release candidate?  Alternatively, if I've missed 
> this somewhere in the current app, could someone please point it out?
This may fall in the "undocumented" category.
> Thank you in advance for any help or insight here.
Cheers,
Jody