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Re: [udig-devel] Exploring uDIG: from a map selection to a database query
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alain.demers@xxxxxxxxxxxxxxxx wrote:
Hi,
Congratulation for uDIG, it is a great tool that I discover with
enthusiasm. I am trying to find my way in the javadoc (uDIG and
GeoTools), which are huge. To understand uDIG plug-in creation, I try
to create a real case. Here my scheme of work (my trouble is in the #4):
Your list always begins with "1." :-)
1. Make a selection on a layer.
This is a user interface operation with the use of selection tool- no
code here
Behind the scenes a GeoTools Filter indicating the selection is stored
for each Layer. The selection tool lets you modify this Filter. If
someone has time a dialog could also be created to let people manually
indicate the selection.
1. Read the filter of the selection of this layer.
I use PostGIS. I have a Geometry table which is link to huge schema
including many descriptive tables. Geometries are points where I have
information on fish or fish habitat. One point may include many
information types (fish inventory, habitats, species observations,
etc.). I know the layer name which is my Geometry Table. I retrieve my
Layer with PlatformGIS. getActiveMap().getMapLayers(). I can make a
check to find the layer to catch the filter with getFilter() on this
layer. I want to use this filter to select the descriptive information
in my database.
You should be able to ask for the FeatureSource associated with the
Layer, and then you can use normal geotools code to access.
(I am doing this from memory so may need correction)
FeatureSource data = layer.getResource( FeatureSource.class );
data.getFeatures( layer.getFilter() );
1. Read the source of the data of the layer.
I can find the URL for the same layer
If you ask the the way in which you want to see the data (using
getResource above) we will be use any metadata around to help out at the
framework level. As an example sometimes a WMS Layer has a data url
which we may be able to use to find a WFS etc ...
1. Make a collection to create an Iterator.
Here is my trouble, is it the right way if I try to create a
FeatureCollection from a FeatureSource? How should I link a
FeatureSource to a Layer? I guess that there is another way than
FeatureSource...
The layer should already be defined by a FeatureSource ... Question:
are you defining your Layer as a program or is the user defining the
layer which you are then operating with?
1. Make a View (in PostGresSQL and Udig) to explore the data based
on the Iterator.
I am not here yet, do you have a suggestion
Making a view is kind of tough, and is a subject of research in the
geotools library right now. Right now a datastore *can* show the
database defined views - the result should be returned as a read-only
FeatureSource. So the suggestion is - define your view on the database
side, and read it through geotools.
Jody
