[udig-devel] Single UDig Layer with Multipe WMS Layers

[Joe Dente]

Thanks for the response.

I'm just getting started with udig, so pardon my ignorance of
terminology and the way things are done.  Anyways, you were correct.  I
added two IGeoResources pointing to different layers on the same WMS
server to the same map using the addLayerCommand().  I then looked at
the WMS request being sent to Geoserver and sure enough both layers were
requested inside a single GetMap command.  This behavior is exactly what
I was looking for.  I was worried that all the layers were sent across
in individual GetMap requests to the same Geoserver.

As far as combining multiple WMS layers into a single GeoResource, this
is unnecessary.  I was trying to do this thinking that it would allow
udig to fetch both layers with a single GetMap command.  But, since udig
was smart enough to combine both layers into a single request anyways, I
do not need to worry about creating a new type of GeoResource.

Thanks again.
Joe

-----Original Message-----
From: udig-devel-bounces at lists.refractions.net
[mailto:udig-devel-bounces at lists.refractions.net] On Behalf Of Jody
Garnett
Sent: Tuesday, April 22, 2008 6:00 PM
To: User-friendly Desktop Internet GIS
Subject: Re: [udig-devel] Single UDig Layer with Multipe WMS Layers

Joe Dente wrote:
>
> Hi,
>
>  
>
> Is it possible to fetch multiple WMS layers merged into a single 
> IGeoResource?
>
Point of interest: uDig will send out a single GetMap request if several

WMS Layers from the same server are on  your Map. So I find your 
question a bit surprising.

Sort of; WMS Layers have a parent / child relationship. Many WMS servers

let you request a folder and will draw you a picture of all of the 
contents. This is especially important when the folder contains the same

information at different scales; it allows you to automatically display 
data at the correct resolution.

The second answer is yes; you can define a GeoResource on your own that 
acts as a "view" combining several existing WMS layers. This is a 
construct that would only be available on the client; it does not 
reflect anything to do with the server, and it would be a fair bit of
work.

Can I ask for clarification; you actually mean IGeoResource and not
Layer?
>
> I have UDig connected to a WMS server on Geotools.  I construct my 
> layers by first adding the WMS server to the catalog and then using 
> ICatalog.getById() to retrieve layers from the WMS server.  This works

> well for adding IGeoResources to my map one at a time.  I would like 
> to fetch multiple layers in a single request so that Geoserver can do 
> all of the work involved in merging multiple WMS images into a single 
> image.  For example, with openMap I can use 
>
http://localhost:8080/geoserver/wms?&request=GetMap&layers=tiger:poly_la
ndmarks,tiger:tiger_roads 
>
<http://localhost:8080/geoserver/wms?&request=GetMap&layers=tiger:poly_l
andmarks,tiger:tiger_roads> 
> to retrieve multiple layers with a single request, so that openMap 
> only receives a single image representing both layers; all of the 
> calculations involving features and combining the two layers into a 
> single image are performed by the non-client computer hosting 
> Geoserver.  I would like to do something similar with UDig while 
> interacting with the catalog containing my WMS.
>
Right so if you have dragged poly_landmarks and tiger_roads onto a Map 
in uDig you will find a single request is sent off to GeoServer as you 
pan around.

Now it could be that as you drag them on one at a time; each request is 
sent off on its own. We could ask the Renderer to not do anything when 
performing a drag with a couple of things selected ....
After you start panning around a bit and you can check your geoserver to

confirm that a single GetMap request is sent with both layers listed.
>
Cheers,
Jody
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