RE : [UMN_MA PSERVER-USERS] Mutiple "DATA " lines in a single l ayer?

[Ed McNierney]

Jeff -

Just use multiple layers in the map file, with a GROUP statement for each,
and a MINSCALE/MAXSCALE value in each.  That will let them appear to the
client as a single logical layer using the GROUP name you specified.

     - Ed

-- 
Ed McNierney
President and Chief Mapmaker
Maps a la carte, Inc. / TopoZone.com
73 Princeton Street, Suite 305
North Chelmsford, MA  01863
Phone: (978) 251-4242
Fax: (978) 251-1396
ed at topozone.com


From: Jeff Dege <jdege at KORTERRA.COM>
Reply-To: Jeff Dege <jdege at KORTERRA.COM>
Date: Fri, 18 May 2007 15:51:34 -0500
To: <MAPSERVER-USERS at LISTS.UMN.EDU>
Conversation: [UMN_MAPSERVER-USERS] RE : [UMN_MAPSERVER-USERS] Mutiple "DATA
" lines in a single layer?
Subject: Re: [UMN_MAPSERVER-USERS] RE : [UMN_MA PSERVER-USERS] Mutiple "DATA
" lines in a single l ayer?

We're using OpenLayers as the map viewer.  MapServer will be running in CGI
mode, either directly or as a WMS server.  So mapscript isn't part of the
equation.
 
I've never looked at the  MapServer source, but I'm wondering if allowing
DATA statements to be placed in CLASS sections would be a reasonable
enhancement.

>  
>  
> 
>  From: UMN MapServer Users List  [mailto:MAPSERVER-USERS at LISTS.UMN.EDU] On
> Behalf Of Guillaume  SUEUR
> Sent: Friday, May 18, 2007 3:04 PM
> To:  MAPSERVER-USERS at LISTS.UMN.EDU
> Subject: [UMN_MAPSERVER-USERS]  RE : [UMN_MAPSERVER-USERS] Mutiple "DATA "
> lines in a single  layer?
> 
>  
>  
>  
> as Stephen said, there is  only ONE data statement per layer. But, if you use
> mapscript, you can change  it dynamically depending on the scale for example
>  
>  
>  
>  
>  
>  
>  
>  
> ---------------------------------------------
>  
> Guillaume SUEUR
>  
> Géosignal - Groupe BVA
>  
> 25bis Avenue Marcel Dassault
>  
> BP  95836
>  
> 31505 Toulouse CEDEX 05
>  
> Tél : 05 61 17 47 17
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> ---------------------------------------------
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>  
>  
> 
>  
> 
>  De: UMN MapServer Users List de la part de  Jeff Dege
> Date: ven. 18/05/2007 20:32
> À:  MAPSERVER-USERS at LISTS.UMN.EDU
> Objet : [UMN_MAPSERVER-USERS] Mutiple  "DATA" lines in a single layer?
> 
>  
>  
> 
> I'm starting to play around with using MapServer to serve maps  from a
> PostGIS database.
> 
> One of the features that MapServer has is  that you can define multiple
> classes within a single layer, so you can  change the way that the map
> looks when drawn at different  scales/resolutions.
> 
> Is there some way to define multiple data sources  within a single layer,
> so that I can change how that data is obtained at  different layers?
> 
> In particular, I'm wondering how to best take  advantage of PostGIS's
> simplify() function - which can be used to reduce  the number of points
> included in a geometry based on resolution.  If  I'm drawing a map at a
> resolution where one pixel equals 2000 meters on the  ground, there is no
> advantage to sending the viewer a geometry defined with  points
> twenty-five meters apart.
> 
> The obvious way is to define  multiple layers, each enabled at certain
> scales, and to include the  resulution appropriate for those scales in
> the DATA keyword's sql  statement.  But this requires that the layer be
> duplicated for each  scale range.  Is there a way to enable different
> DATA sql statements  at different scales/resolutions in a single layer
> definition?
> 
> I  don't see the DATA keyword in the documentation for the CLASS  section.
> Which is where I'd expect it to be if I could do what I  want.
> 
> Is there a way of including a value calculated from the scale in  the SQL
> statement within the LAYER section?
> 
>    DATA  "simplify(the_geom, 1.0/<scale>) from streets"
> 
> Or am I stuck with  using multiple layers?
> 


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