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

[Matthew Perry]

Jeff,

 If you're looking to dynamically change the DATA element of a layer,
you should check out variable substitution
(http://mapserver.gis.umn.edu/docs/reference/mapfile/variable_sub) .
No mapscript required.

- matt

On 5/18/07, Jeff Dege <jdege at korterra.com> wrote:
>
>
> 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
> ---------------------------------------------
>
>
>  ________________________________
>  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?
>
>


-- 
Matthew T. Perry
http://www.perrygeo.net

"You never change things by fighting the existing reality.
To change something, build a new model that makes
the existing model obsolete" - R. Buckminster Fuller