I think what you're really after here is that you only want to request
one named layer, and you want mapserver to return whichever level of
detail is appropriate for the current scale.
The way I do this is just to give all the layers in a "detail set"
the SAME NAME. Try it, it's like magic :-)
Percy
Andrew Wooley wrote:
Dave,
I am not an OpenLayers expert by any means, but as of the 2.4 release
(at least), now with RC5, you can add a Mapserver Layer directly. This
honors the scale dependencies you have set up in your mapfile and you
can have your LOD.
Check out http://trac.openlayers.org/wiki/MappingYourData for a nice
tutorial. Make sure your watch the flash presentation. It makes it seem
so simple.
Andrew
On 5/30/07, *Dave Weaver* <[EMAIL PROTECTED]
<mailto:[EMAIL PROTECTED]>> wrote:
I'm playing around with OpenLayers in conjuntion with MapServer.
What's the best way to have different levels of detail as I zoom in
on my map?
At the moment I've done it like this:
My .map file has one layer per LOD, each using a MINSCALE/MAXSCALE
directive
to determine when it's visible.
But that means I have multiple named layers, so the WMS request made by
OpenLayers needs to request all layers.
e.g: (mapfile)
LAYER
NAME lod1
STATUS OFF
TYPE RASTER
PROJECTION
"init=epsg:4326"
END
MINSCALE 75000000
METADATA
"wms_title" "lod1"
"wms_onlineresource"
"http://example.com/cgi-bin/mapserv?map=map/earth.map&;
<http://example.com/cgi-bin/mapserv?map=map/earth.map&;>"
"wms_srs" "EPSG:4326 EPSG:54004"
END
TILEINDEX "lod1.shp"
TILEITEM "location"
END
LAYER
NAME lod2
STATUS OFF
TYPE RASTER
PROJECTION
"init=epsg:4326"
END
MAXSCALE 74999999
MINSCALE 50000000
METADATA
"wms_title" "lod2"
"wms_onlineresource"
" http://example.com/cgi-bin/mapserv?map=map/earth.map&;
<http://example.com/cgi-bin/mapserv?map=map/earth.map&;>"
"wms_srs" "EPSG:4326 EPSG:54004"
END
TILEINDEX "lod2.shp"
TILEITEM "location"
END
# ... etc ...
then in the OpenLayers code:
layer = new OpenLayers.Layer.WMS( "OpenLayers WMS",
"
http://example.com/cgi-bin/mapserv?map=map/earth2.map&;
<http://example.com/cgi-bin/mapserv?map=map/earth2.map&;>", {layers:
'lod1,lod2,lod3,lod4,lod5'});
Is there a better way to handle multiple LODs ?
Many thanks,
Dave.
--
David Percy
Geospatial Data Manager
Geology Department
Portland State University
http://gisgeek.pdx.edu
503-725-3373
