Multiple Levels-Of-Detail

[Andrew Wooley]

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 <dave.weaver at zen.co.uk> 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&"
>         "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&"
>         "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&",
> {layers:
> 'lod1,lod2,lod3,lod4,lod5'});
>
> Is there a better way to handle multiple LODs ?
>
> Many thanks,
> Dave.
>
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