Preventing an Openlayers WMS layer from updating on zoom-change

Question

I'm using openlayers to overlay a raster. When I zoom out, the overlaid layer expands to cover a larger area than was originally requested. I want the tile to be fixed to a particular boundary, and for the WMS query to end, once the zoom changes. When I get the WMS layer the first time, it looks like this:

However, if I zoom out the screen then looks like this:

My javascript is as follows:

wms_url = 'mysite.com/mapserv.cgi?map=population.map&ny_pop';

oldRaster = new OpenLayers.Layer.WMS( 
               "pop_raster",
               wms_url, 
               {    layers: wms_layer, 
                    transparent: true
                    },
               {    maxExtent: polyBounds, 
                    displayOutsideMaxExtent: false,
                    tileSize: new OpenLayers.Size(tileWidth, tileHeight),                   
                    opacity: 0.3, 
                    gutter: 0
                    }   
           );
           map.addLayer(oldRaster);

I've tried adding the attribute persist: false but it does not change anything. I calculate polyBounds using the screen size, and then tileHeight and tileWidth based on the screen resolution so that one tile fills the box that is drawn on-screen.

When I inspect the GET command using HTTPFox the page seems to be actively pulling down more data from the WMS, but I'm not sure why as there are no fresh requests.

Answer 1

Try appending this to wms_url : &BBOX=-97.105,24.913,78.794,36.358 but replace the values in this order: minimum longitude, minimum latitude, maximum longitude, maximum latitude.

Make sure the Bounding Box area overlaps with the BoundingBox advertised in the Capabilities XML for the requested geodata object.

Your not using a BBox Strategy anywhere else in your code? This would cause it to make new calls to the server.