Highlighting Link in OpenLayers Map dynamically

Question

I'm having a map which is rendered through OpenLayers using GeoServer. The map contains various attribute data field like link_no, X_coord, Y_coord etc.

I want to highlight the link using link_no. I internally use WMS layer to render the map.

I got the following code from this wiki for highlighting purpose:

// define a blank Vector layer and add it to the map
var highlight_style = { fillColor:'#99CCFF', strokeColor:'#3399FF', fillOpacity:0.7 };
hilites = new OpenLayers.Layer.Vector("Highlighted",
            {isBaseLayer:false, features:[], visibility:true, style:highlight_style}
        );
map.addLayer(hilites);

// define the WFS server which will fill requests
var wfs_url = '/cgi-bin/mapserv?map=/maps/spraywatch2/wms/mapfile.map&SERVICE=WFS&VERSION=1.0.0';
/* highlightFeatures() makes the WFS request, then highlight_them() callback does the real work
* Args for WFS filter: typename, attribute, value
*/
function highlightFeatures(typename,attribute,value) {
var wfsurl = wfs_url + '&REQUEST=getfeature&typename=' + typename +
       '&Filter=<Filter><PropertyIsEqualTo><PropertyName>'+attribute+'</PropertyName><Literal>'+value+'</Literal></PropertyIsEqualTo></Filter>';
OpenLayers.loadURL(wfsurl,'',null,highlight_them);
}
function highlight_them(response) {
                      // use the GML parser to turn the XML into a list of Feature objects
                      var features = new OpenLayers.Format.GML().read(response.responseText);
                      // have the Vector layer purge its feature list, replace them with the new ones
                      hilites.destroyFeatures();
                      hilites.addFeatures(features);
                      hilites.setVisibility(true);
                   }

Now what exactly is the typename, attribute and value parameters in the function highlightFeatures ? My aim is to highlight a particular link using a function call like this as explained in the wiki:

highlightFeatures('parcels','parcel_id','123456')

The above function call was an example given in the wiki link.

Answer 1

Typename - this is the name of the feature type you are trying to retrieve Attribute - this is the field of the feature you want to query against (I think this would be link_no in your example) Value - this is the value of link_no for the feature(s) you want to highlight.

You mention in your question that you're got a WMS layer set up, but it's not clear whether you've also set up a corresponding WFS layer to query against. The example you give assumes you have a WMS layer for displaying all your features, but it also requires a WFS layer which is what you need to query when you are highlighting a feature.