[OpenLayers-Dev] Problem with the developpement of a "overlay Strategy"

[Tim Schaub]

Hey-

Jerome Freyre wrote:
> Hi everybody,
> 
> Currently I am trying to developp a new strategy (based on
> OpenLayers.Strategy.Cluster) that can modify the order of features (bigger
> features go downer and small one go higher) to display features with correct
> "overlay" or "superposition".
> 
> To do that, I found that I have to order my features.
> 
> Actually, I am loading my features with HTTP protocol (see:
> http://www.nabble.com/Problem-with-Protocol-HTTP-and-vector-layer-tt20088456.html
> ;) ).
> 
> My "sort algorithm" seems to work because it is ordering features based on
> the "overlayAttribute".
> 
> The problem appears when I select a feature that is "downer". When I
> unselect it, the feature goes "higher" than the smaller one and stays like
> this.

Sounds like this could be accomplished with rule based styling.

You could set the graphicZIndex property of a symbolizer based on your 
feature attributes.

See the ordering example for use of graphicZIndex.
http://openlayers.org/dev/examples/ordering.html

See the StyleMap example for use of rule based styling.
http://openlayers.org/dev/examples/stylemap.html

For a convenience method to deal with unique value rules, see the unique 
styles example.
http://openlayers.org/dev/examples/styles-unique.html

And, if a 1:1 mapping between attribute values and z-index doesn't work 
for you, you might be able to use the context based symbolizer evaluation.
http://openlayers.org/dev/examples/styles-context.html

Finally, if you do need to sort your features, your strategy should set 
the graphicZIndex property.

Tim

> 
> Has somebody got an idea to resolve this problem?
> 
> My strategy function : 
> ============================================
>         if(this.features.length >= 2) {
> 
> 			var tempArray = this.features;
> 			//alert('count = ' + this.features.length);
> 			for (var i=0; i<this.features.length; i++) {	
> 				for(var j=this.features.length-1; j>i;j--) {
> 					//alert('Comparaison de ' +
> this.features[j].attributes[this.overlayAttribute] + ' et ' +
> this.features[j-1].attributes[this.overlayAttribute]);
> 					if (parseInt(this.features[j].attributes[this.overlayAttribute]) >
> parseInt(this.features[j-1].attributes[this.overlayAttribute])) {
> 						var tmp = this.features[j];
> 						this.features[j] = this.features[j-1];
> 						this.features[j-1] = tmp;
> 					}
> 				}
> 			}
> 		}
> 
> 		alert('count = ' + this.features.length);
> 		var attr = "";
> 		for(var i=0; i<this.features.length; ++i) {
> 			attr += this.features[i].attributes[this.overlayAttribute] + ' \\ ';
> 		}
> 
> 	if(this.features.length > 0) {
>                  this.clustering = true;
>                  // A legitimate feature addition could occur during this
>                  // addFeatures call.  For clustering to behave well,
> features
>                  // should be removed from a layer before requesting a new
> batch.
> 				 this.layer.removeFeatures();
>                  this.layer.addFeatures(this.features);
>                  this.clustering = false;
>              }
> ============================================
>  


-- 
Tim Schaub
OpenGeo - http://opengeo.org
Expert service straight from the developers.