[GIS] How to use OpenLayers cluster strategies without using a Protocol

javascriptopenlayers-2

Using OpenLayers with Bing maps, I'm trying to load JSON data from a service URL and assign an array of clustering strategies to the resulting layer. There are plenty of examples of using cluster strategies with OpenLayers.Format.GeoJSON loaded via OpenLayers.Protocol.HTTP, but my data is Plain Ol' JSON, not GeoJSON (and I have no control over the format of it).

So using this code, the points load on the map correctly. But I get an error:
"Uncaught TypeError: Cannot call method 'read' of null". When I open up the OpenLayers source code to the error-causing line, it's this:

 layer.protocol.read(OpenLayers.Util.applyDefaults({

and indeed, protocol is null.

So my question is: How to use OpenLayers cluster strategies without using a Protocol?

Here's the code I'm using:

map = new OpenLayers.Map("project-map");
osm = new OpenLayers.Layer.Bing({ name: 'street', type: 'Road', key : bingApiKey});
map.addLayer(osm);
var cp = new OpenLayers.LonLat(0,20).transform(fromProj, toProj);

var pointLayer = new OpenLayers.Layer.Vector("Markers",{
            strategies: [new OpenLayers.Strategy.Fixed(), 
            new OpenLayers.Strategy.Cluster({distance: 25})]
});

OpenLayers.Request.GET({
    url: "ServiceHandler.json", 
    success: function(response) {
      var jsonReader = new OpenLayers.Format.JSON();
      var sparkle = jsonReader.read(response.responseText);
        $.each(sparkle, function(i,f){
          var point = 
             new OpenLayers.Geometry.Point(f.Long, f.Lat).transform(fromProj, toProj);
          var pointFeature = new OpenLayers.Feature.Vector(point, null, 
        {
          externalGraphic: "http://localhost:8081/Icons/175.png",
          pointRadius: 8
        });
            pointFeature.attributes = f;
            pointLayer.addFeatures(pointFeature);
        });
        }
    });

    map.addLayer(pointLayer);

Best Answer

You get error message by reason of using Fixed strategy. Remove this item from strategies array:

strategies: [new OpenLayers.Strategy.Cluster({distance: 25})]

It is not neccesary use Fixed strategy for manually added features.

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