AW: [OpenLayers-Users] Question re. displaying large dataset

[Arnd Wippermann]

Try

strategies: [
    new OpenLayers.Strategy.Fixed(),
    new OpenLayers.Strategy.Cluster()
],
projection:new OpenLayers.Projection("EPSG:4326"), //if your data is in
projection EPSG:4326
...


Arnd

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Von: openlayers-users-bounces at lists.osgeo.org
[mailto:openlayers-users-bounces at lists.osgeo.org] Im Auftrag von r_mac
Gesendet: Sonntag, 20. Februar 2011 17:00
An: users at openlayers.org
Betreff: [OpenLayers-Users] Question re. displaying large dataset


Hi, I hope it's ok to post a newbie question here, I have searched around
for a few days and have been so far unable to resolve my problem.

I have a large dataset (2850 points) which I would like to display using
OpenLayers. At present, I am using a simple text layer to display the
locations, however it results in extremely slow browser performance.

I have looked at several different solutions to this problem, including
Dynamic POIs and clustering. It seems to me that clustering is probably the
best solution to my problem, but I am having trouble getting it to work. At
present, the location data is in a tabbed text file. In order to implement a
clustering strategy, it seems like I need to change the layer from a text
layer into a Vector layer and then create a clustering strategy.

I have created the following code, but when I load the file (via a
localhost), the POI layer does not display at all. 

  <script src="http://www.openlayers.org/api/OpenLayers.js"></script>
  <script>
    function init(){
	map = new OpenLayers.Map("map");
    map.addLayer(new OpenLayers.Layer.OSM());
	
	var strategy = new OpenLayers.Strategy.Cluster({distance:15,
threshold:3});
	
	var curLayer = new OpenLayers.Layer.Vector("layer", {
			strategies: [strategy],
			protocol: new OpenLayers.Protocol.HTTP({
				url: "location-data.txt",
				format: new OpenLayers.Format.Text()
		})		
	});
	
	map.addLayer(curLayer);
 
    //Set start centrepoint and zoom    
    var lonLat = new OpenLayers.LonLat( -6.25, 53.33 )
          .transform(
            new OpenLayers.Projection("EPSG:4326"), // transform from WGS
1984
            map.getProjectionObject() // to Spherical Mercator Projection
          );
    var zoom=9;
    map.setCenter (lonLat, zoom);
 }

At present, I'm not sure what the problem is. It could be a problem with the
text file (does it need to be in another format to work as a vector layer?)
or it could be something else.. Any help on this would be much appreciated.

Thanks,

Ronan

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