[GIS] Geojson + Ajax to openlayers 3 repeated loading of data

ajaxopenlayers

I'm loading Geojson-data (from Postgis) to Openlayers 3 via bounding box stategy. Everything looks good.

The problem ist, that the data is reloaded all the time even if no change of the boundig box occurs.

Here is my code:

var geoJsonFormat = new ol.format.GeoJSON();
var vectorSource = null;

function loaderFunction(extent, resolution, projection) {
  var extent = ol.proj.transformExtent(extent, projection.getCode(), ol.proj.get('EPSG:4326').getCode());
  var url = "./_mapdata/n2k_dh_geojson.php?bbox=" + extent.join(',');
  $.ajax({
    url: url,
    success: function (data) {
      var features = geoJsonFormat.readFeatures(data, {
        dataProjection: 'EPSG:4326',
        featureProjection: 'EPSG:3857'
      });
      vectorSource.clear(true);
      vectorSource.addFeatures(features);
    }
  });
}

vectorSource = new ol.source.Vector({
  format: geoJsonFormat,
  loader: loaderFunction,
  projection: 'EPSG:4326',
  strategy: ol.loadingstrategy.bbox
});

…. later I add the layer to a layers array

      new ol.layer.Vector({
      source: vectorSource,
      style: new ol.style.Style({
            fill: new ol.style.Fill({color:'rgba(100,250,0,0.1)'}),
                stroke: new ol.style.Stroke({
                    color: 'green',
                    width: 2
                })
            })
   })

How can I prevent, that the data is reloaded all the time?

Best Answer

You should not call vectorSource.clear(true) in your loader function. See this Issue

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