function showTrack() {
   var iconFeatures=[];
   var num = $('#tracker-grid').datagrid('getData').total;

   for(var i=0; i<num; i++){
        var lon=$('#tracker-grid').datagrid('getRows')[i].longitude;
        var lat=$('#tracker-grid').datagrid('getRows')[i].latitude;
        var coord = ol.proj.fromLonLat([lon, lat]);
        var iconFeature = new ol.Feature({
          geometry: new ol.geom.Point(coord)
        });
        iconFeatures.push(iconFeature);
   }

  var vectorSource = new ol.source.Vector({
    features: iconFeatures //add an array of features
  });

  var iconStyle = new ol.style.Style({

    image: new ol.style.Icon(/** @type {olx.style.IconOptions} */ ({
      scale: 0.5,
      anchor: [0.5, 46],
      anchorXUnits: 'fraction',
      anchorYUnits: 'pixels',
      opacity: 0.75,
      src: 'img/pin-blue.png'
    }))
  });

 var vectorLayerLoc = new ol.layer.Vector({
    source: vectorSource,
    style: iconStyle
  });

map.addLayer(vectorLayerLoc);

}