Using OpenLayers 3 forEachFeatureAtPixel to specify layer?

Question

I must first state that my skills at javascript are about the same as my skills in Spanish. I know barely enough to get myself into trouble and then I go looking for help. anyway I have an application that has a few geoJSON layers in it. I have created a map.forEachFeatureAtPixel function to update a div with some information.

The problem is it looks at all of the layers and I just want it to look at one. this way I can create another function to get some different attributes from another layer. I have looked over the documentation and I see the opt_layerFilter option but I dont know how to apply it (due to my lack of Javascript knowledge). If someone could give me a hint here hopefully I will then be able to read the documentation and stop asking these questions.

function:

var displayFeatureInfo = function(pixel ) {
  var feature = map.forEachFeatureAtPixel(pixel, function(feature, layer) {
    return feature;
    });

  var info = document.getElementById('info');
  if (feature) {
    info.innerHTML =  '<div class="panel panel-info"><div class="panel-heading"><h3 class="panel-title">' + feature.get('Name') +
     '</h3></div><div class="panel-body">' + '<dt>API: </dt><dd class="text-info">' + feature.get('API') + '</dd>'
     + '<dt>Status: </dt><dd class="text-info">' + feature.get('Status') +  '</dd>' +
     '<dt>Legal : </dt><dd class="text-info">' + feature.get('Legal') +  '</dd>' +
     '<dt>Site Name: </dt><dd class="text-info">' + feature.get('Site_Name') +  '</dd>'+'</div>';
  } else {
    info.innerHTML = '&nbsp;';
  }

  if (feature !== highlight) {
    if (highlight) {
      featureOverlay.removeFeature(highlight);
    }
    if (feature) {
      featureOverlay.addFeature(feature);
    }
    highlight = feature;
  }

}; 

Answer 1

You can use the opt_layerFilter argument to forEachFeatureAtPixel. See the documentation at http://openlayers.org/en/master/apidoc/ol.Map.html#forEachFeatureAtPixel.

For example, if vectorLayer is a reference to the layer in which you want to detect features you will use the following:

var feature = map.forEachFeatureAtPixel(pixel, function(feature, layer) {
  return feature;
}, null, function(layer) {
  return layer === vectorLayer;
});

With this "filter function" layers that are not vectorLayer will be filtered out.