CODEWITHSUNDEEP
javascriptopenlayers-3
Chris
Chris

Reputation: 677

Openlayers 3 selection by polygon draw interaction

I am trying to modify the Openlayers 3 box selection example here so I can draw a polygon onto the map to select features.

Below is my code - I have added a vector source which will contain the polygon, changed the interaction from 'DragBox' to 'Draw' and changed the box methods to draw methods.

I do not get any errors in the js console so I am not too sure where I might be going wrong with this? Should this produce a result?

<!DOCTYPE html>
<html>
  <head>
    <title>Box Selection</title>
    <link rel="stylesheet" href="http://openlayers.org/en/v3.14.1/css/ol.css" type="text/css">
    <script src="http://openlayers.org/en/v3.14.1/build/ol.js"></script>
    <style>
      .ol-dragbox {
        background-color: rgba(255,255,255,0.4);
        border-color: rgba(100,150,0,1);
      }
    </style>
  </head>
  <body>
    <div id="map" class="map"></div>
    <div id="info">No countries selected</div>
    <script>
      var vectorSource = new ol.source.Vector({
        url: 'countries.geojson',
        format: new ol.format.GeoJSON()
      });

      var source = new ol.source.Vector();

      var map = new ol.Map({
        layers: [
          new ol.layer.Tile({
            source: new ol.source.OSM()
          }),
          new ol.layer.Vector({
            source: vectorSource
          })
        ],
        renderer: 'canvas',
        target: 'map',
        view: new ol.View({
          center: [0, 0],
          zoom: 2
        })
      });

      // a normal select interaction to handle click
      var select = new ol.interaction.Select();
      map.addInteraction(select);

      var selectedFeatures = select.getFeatures();

      // a DragBox interaction used to select features by drawing boxes
      var dragBox = new ol.interaction.Draw({
        source: source,
        type: 'Polygon'
      });

      map.addInteraction(dragBox);

      var infoBox = document.getElementById('info');

      dragBox.on('drawend', function() {
        // features that intersect the box are added to the collection of
        // selected features, and their names are displayed in the "info"
        // div
        var info = [];
        var extent = source.getExtent();
        vectorSource.forEachFeatureIntersectingExtent(extent, function(feature) {
          selectedFeatures.push(feature);
          info.push(feature.get('name'));
        });
        if (info.length > 0) {
          infoBox.innerHTML = info.join(', ');
        }
      });

      // clear selection when drawing a new box and when clicking on the map
      dragBox.on('drawstart', function() {
        selectedFeatures.clear();
        infoBox.innerHTML = '&nbsp;';
      });
      map.on('click', function() {
        selectedFeatures.clear();
        infoBox.innerHTML = '&nbsp;';
      });
    </script>
  </body>
</html>

Upvotes: 1

Views: 2774

Answers (2)

pavlos
pavlos

Reputation: 3081

this is possible a duplicate. check it here

For such action you need to use JSTS lib. Check the link above, it has a fiddle as well, to see it in action

Upvotes: 1

Jonatas Walker
Jonatas Walker

Reputation: 14150

UPDATE:

Note the difference between ol.source.Vector#forEachFeatureInExtent and ol.source.Vector#forEachFeatureIntersectingExtent.

http://jsfiddle.net/jonataswalker/sum62szv/

First, get the drawn polygon extent, then check with ol.source.Vector#forEachFeatureIntersectingExtent like:

draw.on('drawend', function(evt){
  var polygon_extent = evt.feature.getGeometry().getExtent();
  vectorSource.forEachFeatureIntersectingExtent(polygon_extent, function(feature) {
    selectedFeatures.push(feature);
    info.push(feature.get('name'));
  });

});

Upvotes: 1

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