Using GeoWebCache with OpenLayers, Google Maps and Virtual Earth

In this section will learn how to use GeoWebCache with OpenLayers, GoogleMaps and Virtual Earth through the simple examples.

GeoWebCache with OpenLayers

OpenLayers tiling the WMS request splitting it into several sub-requests sent to the geospatial server. To ensure that GeoWebCache returns tiles from the cache consistent with OpenLayers tiles, we should respect some constraints including:

  • The tiles of the OpenLayers and GeoWebCache should have the same size in terms of pixels, both in terms of coverage area.
  • The tiles of the OpenLayers and GeoWebCache should be aligned in the same grid.

Note

This ensures not only an optimal caching of tiles, but also an optimal reuse of the GeoWebCache tiles with other clients as well as OpenLayers.

  1. Create an wmts.html file and enter the following code:

    <!DOCTYPE html>
      <html lang="en">
      <head>
        <meta charset="utf-8"/>
        <title>Counties of Colorado:EPSG:4326 image/png</title>
        <link rel="stylesheet" href="lib/ol3/css/ol.css" type="text/css">
        <!-- Use ol.js for production, and ol-debug.js for development
                script src="lib/ol3/ol.js" type="text/javascript"></script-->
        <script src="lib/ol3/ol-debug.js" type="text/javascript"></script>
    
                        <style>
    
        /* Map settings */
        #map {
           width: 600px;
           height: 400px;
        }
      </style>
    </head>
    <body>
      <div id="map" class="map"></div>
    
      <script>
          var projection = ol.proj.get('EPSG:4326');
          var projectionExtent = projection.getExtent();
          var mapExtent =  [-105.70160457542876, 39.799058451017345, -104.99644707392322, 40.301219114868005];
          var matrixIds = new Array(22);
    
          for (var z = 0; z < 22; ++z) {
            matrixIds[z] = "EPSG:4326:" + z;;
          }
    
          resolutions = [
                0.703125, 0.3515625, 0.17578125, 0.087890625,
                0.0439453125, 0.02197265625, 0.010986328125,
                0.0054931640625, 0.00274658203125, 0.001373291015625,
                6.866455078125E-4, 3.4332275390625E-4, 1.71661376953125E-4,
                8.58306884765625E-5, 4.291534423828125E-5, 2.1457672119140625E-5,
                  1.0728836059570312E-5, 5.364418029785156E-6, 2.682209014892578E-6,
                1.341104507446289E-6, 6.705522537231445E-7, 3.3527612686157227E-7
          ];
    
          bouldersLayerWMTS = new ol.layer.Tile({
                source: new ol.source.WMTS({
                url: 'http://localhost:8083/geoserver/gwc/service/wmts',
                  layer: 'boulder',
                matrixSet: 'EPSG:4326',
                format: 'image/png',
                projection: projection,
                  tileGrid: new ol.tilegrid.WMTS({
                    origin: ol.extent.getTopLeft(projectionExtent),
                  resolutions: resolutions,
                    matrixIds: matrixIds
                  })
            })
        });
    
         var map = new ol.Map({
          layers: [bouldersLayerWMTS],
          target: 'map',
          view: new ol.View({
                extent: mapExtent,
                projection: projection,
                center: [-105.4, 40.03],
                zoom: 10
          })
        });
    
        </script>
      </body>
     </html>
    
  2. Save the file in the Map folder located in:

  • Linux:

    /opt/tomcat_geoserver/webapps/Map
    
  • Windows:

    %TRAINING_ROOT%/tomcat-7.0.72/instances/instance1/webapps/Map
    
  1. Open the working map in your web browser at WMTS Page.

    ../_images/caching1.png

    GeoWebCache with OpenLayers

    Note

    The default values are the following:

    • Tile width: 256px
    • Tile height: 256px
    • Tile origin: EPSG:4326 -180,-90 ; EPSG:900913: -20037508.34,-20037508.34
    • Resolution: EPSG:4326 180 / (2^k) ; EPSG:900913: (2*20037508.34)/(2^k), k represents the zoomlevel.

GeoWebCache with Google Maps

GeoWebCache also supports Google Maps client. An example of Google Maps client, which can be used as a base (template) for more complex client is as follows.

  1. Crate a new index.html file and enter the following code:
<html xmlns="http://www.w3.org/1999/xhtml">
        <head>
                <meta http-equiv="content-type" content="text/html; charset=utf-8"/>
                <title>Google Maps with GeoWebCache</title>
                <script src="https://maps.googleapis.com/maps/api/js?sensor=false" type="text/javascript"></script>
                <script type="text/javascript">
                        function initialize() {
                                var myOptions = {
                                          zoom: 9,
                                          center: new google.maps.LatLng(40, -105.5),
                                          zoomControl: true,
                                          mapTypeId: google.maps.MapTypeId.ROADMAP
                                        }
                                var map = new google.maps.Map(document.getElementById("map_canvas"), myOptions);

                                var countiesTiles = {
                                         getTileUrl: function(coord, zoom) {
                                           return "http://localhost:8083/geoserver/gwc/service/gmaps?layers=boulder&" +
                                                "zoom=" + zoom + "&x=" + coord.x + "&y=" + coord.y + "&format=image/png";
                                         },
                                         tileSize: new google.maps.Size(256, 256),
                                         isPng: true,
                                         opacity: 0.5
                                   };

                           var customMapType = new google.maps.ImageMapType(countiesTiles);
                           map.overlayMapTypes.insertAt(0, customMapType);

                        }
                </script>
                        </head>
        <body onload="initialize()" onunload="GUnload()">
           <div id="map_canvas" style="width: 596px; height: 367px"></div>
        </body>
</html>

Note

The /service/gmaps path tells the dispatcher to use the gwcGmaps service for indexing and generating tiles compatible with this type of requests.

  1. Save the file in the Map folder replacing the previous created.

  2. Open the working map in your web browser at Welcome Page.

    ../_images/caching2.png

    GeoWebCache with Google Maps

GeoWebCache with Virtual Earth

GeoWebCache can also support requests from MS Virtual Earth clients. An example of a client, which can be used as a base (template) for clients more complex is the following.

  1. Crate a new index.html file and enter the following code:

    <html xmlns="http://www.w3.org/1999/xhtml">
                <head>
                        <title>Virtual Earth with GeoWebCache</title>
                        <script type="text/javascript" src="http://dev.virtualearth.net/mapcontrol/mapcontrol.ashx?   v=6.1"></script>
                        <script type="text/javascript">
                                 var map, tileLayer;
                                 var tileLayerURL = 'http://localhost:8083/geoserver/gwc/service/ve?quadkey=%4&format=image/png&layers=boulder';
                         function GetMap(){
                                         var map = new VEMap('myMap');
                                         map.LoadMap(new VELatLong(40, -105.5) , 9, 'r' , false);
                                         var tileSourceSpec = new VETileSourceSpecification('TITLE_OF_LAYER', tileLayerURL);
                                         tileSourceSpec.Opacity = 0.5;
                                         map.AddTileLayer(tileSourceSpec, true);
                                 }
                        </script>
                </head>
                <body onload="GetMap();">
                              <div id='myMap' style="position:relative; width:596px; height:367px;"></div>
                </body>
        </html>
    

    Note

    The /service/ve path tells you to use the service gwcVEConverter for indexing and generating tiles compatible with this type of requests.

  2. Save the file in the Map folder replacing the previous created.

  3. Open the working map in your web browser at Welcome Page.

    ../_images/caching3.png

    GeoWebCache with Virtual Earth