Edit in JSFiddle

var viewer = null

function initMap() {
  viewer = iv.getViewer();

  var layer = new OpenLayers.Layer.Vector("My drawing layer");
  viewer.getMap().addControl(new Geoportal.Control.DrawingToolbar(layer, {
    mode: 'single'
  }));


}

iv = Geoportal.load(
  'viewerDiv', ['jhyvi0fgmnuxvfv0zjzorvdn'], { // Positionnement par coordonnées
    lon: 2.294,
    lat: 48.858
  },
  15, {
    onView: initMap,
    layers: ['ORTHOIMAGERY.ORTHOPHOTOS'],
    viewerClass: Geoportal.Viewer.Default
  }
);

#viewerDiv {
  width: 100%;
  height: 400px;
}
<div id="viewerDiv"></div>

External resources loaded into this fiddle: