s for a
      // projection&#x27;s validity extent can be found at https://epsg.io/.
      //
      // If you use Proj4js only to transform coordinates, you don&#x27;t even need to
      // create an ol.proj.Projection instance. ol.proj.get() will take care of it
      // internally.

      var projection &#x3D; new ol.proj.Projection({
        code: &#x27;EPSG:21781&#x27;,
        extent: [485869.5728, 76443.1884, 837076.5648, 299941.7864]
      });

      var extent &#x3D; [420000, 30000, 900000, 350000];