Ionic 2 ,I can't use getProjection and fromPointToLatLng

Ionic Framework ionic-v3
1

Not overall. On run it show polyfills.js:3 Uncaught TypeError: Cannot read property ‘getProjection’ of undefined.

var SLPLayer = new google.maps.ImageMapType({
getTileUrl: function (coord, zoom) {

                        //var point = overlay.getProjection().fromLatLngToContainerPixel(mEvent.latLng);
                       var proj = this.map.getProjection();
                       alert("666");
                       var zfactor = Math.pow(2, zoom);
                       // get Long Lat coordinates
                       var top = proj.fromPointToLatLng(new google.maps.Point(coord.x * 256 / zfactor, coord.y * 256 / zfactor));
                       var bot = proj.fromPointToLatLng(new google.maps.Point((coord.x + 1) * 256 / zfactor, (coord.y + 1) * 256 / zfactor));

                       //corrections for the slight shift of the SLP (mapserver)
                       var deltaX = 0.0013;
                       var deltaY = 0.00058;

                       //create the Bounding box string
                       var bbox =  (top.lng() + deltaX) + "," +
   	                               (bot.lat() + deltaY) + "," +
   	                               (bot.lng() + deltaX) + "," +
   	                               (top.lat() + deltaY);


                       //base WMS URL
                       var url = "http://tile.gistda.or.th:80/geoserver/gcon/wms?";
                       url += "&REQUEST=GetMap"; //WMS operation
                       url += "&SERVICE=WMS";    //WMS service
                       url += "&VERSION=1.1.1";  //WMS version
                       url += "&LAYERS=hotspot2016_cmi"; //WMS layers
                       url += "&FORMAT=image/gif" ; //WMS format
                       //url += "&BGCOLOR=0xFFFFFF";
                       url += "&TRANSPARENT=TRUE";
                       url += "&SRS=EPSG:4326";     //set WGS84
                       url += "&BBOX=" + bbox;      // set bounding box
                       url += "&WIDTH=512";         //tile size in google
                       url += "&HEIGHT=512";
                       return url;                 // return URL for the tile

                   },
                   tileSize: new google.maps.Size(256, 256),
                   isPng: true
               });

  this.map.overlayMapTypes.push(SLPLayer);