ionic 2 use zone Ngzone()

Question

hi i try to use Zone on my ionic2 app :

i create a provider who take location of my device

import { Injectable,NgZone  } from '@angular/core';
import { Geolocation, Geoposition } from '@ionic-native/geolocation';
import 'rxjs/add/operator/filter';



@Injectable()
export class LocationTracker {

  public watch: any;    
  public lat: number = 0;
  public lng: number = 0;

  constructor(public zone: NgZone,
              public geolocation:Geolocation) {
              console.log('Hello LocationTracker Provider');
  }

  startTracking() {
  console.log("provider startTracking")  


        let options = {
          frequency: 3000, 
          enableHighAccuracy: true
        };

       this.watch = this.geolocation.watchPosition(options).filter((p: any) => p.code === undefined).subscribe((position: Geoposition) => {

                     // Run update inside of Angular's zone
                      this.zone.run(() => {
                      this.lat = position.coords.latitude;
                      this.lng = position.coords.longitude;

               });

      });
  }



}

In the home view html, i have access to the zone with {{locationTracker.lat}}, but in my home component (who call this provider) i don't know how i can't have access to the zone

i try this

 this.locationTracker.lat

but it's undefined

can't you help my ?