Cannot read property 'latitude' undefined

Ionic Framework ionic-v3
1

Hi, Please help me

my ts code

import { Geolocation } from '@ionic-native/geolocation';

 private lat: any;
 private lng: any;
 constructor( private geolocation: Geolocation ) {

 let watch = this.geolocation.watchPosition();
watch.subscribe((data) => {
  
 // data can be a set of coordinates, or an error (if an error occurred).
 this.lat= data.coords.latitude;
 this.lng= data.coords.longitude;
},(error)=>{console.log(error);});

  }