将地图设置为angular6/openlayers中的变量

我使用Angular6和openlayers 5.1.3。我做的 npm install ol --save 成功,然后在我的角度我做到了

import OlMap from 'ol/map';
import OlXYZ from 'ol/source/xyz';
import OlTileLayer from 'ol/layer/tile';
import OlView from 'ol/View';
import * as OlProj from 'ol/proj';
import 'ol/ol.css';

export class myComponent {

 olmap: OlMap;
 source: OlXYZ;
 layer: OlTileLayer;
 view: OlView;
  //other, non-ol stuff
   loading: boolean = false;
   myname: String;

  ngOnInit() {

    this.source = new OlXYZ({
      url:'http://tile.stamen.com/terrain/{z}/{x}/{y}.jpg'
    });

    this.layer = new OlTileLayer({
      source: this.source
    });

    this.view = new OlView({
      center: OlProj.fromLonLat([6.661594, 50.433237]),
      zoom: 3,
    });

    const olmap = new OlMap({
      target: 'map',
      layers: [this.layer],
      view: this.view
    });


    navigator.geolocation.getCurrentPosition(function(pos) {
      const coords = OlProj.fromLonLat([pos.coords.longitude, pos.coords.latitude]);
      olmap.getView().animate({center: coords, zoom: 10});
    });

  }//ngOnInit

这很好,但问题是如果我

    this.olmap = new OlMap({
      target: 'map',
      layers: [this.layer],
      view: this.view
    });

然后

    navigator.geolocation.getCurrentPosition(function(pos) {
      const coords = OlProj.fromLonLat([pos.coords.longitude, pos.coords.latitude]);
      this.olmap.getView().animate({center: coords, zoom: 10});
    });

我无法读取引用此的空属性“olmap” this.olmap.getView().animate({center: coords, zoom: 10});

为什么我不能提到 olmap 与 this.olmap ,因为我正在定义它和Typescript中的其他变量?我再也没有这个问题了,我总是获取 this.x

为什么我会犯这个错误?这是什么意思?

谢谢