如何在网络上的Google Maps API中从基于GPS的位置导航到所需位置？

Question

我正在开展一个项目，我想在其中显示从用户当前位置到google maps API中固定位置的导航路径。到目前为止，我能够从A点导航到B点（两者都是静态的）＆amp;还会向用户显示当前位置。但我根据用户当前位置难以修复A点。我希望你们能帮帮我 这是我的代码：

＆＃13;

＆＃13;

      function initMap() {
        var directionsDisplay = new google.maps.DirectionsRenderer;
        var directionsService = new google.maps.DirectionsService;
        var map = new google.maps.Map(document.getElementById('map'), {
          zoom: 14,
          center: {lat: 19.0730, lng: 72.8997}
        });
        directionsDisplay.setMap(map);

        //<----Geolocation---->
        var infoWindow = new google.maps.InfoWindow({map: map});
        // Try HTML5 geolocation.
        if (navigator.geolocation) {
          navigator.geolocation.getCurrentPosition(function(position) {
            var pos = {
              lat: position.coords.latitude,
              lng: position.coords.longitude
            };
            infoWindow.setPosition(pos);
            infoWindow.setContent('You are here.');
            map.setCenter(pos);
          }, function() {
            handleLocationError(true, infoWindow, map.getCenter());
          });
        } else {
          // Browser doesn't support Geolocation
          handleLocationError(false, infoWindow, map.getCenter());
        }
        function handleLocationError(browserHasGeolocation, infoWindow, pos) {
          infoWindow.setPosition(pos);
          infoWindow.setContent(browserHasGeolocation ?
                                'Error: The Geolocation service failed.' :
                                'Error: Your browser doesn\'t support geolocation.');
        }
        //<-----Geolocation Part Finished----->
        calculateAndDisplayRoute(directionsService, directionsDisplay);
        document.getElementById('mode').addEventListener('change', function() {
          calculateAndDisplayRoute(directionsService, directionsDisplay);
        });
      }

      function calculateAndDisplayRoute(directionsService, directionsDisplay,pos) {
        var selectedMode = document.getElementById('mode').value;
        directionsService.route({
          origin: {lat: 19.0730, lng: 72.8997},  // Haight.
          destination: {lat: 19.0730, lng: 72.8794},  // Ocean Beach.
          // Note that Javascript allows us to access the constant
          // using square brackets and a string value as its
          // "property."
          travelMode: google.maps.TravelMode[selectedMode]
        }, function(response, status) {
          if (status == 'OK') {
            directionsDisplay.setDirections(response);
          } else {
            window.alert('Directions request failed due to ' + status);
          }
        });
      }

＆＃13;

      html, body {
        height: 100%;
        margin: 0;
        padding: 0;
      }
      #map {
        height: 100%;
      }
      #floating-panel {
        position: absolute;
        top: 10px;
        left: 25%;
        z-index: 5;
        background-color: #fff;
        padding: 5px;
        border: 1px solid #999;
        text-align: center;
        font-family: 'Roboto','sans-serif';
        line-height: 30px;
        padding-left: 10px;
      }

＆＃13;

    <select id="mode">
      <option value="DRIVING">Driving</option>
      <option value="WALKING">Walking</option>
      <option value="BICYCLING">Bicycling</option>
      <option value="TRANSIT">Transit</option>
    </select>
    </div>
    <div id="map"></div>
    <script async defer
    src="https://maps.googleapis.com/maps/api/js?key=AIzaSyAYJY_vFKIl-VEdyoEd3hZI8Wv1JdNzTmI&callback=initMap">
    </script>

＆＃13;

＆＃13;

＆＃13;