要获取屏幕上特定位置的纬度和经度（LatLng），可以使用GoogleMapController.getLatLng方法。

LatLng _getLatLng(Offset offset) async {
    return await _mapController.getLatLng(offset);
 }

GoogleMap(
          initialCameraPosition: CameraPosition(target: _initialCameraPosition),
          mapType: MapType.normal,
          onMapCreated: (GoogleMapController _cntlr) {
            _onMapCreated(_cntlr);
          },
          myLocationEnabled: true,
          onTap: (LatLng latLng) {
            if (_controller != null) {
              _controller!.animateCamera(
                CameraUpdate.newCameraPosition(CameraPosition(target: LatLng(latLng.latitude, latLng.longitude), zoom: 15)),
              );
            }
            _handleTap(latLng);
          },
          markers: _markers,
          gestureRecognizers: Set()
            ..add(
              Factory<PanGestureRecognizer>(
                () => PanGestureRecognizer(),
              ),
            )
            ..add(Factory<ScaleGestureRecognizer>(
                () => ScaleGestureRecognizer()))
            ..add(
              Factory<TapGestureRecognizer>(
                () => TapGestureRecognizer(),
              ),
            )
            ..add(
              Factory<VerticalDragGestureRecognizer>(
                () => VerticalDragGestureRecognizer(),
              ),
            ),
        ),

   HandleTap method will give you lat long.

_handleTap(LatLng point) {
   latLng = "${num.parse(point.latitude.toStringAsFixed(6))},${num.parse(point.longitude.toStringAsFixed(6))}";
   print("LAT ::: LNG ${latLng}");
 }