How do I restrict the bounds of a Google Map in Flutter?

Question

I am using google_maps_flutter package and I need to restrict the scrollable area of a map to a specific area. I have both the SW and NE corners, but I can't figure out how to do it.

I have tried the code below, but it's not working.

uniCampusSW and uniCampusNE are both LatLngs.

_userLocation == null // If user location has not been found
          ? Center(
              // Display Progress Indicator
              child: CircularProgressIndicator(
                backgroundColor: UniColors.primaryColour[500],
              ),
            )
          : GoogleMap(
              // Show Campus Map
              onMapCreated: _onMapCreated,
              initialCameraPosition: // required parameter that sets the starting camera position. Camera position describes which part of the world you want the map to point at.
                  CameraPosition(
                      target: _userLocation, zoom: defaultZoom, tilt: 0.0),
              scrollGesturesEnabled: true,
              tiltGesturesEnabled: true,
              trafficEnabled: false,
              compassEnabled: true,
              rotateGesturesEnabled: true,
              myLocationEnabled: true,
              mapType: _currentMapType,
              zoomGesturesEnabled: true,
              cameraTargetBounds: new CameraTargetBounds(
                new LatLngBounds(
                  northeast: UniCampusNE,
                  southwest: UniCampusSW,
                ),
              ),
            ),

This is the error I get

/flutter (12525): The following assertion was thrown building TheMap(dirty, state: _TheMapState#a8840): I/flutter (12525): 'package:google_maps_flutter/src/location.dart': Failed assertion: line 68 pos 16: I/flutter (12525): 'southwest.latitude <= northeast.latitude': is not true.

thanks

Solution 1

I was being stupid with this one.

The Lats in the LatLngs I had in UniCampusNE and SW were the wrong way round. Simple as that. The code I posted is correct.

You have to make sure that the south west latitude is less than (further left) than the north east latitude.

Solution 2

Hello friends!

Solution with Null Safety

Note the error: 'southwest.latitude <= northeast.latitude': is not true.

According to documentation, link below:

https://pub.dev/documentation/google_maps_flutter_platform_interface/2.1.2/google_maps_flutter_platform_interface/LatLngBounds-class.html

It is necessary to check if these values ​​are not static, as southwest.latitude must be less than or equal to northeast.latitude, and northeast.longitude must be less than or equal to southwest.longitude.

LatLng? UniCampusNE;
LatLng? UniCampusSW;

var nLat, nLon, sLat, sLon;

if (UniCampusSW!.latitude <= UniCampusNE!.latitude) {

  sLat = UniCampusSW.latitude;
  nLat = UniCampusNE.latitude;

}else{

  sLat = UniCampusNE.latitude;
  nLat = UniCampusSW.latitude;

}
if (UniCampusSW.longitude <= UniCampusNE.longitude) {

  sLon = UniCampusSW.longitude;
  nLon = UniCampusNE.longitude;

}else{

  sLon = UniCampusNE.longitude;
  nLon = UniCampusSW.longitude;
}

And in cameraTargetBounds: you can use the variables you created:

cameraTargetBounds: CameraTargetBounds(
LatLngBounds(
northeast: LatLng(nLat, nLon),
southwest: LatLng(sLat, sLon),
),

Comments

[Hassan Ansari]

How can I get bounds?

[Andrew Stevenson]

Hi @HassanAnsari - I hope you are well. Simply access Google Maps (maps.google.com/maps) , navigate to the location you want to work with and and right-click at the specific location. You should be presented with a popup menu that includes the co-ordinates. I hope that helps.

[Hassan Ansari]

So means I've to separately take the co or donates?

[Andrew Stevenson]

Basically yes - Get your co-ordinates and them implement the bounding by using the code above. Make sure you pay attention to the accepted answer too.