Center on coordinates

In this guide you will learn how to render an interactive map centered on a desired location, specified by longitude and latitude coordinates, in degrees.

Setup

First, get an API key token, see the Getting Started guide.

Prerequisites

It is required that you complete the Environment Setup - Flutter Examples guide before starting this guide.

Run the example

Start a terminal/command prompt and go to the center_coordinates directory, within the flutter examples directory

Build and run the example:

Build and run

Note - the gem_kit directory containing the Maps SDK for Flutter should be in the plugins directory of the example, e.g. center_coordinates/plugins/gem_kit - see the environment setup guide above.

Download project dependencies:

flutter upgrade

run the following terminal commands in the project directory, where the pubspec.yaml file is located:

flutter clean

flutter pub get

Run the example:

Web browser

flutter run

If such a question appears, select the chrome browser; in the above example, press 2.

Android

First, verify that the ANDROID_SDK_ROOT environment variable is set to the root path of your android SDK.

In android/build.gradle add the maven {} block as shown, within the allprojects {} block, for both debug and release builds, without the line numbers, those are for reference:

allprojects {
    repositories {
        google()
        mavenCentral()
        maven {
           url "${rootDir}/../plugins/gem_kit/android/build"
        }
    }
}

in android/app/build.gradle within the android {} block, in the defaultConfig {} block, the android SDK version minSdkVersion must be set as shown below.

Additionally, for release builds, in android/app/build.gradle, within the android {} block, add the buildTypes {} block as shown:

android {
    defaultConfig {
        applicationId "com.magiclane.gem_kit.examples.center_coordinates"
        minSdkVersion 21
        targetSdkVersion flutter.targetSdkVersion
        versionCode flutterVersionCode.toInteger()
        versionName flutterVersionName
    }
    buildTypes {
        release {
            // TODO: Add your own signing config for the release build.
            // Signing with the debug keys for now, so `flutter run --release` works.
            minifyEnabled false
            shrinkResources false
            signingConfig signingConfigs.debug
        }
    }
}

Then build the apk:

flutter build apk --debug

or

flutter build apk --release

the apk file is located in the build/app/outputs/apk/debug or build/app/outputs/apk/release subdirectory, for debug or release build respectively, within the current project directory, which is center_coordinates in this case.

The apk file name is app-release.apk or app-debug.apk

You can copy the apk to an android device using adb, for example:

adb push app-release.apk sdcard

And then click on the apk in the file browser on the device to install and run it.

iOS

In the ios/Podfile configuration text file, at the top, set the minimum ios platform to 13 like this:

platform :ios, '13.0'

Run pod install in the [ios folder] ./ios/

Then go back to the repository root folder and type flutter build ios to build a Runner.app.

Type flutter run to build and run on an attached device.

You can open the <path/to>/ios/Runner.xcworkspace project in Xcode and execute and debug from there.

How it works

In the center_coordinates project directory, there is a text file named pubspec.yaml which contains project configuration and dependencies. The most important lines from this file are shown here:

name: simulate_route
version: 1.0.0+1

environment:
  sdk: '>=3.0.5 <4.0.0'

dependencies:
  flutter:
    sdk: flutter
  gem_kit:
    path: plugins/gem_kit

  cupertino_icons: ^1.0.2

# The following section is specific to Flutter packages.
flutter:
  uses-material-design: true

The project must have a name and version. The dependencies list the Flutter SDK, and the gem_kit, Maps for Flutter SDK.

The source code is in center_coordinates/lib/main.dart

import 'package:flutter/material.dart';
import 'package:gem_kit/api/gem_coordinates.dart';
import 'package:gem_kit/api/gem_mapviewpreferences.dart';
import 'package:gem_kit/api/gem_sdksettings.dart';
import 'package:gem_kit/gem_kit_map_controller.dart';
import 'package:gem_kit/widget/gem_kit_map.dart';

void main() {
  runApp(const CenterCoordinatesApp());
}

class CenterCoordinatesApp extends StatelessWidget {
  const CenterCoordinatesApp({super.key});

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      debugShowCheckedModeBanner: false,
      title: 'Center Coordinates',
      theme: ThemeData(
        colorScheme: ColorScheme.fromSeed(seedColor: Colors.deepPurple),
        useMaterial3: true,
      ),
      home: CenterCoordinatesPage(),
    );
  }
}

The dart material package is imported, as well as the gem_kit packages for the map controller, which enables user input such as pan and zoom, the map package which draws the map, and the coordinates, settings and mapviewpreferences packages.

The map is in a widget which is the root of the application.

class CenterCoordinatesPage extends StatelessWidget {
  CenterCoordinatesPage({super.key});

  late GemMapController _mapController;

  final token = 'YOUR_API_KEY_TOKEN';

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        backgroundColor: Colors.deepPurple[900],
        title: const Text('Center Coordinates',
            style: TextStyle(color: Colors.white)),
        actions: [
          IconButton(
              onPressed: _onCenterCoordinatesButtonPressed,
              icon: const Icon(
                Icons.adjust,
                color: Colors.white,
              ))
        ],
      ),
      body: GemMap(
        onMapCreated: _onMapCreatedCallback,
      ),
    );
  }

  // The callback for when map is ready to use
  _onMapCreatedCallback(GemMapController controller) async {
    // Save controller for further usage
    _mapController = controller;

    final settings = await SdkSettings.create(controller.mapId);

    settings.setAppAuthorization(token);
  }

  _onCenterCoordinatesButtonPressed() {
    // Predefined coordinates for Rome, Italy
    final targetCoordinates =
        Coordinates(latitude: 41.902782, longitude: 12.496366);

    // Create an animation (optional)
    final animation = GemAnimation(type: EAnimation.AnimationLinear);

    // Use the map controller to center on coordinates
    _mapController.centerOnCoordinates(targetCoordinates, animation: animation);
  }
}

The map is initialized with the map controller and the settings.

The Coordinates() are defined and a GemAnimation() flies the camera to the location specified by the coordinates, using _mapController.centerOnCoordinates()

Setting the API key

The string "YOUR_API_KEY_TOKEN" should be replaced with your actual API key token string.