GeoJson is becoming defacto standard for retrieving spatial data like points, lines and polygons. GeoJson Format specification is defined in RFC7964 - see https://www.rfc-editor.org/rfc/rfc7946 This package parses GeoJson data and creates spatial objects like Markers, Polylines and Polygons, which are defined in flutter_map package.

The creation of these objects is done by default callback functions. However, one can and probably should write his own callback functions which are implementing the necessary customization of creating spatial objects by specifying the color, stroke, label text and other parameters.

Features

The GeoJson parser creates three (four) lists of spatial objects - separate lists of Markers, Polylines and Polygons (and Circles) which are input data for creating layers in flutter_map. The parser supports parsing the following geometries:

• Point - transformed into Markers
• Circle - transformed into CircleMarkers - not part of the spec, but handy to have. Specify radius in the properties.
• Multipoint - transformed into multiple Markers with same ID property
• LineString - tranformed in Polyline
• MultiLineString - transformed into multiple Polylines
• Polygon - transformed into Polygon
• MultiPolygon - transformed into multiple Polygons with same ID property

Getting started

Add the package in pubspec.yaml file:

flutter_map_geojson ^1.0.8

Import it in the code:

import 'package:flutter_map_geojson/flutter_map_geojson.dart';

Usage

 // initiate parser 
 GeoJsonParser myGeoJson = GeoJsonParser();
 
 // parse GeoJson data - GeoJson is stored as [String]
 myGeoJson.parseGeoJsonAsString(testGeoJson);

 // after parsing the results are stored in 
 // myGeoJson.markers -> List<Marker>
 // myGeoJson.polylines -> List<Polyline>
 // myGeoJson.ploygons -> List<Polygon>

 // now create flutter_map layers

 FlutterMap(
          mapController: MapController(),
          options: MapOptions(
            center: LatLng(45.993807, 14.483972),
            zoom: 14,
          ),
          children: [
            TileLayer(
                urlTemplate:
                    "https://{s}.tile.openstreetmap.org/{z}/{x}/{y}.png",
                subdomains: const ['a', 'b', 'c']),
            PolygonLayer(polygons: myGeoJson.polygons),
            PolylineLayer(polylines: myGeoJson.polylines),
            MarkerLayer(markers: myGeoJson.markers)
          ],
        ));

The default Marker, Polyline CircleMarkers and Polygon creation callback functions can be replaced with user-defined highly customized functions. A good starting point are default callback functions which can be custimized to the needs of the project. The default callback functions have only basic functionality to display the spatial objects on the map. The default callback functions support changing the colors, stroke and fill color and marker icon. All these can be defined in default constructor or via setters. One can also apply a filtering function which returns only spatial features that have certian propertis. The filtering function returns a boolean value. For more details see the example program.

For creating tappable polylines one can use package flutter_map_tappable_polyline.