synw/geojson

Geojson

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Utilities to work with geojson data in Dart. Features:

Parser with a reactive api: streams are available to retrieve the geojson features as soon as they are parsed
Search: search for properties
Geofencing: geofence points in a polygon or from a distance

Note: the data is parsed in an isolate to avoid slowing down the main thread

Simple functions

featuresFromGeoJson: get a FeaturesCollection from geojson string data. Parameters:

data: a string with the geojson data, required
nameProperty: the property used for the geoserie name, automaticaly set if null
verbose: print the parsed data if true

featuresFromGeoJsonFile: get a FeaturesCollection from a geojson file. Parameters:

file: the file to load, required
nameProperty: the property used for the geoserie name, automaticaly set if null
verbose: print the parsed data if true

These functions are suitable for small data. Example:

final features = await featuresFromGeoJson(data);

Web support

featuresFromGeoJsonMainThread: as the web do not support isolates use this function to parse in the main thread. Parameters:

data: a string with the geojson data, required
nameProperty: the property used for the geoserie name, automaticaly set if null
verbose: print the parsed data if true

Reactive api

Parse and listen

Typed streams are available to retrieve the features as soon as they are parsed. This is useful when the data is big.

processedFeatures: the parsed features: all the geometries
processedPoints: the parsed points
processedMultipoints: the parsed multipoints
processedLines: the parsed lines
processedMultilines: the parsed multilines
processedPolygons: the parsed polygons
processedMultipolygons: the parsed multipolygons
endSignal: parsing is finished indicator

Example: add assets on a Flutter map:

  import 'package:flutter/services.dart' show rootBundle;
  import 'package:geojson/geojson.dart';
  import 'package:flutter_map/flutter_map.dart';

  /// Data for the Flutter map polylines layer
  final lines = <Polyline>[];

  Future<void> parseAndDrawAssetsOnMap() async {
    final geo = GeoJson();
    geo.processedLines.listen((GeoJsonLine line) {
      /// when a line is parsed add it to the map right away
      setState(() => lines.add(Polyline(
          strokeWidth: 2.0, color: Colors.blue, points: line.geoSerie.toLatLng())));
    });
    geo.endSignal.listen((_) => geo.dispose());
    final data = await rootBundle
        .loadString('assets/railroads_of_north_america.geojson');
    await geo.parse(data, verbose: true);
  }

Data properties

After the data is parsed the GeoJson instance has properties to access the data:

List<GeoJsonFeature> features;
List<GeoJsonPoint> points;
List<GeoJsonMultiPoint> multipoints;
List<GeoJsonLine> lines;
List<GeoJsonMultiLine> multilines;
List<GeoJsonPolygon> polygons;
List<GeoJsonMultiPolygon> multipolygons;

Example:

final List<GeoJsonLine> lines = geo.lines;

Search

Search in a geojson file:

final geo = GeoJson();
await geo.searchInFile("countries.geojson",
    query: GeoJsonQuery(
        geometryType: GeoJsonFeatureType.multipolygon,
        matchCase: false,
        property: "name",
        value: "Zimbabwe"),
    verbose: true);
List<GeoJsonMultiPolygon> result = geo.multipolygons;

A search method is also available, taking string data in parameter instead of a file path. The streams are available to retrieve the data as soon as it is found

Geofencing

Geofence points within a distance of a given point:

final geo = GeoJson();
/// `point` is the [GeoJsonPoint] to search from
/// `points` is the list of [GeoJsonPoint] to search in
/// `distance` is the distance to search in meters
await geo.geofenceDistance(
      point: point, points: points, distance: distance);
 List<GeoPoint> foundPoints = geo.points;

Geofence points in a polygon:

final geo = GeoJson();
/// `polygon` is the [GeoJsonPolygon] to check
/// `points` is the list of [GeoJsonPoint] to search in
await geo.geofencePolygon(polygon: polygon, points: points);
 List<GeoPoint> foundPoints = geo.points;

Note: the processedPoints stream is available to retrieve geofenced points as soon as they are found

Maps

To draw geojson data on a map check the Map controller package

Supported geojson features

All the data structures use GeoPoint and GeoSerie from the GeoPoint package to store the geometry data. Data structures used:

GeoJsonFeatureCollection:

String name
List<GeoJsonFeature> collection

GeoJsonFeature:

GeoJsonFeatureType type: types
Map<String, dynamic> properties: the json properties of the feature
dynamic geometry: the geometry data, depends on the feature type, see below