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

GeoJsonPoint:

• String name
• GeoPoint geoPoint: the geometry data

GeoJsonMultiPoint:

• String name
• GeoSerie geoSerie: the geometry data: this will produce a geoSerie of type GeoSerieType.group

GeoJsonLine:

• String name
• GeoSerie geoSerie: the geometry data: this will produce a geoSerie of type GeoSerieType.line

GeoJsonMultiLine:

• String name
• List<GeoJsonLine> lines

GeoJsonPolygon:

• String name
• List<GeoSerie> geoSeries: the geometry data: this will produce a list of geoSerie of type GeoSerieType.polygon*

GeoJsonMultiPolygon:

• String name
• List<GeoJsonPolygon> polygons

GeoJsonGeometryCollection:

• String name
• List<GeoJsonFeature> geometries

Note: none of the parameters is final for all of these data structures