Geodart #

A geospatial library for Dart. Designed primarily around vector features, this library provides a simple interface for working with geographic data.

It's based heavily on the geojson specification, but has been extended to add functionality directly to the feature types.

Getting started #

Add it to your dependencies:

dependencies:
  geodart: '^0.0.1'

OR run this command to install it:

flutter pub add geodart

Then import it:

import 'package:geodart/features.dart';
import 'package:geodart/measure.dart';

Features #

The following features are included in this library:

• FeatureCollection
• LineString
• MultiLineString
• MultiPoint
• MultiPolygon
• Point
• Polygon

The package also provides a Feature class, which is a abstract class that can be extended to create new feature types.

Positions are stored using Coordinate objects, which has a variety of convenience methods for working with coordinates.

Feature Collection #

A FeatureCollection is a collection of Feature objects.

It functions very similarly to a List of Feature objects, but might extended to include additional properties in the future.

Constructors

• FeatureCollection.fromJson(Map<String, dynamic> json) - Creates a FeatureCollection from a JSON object. Automatically converts features from GeoJSON to their respective types.

Methods

• toJson() - Returns a JSON object representing the FeatureCollection. Automatically converts features to GeoJSON.

Properties

• features - A List of Feature objects.

Point #

A Point is a single position. It is represented by a Coordinate object.

Constructors

• Point.fromJson(Map<String, dynamic> json) - Creates a Point from a Map of GeoJSON data.
• Point.fromLngLat(num lng, num lat) - Creates a Point from a num longitude and latitude.
• Point.fromWKT(String wkt) - Creates a Point from a Well-Known Text string.

Methods

• explode() - Returns a List of itself.
• toJson() - Returns a Map of GeoJSON data.
• toWKT() - Returns a Well-Known Text string representing the Point.

Properties

• coordinates - The Coordinate of the Point.
• type - The type of the Point. Always "Point".
• properties - A Map of properties.

Multi Point #

A MultiPoint is a collection of Coordinate objects, represented by individual and non-connected points.

Constructors

• MultiPoint.fromJson(Map<String, dynamic> json) - Creates a MultiPoint from a Map of GeoJSON data.
• MultiPoint.fromWKT(String wkt) - Creates a MultiPoint from a Well-Known Text string.

Methods

• explode() - Returns a List of Point objects.
• toJson() - Returns a Map of GeoJSON data.
• toWKT() - Returns a Well-Known Text string representing the MultiPoint.
• union(MultiPoint other) - Merges the MultiPoint with another MultiPoint.
• flatten() - Returns a List of Point objects.

Properties

• coordinates - A List of Coordinate objects.
• type - The type of the MultiPoint. Always "MultiPoint".
• properties - A Map of properties.

Line String #

A LineString is a collection of Coordinate objects that form a line.

Constructors

• LineString.fromJson(Map<String, dynamic> json) - Creates a LineString from a Map of GeoJSON data.
• LineString.fromWkt(String wkt) - Creates a LineString from a Well-Known Text string.

Methods

• along(distance) - Returns a Point at the specified distance along the line.
• explode() - Returns a List of Point objects that make up the LineString.
• midpoint() - Returns a Point at the midpoint of the LineString.
• toJson() - Returns a GeoJSON Map of the LineString.
• toPolygon() - Returns a Polygon that is the same as the LineString. LineString must be closed, or an exception will be thrown.
• toWKT() - Returns a String of the LineString in WKT format.

Properties

• coordinates - A List of Coordinate objects that make up the LineString.
• type - The type of the LineString. Always "LineString".
• isClosedRing - A boolean indicating whether the LineString is a closed ring.
• length - The length (in meters) of the LineString.
• properties - A Map of properties.

Multi Line String #

A MultiLineString is a collection of Coordinate objects that form multiple separate LineStrings with one set of shared properties.

Constructor

• MultiLineString.fromJson(Map<String, dynamic> json) - Creates a MultiLineString from a Map of GeoJSON data.
• MultiLineString.fromWkt(String wkt) - Creates a MultiLineString from a Well-Known Text string.

Methods

• explode() - Returns a List of LineString objects.
• toJson() - Returns a Map of GeoJSON data.
• toWKT() - Returns a Well-Known Text string representing the MultiLineString.
• union(MultiLineString other) - Merges the MultiLineString with another MultiLineString.
• flatten() - Returns a List of LineString objects.

Properties

• coordinates - A nested List of Coordinate objects.
• type - The type of the MultiLineString. Always "MultiLineString".
• properties - A Map of properties.

Polygon #

A Polygon is a collection of [LinearRing](#Linear Ring) objects that form a closed ring. The first LinearRing in the list is the outer ring, and any subsequent LinearRings are holes. Holes should be contained within the outer ring - if they are not, some algorithms may not work correctly. A Polygon should also not intersect itself - again, some algorithms may not work correctly if this is not the case.

Constructors

• Polygon.fromJson(Map<String, dynamic> json) - Creates a Polygon from a Map of GeoJSON data.
• Polygon.fromWkt(String wkt) - Creates a Polygon from a Well-Known Text string.

Methods

• explode() - Returns a List of Point objects.
• toJson() - Returns a Map of GeoJSON data.
• toWKT() - Returns a Well-Known Text string representing the Polygon.
• toLineString() - Returns a LineString that is the same geometry as the Polygon.

Properties

• coordinates - A List of [LinearRing](#Linear Ring) objects.
• type - The type of the Polygon. Always "Polygon".
• area - The are (in square meters) of the Polygon.
• properties - A Map of properties.

Multi Polygon #

A MultiPolygon is a collection of Polygon geometries forming one MultiPolygon with shared properties.

Constructors

• MultiPolygon.fromJson(Map<String, dynamic> json) - Creates a MultiPolygon from a Map of GeoJSON data.
• MultiPolygon.fromWkt(String wkt) - Creates a MultiPolygon from a Well-Known Text string.

Methods

• explode() - Returns a List of Point objects.
• toJson() - Returns a Map of GeoJSON data.
• toWKT() - Returns a Well-Known Text string representing the MultiPolygon.
• union(MultiPolygon other) - Merges the MultiPolygon with another MultiPolygon.
• flatten() - Returns a List of Polygon objects.
• toMultiLineString() - Returns a MultiLineString that is the same geometry as the MultiPolygon.

Properties

• coordinates - A List of Polygon objects.
• type - The type of the MultiPolygon. Always "MultiPolygon".
• properties - A Map of properties.
• area - The are (in square meters) of the MultiPolygon.

Coordinate #

A Coordinate is a point in a two-dimensional Cartesian coordinate system.

Constructors

• Coordinate.fromJson(Map<String, dynamic> json) - Creates a Coordinate from a Map of GeoJSON data.
• Coordinate.fromWkt(String wkt) - Creates a Coordinate from a Well-Known Text string.

Methods

• toJson() - Returns a Map of GeoJSON data.
• toWKT() - Returns a Well-Known Text string representing the Coordinate.
• distanceTo(Coordinate other) - Returns the distance (in meters) between the Coordinate and another Coordinate.
• bearingTo(Coordinate other) - Returns the bearing (in degrees) between the Coordinate and another Coordinate.
• destination(num distance, num bearing) - Returns a Coordinate that is the same geometry as the Coordinate but moved a given distance and bearing.
• interpolate(Coordinate other, num fraction) - Returns a Coordinate that is the same geometry as the Coordinate but moved a given fraction of the distance and bearing to another Coordinate.

Properties

• latitude - The latitude of the Coordinate.
• longitude - The longitude of the Coordinate.
• type - The type of the Coordinate. Always "Coordinate".

Usage #

Measure the distance between two points.

import 'package:geodart/measure.dart';
import 'package:geodart/features.dart';

double distanceBetween = distance(
    Point.fromLngLat(1.0, 1.0),
    Point.fromLngLat(2.0, 2.0),
);

Under the hood, this uses the coordinate distanceTo() function, and could be very easily replaced with a different algorithm. I prefer the distanceTo() function because it is more explicit and easier to read.

import 'package:geodart/features.dart';

double distanceBetween = Coordinate(1.0, 1.0).distanceTo(Coordinate(2.0, 2.0));

Measure the area of a polygon.

import 'package:geodart/features.dart';

Polygon polygon = Polygon.fromJson(
    {
      'type': 'Polygon',
      'coordinates': [
        [
          [1.0, 1.0],
          [2.0, 1.0],
          [2.0, 2.0],
          [1.0, 1.0],
        ],
      ],
    }
);
print(polygon.area);

Measure the length of a LineString.

LineString length is calculated on the fly.

import 'package:geodart/features.dart';

LineString lineString = LineString.fromJson(
    {
      'type': 'LineString',
      'coordinates': [
        [1.0, 1.0],
        [2.0, 2.0],
      ],
    }
);
print(lineString.length);

Additional information #

License #

This library is free software under the terms of the MIT license. See the LICENSE file for more details.

Contributing #

If you have any questions or comments, please open an issue on the Github repository.

If you want to make a pull request, please open a pull request on the Github repository. Please make sure to include a test suite. I make no promises that I will accept pull requests, but I will try my best to keep the code up to date.