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.

Conversions

You can convert between different units with the conversions library.

Types of conversions:

• Distance: conversions between meters, kilometers, and miles, etc.
• Area: conversions between square meters, square kilometers, and square miles, etc.
• Angle: conversions between degrees, radians, and gradians, etc.

Here's an example:

import 'package:geodart/conversions.dart';

// Ten miles to kilometers
convertDistance(10, DistanceUnits.miles, DistanceUnits.kilometers); // returns 16.09344

// Ten degrees to radians
convertAngle(10, AngleUnits.degrees, AngleUnits.radians); // returns 0.17453292519943295

// Ten acres to square miles
convertArea(10, AreaUnits.acres, AreaUnits.squareMiles); // returns 0.004046856

There are some static units that are available with the type of DistanceUnit, AngleUnit and AreaUnit. There are some preset units that are available with these types:

DistanceUnit

The following are the available units for length and distance:

• DistanceUnits.meters
• DistanceUnits.kilometers
• DistanceUnits.miles
• DistanceUnits.feet
• DistanceUnits.yards
• DistanceUnits.nauticalMiles
• DistanceUnits.millimeters
• DistanceUnits.centimeters

AngleUnit

The following are the available units for angles:

• AngleUnits.degrees
• AngleUnits.radians
• AngleUnits.gradians
• AngleUnits.turns
• AngleUnits.arcSeconds
• AngleUnits.arcMinutes
• AngleUnits.milliradians

AreaUnit

The following are the available units for area:

• AreaUnits.squareMeters
• AreaUnits.squareKilometers
• AreaUnits.squareMiles
• AreaUnits.acres
• AreaUnits.hectares
• AreaUnits.squareFeet
• AreaUnits.squareYards
• AreaUnits.squareInches

Geometries

To use this library, you'll need to get familiar with the feature types. All other actions taken depend on using the proper feature types. These feature types are very similar to the ones used in the geojson specification.

I'll admit, the feature coordinates are a bit of a mess. I'm working on a better way to handle this.

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.

Bounding boxes (generally used as the minimum surrounding area of a Feature) are stored using BoundingBox objects, which has a variety of convenience methods for working with bounding boxes.

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.
• FeatureCollection.fromWKT(String wkt) - Creates a FeatureCollection from a Well-Known Text string.

Methods

• toJson() - Returns a JSON object representing the FeatureCollection. Automatically converts features to GeoJSON.
• nearestPointTo(Point point) - Returns the nearest Point in the FeatureCollection to the given point.
• explode() - Returns a FeatureCollection of Point objects, one for each coordinate in each geometry in the FeatureCollection.
• isCollectionOf(String type) - Returns true if the FeatureCollection contains only features of the given type.

Properties

• features - A List of Feature objects.
• type - The type of the FeatureCollection. Always "FeatureCollection".
• bbox - The [BoundingBox] of the FeatureCollection.
• envelope - A Polygon representing the envelope of the FeatureCollection.
• center - The Point representing the center of the FeatureCollection.
• isEmpty - Whether or not the FeatureCollection is empty.
• convexHull - The smallest Polygon representing the convex hull of the FeatureCollection.

Feature

A Feature is an abstract class that can be extended to create new feature types.

Because this class is abstract, you cannot instantiate it directly.

Methods

• explode() - Returns a [List] of Point objects, one for each coordinate in the Feature.
• toJson() - Returns a JSON object representing the Feature. Automatically converts features to GeoJSON.
• toWKT() - Returns a WKT string representing the Feature.

Properties

• type - The type of the Feature.
• bbox - The [BoundingBox] of the Feature.
• center - The Point representing the center of the Feature.

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.
• Point.random() - Creates a Point at a random location within the [-180, 180] x [-90, 90] bounding box.

Methods

• explode() - Returns a List of itself.
• toJson() - Returns a Map of GeoJSON data.
• toWKT() - Returns a Well-Known Text string representing the Point.
• isContainedIn(Feature feature) - Returns true if the Point is contained within the given Polygon or MultiPolygon.
• buffer(double distance, {DistanceUnit unit = DistanceUnits.meters, int steps = 40})- Returns a Polygon that is the buffer of the Point of the given distance.

Properties

• coordinates - The Coordinate of the Point.
• type - The type of the Point. Always "Point".
• properties - A Map of properties.
• bbox - a BoundingBox of the Point.
• center - The Point representing the center of the Point, which is same as the point itself.
• lat - The latitude of the Point.
• lng - The longitude of the Point.

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? multi, Point? point}) - Merges the MultiPoint with another MultiPoint or Point.
• 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.
• bbox - a BoundingBox of the MultiPoint.
• center - The Point representing the center of the MultiPoint.

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.
• LineString.random({int length}) - Creates a LineString at a random location within the [-180, 180] x [-90, 90] bounding box with a given number of points (defaults to 2).

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.
• 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.
• pointAt(double percentage) - Returns a Point at the specified percentage along the line.
• reverse() - Returns a LineString that is the reverse of the original LineString.
• isParallelTo(LineString line) - Returns true if the LineString is parallel to the specified LineString, or all segments are parallel in order or reverse order.
• intersections(LineString line) - Returns a FeatureCollection of Point objects where the LineString intersects the specified LineString.
• contains(Point point) - Returns true if the LineString contains the specified Point.

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.
• bbox - a BoundingBox of the LineString.
• segments - A List of LineString objects that make up the LineString.
• midpoint - Returns a Point at the midpoint of the LineString.
• center - The Point representing the center of the LineString's coordinates.
• bearing - The bearing of the LineString. If more than 2 coordinates are provided, 0.0 is returned.
• slope - The slope of the LineString. If more than 2 coordinates are provided, it uses the first and last coordinates.

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.
• MultiLineString.random({int count, int length}) - Creates a MultiLineString at a random location within the [-180, 180] x [-90, 90] bounding box, with a line count (count) and a number of points in each line (length).

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.
• bbox - a BoundingBox of the MultiLineString.

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.
• contains(Point point) - Returns true if the Polygon contains the specified Point.
• intersects(Polygon poly) - Returns true if the Polygon intersects the specified 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.
• bbox - a BoundingBox of the Polygon.

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? multi, Polygon? poly}) - Merges the MultiPolygon with another MultiPolygon and/or Polygon.
• flatten() - Returns a List of Polygon objects.
• toMultiLineString() - Returns a MultiLineString that is the same geometry as the MultiPolygon.
• contains(Point point) - Returns true if the MultiPolygon contains the Point.
• intersects(poly: Polygon, multi: MultiPolygon) - Returns true if this MultiPolygon intersects the passed Polygon or 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.
• bbox - a BoundingBox of the MultiPolygon.
• hasSelfIntersections - Returns true if any of the contained LinearRing geometries intersect.

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.
• Coordinate.random() - Creates a Coordinate at a random location.

Methods

• toJson() - Returns a Map of GeoJSON data.
• toWKT() - Returns a Well-Known Text string representing the Coordinate.
• toENU(Coordinate origin) - Returns the difference in 3 dimensional space (as List<double>[xEast, yNorth, zUp]) between the Coordinate and the passed Coordinate origin.
• 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".

LinearRing

A [LinearRing](#Linear Ring) is a closed LineString that is closed because the first and last coordinate are the same.

Constructors

• LinearRing.random() - Creates a [LinearRing](#Linear Ring) with 3 random Coordinates.

Methods

• toLineString() - Returns a LineString that is the same geometry as the [LinearRing](#Linear Ring).
• reverse() - Returns a [LinearRing](#Linear Ring) that is the same geometry as the [LinearRing](#Linear Ring) but in reverse order.
• explode() - Returns a FeatureCollection of Point objects.

Properties

• coordinates - A List of Coordinate objects.
• type - The type of the [LinearRing](#Linear Ring). Always "LinearRing".
• area - The are (in square meters) of the [LinearRing](#Linear Ring).
• centroid - The Coordinate that is the centroid of the [LinearRing](#Linear Ring).
• bbox - a BoundingBox of the [LinearRing](#Linear Ring).

BoundingBox

A BoundingBox is a rectangular area of the two-dimensional Cartesian coordinate system. Generally, it is used to represent the smallest possible bounds of a Feature in lat/long space.

Constructors

• BoundingBox.fromCoordinates(List<Coordinate> points) - Creates a BoundingBox from a List of Coordinate objects.
• BoundingBox.empty() - Creates an empty BoundingBox.
• BoundingBox.fromPoints(List<Point> points) - Creates a BoundingBox from a List of Point objects.

Methods

• toList() - Returns a List of GeoJSON data.
• toPolygon() - Returns a Polygon that is the same geometry as the BoundingBox.

Properties

• minLong - The minimum longitude of the BoundingBox.
• minLat - The minimum latitude of the BoundingBox.
• maxLong - The maximum longitude of the BoundingBox.
• maxLat - The maximum latitude of the BoundingBox.
• type - The type of the BoundingBox. Always "BoundingBox".
• center - The Coordinate center of the BoundingBox.
• square - The BoundingBox, but made square.

Usage

Measure the distance between two points.

import 'package:geodart/measurements.dart';
import 'package:geodart/geometries.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/geometries.dart';

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

Measure the area of a polygon.

import 'package:geodart/geometries.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/geometries.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.