geocore 0.10.0-dev.0

Geospatial data structures (points, geometry, features, meta) and parsers (GeoJSON, WKT) for Dart.

Geospatial data structures (points, geometry, features, meta) and parsers (GeoJSON, WKT) for Dart.

Features

Key features:

• 🚀 geospatial data structures (geometry, features and metadata)
• 🌐 geographic coordinates (longitude-latitude)
• 🗺️ projected coordinates (cartesian XYZ)
• 🔷 geometry primitives (bounds or bbox, point, line string, polygon)
• 🧩 multi geometries (multi point, multi line string, multi polygon, geometry collections)
• ⭐ feature objects (with id, properties and geometry) and feature collections
• 🌎 GeoJSON data parser
• 🪧 WKT (Well-known text representation of geometry) data parser

Package

The package requires at least Dart SDK 2.17, and it supports all Dart and Flutter platforms.

To use, add the dependency in your pubspec.yaml:

dependencies:
  geocore: ^0.10.0-dev.0

And then import it:

import `package:geocore/geocore.dart`

The package contains also following mini-libraries, that can be used to import only a certain subset instead of the whole geocore library:

Library	Exports also	Description
base		Base classes for geospatial geometry objects.
coordinates	base	Projected and geographic coordinates.
data	base, coordinates	Geospatial features and geometries (linestring, polygon, multi geometries).

All the mini-libraries have dependencies to the equatable and geobase packages.

Please note that some of the most often used classes from geobase are also re-exported by geocore.

Introduction

Geometry primitives supported by this library package (with samples adapted from the samples of the Wikipedia page about WKT):

Geometry	Shape	Samples to create instances
Point		Point2(x: 30.0, y: 10.0) Point2.from([30.0, 10.0]) Point2.parse('30 10')
LineString		LineString.parse('30 10, 10 30, 40 40', Point2.coordinates)
Polygon		Polygon.parse('(30 10, 40 40, 20 40, 10 20, 30 10)', Point2.coordinates)
Polygon (with a hole)		Polygon.parse('(35 10, 45 45, 15 40, 10 20, 35 10), (20 30, 35 35, 30 20, 20 30)', Point2.coordinates)

Also multipart geometry classes are provided:

Geometry	Shape	Samples to create instances
MultiPoint		MultiPoint.parse('10 40, 40 30, 20 20, 30 10', Point2.coordinates)
MultiLineString		MultiLineString.parse('(10 10, 20 20, 10 40), (40 40, 30 30, 40 20, 30 10)', Point2.coordinates)
MultiPolygon		MultiPolygon.parse('((30 20, 45 40, 10 40, 30 20)), ((15 5, 40 10, 10 20, 5 10, 15 5))', Point2.coordinates)
MultiPolygon (with a hole)		MultiPolygon.parse('((40 40, 20 45, 45 30, 40 40)), ((20 35, 10 30, 10 10, 30 5, 45 20, 20 35),(30 20, 20 15, 20 25, 30 20))', Point2.coordinates)
GeometryCollection		GeometryCollection([Point2i(x: 40, y: 10), LineString.make([[10, 10], [20, 20], [10, 40]], Point2i.coordinates), Polygon.parse('(40 40, 20 45, 45 30, 40 40)', Point2i.coordinates)])

Geometry types introduced above are based on the Simple Feature Access - Part 1: Common Architecture standard by The Open Geospatial Consortium (OGC).

Spatial bounds:

  Bounds.of(min: Point2(x: 10.1, y: 10.1), max: Point2(x: 20.2, y: 20.2));
  Bounds.of(min: Point3i(x: 10, y: 10, z: 3), max: Point3i(x: 20, y: 20, z: 5));
  GeoBounds.bboxLonLat(-20.3, 50.2, 20.5, 60.9);

A feature (a geospatial entity) contains an id, a geometry and properties:

  Feature(
    id: 'ROG',
    geometry: GeoPoint3(lon: -0.0014, lat: 51.4778, elev: 45.0),
    properties: {
      'place': 'Greenwich',
      'city': 'London',
    },
  );

Parsing GeoJSON data:

  final geoJsonParser = GeoJSON().parserGeographic(GeoPoint3.coordinates);
  geoJsonParser.feature(
    '''
    {
      "type": "Feature",
      "id": "ROG",
      "geometry": {
        "type": "Point",
        "coordinates": [-0.0014, 51.4778, 45.0]  
      },
      "properties": {
        "place": "Greenwich",
        "city": "London"
      }
    }  
  ''',
  );

Parsing WKT (Well-known text representation of geometry) data:

  // Parse using specific point factories for coordinates with and without M
  final wktParser = WKT().parser(Point2.coordinates, Point2m.coordinates);
  wktParser.parse('POINT (100.0 200.0)'); // => Point2;
  wktParser.parse('POINT M (100.0 200.0 5.0)'); // => Point2m;

  // Projected (or cartesian) coordinates (Point2, Point2m, Point3 or Point3m)
  WKT().parserProjected().parse('LINESTRING (200.1 500.9, 210.2 510.4)');

  // Geographic coordinates (GeoPoint2, GeoPoint2m, GeoPoint3 or GeoPoint3m)
  WKT().parserGeographic().parse(
        'POLYGON ((40 15, 50 50, 15 45, 10 15, 40 15),'
        ' (25 25, 25 40, 35 30, 25 25))',
      );

User guide

Cartesian or projected points

The abstract base class for all point geometries is Point. It's implemented by following concrete classes to represent projected or cartesian (XYZ) coordinates with an optional measure (m) coordinate:

Class	Coordinates	x	y	z	m
Point2	num	+	+
Point2m	num	+	+		+
Point3	num	+	+	+
Point3m	num	+	+	+	+
Point2i	int	+	+
Point3i	int	+	+	+

Points are created by geometry parsers or point factory implementations. Each point geometry class has also multiple factory constructors.

For example Point3 can be created in many ways:

  // Projected point with X, Y and Z coordinates in two ways.
  Point3(x: 708221.0, y: 5707225.0, z: 45.0);
  Point3.xyz(708221.0, 5707225.0, 45.0);

  // The same point created from `Iterable<num>`.
  Point3.from([708221.0, 5707225.0, 45.0]);

  // The same point parsed from WKT compatible text.
  // Actually WKT representation would be : "POINT (708221.0 5707225.0 45.0)",
  // but this parser takes only coordinate data between paranthesis.
  Point3.parse('708221.0 5707225.0 45.0');

  // The `parse` method throws when text is invalid, but `tryParse` returns null
  // in such case. This can be utilized for fallbacks.
  Point3.tryParse('nop') ?? Point3.parse('708221.0 5707225.0 45.0');

  // The same point parsed using the WKT parser for projected geometries.
  // Here `wktProjected` is a global constant for a WKT factory implementation.
  WKT().parserProjected().parse('POINT Z (708221.0 5707225.0 45.0)');

All other point classes have similar constructors.

If you have a point instance of one of the point classes, then there are some methods that help to create another instance of the same type.

  // A sample point with x, y, z and m coordinates.
  final source = Point3m.xyzm(708221.0, 5707225.0, 45.0, 123.0);

  // Return new points of the same type by changing only some coordinate values.
  source.copyWith(m: 150.0);
  source.copyWith(x: 708221.7, z: 46.2);

  // Returns a point of the same type, but no previous values are preserved
  // (result here is Point3m.xyzm(1.0, 2.0, 3.0, 0.0)) with default 0.0 for m).
  source.newWith(x: 1.0, y: 2.0, z: 3.0);

  // This returns also Point3m.xyzm(1.0, 2.0, 3.0, 0.0)).
  source.newFrom([1.0, 2.0, 3.0, 0.0]);

Geographic points

The base class for all geographic point geometries is GeoPoint, that extends also Point. Geographic coordinates are longitude (lon) and latitude (lat), in degrees and preferable always in this order. Elevation (elev) in meters and measure (m) coordinates are optional.

Class	Coordinates	lon (x)	lat (y)	elev (z)	m
GeoPoint2	double	+	+
GeoPoint2m	double	+	+		+
GeoPoint3	double	+	+	+
GeoPoint3m	double	+	+	+	+

In the context of this package geographic coordinate axes are related with axes defined in the base Point-class:

• Longitude: lon == x
• Latitude: lat == y
• Elevation: elev == z

See below how to create GeoPoint3m instances (other classes in similar ways):

  // Geographic point with longitude, latitude, elevation and measure.
  GeoPoint3m(lon: -0.0014, lat: 51.4778, elev: 45.0, m: 123.0);
  GeoPoint3m.lonLatElevM(-0.0014, 51.4778, 45.0, 123.0);

  // Someone might want to represent latitude before longitude, it's fine too.
  GeoPoint3m.latLonElevM(51.4778, -0.0014, 45.0, 123.0);

  // When creating from value array, the order is: lon, lat, elev, m.
  GeoPoint3m.from([-0.0014, 51.4778, 45.0, 123.0]);

  // Also here it's possible to parse from WKT compatible text.
  GeoPoint3m.parse('-0.0014 51.4778 45.0 123.0');

  // The WKT parser for geographic coordinates parses full representations.
  WKT().parserGeographic().parse('POINT ZM (-0.0014 51.4778 45.0 123.0)');

Point series

Other geometries are composed of point geometries in different structures. PointSeries is a collection class with a series of points and it can represent a geometry path, a line string, an outer or inner linear ring of a polygon, a multi point, a vertex array or any any other collection for points.

  // A point series of `Point2` composed of list of points that are of `Point2`
  // or it's sub classes.
  PointSeries<Point2>.from([
    Point2(x: 10.0, y: 10.0),
    Point2(x: 20.0, y: 20.0),
    Point2m(x: 30.0, y: 30.0, m: 5.0),
    Point3(x: 40.0, y: 40.0, z: 40.0),
    Point3m(x: 50.0, y: 50.0, z: 50.0, m: 5.0),
  ]);

  // Making a point series of `Point3` from a list of a list of nums.
  PointSeries.make(
    // three points each with x, y and z coordinates
    [
      [10.0, 11.0, 12.0],
      [20.0, 21.0, 22.0],
      [30.0, 31.0, 32.0],
    ],
    // This is `PointFactory` that converts `Iterable<num>` to a point instance,
    // in this example using a factory creating `Point3` instances.
    Point3.coordinates,
  );

  // Parsing a point series of `GeoPoint` from WKT compatible text with
  // `GeoPoint3` as a concrete point class.
  PointSeries<GeoPoint>.parse(
    '10.0 11.0 12.0, 20.0 21.0 22.0, 30.0 31.0 32.0',
    GeoPoint3.coordinates,
  );

The PointSeries class is not extending the Geometry class, but it's used by actual geometry classes, described in following sections, as a building block.

Line strings

A line string contains a chain of points, implemented using PointSeries.

You can use LineString.any factory constructor to create a line string with any chain, or LineString.ring constructor to create a linear ring with a closed chain. Both constructors simply take an instance of PointSeries.

Or below are examples of more direct ways to construct line strings:

  // This makes a a line string of `Point3m` from a list of points.
  LineString.make(
    [
      [10.0, 11.0, 12.0, 5.1],
      [20.0, 21.0, 22.0, 5.2],
      [30.0, 31.0, 32.0, 5.3],
    ],
    Point3m.coordinates,
  );

  // Using the WKT factory produces the same result as the previous sample.
  WKT().parserProjected().parse<Point3m>(
        'LINESTRING ZM(10.0 11.0 12.0 5.1, 20.0 21.0'
        ' 22.0 5.2, 30.0 31.0 32.0 5.3)',
      );

  // Also this sample, parsing from WKT compatible text, gives the same result.
  LineString.parse(
    '10.0 11.0 12.0 5.1, 20.0 21.0 22.0 5.2, 30.0 31.0 32.0 5.3',
    Point3m.coordinates,
  );

Polygons

A polygon contains one exterior boundary and optional interior boundaries (representing holes). All boundaries are linear rings implemented as LineString instances each with a closed chain of points as a ring.

The default constructor of Polygon takes a series of LineString instances, with at least an exterior boundary at index 0.

Other ways to construct polygons are familiar from previous samples:

  // Making a polygon of `GeoPoint2` from a list of a list of a list of nums:
  Polygon.make(
    [
      // this is an exterior boundary or an outer ring
      [
        [35, 10],
        [45, 45],
        [15, 40],
        [10, 20],
        [35, 10]
      ],
      // this is an interior boundary or an inner ring representing a hole
      [
        [20, 30],
        [35, 35],
        [30, 20],
        [20, 30]
      ],
    ],
    GeoPoint2.coordinates,
  );

  // The same polygon geometry as above, but parsed from a WKT compatible text.
  Polygon.parse(
    '(35 10, 45 45, 15 40, 10 20, 35 10) (20 30, 35 35, 30 20, 20 30)',
    GeoPoint2.coordinates,
  );

Multi geometries

Multi points, multi line strings and multi polygons can also be constructed in similar ways described already for other geometries. Also parsed from text:

  // A multi point of `GeoPoint2` with four lon-lat points.
  MultiPoint.parse('10 40, 40 30, 20 20, 30 10', GeoPoint2.coordinates);

  // A multi line string of `Point2` with two line strings.
  MultiLineString.parse(
    '(10 10, 20 20, 10 40), (40 40, 30 30, 40 20, 30 10)',
    Point2.coordinates,
  );

  // A multi polygon of `GeoPoint2` with two polygon (both with exterior
  // boundary without holes).
  MultiPolygon.parse(
    '((30 20, 45 40, 10 40, 30 20)), ((15 5, 40 10, 10 20, 5 10, 15 5))',
    GeoPoint2.coordinates,
  );

There is also GeometryCollection:

  // A geometry collection can contain any other geometry types. Items for such
  // a collection can be constructed using different ways.
  GeometryCollection([
    // A point with integer values using a constructor with named parameters.
    Point2(x: 40, y: 10),
    // A line string made from a list of points (each a list of nums).
    LineString.make(
      [
        [10, 10],
        [20, 20],
        [10, 40]
      ],
      Point2.coordinates,
    ),
    // A polygon parsed from WKT compatible text.
    Polygon.parse('(40 40, 20 45, 45 30, 40 40)', Point2.coordinates)
  ]);

  // A geometry collection can also be parsed from WKT text.
  WKT().parserProjected().parse<Point2>(
    '''
      GEOMETRYCOLLECTION (
        POINT (40 10),
        LINESTRING (10 10, 20 20, 10 40),
        POLYGON ((40 40, 20 45, 45 30, 40 40)))
      ''',
  );

Spatial bounds

Bounding boxes or spatial bounds objects can be represented in 2D or 3D, and with an optional measure coordinates.

Bounds samples with projected or cartesian coordinates:

  // Bounds (2D) or bounding box from minimum and maximum 2D projected points.
  Bounds.of(min: Point2(x: 10.0, y: 10.0), max: Point2(x: 20.0, y: 20.0));

  // Bounds (3D) made from a list of list of nums.
  Bounds.make(
    [
      [10.0, 10.0, 10.0],
      [20.0, 20.0, 20.0]
    ],
    Point3.coordinates,
  );

  // Bounds (3D with measure) parsed from WKT compatible text.
  Bounds.parse('10.0 10.0 10.0 5.0, 20.0 20.0 20.0 5.0', Point3m.coordinates);

Bounds samples with geographic coordinates:

  // Geographical bounds (-20.0 .. 20.0 in longitude, 50.0 .. 60.0 in latitude).
  GeoBounds.bboxLonLat(-20.0, 50.0, 20.0, 60.0);

  // The same bounds created of 2D geographic point instances.
  GeoBounds.of(
    min: GeoPoint2(lon: -20.0, lat: 50.0),
    max: GeoPoint2(lon: 20.0, lat: 60.0),
  );

Geospatial features

According to the OGC Glossary a geospatial feature is a digital representation of a real world entity. It has a spatial domain, a temporal domain, or a spatial/temporal domain as one of its attributes. Examples of features include almost anything that can be placed in time and space, including desks, buildings, cities, trees, forest stands, ecosystems, delivery vehicles, snow removal routes, oil wells, oil pipelines, oil spill, and so on.

Below is an illustration of features in a simple vector map. Wells are features with a point geometry, rivers with a line string (or polyline) geometry, and finally lakes are features with a polygon geometry. Features normally contain also an identifier and other attributes (or properties) along with a geometry.

The Feature class of this package has geospatial geometry and bounds as fields along with id and properties fields.

  // Geospatial feature with an identification, a point geometry and properties.
  Feature(
    id: 'ROG',
    geometry: GeoPoint3(lon: -0.0014, lat: 51.4778, elev: 45.0),
    properties: {
      'title': 'Royal Observatory',
      'place': 'Greenwich',
      'city': 'London',
      'isMuseum': true,
      'measure': 5.79,
    },
  );

Naturally, the geometry field could also contain other geometries described earlier, not just points.

Parsing GeoJSON data

GeoJSON, as described by Wikipedia, is an open standard format designed for representing simple geographical features, along with their non-spatial attributes.

See also the official GeoJSON website. As specified by the referenced RFC 7946 standard, all GeoJSON geometries use WGS 84 geographic coordinates. Alternative coordinate reference systems can also be used when involved parties have a prior arrangement of using other systems.

Below is an example with sample GeoJSON data and code to parse it.

Imports:

import 'package:geocore/parse.dart';

The sample code:

  // sample GeoJSON data
  const sample = '''
    {
      "type": "FeatureCollection",
      "features": [
        {
          "type": "Feature",
          "id": "ROG",
          "geometry": {
            "type": "Point",
            "coordinates": [-0.0014, 51.4778, 45.0]  
          },
          "properties": {
            "title": "Royal Observatory",
            "place": "Greenwich",
            "city": "London"
          }
        }  
      ]
    }
  ''';

  // parse FeatureCollection using a GeoJSON parser with geographic coordinates
  final format = GeoJSON();
  final parser = format.parserGeographic(geographicPoints);
  final fc = parser.featureCollection(sample);

  // loop through features and print id, geometry and properties for each
  for (final f in fc.features) {
    print('Feature with id: ${f.id}');
    print('  geometry: ${f.geometry}');
    print('  properties:');
    for (final key in f.properties.keys) {
      print('    $key: ${f.properties[key]}');
    }
  }

At this stage the package supports reading following GeoJSON elements:

• FeatureCollection
• Feature
• Point, LineString and Polygon
• MultiPoint, MultiLineString and MultiPolygon
• GeometryCollection

Parsing WKT data

Well-known text representation of geometry (WKT) is a text markup language for representing vector geometry objects. It's specified by the Simple Feature Access - Part 1: Common Architecture standard.

WKT representations for coordinate data has already been discussed on previous sections introducing geometry objects. Geometry classes have factory constructors that allows parsing coordinate values from WKT compatible text (like a point using Point2.parse('100.0 200.0') factory).

When parsing full WKT geometry text representations, with a geometry type id and coordinate values, the WktFactory class can be used. There are two main parser implementations for different use cases:

Parser factory	Use cases
WKT().parserProjected()	Parsing geometries with projected or cartesian coordinates.
WKT().parserGeographic()	Parsing geometries with geographic coordinates (like WGS 84).

Other custom parsers for WKT format can be created via WKT().parser() method.

Imports:

import 'package:geocore/parse.dart';

Samples to parse from WKT text representation of geometry:

  // get WKT format
  final format = WKT();

  // Parse projected points from WKT (result is different concrete classes).
  final parser1 = format.parserProjected();
  parser1.parse('POINT (100.0 200.0)'); // => Point2
  parser1.parse('POINT M (100.0 200.0 5.0)'); // => Point2m
  parser1.parse('POINT (100.0 200.0 300.0)'); // => Point3
  parser1.parse('POINT Z (100.0 200.0 300.0)'); // => Point3
  parser1.parse('POINT ZM (100.0 200.0 300.0 5.0)'); // => Point3m

  // Parse geographical line string, from (10.0 50.0) to (11.0 51.0).
  final parser2 = format.parser(GeoPoint2.coordinates);
  parser2.parse('LINESTRING (10.0 50.0, 11.0 51.0)');

  // Parse geographical polygon with a hole.
  final parser3 = format.parserGeographic();
  parser3.parse(
    'POLYGON ((40 15, 50 50, 15 45, 10 15, 40 15),'
    ' (25 25, 25 40, 35 30, 25 25))',
  );

Supported WKT geometry types: POINT, LINESTRING, POLYGON, MULTIPOINT, MULTILINESTRING, MULTIPOLYGON and GEOMETRYCOLLECTION.

GeoJSON and WKT writers

Content interfaces

Content interfaces are used for two main use cases:

• writing geospatial data (coordinates, geometry and features) to text or binary format encoders
• building objects in decoders reading geospatial data from text or binary formats

Content interface	Description
CoordinateContent	Write coordinate objects (bounding boxes, positions, position arrays).
GeometryContent	Write geometry objects (supported geometry types: point, lineString, polygon, multiPoint, multiLineString, multiPolygon , geometryCollection)
FeatureContent	Write features (with properties and geometry objects) and feature collections

Text format encoders

Text formats supported:

Format	Format class	Content encoders
GeoJSON	GeoJSON	Coordinates, Geometries, Features
WKT	WKT	Coordinates, Geometries

There are also formats DefaultFormat (a text format aligned with GeoJSON but output is somewhat simpler) and WktLikeFormat (a text format aligned with WKT).

All formats mentioned above have following content specific formats:

  /// The text format for coordinate objects.
  static const TextFormat<CoordinateContent> coordinate;

  /// The text format for geometry objects.
  static const TextFormat<GeometryContent> geometry;

GeoJSON provides also:

  /// The text format for feature objects.
  static const TextFormat<FeatureContent> feature;

Formats, content interfaces and writers are re-exported from the geobase package that also provides more documentation.

See samples below how to use text formats and encoders.

A sample to print coordinates of a point geometry below.

  // create a point (XYZ)
  final point = Point3(x: 10.123, y: 20.25, z: -30.95);

  // print with default format
  print('Default format: ${point.toString()}');
  print('Default format (decimals = 0): ${point.toStringAs(decimals: 0)}');

  // print with WKT format
  print('WKT format: ${point.toStringAs(format: WKT.geometry)}');

  // print with GeoJSON format
  print('GeoJSON format: ${point.toStringAs(format: GeoJSON.geometry)}');
  print(
    'GeoJSON (decimals = 1) format: ${point.toStringAs(
      format: GeoJSON.geometry,
      decimals: 1,
    )}',
  );

The sample below creates a GeoJSON format and feature writer, then create a feature collection, and finally uses a writer to print it as GeoJSON text.

  // feature text encoder for GeoJSON
  final encoder = GeoJSON.feature.encoder();

  // create a feature collection with two features
  final collection = FeatureCollection(
    bounds: GeoBounds.of(
      min: GeoPoint2(lon: -1.1, lat: -3.49),
      max: GeoPoint2(lon: 10.12, lat: 20.25),
    ),
    features: [
      Feature(
        id: 'fid-1',
        geometry: GeoPoint2(lon: 10.123, lat: 20.25),
        properties: {
          'foo': 100,
          'bar': 'this is property value',
        },
      ),
      Feature(
        geometry: LineString.make(
          [
            [-1.1, -1.1],
            [2.1, -2.5],
            [3.5, -3.49]
          ],
          GeoPoint2.coordinates,
          type: LineStringType.any,
          bounds: GeoBounds.make(
            [
              [-1.1, -3.49],
              [3.5, -1.1]
            ],
            GeoPoint2.coordinates,
          ),
        ),
        properties: {},
      ),
    ],
  );

  // write the feture collection to the content writer of the encoder
  // (encoder.writer is FeatureContent)
  collection.writeTo(encoder.writer);

  // print GeoJSON text
  print(encoder.toText());

  // the previous line prints (however without line breaks):
  //    {"type":"FeatureCollection",
  //     "bbox":[-1.1,-3.49,10.123,20.25],
  //     "features":[
  //        {"type":"Feature",
  //         "id":"fid-1",
  //         "geometry":{"type":"Point","coordinates":[10.123,20.25]},
  //         "properties":{"foo":100,"bar":"this is property value"}},
  //        {"type":"Feature",
  //         "geometry":{"type":"LineString",
  //                     "bbox":[-1.1,-3.49,3.5,-1.1],
  //                     "coordinates":[[-1.1,-1.1],[2.1,-2.5],[3.5,-3.49]]},
  //         "properties":{}}]}

Authors

This project is authored by Navibyte.

More information and other links are available at the geospatial repository from GitHub.

License

This project is licensed under the "BSD-3-Clause"-style license.

Please see the LICENSE.