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

Geospatial data structures and parsers

pub package License style: very good analysis

Features #

  • πŸš€ geospatial data structures (geometry, features and metadata)
  • πŸ“… temporal data structures (instant, interval)
  • 🌐 geographic coordinates (longitude-latitude)
  • πŸ—ΊοΈ projected coordinates (cartesian XYZ)
  • πŸ”· 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
  • πŸͺ§ WKT (Well-known text representation of geometry) data parser
  • πŸ—οΈ coordinate transformations and projections (initial support)

Package #

This package is at BETA stage, interfaces not fully final yet.

This is a Dart package named geocore under the geospatial code repository.

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

dependencies:
  geocore: ^0.8.0-a.7

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

LibraryExport alsoDescription
baseBase classes for geospatial geometries and temporal objects.
coordinatesbaseCartesian and geographic points with some common coordinate transforms.
database, coordinatesGeospatial features and geometries (linestring, polygon, multi geometries).
parsebase, coordinates, dataGeoJSON and WKT (Well-known text representation of geometry) data parsers.
proj4dbaseProjections provided by the external proj4dart package.

All the mini-libraries have a dependency to the equatable package. The proj4d library depends also on the proj4dart package.

Introduction #

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

GeometryShapeSamples to create instances
PointPoint2(x: 30.0, y: 10.0)
Point2.from([30.0, 10.0])
Point2.parse('30 10')
LineStringLineString.parse('30 10, 10 30, 40 40', Point2.coordinates)
PolygonPolygon.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:

GeometryShapeSamples to create instances
MultiPointMultiPoint.parse('10 40, 40 30, 20 20, 30 10', Point2.coordinates)
MultiLineStringMultiLineString.parse('(10 10, 20 20, 10 40), (40 40, 30 30, 40 20, 30 10)', Point2.coordinates)
MultiPolygonMultiPolygon.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)
GeometryCollectionGeometryCollection([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, temporal instants and intervals, and extents:

  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);

  Instant(DateTime.utc(2020, 10, 31, 09, 30));
  Interval.parse('2020-10-01/2020-10-31');

  Extent.single(
    crs: 'EPSG:4326',
    bounds: GeoBounds.bboxLonLatElev(-20.3, 50.2, 1108.4, 20.5, 60.9, 1251.4),
    interval: Interval.openStart(DateTime.utc(2020, 10, 31)),
  );

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

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

Built-in coordinate projections (currently only between WGS84 and Web Mercator):

  // From GeoPoint2 (WGS 84 longitude-latitude) to Point2 (Web Mercator metric)
  final forward = wgs84ToWebMercator.forward(Point2.coordinates);
  final projected = GeoPoint2(lon: -0.0014, lat: 51.4778).project(forward);

  // From Point2 (Web Mercator metric) to GeoPoint2 (WGS 84 longitude-latitude)
  final inverse = wgs84ToWebMercator.inverse(GeoPoint2.coordinates);
  final unprojected = projected.project(inverse);

Coordinate projections based on the external proj4dart package:

  // A projection adapter from WGS84 (EPSG:4326) to EPSG:23700 (with definition)
  // (based on the sample at https://pub.dev/packages/proj4dart).
  final adapter = proj4dart(
    'EPSG:4326',
    'EPSG:23700',
    toDef: '+proj=somerc +lat_0=47.14439372222222 +lon_0=19.04857177777778 '
        '+k_0=0.99993 +x_0=650000 +y_0=200000 +ellps=GRS67 '
        '+towgs84=52.17,-71.82,-14.9,0,0,0,0 +units=m +no_defs',
  );

  // Apply a forward projection to EPSG:23700 with points represented as Point2.
  GeoPoint2(lon: 17.8880, lat: 46.8922)
      .project(adapter.forward(Point2.coordinates));

Parsing GeoJSON data:

  geoJSON.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:

  wktProjected.parse('LINESTRING (200.1 500.9, 210.2 510.4)');

  wktGeographic.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:

ClassCoordinatesxyzm
Point2num++
Point2mnum+++
Point3num+++
Point3mnum++++
Point2iint++
Point3iint+++

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.
  wktProjected.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.

Latitude and Longitude of the Earth

ClassCoordinateslon (x)lat (y)elev (z)m
GeoPoint2double++
GeoPoint2mdouble+++
GeoPoint3double+++
GeoPoint3mdouble++++

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.
  wktGeographic.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.
  wktProjected.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.
  wktProjected.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),
  );

Temporal instants and intervals #

Temporal data can be represented as instants (a time stamp) and intervals (an open or a closed interval between time stamps).

  // Temporal instants can be created from `DateTime` or parsed from text.
  Instant(DateTime.utc(2020, 10, 31, 09, 30));
  Instant.parse('2020-10-31 09:30Z');

  // Temporal intervals (open-started, open-ended, closed).
  Interval.openStart(DateTime.utc(2020, 10, 31));
  Interval.openEnd(DateTime.utc(2020, 10, 01));
  Interval.closed(DateTime.utc(2020, 10, 01), DateTime.utc(2020, 10, 31));

  // Same intervals parsed (by the "start/end" format, ".." for open limits).
  Interval.parse('../2020-10-31');
  Interval.parse('2020-10-01/..');
  Interval.parse('2020-10-01/2020-10-31');

Extents #

Extent objects have both spatial bounds and temporal interval, and they are useful in metadata structures for geospatial data sources.

  // An extent with spatial (WGS 84 longitude-latitude) and temporal parts.
  Extent.single(
    crs: 'EPSG:4326',
    bounds: GeoBounds.bboxLonLat(-20.0, 50.0, 20.0, 60.0),
    interval: Interval.parse('../2020-10-31'),
  );

  // An extent with multiple spatial bounds and temporal interval segments.
  Extent.multi(
    crs: 'EPSG:4326',
    allBounds: [
      GeoBounds.bboxLonLat(-20.0, 50.0, 20.0, 60.0),
      GeoBounds.bboxLonLat(40.0, 50.0, 60.0, 60.0),
    ],
    allIntervals: [
      Interval.parse('2020-10-01/2020-10-05'),
      Interval.parse('2020-10-27/2020-10-31'),
    ],
  );

The crs property in extents above refer to a Coordinate reference system that is a coordinate-based local, regional or global system used to locate geographical entities.

This library does not define any crs constants, please refer to registries like The EPSG dataset.

Projections between coordinate reference systems #

See the introduction for samples projecting geographic points to projected points, and vice versa.

A forward or inverse projection is implemented by a function defined as:

/// A function to project the [source] point to a point of [R].
///
/// When [to] is provided, then target points of [R] are created using that
/// as a point factory. Otherwise a projection function uses it's own factory.
///
/// Note that a function could implement for example a map projection from
/// geographical points to projected cartesian points, or an inverse
/// projection (or an "unprojection") from projected cartesian points to
/// geographical points. Both are called here "project point" functions.
///
/// Throws FormatException if cannot project.
typedef ProjectPoint<R extends Point> = R Function(
  Point source, {
  PointFactory<R>? to,
});

Projection adapters bundle forward and inverse projections, and are used to access "project point" functions.

For example a built-in adapter wgs84ToWebMercator can be used to get a forward projection and then applied on a geographic point to project it:

  final forward = wgs84ToWebMercator.forward(Point2.coordinates);
  final projected = GeoPoint2(lon: -0.0014, lat: 51.4778).project(forward);

The package has also an adapter to the external proj4dart package. Adapter instances can be accessed using a global function:

/// Resolves a projection adapter between [fromCrs] and [toCrs].
///
/// As based on the Proj4dart package, it has built-in support for following crs
/// codes: "EPSG:4326" (with alias "WGS84"), "EPSG:4269", "EPSG:3857" (with
/// aliases "EPSG:3785", "GOOGLE", "EPSG:900913", "EPSG:102113").
///
/// For all other crs codes, also a projection definition must be given via
/// [fromDef] or [toDef]. Proj4 definition strings, OGC WKT definitions and
/// ESRI WKT definitions are supported. More info from the Proj4dart package.
///
/// Throws FormatException if projections could not be resolved.
Proj4Adapter proj4dart(
  String fromCrs,
  String toCrs, {
  String? fromDef,
  String? toDef,
});

A sample to project from WGS84 to Web Mercator using proj4dart:

  final adapter = proj4dart('EPSG:4326', 'EPSG:3857');
  final forward = adapter.forward(Point2.coordinates);
  final projected = GeoPoint2(lon: -0.0014, lat: 51.4778).project(forward);

Please see the documentation of proj4dart package about it's capabilities, and accuracy of forward and inverse projections.

Coordinate transformations #

Geographical and cartesian points, geometry objects, features and feature collections can be transformed also using coordinate transformations.

Currently this package provides a consistent abstraction. Classes used to represent objects mentioned above contain transform(TransformPoint transform) method returning a transformed object. The transform function is defined as:

/// A function to transform the [source] point to a transformed point.
typedef TransformPoint = T Function<T extends Point>(T source);

Transforms differ from projections in the context of this package so that Point class type on geometries does not change when transforming.

There are some basic (initial support) geometry transforms provided by the package.

For example to translate points you can use:

/// Returns a function to translate points by delta values of each axis.
TransformPoint translatePoint<C extends num>({C? dx, C? dy, C? dz, C? dm});

Similarily scalePoint, scalePointBy and rotatePoint2D returns functions to transform points by scaling with axis-specific factors, scaling with a constant factor, or rotating in 2D.

It's quite simple to define a custom transform function too:

/// Translates X by 10.0 and Y by 20.0, other coordinates (Z and M) not changed.
T _sampleFixedTranslate<T extends Point>(T source) =>
    source.copyWith(x: source.x + 10.0, y: source.y + 20.0) as T;

Now this function can be used to transform points and other geometries:

  // Create a point and transform it with a custom translation that returns
  // `Point3m.xyzm(110.0, 220.0, 50.0, 1.25)` after applying the transform.
  Point3m.xyzm(100.0, 200.0, 50.0, 1.25).transform(_sampleFixedTranslate);

  // The same transform function can be used to transform also geometry objects.
  LineString.parse('100.0 200.0, 400.0 500.0', Point2.coordinates)
      .transform(_sampleFixedTranslate);

  // This returns a line string that has same coordinate values as:
  // LineString.parse('110.0 220.0, 410.0 520.0', Point2.geometry)

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.view(
    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 the default GeoJSON factory
  final fc = geoJSON.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 global constants of class instances for different use cases:

Global constantUse cases
wktProjectedParsing geometries with projected or cartesian coordinates.
wktGeographicParsing geometries with geographic coordinates (like WGS 84).

Imports:

import 'package:geocore/parse.dart';

Samples to parse from WKT text representation of geometry:

  // Parse projected points from WKT (result is different concrete classes).
  wktProjected.parse('POINT (100.0 200.0)'); // => Point2
  wktProjected.parse('POINT M (100.0 200.0 5.0)'); // => Point2m
  wktProjected.parse('POINT (100.0 200.0 300.0)'); // => Point3
  wktProjected.parse('POINT Z (100.0 200.0 300.0)'); // => Point3
  wktProjected.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).
  wktGeographic.parse('LINESTRING (10.0 50.0, 11.0 51.0)');

  // Parse geographical polygon with a hole.
  wktGeographic.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.

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.

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

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BSD-3-Clause (LICENSE)

Dependencies

equatable, meta, proj4dart

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