projections library

WGS84 based projections; ellipsoidal (geographic, geocentric, UTM) and spherical (Web Mercator).

This libary exports a subset of package:geobase/geobase.dart.

See also package:geobase/projections_proj4d.dart that provides a projection adapter using the external proj4dart package.

Usage: import package:geobase/projections.dart

Examples:

  // Projections can be applied on any geometry and feature objects along with
  // positions.

  // The source point geometry with a position in WGS 84 coordinates.
  final positionWgs84 = Geographic(lon: 2.2945, lat: 48.8582);
  final point = Point(positionWgs84);

  // Project to UTM projected coordinates (in zone 31 N).
  final zone31N = UtmZone(31, 'N');
  final wgs84toUtm31N = WGS84.utmZone(zone31N).forward;
  final pointUtm31N = point.project(wgs84toUtm31N);

  // Project back to WGS 84 coordinates.
  final utm31NtoWgs84 = WGS84.utmZone(zone31N).inverse;
  final pointWgs84 = pointUtm31N.project(utm31NtoWgs84);

  // Print the original and projected point coordinates.
  //    {"type":"Point","coordinates":[2.2945,48.8582]} =>
  //    {"type":"Point","coordinates":[448251.80,5411932.68]} =>
  //    {"type":"Point","coordinates":[2.2945,48.8582]}"
  print('${point.toText(decimals: 4)} => ${pointUtm31N.toText(decimals: 2)}'
      ' => ${pointWgs84.toText(decimals: 4)}');

  // Project between WGS84 based UTM zones. Note that resulting coordinates may
  // have strange values if the point do not locate inside the target zone.
  final zone30N = UtmZone(30, 'N');
  final utm31NtoUtm30N = WGS84.utmZoneToZone(zone31N, zone30N).forward;
  final pointUtm30N = pointUtm31N.project(utm31NtoUtm30N);
  print(pointUtm30N.position.toText(decimals: 2)); // 888276.96,5425220.84

  // It's always possible to check the UTM zone a point is located in.
  final zone = UtmZone.fromGeographic(positionWgs84);
  print(zone); // 31 N

  // The source WGS84 geographic position to geocentric cartesian.
  final wgs84toGeocentric = WGS84.geocentric.forward;
  final pointGeocentric = point.project(wgs84toGeocentric);
  // prints "4200952.55,168323.77,4780198.41"
  print(pointGeocentric.position.toText(decimals: 2));

  // The source WGS84 geographic position to WG84 web mercator (metric).
  final wgs84toWebMercator = WGS84.webMercator.forward;
  final pointWebMercator = point.project(wgs84toWebMercator);
  print(pointWebMercator.position.toText(decimals: 2)); // 255422.57,6250835.06

  // Other datum, for example from WGS 84 geographic to ED50 geographic.
  // In this sample `project` is called directly on the position, not on the
  // point geometry object (that is possible too).
  final wgs84toED50Adapter = WGS84.geographicToDatum(
    const CoordRefSys.id('http://www.opengis.net/def/crs/EPSG/0/4230'),
    Datum.ED50,
  );
  final positionED50 = positionWgs84.project(wgs84toED50Adapter.forward);
  // prints : "2.2945,48.8582 => 2.2958,48.8591"
  print('${positionWgs84.toText(decimals: 4)} => '
     '${positionED50.toText(decimals: 4)}');

projections library

Classes

geobase package

projections library