Polygon.build constructor

Polygon.build(Iterable<Iterable<double>> rings, { Coords type = Coords.xy, Box? bounds, })

Builds a polygon geometry from one exterior and 0 to N interior rings.

Use type to specify the type of coordinates, by default Coords.xy is expected.

An optional bounds can used set a minimum bounding box for a geometry.

Each ring in the polygon is represented by an Iterable<double> array. Such arrays contain coordinate values as a flat structure. For example for Coords.xyz the first three coordinate values are x, y and z of the first position, the next three coordinate values are x, y and z of the second position, and so on.

An empty polygon has no rings.

For "normal" polygons the rings list must be non-empty. The first element is the exterior ring, and any other rings are interior rings (or holes). All rings must be closed linear rings. As specified by GeoJSON, they should "follow the right-hand rule with respect to the area it bounds, i.e., exterior rings are counterclockwise, and holes are clockwise".

Examples:

// a polygon (with an exterior ring only) from 2D positions
Polygon.build(
  [
    // an exterior ring with values of five (x, y) positions
    [
      10.0, 20.0,
      12.5, 22.5,
      15.0, 25.0,
      11.5, 27.5,
      10.0, 20.0,
    ],
  ],
  type: Coords.xy,
);

// a polygon (with an exterior and one interior ring) from 2D positions
Polygon.build(
  [
    // an exterior ring with values of five (x, y) positions
    [
      10.0, 20.0,
      12.5, 22.5,
      15.0, 25.0,
      11.5, 27.5,
      10.0, 20.0,
    ],
    // an interior ring with values of four (x, y) positions
    [
      12.5, 23.0,
      11.5, 24.0,
      12.5, 24.0,
      12.5, 23.0,
    ],
  ],
  type: Coords.xy,
);

// a polygon (with an exterior ring only) from 3D positions
Polygon.build(
  [
    // an exterior ring with values of five (x, y, z) positions
    [
      10.0, 20.0, 30.0,
      12.5, 22.5, 32.5,
      15.0, 25.0, 35.0,
      11.5, 27.5, 37.5,
      10.0, 20.0, 30.0,
    ],
  ],
  type: Coords.xyz,
);

// a polygon (with an exterior ring only) from measured 2D positions
Polygon.build(
  [
    // an exterior ring with values of five (x, y, m) positions
    [
      10.0, 20.0, 40.0,
      12.5, 22.5, 42.5,
      15.0, 25.0, 45.0,
      11.5, 27.5, 47.5,
      10.0, 20.0, 40.0,
    ],
  ],
  type: Coords.xym,
);

// a polygon (with an exterior ring only) from measured 3D positions
Polygon.build(
  [
    // an exterior ring with values of five (x, y, z, m) positions
    [
      10.0, 20.0, 30.0, 40.0,
      12.5, 22.5, 32.5, 42.5,
      15.0, 25.0, 35.0, 45.0,
      11.5, 27.5, 37.5, 47.5,
      10.0, 20.0, 30.0, 40.0,
    ],
  ],
  type: Coords.xyzm,
);

Implementation

factory Polygon.build(
  Iterable<Iterable<double>> rings, {
  Coords type = Coords.xy,
  Box? bounds,
}) =>
    Polygon(
      rings
          .map(
            (ring) => PositionSeries.view(
              ring is List<double> ? ring : toFloatNNList(ring),
              type: type,
            ),
          )
          .toList(growable: false),
      bounds: bounds,
    );