flatten function

FeatureCollection<GeometryObject> flatten(GeoJSONObject geojson)

Takes any GeoJSONObject and returns a FeatureCollection of simple features. The function flattens all Multi* geometries into single-geometry Features.

This function is useful when handling complex shapes with multiple parts, making it easier to process each part as a distinct feature.

• geojson - any valid GeoJSONObject (Feature, FeatureCollection, Geometry)
• Returns a FeatureCollection of Features where each feature has a single geometry type

Altitude values (z coordinates) are preserved in all coordinate positions. Properties and other metadata in the input Feature are preserved in each output Feature.

Replicates behavior from: https://turfjs.org/docs/#flatten

Example:

final multiLineString = MultiLineString(coordinates: [
  [Position(0, 0), Position(1, 1)],
  [Position(2, 2), Position(3, 3)]
]);

final flattened = flatten(multiLineString);
// Returns FeatureCollection with 2 LineString features

Throws ArgumentError if:

• A GeometryCollection is provided
• A Feature with null geometry is provided
• An unsupported geometry type is encountered

Implementation

FeatureCollection<GeometryObject> flatten(GeoJSONObject geojson) {
  // Reject GeometryCollection inputs - not supported per the requirements
  if (geojson is GeometryCollection) {
    throw ArgumentError('flatten does not support GeometryCollection input.');
  }

  // Use a list to collect all flattened features
  final List<Feature<GeometryObject>> features = [];

  // Use flattenEach from meta to iterate through each flattened feature
  flattenEach(geojson, (currentFeature, featureIndex, multiFeatureIndex) {
    // If the geometry is null, skip this feature (implementation choice)
    if (currentFeature.geometry == null) {
      return;
    }

    // We know this is a Feature with a GeometryType, but we want to ensure
    // it's treated as a Feature<GeometryObject> to match return type
    final feature = Feature<GeometryObject>(
      geometry: currentFeature.geometry,
      properties: currentFeature.properties,
      id: currentFeature.id,
      bbox: currentFeature.bbox,
    );

    // Add to our features list - this maintains original geometry order
    features.add(feature);
  });

  // Create and return a FeatureCollection containing all the flattened features
  return FeatureCollection<GeometryObject>(
    features: features,
    // If the original object was a Feature, preserve its bbox
    bbox: (geojson is Feature) ? geojson.bbox : null,
  );
}