Implement Sample

lib/combine.dart

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+library turf_combine;
+
+export 'package:geotypes/geotypes.dart';
+export 'src/combine.dart';

lib/flatten.dart

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+library turf_flatten;
+
+export 'package:turf/src/flatten.dart';

lib/points_within_polygon.dart

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+library turf_point_to_line_distance;
+
+export 'package:geotypes/geotypes.dart';
+export 'src/points_within_polygon.dart';

lib/polygon_tangents.dart

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+library turf_polygon_tangents;
+
+export 'package:geotypes/geotypes.dart';
+export 'src/polygon_tangents.dart';

lib/polygonize.dart

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+/// Implementation of the polygonize algorithm that converts a collection of
+/// LineString features to a collection of Polygon features.
+/// 
+/// This module follows RFC 7946 (GeoJSON) standards and provides a robust
+/// implementation for converting line segments into closed polygons.
+
+library polygonize;
+
+export 'src/polygonize.dart';

lib/sample.dart

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+library turf_sample;
+
+export 'package:geotypes/geotypes.dart';
+export 'src/sample.dart';

lib/src/combine.dart

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+import 'package:turf/meta.dart';
+
+/// Combines a [FeatureCollection] of Point, LineString or Polygon features
+/// into a single MultiPoint, MultiLineString or MultiPolygon feature.
+///
+/// The [collection] must be a FeatureCollection of the same geometry type.
+/// Supported types are Point, LineString, and Polygon.
+///
+/// Returns a [Feature] with a Multi* geometry containing all coordinates from the input collection.
+/// Throws [ArgumentError] if features have inconsistent geometry types or unsupported types.
+///
+/// If [mergeProperties] is true, properties from the first feature will be preserved.
+/// Otherwise, properties will be empty by default.
+///
+/// See: https://turfjs.org/docs/#combine
+Feature combine(
+  FeatureCollection collection, {
+  bool mergeProperties = false,
+}) {
+  // Validate that the collection is not empty
+  if (collection.features.isEmpty) {
+    throw ArgumentError('FeatureCollection must contain at least one feature');
+  }
+
+  // Get the geometry type of the first feature to validate consistency
+  final firstFeature = collection.features.first;
+  final geometryType = firstFeature.geometry?.runtimeType;
+  if (geometryType == null) {
+    throw ArgumentError('Feature must have a geometry');
+  }
+
+  final firstGeometry = firstFeature.geometry!;
+
+  // Ensure all features have the same geometry type
+  for (final feature in collection.features) {
+    final geometry = feature.geometry;
+    if (geometry == null) {
+      throw ArgumentError('All features must have a geometry');
+    }
+
+    if (geometry.runtimeType != firstGeometry.runtimeType) {
+      throw ArgumentError(
+        'All features must have the same geometry type. '
+        'Found: ${geometry.type}, expected: ${firstGeometry.type}',
+      );
+    }
+  }
+
+  // Set of properties to include in result if mergeProperties is true
+  final properties = mergeProperties && firstFeature.properties != null 
+      ? Map<String, dynamic>.from(firstFeature.properties!)
+      : <String, dynamic>{};
+
+  // Create the appropriate geometry based on type
+  GeometryObject resultGeometry;
+
+  if (firstGeometry is Point) {
+    // Combine all Point coordinates into a single MultiPoint
+    final coordinates = <Position>[];
+    for (final feature in collection.features) {
+      final point = feature.geometry as Point;
+      coordinates.add(point.coordinates);
+    }
+
+    resultGeometry = MultiPoint(coordinates: coordinates);
+  } else if (firstGeometry is LineString) {
+    // Combine all LineString coordinate arrays into a MultiLineString
+    final coordinates = <List<Position>>[];
+    for (final feature in collection.features) {
+      final line = feature.geometry as LineString;
+      coordinates.add(line.coordinates);
+    }
+
+    resultGeometry = MultiLineString(coordinates: coordinates);
+  } else if (firstGeometry is Polygon) {
+    // Combine all Polygon coordinate arrays into a MultiPolygon
+    final coordinates = <List<List<Position>>>[];
+    for (final feature in collection.features) {
+      final polygon = feature.geometry as Polygon;
+      coordinates.add(polygon.coordinates);
+    }
+
+    resultGeometry = MultiPolygon(coordinates: coordinates);
+  } else {
+    // Throw if unsupported geometry type is encountered
+    throw ArgumentError(
+      'Unsupported geometry type: ${firstGeometry.type}. '
+      'Only Point, LineString, and Polygon are supported.',
+    );
+  }
+
+  // Create the Feature result
+  final result = Feature(
+    geometry: resultGeometry,
+    properties: properties,
+  );
+
+  // Apply otherMembers from the first feature to preserve GeoJSON compliance
+  final resultJson = result.toJson();
+  final firstFeatureJson = firstFeature.toJson();
+
+  // Copy any non-standard GeoJSON fields (otherMembers)
+  firstFeatureJson.forEach((key, value) {
+    if (key != 'type' && key != 'geometry' && key != 'properties' && key != 'id') {
+      resultJson[key] = value;
+    }
+  });
+
+  // Return the result with otherMembers preserved
+  return Feature.fromJson(resultJson);
+}

lib/src/flatten.dart

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+import 'package:turf/helpers.dart';
+import 'package:turf/src/meta/flatten.dart';
+
+/// Takes any [GeoJSONObject] and returns a [FeatureCollection] of simple features.
+/// The function flattens all Multi* geometries and GeometryCollections 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:
+/// ```dart
+/// var multiLineString = MultiLineString(coordinates: [
+///   [Position(0, 0), Position(1, 1)],
+///   [Position(2, 2), Position(3, 3)]
+/// ]);
+/// 
+/// var flattened = flatten(multiLineString);
+/// // Returns FeatureCollection with 2 LineString features
+/// ```
+///
+/// Throws [ArgumentError] if:
+/// - A null [geojson] is provided
+/// - A [GeometryCollection] is provided (explicitly not supported)
+/// - A Feature with null geometry is provided
+/// - An unsupported geometry type is encountered
+FeatureCollection<GeometryObject> flatten(GeoJSONObject geojson) {
+  if (geojson == null) {
+    throw ArgumentError('Cannot flatten null 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,
+  );
+}

lib/src/points_within_polygon.dart

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+
+import 'package:turf/meta.dart';
+import 'package:turf/src/booleans/boolean_point_in_polygon.dart';
+
+/// Returns every Point (or the subset of coordinates of
+/// a MultiPoint) that falls inside at least one Polygon/MultiPolygon.
+///
+/// The geometry type of each returned feature matches
+/// its input type:  Point ➜ Point,  MultiPoint ➜ trimmed MultiPoint.
+FeatureCollection<GeometryObject> pointsWithinPolygon(
+  GeoJSONObject points,
+  GeoJSONObject polygons,
+) {
+  final List<Feature<GeometryObject>> results = [];
+
+  // Iterate over each Point or MultiPoint feature
+  featureEach(points, (Feature current, int? _) {
+    bool contained = false;
+
+    final geom = current.geometry;
+    if (geom is Point) {
+      // Check a single Point against every polygon
+      geomEach(polygons, (poly, __, ___, ____, _____) {
+        if (booleanPointInPolygon(geom.coordinates, poly as GeoJSONObject)) {
+          contained = true;
+        }
+      });
+      if (contained) results.add(current);
+    }
+
+    else if (geom is MultiPoint) {
+      final inside = <Position>[];
+
+      // Test every coordinate of the MultiPoint
+      geomEach(polygons, (poly, __, ___, ____, _____) {
+        for (final pos in geom.coordinates) {
+          if (booleanPointInPolygon(pos, poly as GeoJSONObject)) {
+            contained = true;
+            inside.add(pos);
+          }
+        }
+      });
+
+      if (contained) {
+        results.add(
+          Feature<MultiPoint>(
+            geometry: MultiPoint(coordinates: inside),
+            properties: current.properties,
+            id: current.id,
+            bbox: current.bbox,
+          ) as Feature<GeometryObject>,
+        );
+      }
+    }
+
+    else {
+      throw ArgumentError('Input geometry must be Point or MultiPoint');
+    }
+  });
+
+  return FeatureCollection<GeometryObject>(features: results);
+}