[Feature] created union file

lib/src/union.dart

@@ -0,0 +1,68 @@
+import 'package:geotypes/geotypes.dart';
+import 'package:turf/meta.dart';
+import 'package:polyclip-dart/polyclip.dart'; // TSubject to change as per polyclip-dart changes
+
+/* Takes a collection of input polygons and returns a combined polygon. If the
+  input polygons are not contiguous, this function returns a multi-polygon
+  feature.
+
+  @param features input polygon features
+  @param [properties={}] Optional Properties to assign to output feature
+  @returns a combined polygon or multi-polygon feature, or null if there were no input polygons to combine
+
+  @example
+  var poly1 = polygon([
+    [
+      [-82.574787, 35.594087],
+      [-82.574787, 35.615581],
+      [-82.545261, 35.615581],
+      [-82.545261, 35.594087],
+      [-82.574787, 35.594087],
+    ]
+  ], properties: { 'fill': '#0f0' });
+
+  var poly2 = polygon([
+    [
+      [-82.560024, 35.585153],
+      [-82.560024, 35.602602],
+      [-82.52964, 35.602602],
+      [-82.52964, 35.585153],
+      [-82.560024, 35.585153],
+    ]
+  ]);
+
+ var union = turf.union(featureCollection([poly1, poly2]));
+ */
+Feature<dynamic>? union(FeatureCollection features, {Map<String, dynamic>? properties}) {
+  final geoms = <List<dynamic>>[];
+
+  // Extract geometries from features
+  geomEach(features, (geom, featureIndex, featureProperties, featureBBox, featureId) {
+    if (geom != null && geom.coordinates != null) {
+      geoms.add(geom.coordinates as List<dynamic>);
+    }
+  });
+
+  if (geoms.length < 2) {
+    throw Exception('Must have at least 2 geometries');
+  }
+
+  // Use polyclip library to find union
+  final unioned = Polyclip.union(geoms[0], [...geoms.sublist(1)]);
+
+  if (unioned.isEmpty) {
+    return null;
+  }
+
+  if (unioned.length == 1) {
+    // Create a polygon feature
+    final polygonGeometry = Polygon(coordinates: unioned[0] as List<List<Position>>);
+    return Feature(geometry: polygonGeometry, properties: properties ?? {});
+  }
+
+  // Create a multipolygon feature
+  final multiPolygonGeometry = MultiPolygon(
+    coordinates: unioned as List<List<List<Position>>>
+  );
+  return Feature(geometry: multiPolygonGeometry, properties: properties ?? {});
+}

lib/turf.dart

@@ -35,3 +35,4 @@ export 'polyline.dart';
 export 'square.dart';
 export 'transform.dart';
 export 'truncate.dart';
+export 'union.dart';

lib/union.dart

@@ -0,0 +1,4 @@
+library turf_union;
+
+export 'package:geotypes/geotypes.dart';
+export 'src/union.dart';