[Feature] added intersection feature

lib/intersect.dart

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

lib/src/intersect.dart

@@ -0,0 +1,74 @@
+import 'package:geotypes/geotypes.dart';
+import 'package:turf/meta.dart';
+import 'package:polyclip-dart/polyclip.dart'; // Polyclip-dart import (to be fixed)
+
+// Coded the same as intersect on turf.js. Subject to change based on how polyclip-dart will read geojson objects.
+
+/* Takes [Polygon] or [MultiPolygon] geometries and
+ finds their polygonal intersection. If they don't intersect, returns null.
+
+ @param features the features to intersect
+ @param [properties={}] Optional Properties to translate to Feature
+ @returns returns a feature representing the area they share (either a [Polygon] or
+ [MultiPolygon]). If they do not share any area, returns `null`.
+
+ @example
+ ```dart
+ var poly1 = polygon([
+   [
+     [-122.801742, 45.48565],
+     [-122.801742, 45.60491],
+     [-122.584762, 45.60491],
+     [-122.584762, 45.48565],
+     [-122.801742, 45.48565]
+   ]
+ ]);
+
+ var poly2 = polygon([
+   [
+     [-122.520217, 45.535693],
+     [-122.64038, 45.553967],
+     [-122.720031, 45.526554],
+     [-122.669906, 45.507309],
+     [-122.723464, 45.446643],
+     [-122.532577, 45.408574],
+     [-122.487258, 45.477466],
+     [-122.520217, 45.535693]
+   ]
+ ]);
+
+ var intersection = intersect(featureCollection([poly1, poly2]));
+*/
+Feature<dynamic>? intersect(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 specify at least 2 geometries');
+  }
+
+  // Use polyclip library to find intersection
+  final intersection = Polyclip.intersection(geoms[0], [...geoms.sublist(1)]);
+
+  if (intersection.isEmpty) {
+    return null;
+  }
+
+  if (intersection.length == 1) {
+    // Create a polygon feature
+    final polygonGeometry = Polygon(coordinates: intersection[0] as List<List<Position>>);
+    return Feature(geometry: polygonGeometry, properties: properties ?? {});
+  }
+
+  // Create a multipolygon feature
+  final multiPolygonGeometry = MultiPolygon(
+    coordinates: intersection as List<List<List<Position>>>
+  );
+  return Feature(geometry: multiPolygonGeometry, properties: properties ?? {});
+}

lib/turf.dart

@@ -16,6 +16,7 @@ export 'distance.dart';
 export 'explode.dart';
 export 'extensions.dart';
 export 'helpers.dart';
+export 'intersect.dart';
 export 'invariant.dart';
 export 'length.dart';
 export 'line_intersect.dart';