Implement circle (#187)

* done

* add test

* rename library turf_circle

lib/circle.dart

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

lib/src/circle.dart

@@ -0,0 +1,48 @@
+import 'package:turf/helpers.dart';
+import 'package:turf/invariant.dart';
+import 'package:turf/src/booleans/boolean_helper.dart';
+import 'destination.dart';
+
+/// Takes a [Point] or a [Feature<Point>] and calculates the circle polygon given a radius in degrees, radians, miles, or kilometers; and steps for precision.
+///
+///  example:
+/// ```dart
+/// var properties = { 'foo': 'bar' };
+/// var point = Feature(geometry: Point(coordinates: Position.of([-75.343, 39.984])));
+/// final polygonCircle = circle(
+///                 feature.geometry!,
+///                 radius,
+///                 steps: 32,
+///                 unit: Unit.meters,
+///                 properties: feature.properties,
+///               );
+/// ```
+Feature<Polygon> circle(
+  GeoJSONObject center,
+  num radius, {
+  num? steps,
+  Unit? unit,
+  Map<String, dynamic>? properties,
+}) {
+  steps ??= 64;
+  unit ??= Unit.kilometers;
+  Point origin;
+  final geometry = getGeom(center);
+  if (geometry is Point) {
+    origin = geometry;
+  } else {
+    throw GeometryNotSupported(geometry);
+  }
+  properties ??=
+      center is Feature && center.properties != null ? center.properties : {};
+  final List<Position> coordinates = [];
+  for (var i = 0; i < steps; i++) {
+    final c = destination(origin, radius, (i * -360) / steps, unit).coordinates;
+    coordinates.add(c);
+  }
+  coordinates.add(coordinates[0]);
+  return Feature<Polygon>(
+    properties: properties,
+    geometry: Polygon(coordinates: [coordinates]),
+  );
+}

test/components/circle_test.dart

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+import 'dart:convert';
+import 'dart:io';
+
+import 'package:test/test.dart';
+import 'package:turf/circle.dart';
+import 'package:turf/src/truncate.dart';
+import 'package:turf_equality/turf_equality.dart';
+
+import '../context/helper.dart';
+
+void main() {
+  group(
+    'circle',
+    () {
+      test('circle -- add properties', () {
+        final point = Point(coordinates: Position(0, 0));
+        final out = circle(point, 10, properties: {'foo': 'bar'});
+
+        final isEqual = out.properties?['foo'] == 'bar';
+        expect(isEqual, true);
+      });
+
+      Directory inDir = Directory('./test/examples/circle/in');
+      for (var file in inDir.listSync(recursive: true)) {
+        if (file is File && file.path.endsWith('.geojson')) {
+          test(
+            file.path,
+            () {
+              final inSource = file.readAsStringSync();
+              final feature = Feature.fromJson(jsonDecode(inSource));
+              final properties = feature.properties ?? {};
+              final radius = properties['radius'] ?? 5;
+              final steps = properties['steps'] ?? 64;
+              final unit = properties['units'];
+
+              final C = truncate(circle(feature, radius,
+                  properties: {"marker-symbol": "circle"},
+                  steps: steps,
+                  unit: unit)) as Feature<Polygon>;
+
+              final results = featureCollection([feature, C]);
+
+              Directory outDir = Directory('./test/examples/centroid/out');
+              for (var file2 in outDir.listSync(recursive: true)) {
+                if (file2 is File &&
+                    file2.uri.pathSegments.last == file.uri.pathSegments.last) {
+                  var outSource = file2.readAsStringSync();
+                  var outGeom = GeoJSONObject.fromJson(jsonDecode(outSource));
+                  Equality eq = Equality();
+                  expect(eq.compare(results, outGeom), true);
+                }
+              }
+            },
+          );
+        }
+      }
+    },
+  );
+}

test/examples/circle/in/circle1.geojson

@@ -0,0 +1,10 @@
+{
+  "type": "Feature",
+  "properties": {
+    "radius": 5
+  },
+  "geometry": {
+    "type": "Point",
+    "coordinates": [-75.343, 39.984]
+  }
+}

test/examples/circle/out/circle1.geojson

@@ -0,0 +1,93 @@
+{
+  "type": "FeatureCollection",
+  "features": [
+    {
+      "type": "Feature",
+      "properties": {
+        "radius": 5
+      },
+      "geometry": {
+        "type": "Point",
+        "coordinates": [-75.343, 39.984]
+      }
+    },
+    {
+      "type": "Feature",
+      "properties": {
+        "radius": 5
+      },
+      "geometry": {
+        "type": "Polygon",
+        "coordinates": [
+          [
+            [-75.343, 40.028966],
+            [-75.348756, 40.028749],
+            [-75.354456, 40.028101],
+            [-75.360046, 40.027029],
+            [-75.365472, 40.025541],
+            [-75.37068, 40.023653],
+            [-75.375622, 40.021383],
+            [-75.380248, 40.018753],
+            [-75.384516, 40.015788],
+            [-75.388383, 40.012517],
+            [-75.391813, 40.008972],
+            [-75.394772, 40.005185],
+            [-75.397232, 40.001195],
+            [-75.399169, 39.997039],
+            [-75.400565, 39.992758],
+            [-75.401406, 39.988393],
+            [-75.401685, 39.983985],
+            [-75.401399, 39.979578],
+            [-75.40055, 39.975213],
+            [-75.399148, 39.970934],
+            [-75.397204, 39.96678],
+            [-75.39474, 39.962792],
+            [-75.391777, 39.959008],
+            [-75.388345, 39.955465],
+            [-75.384477, 39.952197],
+            [-75.380211, 39.949235],
+            [-75.375586, 39.946608],
+            [-75.370648, 39.94434],
+            [-75.365444, 39.942455],
+            [-75.360025, 39.940969],
+            [-75.354442, 39.939897],
+            [-75.348748, 39.93925],
+            [-75.343, 39.939034],
+            [-75.337252, 39.93925],
+            [-75.331558, 39.939897],
+            [-75.325975, 39.940969],
+            [-75.320556, 39.942455],
+            [-75.315352, 39.94434],
+            [-75.310414, 39.946608],
+            [-75.305789, 39.949235],
+            [-75.301523, 39.952197],
+            [-75.297655, 39.955465],
+            [-75.294223, 39.959008],
+            [-75.29126, 39.962792],
+            [-75.288796, 39.96678],
+            [-75.286852, 39.970934],
+            [-75.28545, 39.975213],
+            [-75.284601, 39.979578],
+            [-75.284315, 39.983985],
+            [-75.284594, 39.988393],
+            [-75.285435, 39.992758],
+            [-75.286831, 39.997039],
+            [-75.288768, 40.001195],
+            [-75.291228, 40.005185],
+            [-75.294187, 40.008972],
+            [-75.297617, 40.012517],
+            [-75.301484, 40.015788],
+            [-75.305752, 40.018753],
+            [-75.310378, 40.021383],
+            [-75.31532, 40.023653],
+            [-75.320528, 40.025541],
+            [-75.325954, 40.027029],
+            [-75.331544, 40.028101],
+            [-75.337244, 40.028749],
+            [-75.343, 40.028966]
+          ]
+        ]
+      }
+    }
+  ]
+}