Add polygon smooth

README.md

@@ -1,11 +1,11 @@
-# Turf for Swift 
+# Turf for Swift
 
 📱[![iOS](https://app.bitrise.io/app/49f5bcca71bf6c8d/status.svg?token=SzGBTkEtxsbuAnbcF9MTog&branch=main)](https://www.bitrise.io/app/49f5bcca71bf6c8d)    
 🖥💻[![macOS](https://app.bitrise.io/app/b72273651db53613/status.svg?token=ODv2UnyAHoOxV8APATEBFw&branch=main)](https://www.bitrise.io/app/b72273651db53613)    
 📺[![tvOS](https://app.bitrise.io/app/0b037542c2395ffb/status.svg?token=yOtMqbu-5bj8grB1Jmoefg)](https://www.bitrise.io/app/0b037542c2395ffb)    
 ⌚️[![watchOS](https://app.bitrise.io/app/0d4d611f02295183/status.svg?token=NiLB_E_0IvYYqV4Mj973TQ)](https://www.bitrise.io/app/0d4d611f02295183)    
 <img src="https://upload.wikimedia.org/wikipedia/commons/3/3c/TuxFlat.svg" width="20" alt="Linux">[![](https://api.travis-ci.com/mapbox/turf-swift.svg?branch=main)](https://travis-ci.com/mapbox/turf-swift) &nbsp;&nbsp;&nbsp;
-[![codecov](https://codecov.io/gh/mapbox/turf-swift/branch/main/graph/badge.svg?token=WT3aUkO3BM)](https://codecov.io/gh/mapbox/turf-swift)  
+[![codecov](https://codecov.io/gh/mapbox/turf-swift/branch/main/graph/badge.svg?token=WT3aUkO3BM)](https://codecov.io/gh/mapbox/turf-swift)
 [![Carthage compatible](https://img.shields.io/badge/Carthage-compatible-4BC51D.svg?style=flat)](https://github.com/Carthage/Carthage) &nbsp;&nbsp;&nbsp;
 [![CocoaPods](https://img.shields.io/cocoapods/v/Turf.svg)](http://cocoadocs.org/docsets/Turf/) &nbsp;&nbsp;&nbsp;
 [![SPM compatible](https://img.shields.io/badge/SPM-compatible-4BC51D.svg?style=flat)](https://swift.org/package-manager/) &nbsp;&nbsp;&nbsp;
@@ -93,6 +93,7 @@ Turf.js | Turf-swift
 [turf-nearest-point-on-line](https://github.com/Turfjs/turf/tree/master/packages/turf-nearest-point-on-line/) | `LineString.closestCoordinate(to:)`
 [turf-polygon-to-line](https://github.com/Turfjs/turf/tree/master/packages/turf-polygon-to-line/) | `LineString(_:)`<br>`MultiLineString(_:)`<br>`FeatureCollection(_:)`
 [turf-simplify](https://github.com/Turfjs/turf/tree/master/packages/turf-simplify) | `LineString.simplified(tolerance:highestQuality:)`
+[turf-polygon-smooth](https://github.com/Turfjs/turf/tree/master/packages/turf-polygon-smooth) | `Polygon.smooth(iterations:)`
 — | `CLLocationDirection.difference(from:)`<br>`LocationDirection.difference(from:)` on Linux
 — | `CLLocationDirection.wrap(min:max:)`<br>`LocationDirection.wrap(min:max:)` on Linux
 

Sources/Turf/Geometries/Polygon.swift

@@ -76,4 +76,68 @@ extension Polygon {
         }
         return true
     }
+
+    /// Smooths a `.Polygon`. Based on [Chaikin's algorithm](http://graphics.cs.ucdavis.edu/education/CAGDNotes/Chaikins-Algorithm/Chaikins-Algorithm.html).
+    /// Warning: may create degenerate polygons.
+    ///
+    /// Ported from https://github.com/Turfjs/turf/blob/402716a29f6ae16bf3d0220e213e5380cc5a50c4/packages/turf-polygon-smooth/index.js
+    public func smooth(iterations: Int = 3) -> Polygon {
+        var poly = self
+        var tempOutput: [[LocationCoordinate2D]] = [[]];
+        var outCoords: [[LocationCoordinate2D]] = [[]];
+
+        (0..<iterations).forEach({ i in
+            tempOutput = [[]]
+
+            if (i > 0) {
+                poly = Polygon(outCoords);
+            }
+
+            processPolygon(poly, &tempOutput);
+            outCoords = tempOutput
+        })
+
+        return Polygon(outCoords);
+    }
+
+    private func processPolygon(_ poly: Polygon, _ tempOutput: inout [[LocationCoordinate2D]]) {
+        var coordIndex = 0
+        var prevGeomIndex = 0;
+        var geometryIndex = 0;
+        var subtractCoordIndex = 0;
+
+        (0..<poly.coordinates.count).forEach { j in
+            (0..<poly.coordinates[j].count - 1).forEach { k in
+                if (geometryIndex > prevGeomIndex) {
+                    prevGeomIndex = geometryIndex;
+                    subtractCoordIndex = coordIndex;
+                    tempOutput.append([]);
+                }
+
+                let currentCoord = poly.coordinates[j][k]
+                let realCoordIndex = coordIndex - subtractCoordIndex;
+                let p1 = poly.coordinates[geometryIndex][realCoordIndex + 1];
+                let p0x = currentCoord.latitude;
+                let p0y = currentCoord.longitude;
+                let p1x = p1.latitude;
+                let p1y = p1.longitude;
+                tempOutput[geometryIndex].append(LocationCoordinate2D(
+                    latitude: 0.75 * p0x + 0.25 * p1x,
+                    longitude: 0.75 * p0y + 0.25 * p1y
+                ));
+                tempOutput[geometryIndex].append(LocationCoordinate2D(
+                    latitude: 0.25 * p0x + 0.75 * p1x,
+                    longitude: 0.25 * p0y + 0.75 * p1y
+                ));
+
+                coordIndex += 1
+            }
+
+            geometryIndex += 1
+        }
+
+        tempOutput.enumerated().forEach({ i, ring in
+            tempOutput[i] = ring + [ring[0]]
+        })
+    }
 }

Tests/TurfTests/GeoJSONTests.swift

@@ -44,7 +44,7 @@ class GeoJSONTests: XCTestCase {
 
         let polygon = Geometry.polygon(.init(coordinates))
         let polygonFeature = Feature(geometry: polygon)
-        XCTAssertEqual((polygonFeature.geometry.value as! Polygon).coordinates, coordinates)
+        XCTAssertEqual((polygonFeature.geometry.value as! Turf.Polygon).coordinates, coordinates)
     }
 
     func testMultiPoint() {