Add GeoJSON.LineString.encodedPolyline() (#25)

Author: nighthawk

Sources/GeoJSONKitTurf/GeoJSON+LineString+DecodePolyline.swift

@@ -0,0 +1,137 @@
+//
+//  GeoJSON+LineString+EncodedPolyline.swift
+//
+//  Created by Adrian Schoenig on 18/2/17.
+//
+//
+import Foundation
+
+import GeoJSONKit
+
+extension GeoJSON.LineString {
+  
+  // MARK: - Decode
+  
+  public init(encodedPolyline: String) {
+    let bytes = encodedPolyline.utf8CString
+    let length = bytes.count - 1 // ignore 0 at end
+    var idx = 0
+    
+    var array: [GeoJSON.Position] = []
+    
+    var latitude = 0.0
+    var longitude = 0.0
+    while idx < length {
+      var byte = 0
+      var res = 0
+      var shift = 0
+      
+      repeat {
+        if idx > length {
+          break
+        }
+        byte = Int(bytes[idx]) - 63
+        idx += 1
+        res |= (byte & 0x1F) << shift
+        shift += 5
+      } while byte >= 0x20
+      
+      let deltaLat = ((res & 1) != 0 ? ~(res >> 1) : (res >> 1));
+      latitude += Double(deltaLat)
+      
+      shift = 0
+      res = 0
+      
+      repeat {
+        if idx > length {
+          break
+        }
+        byte = Int(bytes[idx]) - 0x3F
+        idx += 1
+        res |= (byte & 0x1F) << shift
+        shift += 5
+      } while byte >= 0x20
+      
+      let deltaLon = ((res & 1) != 0 ? ~(res >> 1) : (res >> 1));
+      longitude += Double(deltaLon)
+      
+      let finalLat = latitude * 1E-5
+      let finalLon = longitude * 1E-5
+      let coordinate = GeoJSON.Position(latitude: finalLat, longitude: finalLon)
+      array.append(coordinate)
+    }
+    
+    self.init(positions: array)
+  }
+  
+  // MARK: - Encode
+  
+  /// Encodes this `GeoJSON.LineString` to a `String`
+  ///
+  /// Adopted from https://github.com/raphaelmor/Polyline/blob/master/Sources/Polyline/Polyline.swift
+  ///
+  /// - parameter precision: The precision used to encode coordinates (default: `1e5`)
+  /// - returns: A `String` representing the encoded polyline
+  public func encodedPolyline(precision: Double = 1e5) -> String {
+    var previousCoordinate = IntegerCoordinates(0, 0)
+    var encodedPolyline = ""
+    
+    for position in positions {
+      let intLatitude  = Int(round(position.latitude * precision))
+      let intLongitude = Int(round(position.longitude * precision))
+      
+      let coordinatesDifference = (intLatitude - previousCoordinate.latitude, intLongitude - previousCoordinate.longitude)
+      encodedPolyline += Self.encodeCoordinate(coordinatesDifference)
+      
+      previousCoordinate = (intLatitude, intLongitude)
+    }
+    
+    return encodedPolyline
+  }
+  
+  private typealias IntegerCoordinates = (latitude: Int, longitude: Int)
+  
+  private static func encodeCoordinate(_ coordinate: IntegerCoordinates) -> String {
+    let latitudeString  = encodeSingleComponent(coordinate.latitude)
+    let longitudeString = encodeSingleComponent(coordinate.longitude)
+    return latitudeString + longitudeString
+  }
+
+  private static func encodeSingleComponent(_ value: Int) -> String {
+    var intValue = value
+    if intValue < 0 {
+      intValue = intValue << 1
+      intValue = ~intValue
+    } else {
+      intValue = intValue << 1
+    }
+    return encodeFiveBitComponents(intValue)
+  }
+
+  private static func encodeLevel(_ level: UInt32) -> String {
+    return encodeFiveBitComponents(Int(level))
+  }
+
+  private static func encodeFiveBitComponents(_ value: Int) -> String {
+    var remainingComponents = value
+    
+    var fiveBitComponent = 0
+    var returnString = String()
+    
+    repeat {
+      fiveBitComponent = remainingComponents & 0x1F
+      
+      if remainingComponents >= 0x20 {
+        fiveBitComponent |= 0x20
+      }
+      
+      fiveBitComponent += 63
+      
+      let char = UnicodeScalar(fiveBitComponent)!
+      returnString.append(String(char))
+      remainingComponents = remainingComponents >> 5
+    } while (remainingComponents != 0)
+    
+    return returnString
+  }
+}

Sources/GeoJSONKitTurf/GeoJSON+LineString+EncodedPolyline.swift

@@ -0,0 +1,28 @@
+//
+//  EncodedPolylineTests.swift
+//  GeoJSONKitTurf
+//
+//  Created by Adrian Schönig on 14/2/2025.
+//
+
+#if canImport(Testing) && swift(>=6)
+import Testing
+
+import GeoJSONKit
+import GeoJSONKitTurf
+
+struct EncodedPolylineTests {
+  
+  @Test func testPalermoToRome() async throws {
+    
+    let polyline = "iasgFkxqpAbbCseDtrBmpDv_BgeEvtB_mDdjB_}Dz|@iuEjc@ihF`YcdFnn@__FjiAowErgAmoEvCwgFqOkbFiPghFoI{hFwNgfFcS}eFa}@e}EpRgyE|UslFfEgcFtWihFvSqhFbZi_Fm_AaoEknA}xDcBwiF}MsgF}IahF{EegFo_@kdFcNshFqYeiFmW}`FoVefF_NslFkyAeeEkrAilEw~AoeEyiAwpEcyBwpD{hAgqEc[weFyc@qbFiy@s|Ea`BkbEaUk`FvcAouEfiAaqE]{hFqf@uaFky@gsEymBavDytBkyDqaCw_DkbBu~De`Au_Fsj@wyEk\\agFrUycFfx@ozEdfBc`EhBarEclBiaEws@mtEgXijFMkjFeEmdFyn@mbFemAomE}fAwyE{yB_cDanDyy@_{C}nBu_DqlByaDqmBegDmuAitDkSknDwo@akAmjEyrAewEcsAavEwqAwfEo|AwlE_}AgbEkoC{iCmuCoyBahDu_BcsDcNcoDys@aqDq\\gwD{EyqD{h@uhD{eAmrDuIwuD^grD~VodDbvAizC`zBm`DncBgbDryBa~C{\\qoDomAwoDmg@euDwJ{nDlp@_fDvtAmeDx{AgoDbhAenDz]{pD~a@}kDf`AqjDdiA_oD~t@ymDlLizDlLicDxgAw_DnoBgmDnn@_sDtEyrDfTulDrl@ymDt_AolD~}@irDb{@ycD`~@ouDnr@agDxr@unD~q@anDbq@skDby@icDh_BmnD|z@meDxm@qpDzr@yxDj_@s|Cdl@krBxzDaqBzwDu{B~yCg_DnxB_gC~jCgpC`eC{cCb{C}qBluDijBlrD_|BxkDuiChlCotB|{CquBt|DutB~wDmeB`oDcbBnlE{mAjlEciC|dAygDhaAeqCvdCk_CljDe{BzcDg~B~`D{zBdeD{}Bh_Ds}BxlDivB|kD_nBvmDueBnaEugBtvDu~Ax}DgcCxdDgsBzeDgkBxyDu}AdcEgt@`wEqr@pgF{^v{E_PngF_W|gF}s@x~E}^tbFef@r`Fu`AhvEay@l}E}o@tdFqlAzgE}z@~xEmjBfvDmnAhmE}bBrvDwcAh_Fyp@h|EewAxbEosA|nDu|BlxCkjBv{D}gB|aEyeB`bEw`B||Dq~Az}D}tBznDy}BnwCmjB~vDoiB|_EigBjxDwgBr~D{_BlcE{uA`gEozAvcEylBhvDa{BhdDioBlqDulBf~D}_BtuDm_CfhDo~CrqAscC`lC_eCfzCuzBffDe|AnbE{mBhuDogClnCquC~pBo_Cr|CeqBhnDeiB`{DudBnzDeqBtnDuoBhpD_qBdrDwcBn}D{aBn`EefBdxDshBtzDumBdxDotAbeEazAzhEm_Bj}DcdB|zDylBpiDadBr|DqdBheEs_Bj~D{~A`cEiuAdlEm`AjsEsv@x`Feu@`mFcf@t}EmCfaF}s@jzDs{CfiBsuB|zCusB|jDedB|zDaxBjiDgNpR"
+    
+    let decoded = GeoJSON.LineString(encodedPolyline: polyline)
+    #expect(decoded.positions.count == 256)
+    
+    #expect(decoded.encodedPolyline() == polyline)
+  }
+  
+}
+
+#endif