Update polygon area function to take a tuple array for lat/lon as opposed to 2 separate arrays.

Author: scottrhoyt

Changelog.md

@@ -0,0 +1,7 @@
+#  Changelog
+
+## `main`
+* Update polygon area function to take a tuple array for lat/lon as opposed to 2 separate arrays.
+
+## 0.1.0
+* Initial releas

README.md

@@ -136,10 +136,8 @@ let antarctica = [
     (-70.0, -4), (-71.0, -14), (-77.3, -33), (-77.9, -46), (-74.7, -61)
 ]
 
-let (area, perimeter) = geodesic.polygonArea(
-    latitudes: antarctica.map { $0.0 },
-    longitudes: antarctica.map { $0.1 }
-)
+let (area, perimeter) = geodesic.polygonArea(coordinates: antarctica)
+
 print("Antarctica area: \(area) m²")
 print("Antarctica perimeter: \(perimeter) m")
 

Sources/GeographicLib/GeodesicPolygon.swift

@@ -193,25 +193,18 @@ public extension Geodesic {
     /// Compute the area and perimeter of a polygon defined by arrays of coordinates.
     ///
     /// - Parameters:
-    ///   - latitudes: Array of latitudes in degrees [-90, 90]
-    ///   - longitudes: Array of longitudes in degrees [-180, 180]
+    ///   - coordinates: Array of (latitudes, logitude) pairs in degrees ([-90, 90], [-180, 180])
     /// - Returns: A tuple containing the area in square meters and perimeter in meters
     /// - Precondition: latitudes and longitudes must have the same count
-    func polygonArea(latitudes: [Double], longitudes: [Double]) -> (area: Double, perimeter: Double) {
-        precondition(latitudes.count == longitudes.count, "Latitude and longitude arrays must have the same count")
-        
+    func polygonArea(coordinates: [(latitude: Double, longitude: Double)]) -> (area: Double, perimeter: Double) {
         var area: Double = 0
         var perimeter: Double = 0
 
         withUnsafePointer(to: geod) { geodPtr in
-            latitudes.withUnsafeBufferPointer { latPtr in
-                longitudes.withUnsafeBufferPointer { lonPtr in
-                    var mutableLats = Array(latPtr)
-                    var mutableLons = Array(lonPtr)
-                    
-                    geod_polygonarea(geodPtr, &mutableLats, &mutableLons, Int32(latitudes.count), &area, &perimeter)
-                }
-            }
+            var latitudes = coordinates.map { $0.latitude }
+            var longitudes = coordinates.map { $0.longitude }
+            
+            geod_polygonarea(geodPtr, &latitudes, &longitudes, Int32(coordinates.count), &area, &perimeter)
         }
 
         return (area: area, perimeter: perimeter)

Tests/GeographicLibTests/GeodesicPolygonTests.swift

@@ -108,13 +108,28 @@ struct GeodesicPolygonTests {
 
     @Test("Antarctica area from coordinates")
     func testAntarcticaArea() {
-        let latitudes: [Double] = [-72.9, -71.9, -74.9, -74.3, -77.5, -77.4, -71.7, -65.9, -65.7,
-                                   -66.6, -66.9, -69.8, -70.0, -71.0, -77.3, -77.9, -74.7]
-        let longitudes: [Double] = [-74, -102, -102, -131, -163, 163, 172, 140, 113,
-                                    88, 59, 25, -4, -14, -33, -46, -61]
+        let antarctica = [
+            (-72.9, -74.0),
+            (-71.9, -102.0),
+            (-74.9, -102.0),
+            (-74.3, -131.0),
+            (-77.5, -163.0),
+            (-77.4, 163.0),
+            (-71.7, 172.0),
+            (-65.9, 140.0),
+            (-65.7, 113.0),
+            (-66.6, 88.0),
+            (-66.9, 59.0),
+            (-69.8, 25.0),
+            (-70.0, -4.0),
+            (-71.0, -14.0),
+            (-77.3, -33.0),
+            (-77.9, -46.0),
+            (-74.7, -61.0)
+        ]
 
         let geodesic = Geodesic()
-        let (area, perimeter) = geodesic.polygonArea(latitudes: latitudes, longitudes: longitudes)
+        let (area, perimeter) = geodesic.polygonArea(coordinates: antarctica)
 
         // Expected values from GeographicLib implementation
         let expectedArea = 13376856682207.4 // square meters