From 2a6717d852b1de573a340219fd2d350bf63e77ad Mon Sep 17 00:00:00 2001
From: Thomas Rasch <thomas.rasch@outdooractive.com>
Date: Mon, 29 Jul 2024 16:40:59 +0200
Subject: [PATCH] Bugfix: Holes in polygons where not subtracted from the outer
 ring area

---
 Sources/GISTools/Algorithms/Area.swift        |  2 +-
 .../GISToolsTests/Algorithms/AreaTests.swift  | 32 +++++++++++++++++++
 2 files changed, 33 insertions(+), 1 deletion(-)
 create mode 100644 Tests/GISToolsTests/Algorithms/AreaTests.swift

diff --git a/Sources/GISTools/Algorithms/Area.swift b/Sources/GISTools/Algorithms/Area.swift
index a35d59a..9b7b20e 100644
--- a/Sources/GISTools/Algorithms/Area.swift
+++ b/Sources/GISTools/Algorithms/Area.swift
@@ -16,7 +16,7 @@ extension Polygon {
         var area: Double = abs(outerRing.area)
 
         if let innerRings = innerRings {
-            area += innerRings.reduce(0.0, { $0 + abs($1.area) })
+            area -= innerRings.reduce(0.0, { $0 + abs($1.area) })
         }
 
         return area
diff --git a/Tests/GISToolsTests/Algorithms/AreaTests.swift b/Tests/GISToolsTests/Algorithms/AreaTests.swift
new file mode 100644
index 0000000..39c40e7
--- /dev/null
+++ b/Tests/GISToolsTests/Algorithms/AreaTests.swift
@@ -0,0 +1,32 @@
+@testable import GISTools
+import XCTest
+
+final class AreaTests: XCTestCase {
+
+    func testArea() throws {
+        let polygon1 = try XCTUnwrap(Polygon([[
+            Coordinate3D(x: 0.0, y: 0.0),
+            Coordinate3D(x: 100.0, y: 0.0),
+            Coordinate3D(x: 100.0, y: 100.0),
+            Coordinate3D(x: 0.0, y: 100.0),
+            Coordinate3D(x: 0.0, y: 0.0)
+        ]]))
+        let polygon2 = try XCTUnwrap(Polygon([[
+            Coordinate3D(x: 0.0, y: 0.0),
+            Coordinate3D(x: 100.0, y: 0.0),
+            Coordinate3D(x: 100.0, y: 100.0),
+            Coordinate3D(x: 0.0, y: 100.0),
+            Coordinate3D(x: 0.0, y: 0.0)
+        ], [
+            Coordinate3D(x: 25.0, y: 25.0),
+            Coordinate3D(x: 75.0, y: 25.0),
+            Coordinate3D(x: 75.0, y: 75.0),
+            Coordinate3D(x: 25.0, y: 75.0),
+            Coordinate3D(x: 25.0, y: 25.0)
+        ]]))
+
+        XCTAssertEqual(polygon1.area, 10000.0, accuracy: 0.1)
+        XCTAssertEqual(polygon2.area, 7500.0, accuracy: 0.1)
+    }
+
+}